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Vandenberk B, Lei LY, Ballantyne B, Vickers D, Liang Z, Sheldon RS, Chew DS, Aksu T, Raj SR, Morillo CA. Syncope recurrence and long-term heart rate variability after cardioneuroablation for vasovagal syncope: a systematic review and meta-analysis. Eur Heart J 2022. [DOI: 10.1093/eurheartj/ehac544.655] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Abstract
Background
Cardioneuroablation (CNA) has emerged as a promising therapy in patients with refractory vasovagal syncope (VVS). Well-designed randomized clinical trials (RCT) are lacking.
Purpose
To provide an estimate of the procedural success rate of CNA, including subgroup analysis by method and target of ablation, as well as serial measurements of autonomic tone after CNA with heart rate variability (HRV).
Methods
A systematic search of studies was performed in MEDLINE and EMBASE according to the PRISMA guidelines, from inception to 14 February 2022. Observational studies and clinical trials reporting success rates were included. Quality assessment was performed using the CONSORT and STROBE recommendations. The primary outcome was freedom from syncope after CNA. Meta-analysis was performed with a random-effects model. The secondary outcome was serial HRV analysis (heart rate, SDNN, rMSSD and LF/HF ratio) analysed with one-way ANOVA with Bonferroni's correction for multiple testing.
Results
A total of 465 patients were included across 14 studies (mean age 40±4 years; 54% females). All included studies were of intermediate quality (median 17, IQR 16–18). Procedural approach to CNA was variable: 50 patients (10.8%) by mapping of fractionated electrograms, 73 patients (15.7%) with the spectral method, 210 (45.2%) with high frequency stimulation, 73 (15.7%) with a purely anatomically guided method, and 59 patients (12.6%) with a combination. The target was bi-atrial in 168 patients (36.1%), left atrium only in 259 patients (55.7%), and right atrium only in 38 patients (8.2%).
The freedom from syncope was 91.9% (95% CI 88.1–94.6%; I2=6.9%, p=0.376; Figure 1). CNA limited to right atrial ablation was associated with a significantly lower success rate (p<0.0001; 81.5%, 95% CI 51.9–94.7%) versus left atrial ablation only (94.0%, 95% CI 88.6–96.9%) and bi-atrial ablation (92.7%, 95% CI 86.8–96.1%). Subgroup analysis according to the technique used to identify GPs did not show any significant difference in success rate (p=0.206).
Ten studies (n=317, 68.2%) reported at least one HRV parameter. Results are presented in Figure 2 with the mean and standard deviations. There were significant increases in heart rate, and significant decrease in SDNN, rMSSD and LF/HF ratios for each follow-up timepoint available (p<0.0001 for all analyses). Recovery of these parameters was observed in 2 studies, but these were not associated with an increased risk in syncope recurrence.
Conclusion
This meta-analysis suggests a high procedural success rate of CNA in VVS of 92%. CNA induces long-term changes in HRV, however some studies reported recovery of these parameters without an association with syncope recurrence. Therefore, HRV changes may not be an appropriate surrogate endpoint for clinical response. Well-designed double-blind, multi-center sham controlled RCTs are needed to provide evidence for future treatment guidelines.
Funding Acknowledgement
Type of funding sources: Foundation.
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Affiliation(s)
- B Vandenberk
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - L Y Lei
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - B Ballantyne
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - D Vickers
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - Z Liang
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - R S Sheldon
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - D S Chew
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - T Aksu
- Yeditepe University Hospital , Istanbul , Turkey
| | - S R Raj
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
| | - C A Morillo
- Libin Cardiovascular Institute of Alberta , Calgary , Canada
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Shaw BH, Stiles LE, Bourne K, Green EA, Shibao CA, Okamoto LE, Garland EM, Gamboa A, Diedrich A, Raj V, Sheldon RS, Biaggioni I, Robertson D, Raj SR. The face of postural tachycardia syndrome - insights from a large cross-sectional online community-based survey. J Intern Med 2019; 286:438-448. [PMID: 30861229 PMCID: PMC6790699 DOI: 10.1111/joim.12895] [Citation(s) in RCA: 144] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
BACKGROUND Patients with postural tachycardia syndrome (POTS) experience chronic symptoms of orthostatic intolerance. There are minimal data detailing the demographics, clinical features and clinical course of this condition. This online, community-based survey highlights patients' experience with POTS. It consists of the largest sample of POTS patients reported to date. OBJECTIVES To describe the demographics, past medical history, medications, treatments and diagnostic journey for patients living with POTS. METHODS Postural tachycardia syndrome patients completed an online, community-based, cross-sectional survey. Participants were excluded if they had not received a diagnosis of POTS from a physician. The questions focused on the patient experience and journey, rather than physiological responses. RESULTS The final analysis included 4835 participants. POTS predominantly affects white (93%) females (94%) of childbearing age, with approximately half developing symptoms in adolescence (mode 14 years). POTS is a chronic multisystem disorder involving a broad array of symptoms, with many patients diagnosed with comorbidities in addition to POTS. POTS patients often experience lengthy delays [median (interquartile range) 24 (6-72) months] and misdiagnosis, but the diagnostic delay is improving. POTS patients can present with a myriad of symptoms most commonly including lightheadedness (99%), tachycardia (97%), presyncope (94%), headache (94%) and difficulty concentrating (94%). CONCLUSIONS These data provide important insights into the background, clinical features and diagnostic journey of patients suffering from POTS. These data should serve as an essential step for moving forward with future studies aimed at early and accurate diagnoses of these patients leading to appropriate treatments for their symptoms.
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Affiliation(s)
- B H Shaw
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - L E Stiles
- Department of Neurology, Stony Brook University School of Medicine, Stony Brook, NY, USA.,Dysautonomia International, East Moriches, NY, USA
| | - K Bourne
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - E A Green
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - C A Shibao
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - L E Okamoto
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - E M Garland
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - A Gamboa
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - A Diedrich
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - V Raj
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada.,Department of Psychiatry, University of Calgary, Calgary, AB, Canada
| | - R S Sheldon
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - I Biaggioni
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - D Robertson
- Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - S R Raj
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada.,Autonomic Dysfunction Center, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
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Raj SR, Guzman JC, Kus T, Araya-Paredes FA, Angihan J, Lei L, Bennett G, Maxey C, Sheldon RS. P4832Norepinephrine transporter inhibition prevents tilt-induced vasovagal syncope: a randomized, placebo controlled trial. Eur Heart J 2018. [DOI: 10.1093/eurheartj/ehy563.p4832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- S R Raj
- Libin Cardiovascular Institute of Alberta, Cardiac Sciences, Calgary, Canada
| | - J C Guzman
- McMaster University, Medicine, Hamilton, Canada
| | - T Kus
- Hospital du Sacre-Coeur, Cardiologie, Montreal, Canada
| | - F A Araya-Paredes
- University Hospital of Sherbrooke (CHUS), Cardiologie, Sherbrooke, Canada
| | - J Angihan
- Libin Cardiovascular Institute of Alberta, Cardiac Sciences, Calgary, Canada
| | - L Lei
- Libin Cardiovascular Institute of Alberta, Cardiac Sciences, Calgary, Canada
| | - G Bennett
- Libin Cardiovascular Institute of Alberta, Cardiac Sciences, Calgary, Canada
| | - C Maxey
- Libin Cardiovascular Institute of Alberta, Cardiac Sciences, Calgary, Canada
| | - R S Sheldon
- Libin Cardiovascular Institute of Alberta, Cardiac Sciences, Calgary, Canada
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Krahn AD, Morillo CA, Kus T, Manns B, Rose S, Brignole M, Sheldon RS. Empiric pacemaker compared with a monitoring strategy in patients with syncope and bifascicular conduction block--rationale and design of the Syncope: Pacing or Recording in ThE Later Years (SPRITELY) study. Europace 2012; 14:1044-8. [DOI: 10.1093/europace/eus005] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Gillis AM, Morck M, Exner DV, Sheldon RS, Duff HJ, Mitchell BL, Wyse GD. Impact of atrial antitachycardia pacing and atrial pace prevention therapies on atrial fibrillation burden over long-term follow-up. Europace 2009; 11:1041-7. [DOI: 10.1093/europace/eup115] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Gillis AM, Morck M, Exner DV, Soo A, Rose MS, Sheldon RS, Duff HJ, Kavanagh KM, Mitchell LB, Wyse DG. Beneficial effects of statin therapy for prevention of atrial fibrillation following DDDR pacemaker implantation. Eur Heart J 2008; 29:1873-80. [DOI: 10.1093/eurheartj/ehn192] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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7
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Guo J, Zhan S, Somers J, Westenbroek RE, Catterall WA, Roach DE, Sheldon RS, Lees-Miller JP, Li P, Shimoni Y, Duff HJ. Decrease in density of INa is in the common final pathway to heart block in murine hearts overexpressing calcineurin. Am J Physiol Heart Circ Physiol 2006; 291:H2669-79. [PMID: 16751287 DOI: 10.1152/ajpheart.01247.2005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Overexpression of calcineurin in transgenic mouse heart results in massive cardiac hypertrophy followed by sudden death. Sudden deaths are caused by abrupt transitions from sinus rhythm to heart block (asystole) in calcineurin-overexpressing (CN) mice. Preliminary studies showed decreased maximum change in potential over time (d V/d tmax) of phase 0 of the action potential. Accordingly, the hypothesis was tested that decreased activity of the sodium channel contributes to heart block. Profound decreases in activity of sodium currents ( INa) paralleled the changes in action potential characteristics. Progressive age-dependent decreases were observed such that at 42–50 days of life little sodium channel function existed. However, this was not paralleled by decreased protein expression as assessed by immunocytochemistry or by Western blot. Since calcineurin can interact with the ryanodine receptor, we assessed whether chronic in vitro treatment with BAPTA-AM, thapsigargin, and ryanodine could rescue the decrease of INa. All of these treatments rescued INa to levels indistinguishable from wild type. The nonspecific PKC inhibitor bisindolylmaleimide I also rescued the decrease of INa. To assess whether decreased sodium channel activity contributes to sudden death in vivo, the response to encainide (20 mg/kg) was assessed: 6 of 10 young CN mice died because of asystole, whereas 0 of 10 wild-type mice died ( P < 0.01). Moreover, encainide produced exaggerated prolongation of the QRS width in sinus beats before the heart block. Catecholamine tone appears necessary to support life in older CN mice because propranolol (1 mg/kg) triggered asystolic death in five of six CN mice. We conclude that decrease in sodium channel activity is in the common final pathway to asystole in CN mice.
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Affiliation(s)
- J Guo
- Dept. of Cardiac Sciences, University of Calgary, AB, Canada T2N 4N1
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8
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Dong D, Duan Y, Guo J, Roach DE, Swirp SL, Wang L, Lees-Miller JP, Sheldon RS, Molkentin JD, Duff HJ. Overexpression of calcineurin in mouse causes sudden cardiac death associated with decreased density of K+ channels. Cardiovasc Res 2003; 57:320-32. [PMID: 12566105 DOI: 10.1016/s0008-6363(02)00661-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
BACKGROUND Overexpression of calcineurin in transgenic (TG) mice results in cardiac hypertrophy and unexpected deaths. METHODS AND RESULTS None of the TG survived beyond 24 weeks (n=38) whereas all of the wildtype (WT, n=47) survived. Prolongation of repolarization preceded the development of sustained pleomorphic ventricular tachycardia and high degree atrioventricular block, which occurred during spontaneous sudden deaths. Since depolarization-activated K(+) channels contribute dominantly to repolarization in mice, we hypothesized that the TG would decrease these K(+) currents and that the in vivo administration of cyclosporin A (CsA), a calcineurin inhibitor, would reduce this effect. CsA reversed cardiac hypertrophy: capacitance measurements of WT left ventricular myocytes (127+/-7 pF; n=45) and CsA-treated TG (129+/-14 pF; n=17) were significantly lower than in placebo-treated TG (220+/-11 pF; n=41; P<0.001 by ANOVA). Independent of whether the data fit a bi- or a tri-exponential model, the density of I(tof) was significantly reduced in TG versus WT and CsA reversed this effect. While I(tos) and I(Kslow) were also reduced in TG, CsA does not reverse this change because long-term in vivo CsA treatment of WT also reduces I(tos) and I(Kslow.) To assess whether the decreased 'repolarization reserve' contributed to arrhythmogenesis, the residual I(Kr) was blocked by dofetilide precipitating pleomorphic ventricular tachycardias. CONCLUSION Since the downregulation of I(tof) was observed with overexpression of calcineurin and was also reversed by the calcineurin inhibitor CsA, we conclude that downregulation of I(tof) is a consequence of calcineurin overexpression.
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Affiliation(s)
- Deli Dong
- Cardiovascular Research Group, Department of Medicine, University of Calgary, 3330 Hospital Drive N.W., Calgary, Alberta, Canada T2N 4N1
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Raj SR, Sheldon RS. The implantable cardioverter-defibrillator. Current indications and controversies. Minerva Cardioangiol 2002; 50:273-90. [PMID: 12147959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023]
Abstract
The implantable cardioverter-defibrillator (ICD) has become a highly effective, but expensive therapy for sudden cardiac death due to ventricular tachyarrhythmias. ICD use has been increasing at 20-30% per year, and is expected to rise at a faster rate. Clinical trials have now shown that the ICD can be effective for the secondary prevention, and more recently for the primary prevention, of sudden cardiac death in selected populations. Despite the high quality trial evidence that is currently available, several issues pertaining to ICD use remain unresolved. These relate to the management of patient groups who were not included in the clinical trials, optimizing the selection of patients who will benefit from an ICD, determining the duration of survival benefit from an ICD, assessing and optimizing a patient's quality of life with an ICD, and determining the cost-effectiveness and cost-impact of the ICD. These considerations are discussed in this article.
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Affiliation(s)
- S R Raj
- Cardiovascular Research Group, University of Calgary, Calgary, Alberta, Canada
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11
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Abstract
The implantable cardioverter-defibrillator (ICD) has emerged as an effective, but expensive, therapy for arrhythmic sudden cardiac death. ICD use has been increasing by 20% to 30% per year. Clinical trials have shown that the ICD can be effective for both the primary prevention and the secondary prevention of sudden cardiac death in selected populations. Despite the available trial evidence, several issues pertaining to ICD use remain unresolved, including the treatment of patients not represented in clinical trials, the optimal selection of patients who will benefit from an ICD, the duration of benefit from an ICD, the quality of life for patients with an ICD, and both the cost-effectiveness and the cost impact of the ICD. These considerations are discussed in this article.
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Affiliation(s)
- S R Raj
- Cardiovascular Research Group, Health Sciences Center, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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12
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Exner DV, Sheldon RS, Pinski SL, Kron J, Hallstrom A. Do baseline characteristics accurately discriminate between patients likely versus unlikely to benefit from implantable defibrillator therapy? Evaluation of the Canadian implantable defibrillator study implantable cardioverter defibrillatory efficacy score in the antiarrhythmics versus implantable defibrillators trial. Am Heart J 2001; 141:99-104. [PMID: 11136493 DOI: 10.1067/mhj.2001.111768] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVE Our purpose was to evaluate whether baseline characteristics predictive of implantable cardioverter defibrillator (ICD) efficacy in the Canadian Implantable Defibrillator Study (CIDS) are predictive in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial. BACKGROUND ICD therapy is superior to antiarrhythmic drug use in patients with life-threatening arrhythmias. However, identification of subgroups most likely to benefit from ICD therapy may be useful. Data from CIDS suggest that 3 characteristics (age > or =70 years, ejection fraction [EF] < or =0.35, and New York Heart Association class >II) can be combined to reliably categorize patients as likely (> or =2 characteristics) versus unlikely to benefit (<2 characteristics) from ICD therapy. METHODS The utility of the CIDS categorization of ICD efficacy was assessed by Kaplan-Meier analysis and Cox hazards modeling. The accuracy of the CIDS score was formally tested by evaluating for interaction between categorization of benefit and treatment in a Cox model. RESULTS ICD therapy was associated with a significantly lower risk of death in the 320 patients categorized as likely to benefit (relative risk [RR] 0.57, 95% confidence interval [CI] 0.37-0.88, P =.01) and a trend toward a lower risk of death in the 689 patients categorized as unlikely to benefit (RR 0.70, 95% CI 0.48-1.03, P =.07). Categorization of benefit was imperfect, as evidenced by a lack of statistical interaction (P =.5). Although 32 of the 42 deaths prevented by ICD therapy in AVID were in patients categorized as likely to benefit, all 42 of these patients had EF values < or =0.35. Neither advanced age nor poorer functional class predicted ICD efficacy in AVID. CONCLUSION Of the 3 characteristics identified to predict ICD efficacy in CIDS, only depressed EF predicted ICD efficacy in AVID. Thus physicians faced with limited resources might elect to consider ICD therapy over antiarrhythmic drug use in patients with severely depressed EF values.
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Affiliation(s)
- D V Exner
- University of Calgary, Calgary, Alberta, Canada
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14
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Exner DV, Mitchell LB, Wyse DG, Sheldon RS, Gillis AM, Cassidy P, Duff HJ. Conduction time oscillations precede the spontaneous termination of human atrioventricular reciprocating tachycardia. J Interv Card Electrophysiol 2000; 4:231-9. [PMID: 10729839 DOI: 10.1023/a:1009821830582] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Prior clinical research indicates that conduction slowing is the primary mechanism leading to the spontaneous termination of reentrant tachycardia in humans. Yet, some experimental models indicate that cycle length oscillations and enhanced conduction are important prerequisites. The role of oscillations in conduction times and enhanced conduction in the spontaneous termination of human reentrant tachycardia has not been adequately investigated. The electrophysiologic features preceding the spontaneous termination of orthodromic atrioventricular (AV) reciprocating tachycardia (RT) were evaluated in 21 patients, each of whom had a sustained (>60 seconds) and a spontaneously terminating (>/=10 beats and </=60 seconds) episode of AVRT during the same electrophysiologic study. Atrio-His, His-ventricular, interventricular, ventriculoatrial and atrial conduction times were measured for each beat of spontaneously terminating AVRT and for paired beats of sustained AVRT. Beats of spontaneously terminating and sustained tachycardia were pooled and Hadi multivariate outlier analysis was used to identify whether significant beat-to-beat alterations in conduction times preceded the spontaneous termination of reentry. Cycle lengths of sustained (348+/-62 msec) and spontaneously terminating AVRT (351+/-70 msec) were similar. Significant beat-to-beat oscillations in conduction times preceded the spontaneous termination of AVRT in 10 of the 21 (48%) patients. An apparent enhancement in atrio-His or ventriculoatrial conduction times immediately preceded the spontaneous termination of AVRT in 11 patients (52%), while an apparent conduction delay occurred in only 2 patients (10%). Moreover, significant oscillations in conduction times were present in 9 of the 11 patients (82%) with enhanced conduction, but only in 1 of the 10 (10%) remaining patients (p=0.002. Conduction time oscillations, which are related to apparent enhancement in atrio-His or ventriculoatrial conduction, frequently precede the spontaneous termination of reentry in humans.
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Affiliation(s)
- D V Exner
- Department of Medicine, Division of Cardiology, University of Calgary, Canada.
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15
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Connolly SJ, Gent M, Roberts RS, Dorian P, Roy D, Sheldon RS, Mitchell LB, Green MS, Klein GJ, O'Brien B. Canadian implantable defibrillator study (CIDS) : a randomized trial of the implantable cardioverter defibrillator against amiodarone. Circulation 2000; 101:1297-302. [PMID: 10725290 DOI: 10.1161/01.cir.101.11.1297] [Citation(s) in RCA: 940] [Impact Index Per Article: 39.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Patients surviving ventricular fibrillation (VF) or sustained ventricular tachycardia (VT) are at a high risk of death due to a recurrence of arrhythmia. The implantable cardioverter defibrillator (ICD) terminates VT or VF, but it is not known whether this device prolongs life in these patients compared with medical therapy with amiodarone. METHODS AND RESULTS A total of 659 patients with resuscitated VF or VT or with unmonitored syncope were randomly assigned to treatment with the ICD or with amiodarone. The primary outcome measure was all-cause mortality, and the secondary outcome was arrhythmic death. A total of 328 patients were randomized to receive an ICD. A thoracotomy was done in 33, no ICD was implanted in 18, and the rest had a nonthoracotomy ICD. All 331 patients randomized to amiodarone received it initially. At 5 years, 85.4% of patients assigned to amiodarone were still receiving it at a mean dose of 255 mg/day, 28.1% of ICD patients were also receiving amiodarone, and 21.4% of amiodarone patients had received an ICD. A nonsignificant reduction in the risk of death was observed with the ICD, from 10.2% per year to 8.3% per year (19.7% relative risk reduction; 95% confidence interval, -7.7% to 40%; P=0.142). A nonsignificant reduction in the risk of arrhythmic death was observed, from 4.5% per year to 3.0% per year (32.8% relative risk reduction; 95% confidence interval, -7.2% to 57.8%; P=0.094). CONCLUSIONS A 20% relative risk reduction occurred in all-cause mortality and a 33% reduction occurred in arrhythmic mortality with ICD therapy compared with amiodarone; this reduction did not reach statistical significance.
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Affiliation(s)
- S J Connolly
- Departments of Medicine, McMaster University, Hamilton, Ontario, Canada.
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Abstract
Dual-chamber pacing is a promising treatment for patients with very frequent vasovagal syncope, but its cost utility is unknown. We report that the incremental cost per quality-adjusted life-year gained is $13,159 Canadian dollars (about $8,600 US dollars), and therefore this pacemaker therapy for vasovagal syncope has a favorable cost-utility ratio.
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Affiliation(s)
- C R Mitton
- Health Research Group, University of Calgary, Alberta, Canada
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17
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Abstract
We propose that heart period sequences are organized similarly to sentences, with a lexicon of recurrent, similarly shaped words. These words should fulfill four criteria: universality, nonrandomness, central statistical tendencies, and specific associated physiology. Here we describe a large-magnitude, transient bradycardia (LMTB) and assess whether it constitutes a word. LMTBs were seen in 11 of 12 adult female rabbits. All shape parameters were different than those of the beat-randomized and phase-randomized surrogate sequences (P < 0.05-0.001). LMTBs were 8. 4 +/- 2.9 beats and 2.64 +/- 0.87 s long and were characterized by bradycardia of 77 +/- 49 ms over 1.09 +/- 0.49 s with a recovery to baseline over 1.56 +/- 0.61 s. The LMTBs had a slower recovery than onset in 9 of 11 rabbits and were highly peaked in 10 of 11 rabbits (P < 0.05). Scalar, magnitude, and shape parameters had values with central statistical tendencies. About 76% of LMTBs were accompanied by hypotension (mean -6.1 +/- 3.9 mmHg) that lagged 2 beats behind the onset of the bradycardia and that correlated with the bradycardia (-10.5 +/- 4.1 ms/mmHg). Thus transient bradycardic events are a distinct "word" in the lexicon of heart rate variability.
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Affiliation(s)
- D Roach
- Cardiovascular Research Group, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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18
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Abstract
Currently the analysis of clinical trials for treatment of paroxysmal atrial fibrillation (PAF) relies on the assumption that the events are distributed according to a Poisson distribution. We contend that the occurrence of PAF events are clearly not Poisson and tend to occur in clusters. A candidate parametric model of the inter-event interval, the Weibull distribution, is presented. When the events are distributed according to a Poisson distribution, the time to the first event (TFE) has the same distribution as the inter-event intervals (IEI) due to the 'memoryless' property of the Poisson distribution, hence the TFE can be used instead of the IEI. When the events do not form a Poisson distribution, the TFE does not have the same distribution as the IEI. We show that for the Weibull distribution, when the TFE is used to model the IEI, both the mean and the survivor distribution are biased. The bias in the survivor function is a function both of time and the parameters of the distribution. Therefore when two groups have different parameters for their distributions (as in the case of different treatment effects), the discrepancy between the survivor distribution of the IEI and the survivor distribution of the TFE is affected differentially. We demonstrate the low coverage probabilities of the mean and the survivor function which result when the underlying distribution is Weibull with shape parameter kappa < 1.0. It is likely that this problem will arise for other clustered event processes. This suggests that careful empirical investigation of the distribution of IEI for recurrent events is necessary before choosing to analyse the data using the TFE.
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Affiliation(s)
- M S Rose
- Department of Community Health Sciences, Faculty of Medicine, University of Calgary, Alberta, Canada
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Abstract
Many chaos detection methods have proven inherently ambiguous in that they yield similar results for chaotic signals and correlated noise. The purpose of this work was to determine whether human resting heart period sequences have global properties characteristic of chaotic systems. We investigated the inherent global organization of heart period sequences by quantifying how the information content of the embedded sequences varied as a function of scale. We compared the information scaling characteristics of 60-min heart period sequences obtained from 10 healthy resting volunteers with those obtained from numerous periodic and chaotic control sequences. The information scaling properties of the heart period sequences were significantly different from those obtained for the controls, particularly at the coarsest scales (P = 0.0003 vs. low-dimensional periodic controls; P = 0.0005 vs. low-dimensional chaotic controls; P = 0.0003 vs. low-dimensional periodic and chaotic controls). We also showed that nondeterministic components, such as large tachycardic (or bradycardic) events or aperiodic fluctuations, can lead to scaling characteristics similar to those observed for the resting heart period sequences. This, in addition to previous evidence from spectral, nonlinear predictability and lexical studies, favors an events-based approach to understanding heart rate variability.
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Affiliation(s)
- D E Roach
- Cardiovascular Research Group, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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20
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Sheldon RS, Koshman ML, Murphy WF. Electroencephalographic findings during presyncope and syncope induced by tilt table testing. Can J Cardiol 1998; 14:811-6. [PMID: 9676166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
OBJECTIVE To determine electroencephalographic (EEG) changes occurring during syncope induced by headup tilt table testing. DESIGN Prospective observational study. SETTING Calgary General Hospital Syncope Clinic, Calgary, Alberta. PATIENTS Eighteen patients with a history of recurrent syncope who developed syncope while undergoing diagnostic isoproterenol tilt table testing. INTERVENTIONS Continuous EEGs were recorded in 18 sequentially consenting patients while they underwent diagnostic headup tilt table testing. MAIN RESULTS Patients developed presyncope after 2.6 +/- 2.4 mins and syncope after 3.7 +/- 2.5 minutes. Systolic blood pressure dropped from 117 +/- 17 mmHg to 65 +/- 9 mmHg, and heart rate dropped from 124 +/- 26 beats/min to 65 +/- 27 beats/min. Fourteen patients developed presyncope, while five developed syncope without appreciable presyncope. Abnormal EEGs were recorded in 13 of 14 patients during presyncope and in 18 of 18 patients during syncope. No patients developed EEG abnormalities before the onset of presyncope, and the proportion of patients with EEG abnormalities gradually increased throughout presyncope. During presyncope, theta and delta wave slowing, and background suppression were noted in eight of 14, nine of 14 and one of 14 patients, respectively. During syncope, theta and delta wave slowing, and background suppression were noted in nine of 18, 11 of 18 and six of 18 patients, respectively (not significant versus presyncope). There were strikingly abrupt changes in the EEG rhythm within 15 s of the transition to syncope in 14 of 18 patients. Six patients developed new theta wave slowing, 11 developed new delta wave slowing, and seven developed background suppression. No epileptiform activity was recorded. CONCLUSIONS Both presyncope and syncope induced by tilt testing are associated with EEG abnormalities, and no single EEG pattern is pathognomonic of either. The transition from presyncope to syncope is marked by abrupt EEG changes.
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Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, Faculty of Medicine, University of Calgary, Alberta.
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21
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Sheldon RS. Syncope and sudden death in hypertrophic cardiomyopathy. Clin Sci (Lond) 1998; 94:335-6. [PMID: 9640336 DOI: 10.1042/cs0940335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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22
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Exner DV, Gillis AM, Sheldon RS, Wyse DG, Duff HJ, Cassidy PR, Mitchell LB. Telemetry-documented, pace-terminable ventricular tachycardia in patients with ventricular fibrillation. Am J Cardiol 1998; 81:235-8. [PMID: 9591912 DOI: 10.1016/s0002-9149(97)00880-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The follow-up prevalence of electrogram-confirmed spontaneous ventricular tachycardia with a cycle length of >280 ms (53%) exceeds the prevalence of ventricular fibrillation (23%) in patients whose only spontaneous arrhythmia before implantable cardioverter defibrillator implantation was ventricular fibrillation. Antitachycardia pacing therapy safely terminates most (89%) of these slower ventricular tachycardia episodes, recommending the use of tiered-therapy devices and anticipatory activation of ventricular tachycardia detection and treatment algorithms for ventricular fibrillation patients who receive an implantable cardioverter defibrillator.
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Affiliation(s)
- D V Exner
- Department of Medicine, the University of Calgary, Alberta, Canada
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23
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Mitchell LB, Sheldon RS, Gillis AM, Connolly SJ, Duff HJ, Gardner MJ, Hui WK, Ramadan D, Wyse DG. Definition of predicted effective antiarrhythmic drug therapy for ventricular tachyarrhythmias by the electrophysiologic study approach: randomized comparison of patient response criteria. J Am Coll Cardiol 1997; 30:1346-53. [PMID: 9350938 DOI: 10.1016/s0735-1097(97)00294-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
OBJECTIVES We sought to compare efficacies of therapy for ventricular tachyarrhythmias selected by programmed stimulation using two different patient response efficacy criteria: <5 versus <16 repetitive ventricular responses. BACKGROUND Therapy selection for ventricular tachyarrhythmias by programmed stimulation requires definition of a patient response that predicts long-term efficacy. Such definitions have not been previously compared prospectively. METHODS Patients with sustained ventricular tachyarrhythmias were randomized to therapy selection using either the <5 or <16 repetitive response criterion of predicted effective therapy. The primary end point was sudden death or recurrence of ventricular tachyarrhythmia requiring intervention. RESULTS Predicted effective drug therapy was found for 23 (34%) of 68 patients randomized to the <5 criterion and 29 (36%) of 81 patients randomized to the <16 criterion (p = NS). Definition of therapy required 3.0 +/- 1.6 drug trials (mean +/- SD) in patients randomized to the <5 criterion and 2.9 +/- 1.8 trials in patients randomized to the <16 criterion (p = NS). Patients randomized to the <5 criterion had a lower 2-year probability of the primary end point (0.20 +/- 0.05) than did patients randomized to the <16 criterion (0.33 +/- 0.05, one-tailed p = 0.004). The advantage of the <5 criterion was also seen in subgroup analyses involving patients with and without an initial drug efficacy prediction. CONCLUSIONS The programmed stimulation approach to the selection of antiarrhythmic therapy for ventricular tachyarrhythmias using a patient response criterion of <5 repetitive ventricular responses results in a lower probability of recurrence of ventricular tachyarrhythmia than does use of a <16 repetitive response criterion.
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Affiliation(s)
- L B Mitchell
- Department of Medicine, Foothills Hospital and University of Calgary, Alberta, Canada
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24
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Sheldon RS. Outcome of patients with neurally mediated syncope following tilt table testing. Cardiologia 1997; 42:795-802. [PMID: 9286117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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25
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Duff HJ, Feng ZP, Wang L, Sheldon RS. Regulation of expression of the [3H]-dofetilide binding site associated with the delayed rectifier K+ channel by dexamethasone in neonatal mouse ventricle. J Mol Cell Cardiol 1997; 29:1959-65. [PMID: 9236149 DOI: 10.1006/jmcc.1997.0437] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Developmental shortening of cardiac action potential duration in mouse appears to result, at least in part, from replacement of the rapid component of the delayed rectifying potassium current (IKr) with the transient outward current (ItO1). This developmental decrease in the IKr current density was paralleled by a loss of the high affinity [3H]-dofetilide binding site and loss of prolongation of action potential duration by dofetilide. Since glucocorticoid treatment prevented the developmental shortening of action potential duration in rats in the perinatal period, we hypothesized that chronic dexamethasone treatment would alter the developmental loss of IKr channel expression in mice. Accordingly, 10-day-old mice were randomly allocated to chronic in vivo dexamethasone treatment (1 mg/kg) or placebo treatment for 3-5 days. At 15 days of life, transmembrane action potentials were recorded in right ventricular endocardium and [3H]-dofetilide equilibrium binding studies were performed. The baseline action potential duration in the dexamethasone-treated animals was significantly greater than that in the control group (66+/-3 v 54+/-10 ms, respectively; P<0.01). Moreover, dofetilide significantly prolonged action potential duration in the dexamethasone-treated animals, but had no effect on the placebo-treated group (P<0.01). In addition, a high affinity [3H]-dofetilide binding site (Kd 96+/-21 nM and Bmax 69+/-13 fmoles/mg protein) was observed in the dexamethasone-treated group (n=5), whereas no specific [3H]-dofetilide binding was observed in the placebo-treated group. In conclusion, dexamethasone modulates developmental regulation of IKr channel expression in mouse ventricle.
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Affiliation(s)
- H J Duff
- Cardiovascular Research Group, Department of Medicine, University of Calgary, Calgary, Alberta, Canada
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26
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Abstract
The North American Vasovagal Pacemaker Study is an ongoing multicenter randomized, clinical trial that assesses the efficacy of dual chamber pacing utilizing rate drop sensing in patients with frequent syncopal spells. Patients are eligible if they have had at least six syncopal spells and a positive tilt table test, or a recurrence of syncope within 6 months of a positive tilt test. The tilt table test must have provoked a relative bradycardia. Patients are randomized to receive a Medtronic Thera DR with rate drop sensing, or to continue on their usual therapy. All patients complete a log of their presyncopal and syncopal spells daily, and are contacted every 2 months. The primary outcome measure is the time to the first recurrence of syncope. The goal of the main study is to recruit 284 patients in 3 years with a final fourth year of follow-up; this will result in an 80% chance of detecting a 30% reduction in the risk of syncope. A pilot study is under way with the aim to recruit 60 patients over a period of 2 years with a final third year of follow-up. Recruitment began in July 1995 and 47 patients have been enrolled to date.
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Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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27
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Wyse DG, Mitchell LB, Sheldon RS, Gillis AM, Duff HJ. Divergence of endocardial QT interval components during programmed electrical stimulation including observations during induction of sustained ventricular tachyarrhythmias. J Interv Card Electrophysiol 1997; 1:23-31. [PMID: 9869947 DOI: 10.1023/a:1009706516217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Measurements were made in 12 normal subjects and during induction of sustained ventricular tachyarrhythmias in 31 patients with remote myocardial infarction. QT interval measurements were made semiautomatically with computer assistance and the total QT interval was divided into early (QT1) and late (QT2) components. QT intervals and QT interval dispersion between two right ventricular endocardial sites were plotted against the degree of prematurity of the last extrastimulus (S2, S3, or S4). In the control group, total QT and QT1 intervals shortened with increasing prematurity of the last extrastimulus (p < 0.001). Slopes (positive) were steeper with faster pacing rates (600, 500, or 400 ms) and more extrastimuli (1 to 3). The relationship between QT2 intervals and prematurity of the last extrastimulus was flat, but the slope was slightly negative (p = 0.05 to < 0.001) and did not vary with changes in pacing cycle length or number of extrastimuli. QT interval dispersion in the control group was minor (95% CI 0-40 ms). During induction of sustained ventricular tachyarrhythmias, total QT and QT1 intervals were longer (y intercepts) than in the control group (p < 0.05 at 400-ms pacing cycle length) and their dispersion was increased (p < 0.05). Generally, QT2 intervals were shorter (p < 0.05 at 600-ms pacing cycle length) during induction of ventricular arrhythmias in comparison with the control group but dispersion was increased (p < 0.05 at 400-ms pacing cycle length). QT intervals and QT interval dispersion show an orderly and predictable relationship with prematurity of the last extrastimulus in normal subjects. These patterns differ during induction of sustained ventricular tachyarrhythmias. Such differences may be exploited to derive clinically predictive and useful measurements.
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Affiliation(s)
- D G Wyse
- University of Calgary Medical Clinic, Alberta, Canada
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28
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Abstract
UNLABELLED The radioligand [3H]dofetilide binds specifically to the delayed rectifier potassium channel and provides a biochemical approach to study interactions of Class III drugs with this channel. However, previous studies have examined the binding of [3H]dofetilide to cardiac myocytes only at extracellular potassium of 135 mM. Because previous electrophysiological studies have shown that hyperkalemia could alter the pharmacological responses to I(Kr) channel blockers, the hypothesis tested in this study was that changing ionic conditions would alter characteristics of [3H]dofetilide binding. RESULTS under physiological conditions (Na+ 135 mM, K+ 5 mM), [3H]dofetilide bound to two sites on guinea-pig ventricular myocytes (a high-affinity site, K(d) 26+/-8 nM, B(max) 81+/-12 fmol/10(6) cells: and a low-affinity site, K(d) 1.6+/-0.8 microM, B(max) 1003+/-173 fmol/10(6) cells, n=11). Binding properties were not altered by changes in osmolarity or extracellular sodium. However, when extracellular K+ was increased to 20 mM, a single binding site was observed with an affinity K(d) of 120+12 nM and a B(max) of 303+/-57 fmol/10(6) cells (P<0.05; n=6). To establish whether this effect was mediated at the high-affinity site we assessed the effects of elevated extracellular potassium on a biological model, neonatal mouse myocytes, that expressed solely the high-affinity binding sites. The K(d) values for binding to fetal mouse cardiac myocytes at an extracellular K+ of 5 mM and 20 mM were also significantly different, 29+/-10 and 230+/-46 nM, respectively. In conclusion, [3H]dofetilide binding to its high-affinity site is modulated by extracellular potassium.
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Affiliation(s)
- H J Duff
- Department of Medicine, University of Calgary, Alberta, Canada
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29
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Abstract
Expression of cardiac transient outward current and inwardly rectifying K+ current is age dependent. However, little is known about age-related changes in cardiac delayed rectifier K+ current (IK, with rapidly and slowly activating components, IKr and IKs, respectively). Accordingly, the purpose of the present study was to assess developmental changes in IK channels in fetal, neonatal, and adult mouse ventricles. Three techniques were used: conventional microelectrode to measure the action potential, voltage clamp to record macroscopic currents of IK, and radioligand assay to examine [3H]dofetilide binding sites. The extent of prolongation of action potential duration at 95% repolarization (APD95) by a selective IKr blocker, dofetilide (1 mumol/L), dramatically decreased from fetal (137% +/- 18%) to day-1 (75% +/- 29%) and day-3 (20% +/- 15%) neonatal mouse ventricular tissues (P < .01). Dofetilide did not prolong APD95 in adult myocardium. IKr is the sole component of IK in day-18 fetal mouse ventricular myocytes. However, both IKr and IKs were observed in day-1 neonatal ventricular myocytes. With further development, IKs became the dominant component of IK in day-3 neonates. In adult mouse ventricular myocytes, neither IKr nor IKs was observed. Correspondingly, a high-affinity binding site for [3H]dofetilide was present in fetal mouse ventricles but was absent in adult ventricles. The complementary data from microelectrode, voltage-clamp, and [3H]dofetilide binding studies demonstrate that expression of the IK channel is developmentally regulated in the mouse heart.
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Affiliation(s)
- L Wang
- Department of Medicine, University of Calgary, Alberta, Canada
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30
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Abstract
OBJECTIVES We sought to compare the forearm reflex venous response to mental arithmetic stress in patients with neuromediated syncope and in normal subjects. BACKGROUND Patients with neuromediated syncope have a paradoxic arterial vasodilation in response to stressors that usually provoke vasoconstriction. Given the postulated role of diminished preload in provoking the reflex responses resulting in syncope, we hypothesized that mental stress might provoke paradoxic reflex venodilation in patients with neuromediated syncope. METHODS Twelve normal subjects (mean age [+/-SD] 47 +/- 9 years) and 27 patients with neuromediated syncope (mean age 42 +/- 13 years) were studied before and during a mental arithmetic stress test. Forearm venous pressure-volume relations were determined by using radionuclide plethysmography. RESULTS During mental arithmetic stress, heart rate and systolic and diastolic blood pressure increased significantly and similarly both in normal subjects and in patients with neuromediated syncope. The heart rate and blood pressure changes were qualitatively similar in both groups. However, with mental arithmetic stress, forearm venoconstriction of 13 +/- 2% (mean +/- SEM) was noted in normal subjects (p < 0.001) but not in patients with neuromediated syncope (mean 2%, p = NS). This group response of patients with neuromediated syncope did not result from a lack of individual responses but occurred because these patients had a wide range of responses. The normal physiologic and methodologic variability of the method was +/- 4%. Thirteen of the 27 patients with neuromediated syncope had forearm venoconstriction of 14.5 +/- 6.8% during mental arithmetic stress, whereas 7 had paradoxic forearm venodilation of 14.6 +/- 8.8%, and 7 were considered nonresponders (-1.3 +/- 3.4%). Thus, 14 (52%) of the 27 patients with syncope did not have normal vasoconstriction in response to mental stress. CONCLUSIONS Patients with neuromediated syncope have an abnormal range of forearm venomotor responses to mental arithmetic stress. Reflex control of the veins may play an important role in the pathogenesis of neuromediated syncope.
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Affiliation(s)
- D E Manyari
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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31
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Abstract
Dofetilide is a Class III antiarrhythmic agent known to selectively block the rapid component of the delayed rectifier K+ current (IKr). [3H]Dofetilide binds to a low and a high affinity sites on guinea-pig myocytes. The purposes of this study were: (1) to find biological models which express solely the high or the low [3H]dofetilide binding sites; (2) to characterize the single binding site models; and (3) to establish which of the high or the low affinity binding sites is associated with IKr. We compared and characterized the [3H]dofetilide binding on guinea-pig myocytes, neonatal mouse ventricular homogenate and untransfected CHO cells. These tissue preparations were selected since the neonatal mouse tissue expresses IKr while this current is absent from CHO cells. We compared the IC50 concentrations of dofetilide and two other known IKr blockers E-4031 and sotalol, on [3H]dofetilide binding to these three preparations. Using steady-state and kinetic binding techniques, we characterized the interaction of E-4031 and sotalol with the high and the low [3H]dofetilide binding sites. We found that neonatal mouse ventricle manifest solely the high affinity site (Kd 20 +/- 4 nmol/l, Bmax 18 +/- 4 fmol/mg) while CHO cells manifest solely the low affinity binding site (Kd 1.6 +/- 0.1 mumol/l, Bmax 5.8 +/- 0.8 pmol/mg). We demonstrated that the high and low affinity binding sites present on guinea-pig myocytes show characteristics similar to the single high affinity site expressed on neonatal mouse homogenate and to the single low affinity site expressed on CHO cells, respectively. Class III antiarrhythmic drugs inhibited binding to the high affinity site at concentrations similar to those required to inhibit 50% of IKr current in electrophysiologic studies. In contrast, dofetilide and E-4031 inhibited [3H]dofetilide binding to the low affinity site only at supra-pharmacologic concentrations. We next demonstrated that Class III drugs interact in a competitive manner with the high affinity site on neonatal mouse tissue while they interact with a site allosterically coupled to the low binding site on CHO cells. These data suggest that dofetilide interacts with the high and low affinity sites in a fundamentally different manner. We defined biological models which express solely the high or low [3H]dofetilide binding sites. Only the high affinity site is related to IKr.
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Affiliation(s)
- C Fiset
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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Abstract
BACKGROUND The purpose of this study was to assess the effect of pericardial constraint on the activity of left ventricular (LV) mechanoreceptors with nonmyelinated vagal afferents. METHODS AND RESULTS Single-unit activity of cervical vagal afferents (conduction velocity, 1.6 +/- 0.5 m/s) was recorded in six cats anesthetized with alpha-chloralose. Discharge frequency during diastole (DFdiastole) and systole (DFsystole) was determined after correction for conduction delay of the nerve action potential. When the pericardium was closed and LV end-diastolic pressure (LVEDP) was approximately 5 mm Hg, DFdiastole and DFsystole were 1.3 +/- 1.0 and 0.3 +/- 0.1 impulses per second, respectively. Volume expansion increased LVEDP, LV transmural LVEDP, and segment length and was associated with a significant increase in DFdiastole. At a given LVEDP, DFdiastole was significantly greater in the absence of the pericardium than with the pericardium closed. Removal of the pericardium increased the slope of the relation between DFdiastole and intracavitary LVEDP but did not alter the slope of the relations between DFdiastole and transmural LVEDP and LV segment length. CONCLUSIONS These results suggest that, rather than the absolute value of intracavitary LVEDP, transmural LVEDP and distension appear to be more important determinants of diastolic LV mechanoreceptor activity and that pericardial constraint may attenuate mechanoreceptor activity by limiting cardiac distension.
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Affiliation(s)
- S Y Wang
- Department of Medicine, University of Calgary, Alberta, Canada
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33
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Abstract
Dofetilide specifically blocks the rapid component of the delayed rectifier current (IKr) at nanomolar concentrations in a saturable manner, suggesting the presence of a receptor. We characterized two [3H]dofetilide binding sites to ventricular myocytes from adult guinea pigs by using a conventional filter assay. Scatchard analysis revealed two binding sites with different affinities: a high-affinity site (Kd, 2.8 +/- 0.3 x 10(-8) mol/L; Bmax, 76 +/- 15 fmol/10(6) myocytes) and a low-affinity site (Kd, 1.64 +/- 0.4 x 10(-6) mol/L; Bmax, 1620 +/- 260 fmol/10(6) myocytes) (n = 11). Kinetic studies showed that there were two dissociation rate constants for [3H]dofetilide (0.02 +/- 0.005 min-1 [high-affinity site] and 0.22 +/- 0.064 min-1 [low-affinity site], n = 4), although the observed association rate constant is equally well fit to a single- or two-site model. The ability of known IKr blockers to compete with [3H]dofetilide binding to both sites was assessed. E4031, clofilium, quinidine, and sotalol competed for binding at both sites. Disopyramide and NAPA only competed for a single binding site. The mean IC50 values for inhibition of binding to both the high- and low-affinity binding sites correlated with their concentrations required to inhibit IKr in electrophysiological studies. However, inhibition of [3H]dofetilide binding to the high-affinity site by class III antiarrhythmic drugs occurred at pharmacological concentrations, whereas suprapharmacological concentrations were required to inhibit binding to the low-affinity site.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- H J Duff
- Cardiovascular Research Group, University of Calgary, Canada
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Gillis AM, Sheldon RS, Wyse DG, Leitch JW, Yee R, Klein GJ, Duff HJ, Mitchell LB. Long-term reproducibility of ventricular tachycardia induction in patients with implantable cardioverter/defibrillators. Serial noninvasive studies. Circulation 1995; 91:2605-13. [PMID: 7743623 DOI: 10.1161/01.cir.91.10.2605] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND Noninvasive electrophysiological studies (EPSs) can be performed in current implantable antitachycardia pacemaker/cardioverter/defibrillators (ICDs). Thus, these devices may be used as tools to study changes in the electrophysiological substrate and ventricular tachycardia characteristics over time. METHODS AND RESULTS Fifty-five patients receiving an ICD for treatment of sustained ventricular tachyarrhythmias underwent serial EPSs after implantation of the ICD. Studies were performed before hospital discharge and 1, 3, 5, 9, 12, 18, 24, and 36 months after ICD implantation. Sustained monomorphic ventricular tachycardia (VT) was induced in 37 patients (group 1) at the predischarge EPS, whereas no sustained arrhythmia could be induced in 18 patients (group 2) at baseline. Group 1 patients underwent 165 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 72% of the follow-up EPSs, ventricular fibrillation (VF) was induced during 11% of follow-up EPSs, and no sustained VT or VF was induced during 17% of follow-up visits. Sustained VT was induced at every follow-up EPS in 23 patients (62%), whereas no sustained VT/VF could be induced at least once during follow-up in 14 patients (38%). Clinical or electrophysiological variables did not predict noninducibility during follow-up. However, the probability that a patient would experience spontaneous VT decreased significantly over time in patients in whom VT was not inducible during at least 1 follow-up EPS (P = .05). Group 2 patients underwent 86 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 22% of follow-up EPSs, VF was induced during 19% of follow-up EPSs, and no sustained VT/VF could be induced during 68% of follow-up EPSs. No sustained VT/VF could be induced during every follow-up EPS in 9 patients (50%), whereas sustained monomorphic VT was induced at least once during follow-up in 7 patients (34%). Persistent noninducibility of VT during follow-up was associated with low probability of occurrence of spontaneous VT (11%), whereas inducibility of VT at least once during follow-up was associated with the occurrence of spontaneous VT (89%, P = .003). CONCLUSIONS Considerable variability of VT induction is observed over a lengthy period in patients presenting with sustained VT/VF. Persistent noninducibility of VT is associated with a reduced probability of spontaneous VT. These observations suggest that the substrates for inducible and spontaneous VT change in parallel over time.
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Affiliation(s)
- A M Gillis
- Department of Medicine, Foothills Medical Centre, Alberta, Canada
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Sheldon RS, Thakore E. Ring and link requirements for tocainide binding to the class I antiarrhythmic drug receptor on rat cardiac myocytes. J Pharmacol Exp Ther 1995; 272:1005-10. [PMID: 7891310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Our purpose was to assess the structural and physicochemical determinants of the binding of tocainide and several of its homologs to the class I antiarrhythmic drug receptor associated with rat cardiac sodium channels. The homologs were chosen to assess the contributions of substituents of the aryl ring and the arylamine link on drug binding. Drug affinity was measured with a radioligand binding assay using [3H]Batrachotoxin A 20 alpha-Benzoate and freshly isolated cardiac myocytes. The affinities of the homologs were compared to determine the relationship between the affinity for the receptor and the physicochemical and structural properties of the parent drug. The contributions to the free energy of binding were determined with the Gibb's equation delta G = -RT In (1/Ki). Hydrophobic interactions are important at most sites. Meta substituents on the aryl ring and substituents on the link each interact hydrophobically with the receptor and contribute about 0.3 kcal/mol of carbon. The hydrophobic pocket near the link binding site accommodates at least six carbons. A para methoxy substituent reduces the free energy of tocainide binding by 43%. This profound reduction in the free energy of binding might be due to anomolously high aqueous solubility of alkyl aryl ethers. Longer alkoxy chains contribute 1.09 kcal/mol of carbon to the binding energy. Ortho substituents contribute little to binding specificity. These findings support a notion of a complex drug receptor with hydrophilic and hydrophobic domains that recognize specific moieties on class I antiarrhythmic drugs.
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Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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36
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Abstract
OBJECTIVES Previous studies have reported beneficial antiarrhythmic effects when selected drugs were combined. The purpose of this study was to assess whether a favorable interaction would occur with amiloride and quinidine. DESIGN The antiarrhythmic and electrophysiologic effects of quinidine alone and in combination with amiloride were assessed in 10 patients with inducible sustained ventricular tachycardia. Parallel electrophysiologic studies assessed this drug combination in guinea pig papillary muscle. RESULTS None of the patients had adverse effects during quinidine monotherapy. However, seven of 10 patients had adverse responses to the combination treatment: three patients had suppression of inducible ventricular tachycardia during quinidine monotherapy but had sustained ventricular tachycardia induced during combination treatment; three other patients had somatic side effects that resulted in discontinuation of the combination therapy but were absent during quinidine monotherapy; and one patient had 12 episodes of sustained ventricular tachycardia during this combination therapy. The patient had no such response during monotherapy. Surface QRS duration was significantly more prolonged during combination therapy than during monotherapy. Parallel electrophysiologic effects assessed this drug combination in guinea pig papillary muscle. The combination of amiloride (1 mumol/L) and quinidine (10 mumol/L) synergistically decreased the maximum rate of rise of phase 0 of the action potential (Vmax) (43 +/- 12 V/sec) compared with quinidine alone (24 +/- 9 V/sec) because of a greater degree of tonic block of Vmax (14% +/- 6%) as compared to quinidine alone (3% +/- 3%) with no significant change in action potential duration. CONCLUSIONS Amiloride exaggerates the effects of quinidine on QRS duration in patients and on Vmax during in vitro study, which implies that the proarrhythmic effect of the combination of amiloride and quinidine may be associated with synergistic increase in sodium channel blockade.
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Affiliation(s)
- L Wang
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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37
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Sheldon RS, Duff HJ, Thakore E, Hill RJ. Class I antiarrhythmic drugs: allosteric inhibitors of [3H] batrachotoxinin binding to rat cardiac sodium channels. J Pharmacol Exp Ther 1994; 268:187-94. [PMID: 8301556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
This study assessed whether class I antiarrhythmic drugs allosterically inhibit [3H]batrachotoxinin A 20-alpha-benzoate ([3H]BTXB) binding to sodium channels on freshly isolated rat cardiac myocytes. All class I drugs tested inhibited equilibrium [3H]BTXB binding in a concentration-dependent manner. Scatchard analysis showed that disopyramide, flecainide, transcainide, lidocaine and amiodarone reduced [3H]BTXB maximum binding (Bmax) whereas procainamide, mexiletine, quinidine, quinine, tocainide, propafenone, encainide and O-demethylencainide increased [3H]BTXB KD but had little effect on Bmax. Kinetic [3H]BTXB binding assays were used to assess the mechanism by which class I drugs inhibit [3H]BTXB binding. Drugs that increase the unidirectional dissociation rate constant (k-1) of [3H]BTXB probably bind to sodium channels to which [3H]BTXB is already bound. Although all class I drugs increased the k-1 of [3H]BTXB, they did so weakly and at concentrations above the IC50 values of the drugs. Thus, drug binding to [3H]BTXB-bound channels does not appear to be the predominant mechanism underlying their ability to inhibit [3H]BTXB binding. Conversely, drugs which allosterically decrease the unidirectional association rate constant (K+1) of [3H]BTXB probably bind to channels to which [3H]BTXB is not already bound. All class I drugs decreased the k+1 of [3H]BTXB, indicating drug binding to [3H]BTXB-free channels. The estimated affinities of drugs for [3H]BTXB-free channels correlated closely with the IC50 values of these drugs (r = 0.94, P < .001), suggesting that this effect is a common and major determinant in their ability to inhibit [3H]BTXB binding. The results are discussed in light of electrophysiologic theories of class I antiarrhythmic drug action.
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Affiliation(s)
- R S Sheldon
- Department of Medicine, University of Calgary, Alberta, Canada
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38
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Connolly SJ, Gent M, Roberts RS, Dorian P, Green MS, Klein GJ, Mitchell LB, Sheldon RS, Roy D. Canadian Implantable Defibrillator Study (CIDS): study design and organization. CIDS Co-Investigators. Am J Cardiol 1993; 72:103F-108F. [PMID: 8237822 DOI: 10.1016/0002-9149(93)90972-f] [Citation(s) in RCA: 121] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The Canadian Implantable Defibrillator Study (CIDS) is an on-going randomized multicenter clinical trial that compares implantable cardioverter-defibrillator (ICD) therapy against amiodarone in patients with prior cardiac arrest or hemodynamically unstable ventricular tachycardia. Eligible patients are equally randomized to receive or not receive an ICD as initial management. Those not receiving an ICD receive amiodarone. All patients are seen in follow-up every 6 months. The primary outcome event cluster is arrhythmic death or any other death occurring within 30 days of therapy initiation. Secondary outcomes are all-cause mortality and nonfatal occurrences of ventricular tachycardia or fibrillation. The goal of the study is to recruit 400 patients over 4 years. All patients will be followed to the end of the year. This will result in an 80% chance of detecting a reduction in arrhythmic death of 58% by ICD if such a difference in truth exists. Recruitment began in October 1990 and 184 patients have been enrolled to date.
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Affiliation(s)
- S J Connolly
- McMaster Clinic, Hamilton General Hospital, McMaster University, Hamilton, Ontario, Canada
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39
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Gillis AM, Leitch JW, Sheldon RS, Morillo CA, Wyse DG, Yee R, Klein GJ, Mitchell LB. A prospective randomized comparison of autodecremental pacing to burst pacing in device therapy for chronic ventricular tachycardia secondary to coronary artery disease. Am J Cardiol 1993; 72:1146-51. [PMID: 8237804 DOI: 10.1016/0002-9149(93)90984-k] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A number of modes of antitachycardia pacing therapies are available in the newer generations of implantable cardioverter/defibrillators. The efficacy of synchronized burst overdrive pacing for the termination of induced and spontaneous monomorphic ventricular tachycardia (VT) was compared with synchronized autodecremental (ramp) pacing in 21 patients who received an implantable antitachycardia pacemaker/cardioverter/defibrillator for treatment of recurrent sustained monomorphic VT. Patients undergoing serial noninvasive VT induction studies after device implantation were prospectively randomized to receive trials of burst or ramp pacing therapies in a crossover study design. Antitachycardia pacing therapies were equally efficacious in treating induced VT (68% for ramp, 76% for burst pacing trials). The efficacy of ramp (93%) and burst (96%) pacing therapies was significantly higher in terminating spontaneously occurring episodes of VT than in terminating induced episodes (p = 0.001). The incidence of tachycardia acceleration was similar for both modes of pacing. The incidence of VT acceleration was lower for spontaneously occurring episodes of VT (0.01%) than for induced episodes of VT (6%, p < 0.01). Thus, antitachycardia pacing is an effective therapy for episodes of monomorphic VT, and the risk of accelerating VT to a hemodynamically unstable form is low. Antitachycardia pacing therapies are more effective against spontaneously occurring episodes than induced episodes of VT. Differences in tachycardia cycle length and duration may contribute to these effects.
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Affiliation(s)
- A M Gillis
- Divisions of Cardiology, Foothills Medical Centre, Calgary, Alberta, Canada
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40
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Sheldon RS, Wyse DG, Mitchell LB, Gillis AM, Kavanagh KM, Duff HJ. Characteristics of patients with nonfatal cardiac arrest 3 to 180 days after acute myocardial infarction. Am J Cardiol 1993; 72:753-8. [PMID: 8213505 DOI: 10.1016/0002-9149(93)91057-o] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Patients who survive a tachyarrhythmic cardiac arrest in the first 6 months after acute myocardial infarction (AMI) are at risk for recurrent arrests, but the magnitude, timing and characteristics of this phenomenon are unknown. This study characterizes the nature of recurrent tachyarrhythmic cardiac arrests in the absence of reversible factors or new myocardial necrosis in patients between 3 and 180 days after AMI. We retrospectively assessed 28 patients (mean age 61 +/- 12 years) who survived an initial cardiac arrest a median of 10 days after AMI. Mean left ventricular ejection fraction was 36 +/- 9%. Fourteen patients (50%) had at least 1 recurrence of cardiac arrest, and 10 had > 2 arrests. Almost all (92%) recurrent cardiac arrests occurred within 5 days of the preceding arrest, and the high-risk periods were similar after the first, second or third cardiac arrest. Very fast ventricular tachycardia (mean cycle length 212 +/- 30 ms) was the documented responsible arrhythmia in 44 of 51 cardiac arrests. The morphology was either polymorphic, monomorphic or sinusoidal. No clinical or laboratory values could be found that predicted whether a patient would have a recurrent arrest. Nineteen patients (68%) survived to leave the hospital and have been followed for up to 96 months. For these, actuarial 5-year overall survival was 76% and actuarial 5-year arrhythmia-free probability was 80%. Thus, patients who survive a cardiac arrest in the first 6 months after AMI are at high risk of recurrent cardiac arrest for a further 5 days, and the arrests are due to characteristically fast ventricular tachycardias.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
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41
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Duff HJ, Mitchell LB, Gillis AM, Sheldon RS, Chudleigh L, Cassidy P, Chiamvimonvat N, Wyse DG. Electrocardiographic correlates of spontaneous termination of ventricular tachycardia in patients with coronary artery disease. Circulation 1993; 88:1054-62. [PMID: 8353867 DOI: 10.1161/01.cir.88.3.1054] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
BACKGROUND In vitro studies have reported that beat-to-beat variance in tachycardia cycle length and in conduction and repolarization properties can result in spontaneous termination of reentrant arrhythmias. The purpose of this study was to define the ECG patterns associated with spontaneous termination of ventricular tachycardia in humans late after myocardial infarction. METHODS AND RESULTS The QRS durations, QT intervals, and cycle lengths were measured on a beat-to-beat basis during episodes of sustained and spontaneously terminating ventricular tachycardias (VT) induced at antiarrhythmic drug-free and drug-assessment electrophysiological studies. Twenty-six patients were studied. Four categories of inducible ventricular tachycardia were studied: inducible sustained ventricular tachycardia in an antiarrhythmic drug-free state, spontaneously terminating ventricular tachycardia in an antiarrhythmic drug-free state, sustained ventricular tachycardia on antiarrhythmic therapy, and spontaneously terminating ventricular tachycardia on antiarrhythmic therapy. The ECG patterns that were statistically related to spontaneous termination of ventricular tachycardia included impingement of the QTP interval on the tachycardia cycle length (P < .001) both in the presence and absence of drugs, transient shortening of QRS just before termination, and paradoxical prolongation of QTP after abrupt shortening of ventricular tachycardia cycle length. In addition, greater beat-to-beat variances in tachycardia cycle lengths, QT intervals, and QRS durations were statistically associated with spontaneously terminating ventricular tachycardia. These ECG patterns did not occur during sustained episodes of ventricular tachycardia during the antiarrhythmic drug-free state or during ineffective antiarrhythmic drug therapy. CONCLUSIONS A dynamic interplay between QRS duration, QT interval, and cycle length of tachycardia and their variances are associated with spontaneous termination of ventricular tachycardia in humans late after infarction. This study of ECG changes associated with spontaneous termination of ventricular tachycardia provides insight into potential mechanisms of antiarrhythmic drug efficacy.
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Affiliation(s)
- H J Duff
- Department of Medicine, University of Calgary, Foothills Hospital, Alberta, Canada
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42
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Hii JT, Gillis AM, Wyse DG, Sheldon RS, Duff HJ, Mitchell LB. Risks of developing supraventricular and ventricular tachyarrhythmias after implantation of a cardioverter-defibrillator, and timing the activation of arrhythmia termination therapies. Am J Cardiol 1993; 71:565-8. [PMID: 8438742 DOI: 10.1016/0002-9149(93)90512-b] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The clinical courses of 39 consecutive recipients (mean age 61 +/- 12 years, and mean left ventricular ejection fraction 0.32 +/- 0.15) of an automatic implantable cardioverter-defibrillator (ICD) were examined to determine the risks of developing ventricular tachycardia (VT) and supraventricular tachyarrhythmias (SVT) after surgery, with ventricular response rates fulfilling ICD detection criteria. ICD system leads were implanted by thoracotomy in 25 patients and by using nonthoracotomy lead systems in 14. Six patients (18%) developed SVT after surgery, whereas 14 (36%) developed sustained VT. The median times to the development of both SVT and VT were 2 days. By actuarial analysis, the probability of developing VT after surgery was significantly greater than that of SVT during hospitalization (p = 0.04). This significant excess of postoperative VT over SVT was most marked in patients aged < or = 61 years, those who received nonthoracotomy rather than epicardial lead systems, those who presented with VT rather than ventricular fibrillation, and those who received > 20 intraoperative defibrillation shocks. These observations recommend the activation of ICD therapies immediately after implantation.
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Affiliation(s)
- J T Hii
- Department of Medicine, Foothills Medical Center, Calgary, Alberta, Canada
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43
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Wyse DG, Kavanagh KM, Gillis AM, Mitchell LB, Duff HJ, Sheldon RS, Kieser TM, Maitland A, Flanagan P, Rothschild J. Comparison of biphasic and monophasic shocks for defibrillation using a nonthoracotomy system. Am J Cardiol 1993; 71:197-202. [PMID: 8421983 DOI: 10.1016/0002-9149(93)90738-x] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A comparison of defibrillation thresholds was made using biphasic and monophasic shocks delivered by a nonthoracotomy lead system in 2 clinically distinct groups of patients. The first group were patients receiving an implantable cardioverter-defibrillator who were studied before surgery with their chests closed. The second group were patients undergoing coronary artery bypass grafting (CABG) who were studied before surgery with their chests open but reapproximated. Biphasic defibrillation thresholds (stored energy) were significantly (p < 0.001) less than monophasic ones in subjects with the implantable cardioverter-defibrillator (12.3 +/- 5.3 vs 21.1 +/- 9.3 J) or CABG (14.6 +/- 7.1 vs 24.2 +/- 12.6 J). These values are less than were previously reported with a similar nonthoracotomy lead configuration. There were no significant differences between the 2 groups in all measurements derived from corresponding shock waveforms, although impedance tended to be greater in patients with CABG. However, subjects with CABG had greater left ventricular ejection fractions and did not have history of potentially lethal ventricular arrhythmias. Despite these differences, the conclusion that biphasic shocks are more effective would have been made in a study of either group alone. It is concluded that patients with CABG who have not had preceding potentially lethal ventricular arrhythmias may be a potential source of surrogate subjects for defibrillation research such as epicardial mapping, which requires that the chest be open.
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Affiliation(s)
- D G Wyse
- Division of Cardiology, University of Calgary/Foothills Hospital, Alberta, Canada
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44
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Chiamvimonvat N, Mitchell LB, Gillis AM, Wyse DG, Sheldon RS, Duff HJ. Use-dependent electrophysiologic effects of amiodarone in coronary artery disease and inducible ventricular tachycardia. Am J Cardiol 1992; 70:598-604. [PMID: 1324598 DOI: 10.1016/0002-9149(92)90198-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Amiodarone produces use-dependent block of cardiac sodium channels in vitro. This study assessed whether similar use-dependent block occurred in 19 patients with coronary artery disease and inducible, sustained, monomorphic ventricular tachycardia treated with amiodarone. Beat-to-beat measurements of ventricular paced QRS durations during 12-beat trains at cycle lengths of 700, 600, 400 and 300 ms were analyzed at a baseline antiarrhythmic drug-free study and after 2 and 10 weeks of amiodarone therapy. At the drug-free study, there were no significant changes in paced QRS durations within the 12-beat trains at any pacing cycle lengths. After 2 and 10 weeks of amiodarone therapy, progressive prolongation of paced QRS durations occurred over the 12-beat trains at pacing cycle lengths of 600, 400 and 300 ms (p less than 0.05). Significant changes in QRS duration were not observed at a pacing cycle length of 700 ms. This progressive prolongation in QRS duration can be fitted as a function of beat number to a monoexponential equation and occurred with an onset time constant of 1.02 +/- 0.41 beats (306 +/- 122 ms) at a pacing cycle length of 300 ms. The magnitude of QRS prolongation increased as the pacing cycle length was shortened. The magnitudes of QRS prolongation were similar after 2 and 10 weeks of amiodarone therapy. In conclusion, use-dependent prolongation in QRS duration occurs at rapid pacing cycle lengths in humans receiving amiodarone.
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Affiliation(s)
- N Chiamvimonvat
- Department of Medicine, University of Calgary, Alberta, Canada
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45
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Hill RJ, Thakore E, Taouis M, Duff HJ, Sheldon RS. Transcainide: biochemical evidence for state-dependent interaction with the class I antiarrhythmic drug receptor. Eur J Pharmacol 1991; 203:51-8. [PMID: 1665791 DOI: 10.1016/0014-2999(91)90789-s] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The mechanism of action of the lidocaine derivative transcainide was examined using [3H]batrachotoxinin 20 alpha-benzoate, which binds specifically to and stabilizes activated states of the sodium channel. Transcainide (IC50 0.3 microM) inhibited equilibrium [3H]batrachotoxinin binding to sodium channels present on freshly isolated rat cardiac myocytes. Scatchard analysis of [3H]batrachotoxinin binding showed that transcainide both reduced maximal binding and altered the KD for [3H]batrachotoxinin binding, indicating noncompetitive, allosteric inhibition. Inhibition by transcainide of [3H]batrachotoxinin binding was reversible within 60 min. We used state-dependent [3H]batrachotoxinin binding assays to examine whether transcainide preferentially binds to activated or nonactivated sodium channels. Transcainide had little effect on the k-1 of [3H]batrachotoxinin even at concentrations 1000-fold greater than its IC50, indicating low affinity of transcainide for activated channels. However, transcainide decreased the k + 1 of [3H]batrachotoxinin at a concentration very close to its IC50 concentration for inhibiting equilibrium [3H]batrachotoxinin binding. The results are discussed in terms of a model in which transcainide inhibits [3H]batrachotoxinin binding by binding specifically to and stabilizing a nonactivated state of the cardiac sodium channel.
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Affiliation(s)
- R J Hill
- Department of Medicine, University of Calgary, Alberta, Canada
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46
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Sheldon RS, Duff HJ, Hill RJ. Class I anti-arrhythmic drugs: structure and function at the cardiac sodium channel. CLIN INVEST MED 1991; 14:458-65. [PMID: 1660368] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The major electrophysiologic effect of Class I anti-arrhythmic drugs is blockade of the cardiac sodium channel thereby reducing the initial depolarization of the action potential and slowing impulse propagation. Despite the widespread use of these drugs, our understanding of their mechanism of action is incomplete. Models based on electrophysiologic studies predict that a receptor for Class I drugs is associated with the sodium channel, and that occupancy of this receptor causes sodium channel blockade. Recent radioligand studies with [3H]batrachotoxin A benzoate have identified a binding site for Class I drugs associated with rat cardiac myocyte sodium channels which may be the predicted receptor. Binding of drugs to this site is saturable, reversible, stereospecific, and occurs at pharmacologically relevant concentrations with similar rank order of potency in vivo and in vitro. Drugs appear to bind preferentially to a closed state of the channel, thereby preventing channel opening and subsequent sodium influx.
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Affiliation(s)
- R S Sheldon
- Cardiovascular Research Group, University of Calgary, Alberta
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47
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Duff HJ, Mitchell LB, Wyse DG, Gillis AM, Sheldon RS. Mexiletine/quinidine combination therapy: electrophysiologic correlates of anti-arrhythmic efficacy. CLIN INVEST MED 1991; 14:476-83. [PMID: 1660369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This article reviews the data which support the use of selected drug combinations to enhance anti-arrhythmic activity. Specifically, we have focused on the mexiletine-quinidine interaction and the relation between anti-arrhythmic efficacy and electrophysiologic effects. In an initial clinical study, we found that combination therapy with mexiletine-quinidine produced enhanced efficacy in suppressing spontaneous ventricular tachycardia with fewer side-effects than high dose monotherapy. This enhanced efficacy has been confirmed in other laboratories. Combination therapy also enhanced suppression of inducible ventricular tachycardia in patients and in animal models. Animal models were used to assess the relation between electrophysiologic effects and anti-arrhythmic efficacy. In the animal studies, combination therapy produced selective prolongation of refractoriness and conduction in the infarct and peri-infarct zones without significant changes in the normal zone. Subsequent studies focused on the relative contribution of sodium channel and potassium channel blocking properties of these drugs to the enhanced activity seen with the combination. Studies using the selective sodium channel blocker tetrodotoxin confirmed that sodium channel blockade was necessary for this interaction. To assess the contribution of prolongation of action potential duration by quinidine to the combined effect we compared the anti-arrhythmic and electrophysiologic effects of the stereoisomers quinidine and quinine given alone and in combination with mexiletine. These experimental data confirm that the property of prolongation of action potential duration by quinidine is essential to the interaction. When comparing quinidine and quinine it is apparent that prolongation of refractoriness in the peri-infarct zone is essential for anti-arrhythmic activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- H J Duff
- Department of Medicine, University of Calgary, Faculty of Medicine, Alberta
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48
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Abstract
Class I antiarrhythmic drugs inhibit the sodium channel by binding to a drug receptor associated with the channel. In this report we show that in vivo administration of the class I antiarrhythmic drug mexiletine to rats induces sodium channel upregulation in isolated cardiac myocytes. The number of sodium channels was assessed with a radioligand assay using the sodium channel-specific toxin [3H]batrachotoxinin benzoate ([3H]BTXB). The administration of mexiletine to rats induced a dose-dependent increase in [3H]BTXB total specific binding (Bmax) on isolated cardiac myocytes. Sodium channel numbers were 15 +/- 5, 29 +/- 9, and 54 +/- 4 fmol/10(5) cells after 3 d treatment with 0, 50 mg/kg per d, and 150 mg/kg per d mexiletine (P less than 0.001, analysis of variance). Sodium channel number increased monoexponentially to a steady-state value within 3 d with a half-time of increase of 1.0 d. After cessation of treatment with mexiletine the number of sodium channels returned to normal within 12 d. Finally, treatment with mexiletine altered only sodium channel number; the Kd for [3H]BTXB and the IC50 for mexiletine were not different for myocytes prepared from control and mexiletine-treated rats.
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Affiliation(s)
- M Taouis
- Department of Medicine, University of Calgary, Alberta, Canada
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49
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Leitch JW, Gillis AM, Wyse DG, Yee R, Klein GJ, Guiraudon G, Sheldon RS, Duff HJ, Kieser TM, Mitchell LB. Reduction in defibrillator shocks with an implantable device combining antitachycardia pacing and shock therapy. J Am Coll Cardiol 1991; 18:145-51. [PMID: 2050917 DOI: 10.1016/s0735-1097(10)80232-3] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Implantable defibrillators reduce the risk of sudden death in patients with malignant ventricular arrhythmias, but significant restriction in quality of life can occur as a result of frequent device activation. To determine if a device that provides both antitachycardia pacing and shock therapy can safely reduce the frequency of shocks after implantation, 46 consecutive patients undergoing initial implantation of a defibrillator were studied. In all patients, the implanted device provided antitachycardia pacing and shock therapy. Detected tachycardia characteristics and the results of therapy were stored in the device's memory. There were 42 men and 4 women, aged 26 to 71 years (mean 58.7 +/- 13.5). Left ventricular ejection fraction ranged from 13% to 67% (mean 32.2 +/- 13.4%) and 31 patients had experienced one or more episodes of cardiac arrest. Induced arrhythmias included sustained monomorphic ventricular tachycardia in 38 patients, nonsustained polymorphic ventricular tachycardia in 2 and ventricular fibrillation in 4. Over a total follow-up period of 255 patient-months (range 1 to 13, mean 6.1), 25 patients experienced spontaneous arrhythmic events. In 22 patients, 909 episodes of tachycardia were treated by antitachycardia pacing, which was successful on 840 occasions (92.4%). Acceleration of ventricular tachycardia by pacing therapy was estimated to have occurred 39 times. Syncope occurred once during pacing-induced acceleration of ventricular tachycardia. Forty-four episodes of tachycardia in seven patients were treated directly by shocks because of short tachycardia cycle length; 88% of all detected tachycardias were treated without the need for shocks. Four patients died from cardiorespiratory failure and one patient died suddenly without any detected tachyarrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J W Leitch
- Department of Medicine, University Hospital, London, Ontario, Canada
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50
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Taouis M, Sheldon RS, Hill RJ, Duff HJ. Cyclic AMP-dependent regulation of the number of [3H]batrachotoxinin benzoate binding sites on rat cardiac myocytes. J Biol Chem 1991; 266:10300-4. [PMID: 1645346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We sought to assess the effect of an increase in cAMP on sodium channels on adult rat cardiac ventricular myocytes. Sodium channels were studied with the use of the radiolabeled sodium channel-specific toxin [3H] batrachotoxinin benzoate ([3H]BTXB). Forskolin, isoproterenol, prostaglandin E1, cholera toxin, and pertussis toxin each increased cAMP levels and decreased the number of [3H]BTXB binding sites without changing the affinity of [3H]BTXB for the sodium channel. The cAMP analog 8-bromo-cyclic AMP (8-Br-cAMP) reduced the number of [3H]BTXB binding sites from 19 fmol/10(5) cells to 11 fmol/10(5) cells. [3H]BTXB binding site down-regulation was reversible, cAMP dose-dependent, and time-dependent. To test the hypothesis that the cAMP effect was mediated by cAMP-dependent phosphorylation, we determined the effect of 8-Br-cAMP on [3H]BTXB binding after preincubation of myocytes with N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide dihydrochloride (H8), a protein kinase A inhibitor. H8 inhibited 70% of the decrease in the number of [3H]BTXB binding sites induced by 8-Br-cAMP. Thus increases in intracellular cAMP in cardiac myocytes reversibly induced a decrease in the number of [3H]BTXB binding sites via cAMP-dependent protein phosphorylation, possibly of the sodium channel.
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Affiliation(s)
- M Taouis
- Department of Medicine, University of Calgary, Alberta, Canada
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