Long-Term Outcomes of Resynchronization-Defibrillation for Heart Failure

BACKGROUND

The Resynchronization-Defibrillation for Ambulatory Heart Failure Trial (RAFT) showed a greater benefit with respect to mortality at 5 years among patients who received cardiac-resynchronization therapy (CRT) than among those who received implantable cardioverter-defibrillators (ICDs). However, the effect of CRT on long-term survival is not known.

METHODS

We randomly assigned patients with New York Heart Association (NYHA) class II or III heart failure, a left ventricular ejection fraction of 30% or less, and an intrinsic QRS duration of 120 msec or more (or a paced QRS duration of 200 msec or more) to receive either an ICD alone or a CRT defibrillator (CRT-D). We assessed long-term outcomes among patients at the eight highest-enrolling participating sites. The primary outcome was death from any cause; the secondary outcome was a composite of death from any cause, heart transplantation, or implantation of a ventricular assist device.

RESULTS

The trial enrolled 1798 patients, of whom 1050 were included in the long-term survival trial; the median duration of follow-up for the 1050 patients was 7.7 years (interquartile range, 3.9 to 12.8), and the median duration of follow-up for those who survived was 13.9 years (interquartile range, 12.8 to 15.7). Death occurred in 405 of 530 patients (76.4%) assigned to the ICD group and in 370 of 520 patients (71.2%) assigned to the CRT-D group. The time until death appeared to be longer for those assigned to receive a CRT-D than for those assigned to receive an ICD (acceleration factor, 0.80; 95% confidence interval, 0.69 to 0.92; P = 0.002). A secondary-outcome event occurred in 412 patients (77.7%) in the ICD group and in 392 (75.4%) in the CRT-D group.

CONCLUSIONS

Among patients with a reduced ejection fraction, a widened QRS complex, and NYHA class II or III heart failure, the survival benefit associated with receipt of a CRT-D as compared with ICD appeared to be sustained during a median of nearly 14 years of follow-up. (RAFT ClinicalTrials.gov number, NCT00251251.).

Identification and in-silico characterization of splice-site variants from a large cardiogenetic national registry

Splice-site variants in cardiac genes may predispose carriers to potentially lethal arrhythmias. To investigate, we screened 1315 probands and first-degree relatives enrolled in the Canadian Hearts in Rhythm Organization (HiRO) registry. 10% (134/1315) of patients in the HiRO registry carry variants within 10 base-pairs of the intron-exon boundary with 78% (104/134) otherwise genotype negative. These 134 probands were carriers of 57 unique variants. For each variant, American College of Medical Genetics and Genomics (ACMG) classification was revisited based on consensus between nine in silico tools. Due in part to the in silico algorithms, seven variants were reclassified from the original report, with the majority (6/7) downgraded. Our analyses predicted 53% (30/57) of variants to be likely/pathogenic. For the 57 variants, an average of 9 tools were able to score variants within splice sites, while 6.5 tools responded for variants outside these sites. With likely/pathogenic classification considered a positive outcome, the ACMG classification was used to calculate sensitivity/specificity of each tool. Among these, Combined Annotation Dependent Depletion (CADD) had good sensitivity (93%) and the highest response rate (131/134, 98%), dbscSNV was also sensitive (97%), and SpliceAI was the most specific (64%) tool. Splice variants remain an important consideration in gene elusive inherited arrhythmia syndromes. Screening for intronic variants, even when restricted to the ±10 positions as performed here may improve genetic testing yield. We compare 9 freely available in silico tools and provide recommendations regarding their predictive capabilities. Moreover, we highlight several novel cardiomyopathy-associated variants which merit further study.

Patients acceptance and comprehension to written and verbal consent (PAC-VC)

BACKGROUND

Acute myocardial infarction (AMI) research is challenging as it requires enrollment of acutely ill patients. Patients are generally in a suboptimal state for providing informed consent. Patients' understanding to verbal assents have not been previously examined in AMI research. Patients Acceptance and Comprehension to Written and Verbal Consent (PAC-VC) compared patients' understanding and attitudes to verbal and written consents in AMI RCTs.

METHODS

PAC-VC recruited patients from 3 AMI trials using both verbal N = 12 and written N = 6 consents. We compared patients' understanding using two survey questionnaires. The first questionnaire used open-ended questions with multiple choice answers. The second questionnaire used a 5-point Likert scale to measure patients understanding and attitudes to the consent process. Overall answers average scores were categorized into three groups: Adequate understanding (71-100) %, Partial understanding (41-70)% and Inadequate understanding (0-40)%.

RESULTS

Responses showed patients with verbal assent had adequate understanding to most components of informed consent, close to those of written consent. Most patients did not read written information entirely and believed that it is not important to make a final decision. Patients favoured to have written information be part of the consent but not necessarily presented during the initial consent process. Patients felt less pressured in the verbal assent arm than those of written consent.

CONCLUSION

Patients had adequate understanding to most components of verbal assent and comparable to those of written consent. Utilizing verbal assents in the acute care setting should be further assessed in larger trials.

Management of Inherited Arrhythmia Syndromes: a HiRO Consensus Handbook on Process of Care

Inherited arrhythmia syndromes are rare genetic conditions that predispose seemingly healthy individuals to sudden cardiac arrest and death. The Hearts in Rhythm Organization is a multidisciplinary Canadian network of clinicians, researchers, patients, and families that aims to improve care for patients and families with inherited cardiac conditions, focused on those that confer predisposition to arrhythmia and sudden cardiac arrest and/or death. The field is rapidly evolving as research discoveries increase. A streamlined, practical guide for providers to diagnose and follow pediatric and adult patients with inherited cardiac conditions represents a useful tool to improve health system utilization, clinical management, and research related to these conditions. This review provides consensus care pathways for 7 conditions, including the 4 most common inherited cardiac conditions that confer predisposition to arrhythmia, with scenarios to guide investigation, diagnosis, risk stratification, and management. These conditions include Brugada syndrome, long QT syndrome, arrhythmogenic right ventricular cardiomyopathy and related arrhythmogenic cardiomyopathies, and catecholaminergic polymorphic ventricular tachycardia. In addition, an approach to investigating and managing sudden cardiac arrest, sudden unexpected death, and first-degree family members of affected individuals is provided. Referral to specialized cardiogenetic clinics should be considered in most cases. The intention of this review is to offer a framework for the process of care that is useful for both experts and nonexperts, and related allied disciplines such as hospital management, diagnostic services, coroners, and pathologists, in order to provide high-quality, multidisciplinary, standardized care.

Sex Differences and Utility of Treadmill Testing in Long‐QT Syndrome

Background

Diagnosis of congenital long‐QT syndrome (LQTS) is complicated by phenotypic ambiguity, with a frequent normal‐to‐borderline resting QT interval. A 3‐step algorithm based on exercise response of the corrected QT interval (QTc) was previously developed to diagnose patients with LQTS and predict subtype. This study evaluated the 3‐step algorithm in a population that is more representative of the general population with LQTS with milder phenotypes and establishes sex‐specific cutoffs beyond the resting QTc.

Methods and Results

We identified 208 LQTS likely pathogenic or pathogenic KCNQ1 or KCNH2 variant carriers in the Canadian NLQTS (National Long‐QT Syndrome) Registry and 215 unaffected controls from the HiRO (Hearts in Rhythm Organization) Registry. Exercise treadmill tests were analyzed across the 5 stages of the Bruce protocol. The predictive value of exercise ECG characteristics was analyzed using receiver operating characteristic curve analysis to identify optimal cutoff values. A total of 78% of male carriers and 74% of female carriers had a resting QTc value in the normal‐to‐borderline range. The 4‐minute recovery QTc demonstrated the best predictive value for carrier status in both sexes, with better LQTS ascertainment in female patients (area under the curve, 0.90 versus 0.82), with greater sensitivity and specificity. The optimal cutoff value for the 4‐minute recovery period was 440 milliseconds for male patients and 450 milliseconds for female patients. The 1‐minute recovery QTc had the best predictive value in female patients for differentiating LQTS1 versus LQTS2 (area under the curve, 0.82), and the peak exercise QTc had a marginally better predictive value in male patients for subtype with (area under the curve, 0.71). The optimal cutoff value for the 1‐minute recovery period was 435 milliseconds for male patients and 455 milliseconds for femal patients.

Conclusions

The 3‐step QT exercise algorithm is a valid tool for the diagnosis of LQTS in a general population with more frequent ambiguity in phenotype. The algorithm is a simple and reliable method for the identification and prediction of the 2 major genotypes of LQTS.

Bidirectional Ventricular Tachycardia: Challenges and Solutions

Bidirectional ventricular tachycardia (BiVT) is a rare form of ventricular tachycardia that manifests on surface electrocardiogram by dual QRS morphologies alternating on a beat-to-beat basis. It was first reported in the 1920s as a complication of digoxin, and since then, it has been reported in other conditions including fulminant myocarditis, sarcoidosis, catecholaminergic polymorphic ventricular tachycardia, and Andersen-Tawil syndrome. The mechanism for BiVT is not as well known as other forms of ventricular tachycardia but appears to include typical mechanisms including triggered activity from afterdepolarizations, abnormal automaticity, or reentry. This review will go beyond the definition, surface electrocardiogram, mechanisms, causes, and treatment of BiVT as per our current understanding.

Return of Results Policies for Genomic Research: Current Practices & The Hearts in Rhythm Organization Approach

Research teams developing biobanks and/or genomic databases must develop policies for the disclosure and reporting of potentially actionable genomic results to research participants. Currently, a broad range of approaches to the return of results exist, with some studies opting for non-disclosure of research results while others follow clinical guidelines for the return of potentially actionable findings from sequencing. In this review, we describe current practices and highlight decisions a research team must make when designing a return of results policy, from informed consent to disclosure practices and clinical validation options. The unique challenges of returning incidental findings in cardiac genes, including reduced penetrance and the lack of clinical screening standards for phenotype-negative individuals are discussed. Lastly, the National Hearts in Rhythm Organization (HiRO) Registry approach is described to provide a rationale for the selective return of field-specific variants to those participating in disease-specific research. Our goal is to provide researchers with a resource when developing a return of results policy tailored for their research program, based on unique factors related to study design, research team composition and availability of clinical resources.

Clinical utility of 12-lead electrocardiogram in evaluating heart disease in patients with muscular dystrophy: Assessment of left ventricular hypertrophy, conduction disease, and cardiomyopathy

Introduction

Heart disease remains a leading cause of mortality in patients with muscular dystrophy (MD), and cardiac assessment by standard imaging modalities is challenging due to the prominence of physical limitations.

Methods

In this prospective cohort study of 169 MD patients and 34 negative control patients, we demonstrate the clinical utility of a 12‐lead electrocardiogram (ECG) as an effective modality for the assessment of cardiac status in patients with MD. We assessed the utility of conventional criteria for electrocardiogram‐indicated left ventricular hypertrophy (ECG‐LVH) as well as ECG morphologies.

Results

Cornell voltage, Cornell voltage‐duration, Sokolow–Lyon voltage, and Romhilt‐Estes point score criteria demonstrated low sensitivity and minimal positive predictive value for ECG‐LVH when compared with cardiac imaging. Patients with LBBB had a high probability of a cardiomyopathy (relative risk [RR], 2.75; 95% confidence interval [CI], 2.14–3.53; p < .001), and patients with QRS fragmentation (fQRS) had a high probability of a cardiomyopathy (RR, 1.76; 95% CI, 1.20–2.59; p = .004), requiring cardiac medication and device intervention. We found that an R/S ratio >1 in V1 and V2 is highly specific (specificity, 0.89; negative predictive value [NPV], 0.89 and specificity, 0.82; NPV, 0.89, respectively) for patients with dystrophinopathies compared with other types of MD.

Conclusion

The identification of LBBB and fQRS was linked to cardiomyopathy in patients with MD, while ECG‐LVH was of limited utility. Importantly, these findings can be applied to effectively screen a broad cohort of MD patients for structural heart disease and prompt further evaluation and therapeutic intervention.

Plasma Exchange for Immune Checkpoint Inhibitor-Induced Myocarditis

Immune checkpoint inhibitor therapy has been shown to improve outcomes across many types of malignancies. However, immune checkpoint inhibitor has been associated with several immune-related adverse events including myocarditis. We describe the case of a 69-year-old man with fulminant myocarditis likely due to pembrolizumab therapy, complicated by biventricular failure with cardiogenic shock. Because of deterioration in hemodynamic status refractory to conventional immunosuppression, therapeutic plasma exchange was performed, resulting in a rapid reduction of serum pembrolizumab levels, and marked clinical, radiological, and biochemical improvement. To our knowledge, this is the first reported case on the successful use of plasma exchange for pembrolizumab-associated fulminant myocarditis.

Comparison of Usefulness of Cardiac Resynchronization Therapy in Patients With Type 1 Myotonic Dystrophy With Versus Without Left Bundle Branch Block

Patients with type 1 myotonic dystrophy show reduced left ventricular systolic function in the presence of left bundle branch block due to electromechanical dys-synchrony. Our prospective study tracked a cohort of 64 type 1 myotonic dystrophy patients that demonstrated a high burden of atrial and ventricular arrhythmias and conduction delays. Of these patients, 12 (19%) patients had left bundle branch block, which was associated with reduced left ventricular systolic function. Eight of these patients received cardiac resynchronization therapy devices resulting in reduction of median QRS complex duration from 173 to 166 ms (p = 0.04), and improvement in median left ventricular ejection fraction from 37% to 46% (p = 0.007). In conclusion, cardiac resynchronization therapy device therapy is both feasible and effective in treating advanced cardiac disease in this vulnerable group of patients by improving left ventricular function.

A Population-Based Study of Adherence to Guideline Recommendations and Appropriate-Use Criteria for Implantable Cardioverter Defibrillators

Studies evaluating physician adherence to guideline recommendations for implantable cardioverter defibrillator (ICD) therapy are sparse, and none exist for the application of appropriate-use criteria (AUC) in clinical practice. As part of a quality improvement initiative, a review of all ICD procedures was performed from January 1, 2015 to December 31, 2016 in Alberta, Canada, to evaluate the proportion of patients receiving appropriate ICD therapy and to identify reasons for nonadherence. Our device-implant process involves an electrophysiologist or implanting cardiologist evaluation, reminders of ICD eligibility criteria on the device requisition, and peer-review consensus. Implants were classified according to the 2008 American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) ICD guidelines, 2013 Canadian Cardiovascular Society (CCS) Cardiac Resynchronization Therapy (CRT) guidelines, and 2013 AUC. There were 1,300 ICD procedures performed, and the mean age was 63.8 ± 12.9 years; 79% were male; the mean ejection fraction was 0.32 ± 0.13, and 69% were for primary prevention. Among all implants, < 1% were discordant with American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) recommendations. Among CRT implants, 10% were inconsistent with Canadian Cardiovascular Society (CCS) recommendations. According to AUC, 92% of implants were appropriate. Reasons for nonadherence to ACC/AHA/HRS recommendations included QRS width < 120 msec (n = 3), LVEF > 0.35 (n = 2) and recent myocardial infarction (MI) (n = 1). The most common reason for nonadherence to AUC was the absence of criteria for classification (n = 57, 4%). In this population-based study, we found that a process of specialist evaluation, eligibility reminders on device forms, and peer-review consensus may improve adherence to guideline recommendations and AUC for ICD therapy.

Chemical and structural analysis of enhanced biochars: thermally treated mixtures of biochar, chicken litter, clay and minerals

In this study biochar mixtures comprising a Jarrah-based biochar, chicken litter (CL), clay and other minerals were thermally treated, via torrefaction, at moderate temperatures (180 and 220 °C). The objectives of this treatment were to reduce N losses from CL during processing and to determine the effect of both the type of added clay and the torrefaction temperature on the structural and chemical properties of the final product, termed as an enhanced biochar (EB). Detailed characterisation indicated that the EBs contained high concentrations of plant available nutrients. Both the nutrient content and plant availability were affected by torrefaction temperature. The higher temperature (220 °C) promoted the greater decomposition of organic matter in the CL and dissociated labile carbon from the Jarrah-based biochar, which produced a higher concentration of dissolved organic carbon (DOC). This DOC may assist to solubilise mineral P, and may also react with both clay and minerals to block active sites for P adsorption. This subsequently resulted in higher concentrations of plant available P. Nitrogen loss was minimised, with up to 73% of the initial total N contained in the feedstock remaining in the final EB. However, N availability was affected by both torrefaction temperature and the nature of the clay minerals added.

Predicting defibrillation outcome based on phase of ventricular activity during ICD implantation

Implantable cardioverter-defibrillators (ICDs) are well known medical device for patients who are at a risk of sudden cardiac death caused by ventricular fibrillation (VF). The relationship between VF mechanisms and successful ICD therapy to terminate of VF is still not well understood. The purpose of this work is to evaluate the timing of ICD therapy as a predictor of successful VF termination. Clinical data sets were recorded from the patients who underwent ICD implantation in 6 Canadian centers. Timing of the defibrillation attempt (phase) was analyzed by using the ICD Marker Channel which monitors and displays cardiac events sensed by ICD. Phase, based on the VF period, was divided into 10 equally distributed bins and number of successful defibrillation episodes in each bin was compared. A total of 187 defibrillation attempts were identified from the 65 subjects. 126 of the defibrillation attempts were successful, while 61 failed. The optimal case was observed at a phase value of 1.2pi with 2 successful attempts. The lowest performance rate was found at a phase value of 1.4pi and 1.8pi with 50% (3 and 2 successful attempts, respectively). The probability of success was analyzed by using generalized estimating equations (GEE) approach with an exchangeable correlation structure. The results of the GEE logistic regression model indicate no correlation between successful defibrillation attempts and phase of ventricular activity during VF (p-value = 0.78). From our results, timing of defibrillation shock attempt is not a factor in successful termination of VF for patients undergoing ICD implantation.

Fibrillation complexity as a predictor of successful defibrillation

A major focus of Implantable Cardioverter Defibrillator (ICD) research has been to reduce the defibrillation shock energy to prolong battery life and provide an enhanced quality of life for the patient. We investigated whether the degree of disorganization (complexity) of the electrogram is correlated with defibrillation shock outcome. The study data sets were recorded using the high voltage leads of an ICD during device implantation. A total 57 data segments from 19 patients were analyzed. Beat cycles were identified using a novel wavelet based method. Two algorithms were proposed and implemented to quantify the disorganization of the electrogram signals: Approximate Entropy and Cross Correlation. Entropy Index based on the ApEn method, was able to discriminate successful episodes from failure ones with a specificity of 93% and sensitivity of 100%. Similarity Index based on Cross correlation method, obtained a specificity of 72% and sensitivity of 66%. We conclude that the organization of a VF episode is related to the minimum energy required for successful defibrillation.

Fibrillation complexity as a predictor of successful defibrillation

A major focus of Implantable Cardioverter Defibrillator (ICD) research has been to reduce the defibrillation shock energy to prolong battery life and provide an enhanced quality of life for the patient. We investigated whether the degree of disorganization (complexity) of the electrogram is correlated with defibrillation shock outcome. The study data sets were recorded using the high voltage leads of an ICD during device implantation. A total 57 data segments from 19 patients were analyzed. Beat cycles were identified using a novel wavelet based method. Two algorithms were proposed and implemented to quantify the disorganization of the electrogram signals: Approximate Entropy and Cross Correlation. Entropy Index based on the ApEn method, was able to discriminate successful episodes from failure ones with a specificity of 93% and sensitivity of 100%. Similarity Index based on Cross correlation method, obtained a specificity of 72% and sensitivity of 66%. We conclude that the organization of a VF episode is related to the minimum energy required for successful defibrillation.

Proportion of patients followed in a specialized heart failure clinic needing an implantable cardioverter defibrillator as determined by applying different trial eligibility criteria

Numerous trials have demonstrated survival benefits using implantable cardioverter defibrillators (ICDs) for primary prevention in selected patients with left ventricular (LV) systolic dysfunction. However, eligibility criteria differed across these trials. Without a risk stratification scheme that clearly identifies those who will benefit, there remains debate about which patients with heart failure (HF) should receive ICDs for primary prevention. To explore the implications of applying different eligibility criteria, this study evaluated all patients seen in a specialized HF clinic from August 2003 to January 2004. Of the 309 consecutive patients in the cohort, 46 were excluded because their HF complicated recent myocardial infarcts (n = 3); their LV ejection fractions were not measured (n = 9); or their HF was due to valvular disease, myocarditis, or peripartum cardiomyopathy (n = 34). The Multicenter Automatic Defibrillator Implantation Trial-II criteria were met by 85 patients (32%), and 134 patients (51%) met the Sudden Cardiac Death in Heart Failure Trial criteria. Even allocation decisions based on randomized trial evidence can have vastly different resource implications depending on which trial is chosen. Thus, the development and validation of a risk stratification scheme to identify those patients most likely to benefit from ICDs for primary prophylaxis should be a research priority.

How many patients with heart failure are eligible for cardiac resynchronization? Insights from two prospective cohorts

AIMS

To determine what proportion of patients with heart failure are eligible for cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Eligibility criteria from the trials establishing the efficacy of CRT were applied to two prospective cohorts: the first enrolled patients with newly diagnosed heart failure discharged from 103 hospitals between April 1999 and March 2001 ('the hospital discharge cohort'); the second enrolled patients seen in a specialized clinic between August 2003 and January 2004 ('the specialty clinic cohort'). In the hospital discharge cohort, 73 patients (3% of the 2640 patients with ischaemic or dilated cardiomyopathy and 1% of all 9096 patients with heart failure discharged alive) met trial eligibility criteria: LVEF< or =0.35, QRS > or =120 ms, sinus rhythm, and NYHA class III or IV symptoms despite the treatment with ACE-inhibitor/angiotensin receptor blocker and beta-blocker. In the specialty clinic cohort, 54 patients (21% of the 263 patients with ischaemic or dilated cardiomyopathy and 17% of all 309 patients with heart failure) met these criteria. If persistent symptoms despite taking spironolactone were required for CRT eligibility, then the proportions qualifying dropped to 1% in the hospital discharge cohort and 18% in the specialty clinic cohort.

CONCLUSION

Few heart failure patients meet trial eligibility criteria for CRT.

Defibrillation Depends on Conductivity Fluctuations and the Degree of Disorganization in Reentry Patterns

Defibrillation depends on conductivity and disorganization.

INTRODUCTION

Cardiac fibrillation is the deterioration of the heart's normally well-organized activity into one or more meandering spiral waves, which subsequently break up into many meandering wave fronts. Delivery of an electric shock (defibrillation) is the only effective way of restoring the normal rhythm. This study focuses on examining whether higher degrees of disorganization requires higher shock strengths to defibrillate and whether microscopic conductivity fluctuations favor shock success.

METHODS AND RESULTS

We developed a three-dimensional computer bidomain model of a block of cardiac tissue with straight fibers immersed in a conductive bath. The membrane behavior was described by the Courtemanche human atrial action potential model incorporating electroporation and an acetylcholine- (ACh) dependent potassium current. Intracellular conductivities were varied stochastically around nominal values with variations of up to 50%. A single rotor reentry was initiated and, by adjusting the spatial ACh variation, the level of organization could be controlled. The single rotor could be stabilized or spiral wave breakup could be provoked leading to fibrillatory-like activity. For each level of organization, multiple shock timings and strengths were applied to compute the probability of shock success as a function of shock strength.

CONCLUSIONS

Our results suggest that the level of the small-scale conductivity fluctuations is a very important factor in defibrillation. A higher variation significantly lowers the required shock strength. Further, we demonstrated that success also heavily depends on the level of organization of the fibrillatory episode. In general, higher levels of disorganization require higher shock strengths to defibrillate.

Randomized controlled study of detection enhancements versus rate-only detection to prevent inappropriate therapy in a dual-chamber implantable cardioverter-defibrillator

OBJECTIVES

The purpose of this study was to compare rate-only detection to enhanced detection in a dual-chamber implantable cardioverter-defibrillator (ICD), to discriminate ventricular tachycardia from supraventricular tachycardia.

BACKGROUND

ICDs are highly effective in treating ventricular tachycardia (VT) or ventricular fibrillation (VF). However, they frequently deliver inappropriate therapy during supraventricular tachycardia (SVT).

METHODS

We conducted a randomized clinical trial of detection enhancements in a dual-chamber ICD compared to control (rate-only) detection to discriminate VT from SVT. Detection enhancements included a specific standardized protocol identical for all patients for programming rate stability, sudden onset, atrial-to-ventricular relationship (sudden onset = 9% and rate stability = 10 ms; V > A "on"), and "sustained rate duration" (3 minutes). The primary endpoint was the time to first inappropriate therapy classified by a blinded events committee.

RESULTS

One hundred forty-nine patients had a history of sustained VT or VF. Mean age (+/- SD) was 60 +/- 13 years; 83% were male, and mean ejection fraction was 35 +/- 15%. Control (n = 70) and "enhanced" (n = 79) groups did not differ with regard to age, sex, ejection fraction, or primary arrhythmia. The proportion of patients free of inappropriate therapy over time was significantly higher in the enhanced versus the control group (hazard ratio = 0.47, P = .011). High-energy shocks were reduced from 0.58 +/- 4.23 shocks/patient/month in the control group to 0.04 +/- 0.15 shocks/patient/month in the enhanced group (P = .0425). No patient programmed per protocol failed to receive therapy for VT detected by the ICD (422 VT episodes).

CONCLUSIONS

Standardized programming in a dual-chamber ICD leads to a significant and clinically important reduction in inappropriate therapies compared to rate-only detection and does not compromise safety with respect to appropriate treatment of VT.

Identification of Genes Regulated by Leukemia-Inhibitory Factor in the Mouse Uterus at the Time of Implantation

The endometrium is prepared for implantation by the actions of estradiol (E2) and progesterone (P4). In mice the luminal epithelium (LE) only becomes fully receptive to the attaching blastocyst in response to the nidatory estrogen surge on d 4 of pregnancy. The cytokine leukemia-inhibitory factor (LIF) is rapidly induced by nidatory estrogen and has been shown to be the primary mediator of its action. Implantation fails in the absence of LIF, and injection of LIF on d 4 of pregnancy can substitute for the nidatory estrogen. In this study, we sought to identify genes regulated by LIF in the uterine epithelium. We used oligonucleotide microarrays to compare the transcript profiles of paired uterine horns from LIF-deficient MF1 mice after intraluminal injection of LIF or PBS on d 4 of pseudopregnancy. IGF-binding protein 3 was identified as a gene up-regulated by LIF; this was confirmed by RT-PCR. In situ hybridization showed that the primary site of IGF-binding protein 3 expression is the luminal epithelium (LE), the known site of LIF action in the uterus. We identified two other genes: amphiregulin and immune response gene-1, the expression of which were also up-regulated by LIF. Immune response gene 1 has recently been shown to be essential for implantation. Expression of all three of these genes in the LE is known to be regulated by P4. The expression of osteoblast-specific factor 2 and leukocyte 12/15 lipoxygenase, which are also expressed in LE under the control of P4, were not increased by LIF. This suggests that one of the actions of LIF on LE may be to enhance the expression of a subset of P4-regulated genes.

An evaluation of the effects of high-dose fexofenadine on the central nervous system: a double-blind, placebo-controlled study in healthy volunteers

BACKGROUND

As regards central nervous system (CNS) effects there are three types of antihistamines. Those that cross the blood-brain barrier and cause widespread impairment of cognitive and psychomotor function; those that cross into the brain and, although without much impairment at low clinical doses, have a dose-related relationship to impairment; and those that do not cross into the brain and therefore possess no intrinsic potential for impairing CNS function.

OBJECTIVE

[corrected] To investigate the acute effects of fexofenadine (360 mg) on various aspects of cognitive and psychomotor function in comparison to placebo and promethazine (positive internal control), an antihistamine known to produce psychomotor and cognitive impairment.

METHODS

Fifteen healthy volunteers received fexofenadine 360 mg, promethazine 30 mg and placebo in a 3-way cross-over, double-blind study. For each treatment condition, subjects were required to perform a series of tests of cognitive function and psychomotor performance at baseline and 1, 3, 5 and 7 h post-dose. The test battery consisted of critical flicker fusion (CFF), choice reaction time (CRT), compensatory tracking task (CTT) and a subjective assessment of sedation (LARS).

RESULTS

Fexofenadine was not distinguishable from placebo in any of the objective and subjective tests for up to seven hours following drug administration. However, all measures were significantly impaired following the administration of promethazine, which confirms the sensitivity of the test battery for sedation. The effects of fexofenadine and placebo were not significantly different from one another, whereas promethazine caused an overall reduction in CFF thresholds when compared to placebo (P < 0.05). There was an overall significant increase (impairment) in recognition, motor and total reaction time (P < 0.05), and both the tracking accuracy and reaction time aspects of CTT were significantly impaired (P < 0.05) following the administration of promethazine. In contrast, the effects of fexofenadine could not be distinguished from the placebo condition. Subjective ratings of sedation were significantly higher with promethazine when compared to placebo (P < 0.05) and fexofenadine (P< 0.05).

CONCLUSIONS

Fexofenadine at a dose of 360mg is demonstrably free from disruptive effects on aspects of psychomotor and cognitive function in a study where the psychometric assessments have been shown to be sensitive to impairment, as evidenced by the effects of the verum control promethazine 30 mg. The identification of an antihistamine (fexofenadine) devoid of central effects even at supraclinical doses separates it from currently available first and second generation drugs with no objective evidence of CNS side-effects on cognition and psychomotor function, and highlights the need for the introduction of a third generation of non-sedative antihistamines.

Circadian variation of paroxysmal atrial fibrillation. PA3 Investigators. Atrial Pacing Peri-ablation for Prevention of Atrial Fibrillation Trial

The circadian variation of paroxysmal atrial fibrillation (AF) was studied in 67 patients who received a dual-chamber pacemaker 3 months before a planned atrioventricular node ablation. A distinct circadian variation of AF was observed with 2 time peaks in initiation (1 in the early morning and 1 in the early evening hours), which was modulated by atrial pacing, the duration of AF, and the use of beta-adrenergic blocking agents.

An investigation into the effects of cetirizine on cognitive function and psychomotor performance in healthy volunteers

OBJECTIVE

The cognitive and psychomotor effects of 2.5, 5 and 10 mg cetirizine, a second-generation H1 receptor antagonist, were compared with loratadine 10, 20 and 40 mg, promethazine 25 mg and placebo in 24 healthy volunteers in a double-blind, randomised cross-over study.

METHODS

Following each dose, subjects were required to perform a series of tests of cognitive function and psychomotor performance at 1.5, 3 and 6 h post-dose. The test battery consisted of critical flicker fusion (CFF), choice reaction time (CRT), compensatory tracking task (CTT) and assessment of subjective sedation (LARS).

RESULTS

Cetirizine and loratadine at all doses tested were not significantly different from placebo in any of the tests used. However, as expected for a verum, all measures with the exception of CTT were significantly disrupted by promethazine (P < 0.05). Promethazine caused a reduction in CFF threshold at all test points; these differences were significant at 3 h and 6 h post-dose (P < 0.05). There was also a significant increase in total reaction time at 3 h post-promethazine administration. Subjective reports of sedation were significantly greater following the administration of promethazine at all time points (P < 0.05).

CONCLUSIONS

These results allow the conclusion that cetirizine at its recommended therapeutic dose of 10 mg is demonstrably free from disruptive effects on aspects of psychomotor and cognitive function in a study where the psychometric assessments have been shown to be sensitive to impairment, as evidenced by the effects of the positive control, promethazine 25 mg.

Abrupt and brief discontinuation of antidepressant treatment: effects on cognitive function and psychomotor performance

The abrupt discontinuation of antidepressants can result in a syndrome of adverse events, including somatic, mood and psychomotor reactions. This study examined the effects of discontinuing and resuming antidepressant treatment with four selective serotonin reuptake inhibitors (SSRIs) on cognitive and psychomotor function. Eighty-seven patients receiving maintenance therapy with fluoxetine, sertraline, paroxetine or citalopram had their treatment interrupted for 4-7 days using double-blind placebo. Assessments of aspects of cognitive and psychomotor performance, mood and symptoms were carried out at each visit. Following interruption of treatment, significant differences between the groups emerged. Paroxetine treated patients experienced significantly more cognitive failures (P = 0.007), poorer quality of sleep (P = 0.016), and an increase in depressive symptoms, as rated both subjectively, using the Zung scale (P = 0.006) and by the clinician, using the Montgomery-Asberg Depression Rating Scale (P = 0.0003) and Clinical Global Impression (P = 0.0003), compared to some or all of the other drugs. All changes were reversed on reinstatement of treatment. Abrupt discontinuation of treatment with paroxetine leads to deterioration in various aspects of health and functioning, which may be related to the antidepressant discontinuation syndrome. These effects are not evident in patients receiving fluoxetine, sertraline and citalopram, suggesting they are not an SSRI class phenomenon.

The effects of Ginkgo biloba extract (LI 1370) supplementation on activities of daily living in free living older volunteers: a questionnaire survey

This survey assessed the impact of four months supplementation with 120 mg/day of the standardized Ginkgo biloba special extract (LI 1370) on activities of daily living and various aspects of mood and sleep in a population of free living older volunteers using both observer- and self-rated scales. 5028 Participants (mean age 68.9 years) were recruited through a magazine editorial. One thousand received Ginkgo biloba extract (GBE) and the remainder were allocated to the Control group. The B-ADL (activities of daily living) Scale was completed at baseline and at the end of month 4 by an informant familiar with the participant, a Self-rating ADL scale and Line Analogue Ratings Scales of mood and sleep were completed by the participants at the end of months 1, 2, 3, and 4. There were significant differences between the GBE and Control groups on all scales at each time point. The GBE group felt better able to cope with their daily activities and showed positive changes in mood and sleep compared to the Control group. These results suggest that GBE supplementation has beneficial effects on areas of functioning that have implications for quality of life in an older population. Copyright 2000 John Wiley & Sons, Ltd.

The effects of acute doses of standardized Ginkgo biloba extract on memory and psychomotor performance in volunteers

This study investigated the effects of acute doses of Ginkgo biloba extract (GBE) on memory and psychomotor performance in a randomized, double-blind and placebo controlled 5-way cross-over design. Thirty-one volunteers aged 30-59 years received GBE 150 mg (50 mg t. d.s), GBE 300 mg (100 mg t.d.s.), GBE 120 mg mane and GBE 240 mg mane and placebo for 2 days. Following baseline measures, the medication was administered at 0900 h for the single doses and at 0900, 1500 and 2100 h for the multiple doses. The psychometric test battery was administered pre-dose (0830 h) and then at frequent intervals until 11 h post dose. The results confirm that the effects of GBE extract on aspects of cognition in asymptomatic volunteers are more pronounced for memory, particularly working memory. They also show that these effects may be dose dependent though not in a linear dose related manner, and that GBE 120 mg produces the most evident effects of the doses examined. Additionally, the results suggest that the cognitive enhancing effects of GBE are more likely to be apparent in individuals aged 50-59 years.

Contemporary utilization of digoxin in patients with atrial fibrillation. Clinical Quality Improvement Network Investigators

OBJECTIVE

To define the contemporary practice patterns of digoxin utilization for the management of patients with atrial fibrillation (AF).

METHODS

A retrospective medical records audit of 2490 patients with documented AF, from 12 Canadian hospitals and six outpatient clinics, during fiscal year 1993-1994, was conducted.

RESULTS

There were 1158 women and 1332 men, with a mean age of 72 years; 956 patients were < 70 years of age and 1534 were > or = 70 years old. The majority of patients had nonvalvular AF (75% of those with a documented etiology). Paroxysmal AF (PAF) was documented in 800 patients, 936 had chronic AF, and 754 had new-onset AF. While the prescribing patterns were heterogeneous, the predominant strategy pursued in all subgroups appeared to be that of achieving rate control. Digoxin was the most commonly prescribed medication (79%) and was prescribed for the majority of patients in all subgroups, including patients with PAF (74%) and patients with a history of chronic AF who were currently in sinus rhythm (83%). Only 10% of the patients with PAF who were prescribed digoxin had congestive heart failure. Similarly, less than 25% of the patients with chronic AF who were prescribed digoxin after conversion to sinus rhythm had evidence of heart failure.

CONCLUSIONS

In the absence of clinical trial evidence supporting either a strategy of antiarrhythmic therapy or rate control with anticoagulation, the appropriateness of the observed prescribing practices cannot be judged. However, digoxin is not the best rate-controlling agent for all patients and may be overused in certain subgroups of patients, such as those with PAF and those successfully converted to sinus rhythm.

Multisite pacing as a supplemental treatment of congestive heart failure: preliminary results of the Medtronic Inc. InSync Study

This report describes the initial results of the "InSync" study, a European and Canadian multicenter trial that examines the safety and efficacy of a multisite pacemaker (Medtronic InSync) and of left ventricular pacing leads (Medtronic 2187 and 2188) implanted via a cardiac vein as a supplemental treatment of refractory congestive heart failure. Over a 10-month period, the system was implanted successfully in 68 of the 81 (84%) patients who had been enrolled in the study. The 68 patients were, on average, 66 +/- 10 years old, had a mean left ventricular ejection fraction (LVEF) = 21% +/- 9%, and 63% were in NYHA functional Class III and 37% were in Class IV. No system implant related complication occurred. During follow-up, 7 of 10 patients who exited the study had died, 4 suddenly. There was a clinical benefit among surviving patients, which was corroborated by a significant improvement in NYHA functional class and in the Minnesota Living with Heart Failure Quality of Life Questionnaire Score (MLS) and by a longer distance covered during a 6-minute walk test. This clinical improvement was associated with a significant narrowing of the paced QRS complex during biventricular pacing, a significant decrease in the interventricular mechanical delay, and a trend towards an increase in the duration of ventricular filling. These encouraging preliminary results confirm the feasibility and reliability of this new multisite pacing system in the management of dilated cardiomyopathy and support the continuation of further evaluations of this complementary treatment of refractory congestive heart failure.

Characteristics of local electrograms with diastolic potentials: identification of different components of return pathways in ventricular tachycardia

BACKGROUND

Diastolic potentials are often sought as a possible site for catheter ablation in post-infarct ventricular tachycardia. However, delivery of energy at such sites is often unsuccessful. The purpose of this study was to determine the characteristics of local electrograms with diastolic potentials and to identify activation pattern which might indicate the critical portion of the return path of the ventricular tachycardia reentry circuit.

METHODS

In 17 patients with post-myocardial infarction ventricular tachycardia, 30 ventricular tachycardias were mapped with an 112 bipolar endocardial balloon at the time of surgery. Diastolic mapping of the return tract in ventricular tachycardia was performed. Four activation patterns were observed (15 figure 8 patterns, 2 circular patterns, 2 biregional patterns and 11 monoregional patterns). Of 3,360 local electrograms, 207 (6.2%) demonstrated a diastolic potential in ventricular tachycardia. They were classified into following four categories, based on the appearance and timing of the systolic component. Type A-1 electrogram: systolic activation was of low amplitude (< 2 mV) and was prolonged (> or = 100 msec), but preceded the onset of the surface QRS in ventricular tachycardia. Type A-2 electrogram: systolic activation was of low amplitude, was prolonged, but followed the onset of the surface QRS. Type B electrogram: systolic electrogram was fractionated, but relatively normal amplitude (2.0-3.6 mV). Type C electrogram: systolic electrogram was almost normal.

RESULTS

Of all electrograms with diastolic potentials, three type A-1 electrograms (1.4%) were located at the exit of the return pathway, 11 type A-1 electrograms (5.3%) were located at the pre-exit site. No type A-1 was found at an entrance/bystander area. 21 type A-2 electrograms (10.1%) were at the pre-exit and 83 type A-2 electrograms (40.2%) were located at the entrance/bystander area, but such electrograms were never found at the exit site. 71 type B electrograms (34.3%) and 18 type C electrograms (8.7%) were located at the entrance/bystander area. To distinguish the type A-2 electrograms at the pre-exit site from those at the entrance/bystander area, the diastolic potential to QRS interval was measured. This interval at the pre-exit was significantly shorter than that at the entrance/bystander area (-47.2 +/- 10.7 vs -96.3 +/- 31.3 msec, p = 0.0001).

CONCLUSION

Type A-1 electrograms indicated the exit or pre-exit site of return pathway. Type A-2 electrograms with diastolic potential to QRS interval < -50 msec indicated the pre-exit site. However, the other types of local electrograms with diastolic potential did not indicate the critical portion of the ventricular tachycardia circuit. These observations may be helpful during catheter mapping and ablation of patients with post-infarct ventricular tachycardia.

CONDENSED ABSTRACT

Diastolic potentials are often sought to direct catheter ablation in post-infarct ventricular tachycardia. We investigated the characteristics of local electrograms showing diastolic activity in an attempt to determine whether critical portions of the ventricular tachycardia circuit could be identified by a typical "signature." In 17 patients with a remote myocardial infarction, 30 ventricular tachycardias were mapped with 112 bipolar endocardial balloon at the time of surgery. Diastolic potentials in association with low amplitude (< 2 mV) and prolonged (> or = 100 msec) systolic electrograms preceding the onset of QRS were found at the exit site and pre-exit site of return pathway. A similar systolic electrogram occurring after QRS onset with a diastolic potential to QRS interval of < -50 msec was found at the pre-exit site. However, other local electrograms with diastolic activity were at sites remote from the exit or pre-exit of the return pathway. These observations may be helpful during catheter mapping and ablation in patients with ventricular tachycardia.

Cell surface carbohydrates and lectins in early development

Current knowledge on the development regulation of cell surface carbohydrates and lectins in mammalian embryos is summarized. Much of this data comes from observations on mouse embryos but information on the human embryo is included where it is available. Over the last few years, numerous studies have indicated that carbohydrates play a critical role in the cell-cell interactions of the pre- and peri-implantation embryo. Functional tests suggest a role for terminal fucosylated Galbeta1-3/4GlcNAc structures in the early steps of implantation. We also now have clear evidence for the expression of lectins in the trophectoderm just prior to implantation. Mouse mutants have been generated which lack particular enzymes involved in glycosylation or particular lectins, but so far they have not been informative about the role of glycoconjugates or lectins in the very early embryo.

A comparison of unipolar and bipolar electrodes during cardiac mapping studies

Controversy exists as to whether the unipolar or bipolar electrode configuration is superior in detecting local activations during cardiac mapping studies. However, the strengths and weaknesses of each mode suggest that they may provide complementary information. To examine the relative merits of unipolar and bipolar electrode configurations, recordings by each were simultaneously acquired during episodes of ventricular tachycardia in eight consecutive patients undergoing map guided arrhythmia surgery. Unipolar electrograms were classified as either unambiguous or ambiguous according to whether or not they were polyphasic in nature. The activation times from the unambiguous electrograms were compared with activation times from the corresponding bipolar signals where local activation was measured both at the signal's peak amplitude (BI-PK), and at the point at which the waveform's first major, rapid transient crossed baseline (BI-TRN). Occurrences of discrete diastolic activations were also quantified from the unipolar and bipolar tracings. From a total of 415 unipolar electrograms, 301 unambiguous signals were identified as suitable for comparison with the bipolar signals. Both BI-PK and BI-TRN criteria for the determination of local activation were highly correlated with and not significantly different from the local activation from the unipolar electrogram. From 85 ambiguous unipolar electrograms, it was possible to determine local activation from the corresponding bipolar signal in 33% of the occurrences. From the eight patients, 64 diastolic potentials were recorded of which 42 were seen only in bipolar mode, 7 in only unipolar mode, and 15 were evident in both tracings. The prevalence of diastolic potentials was significantly greater in recordings made using bipolar mode. The results demonstrate that complementary information regarding local activations and diastolic potentials can be derived from unipolar and bipolar recordings and suggest that both electrode configurations should be used in multichannel cardiac mapping systems.

Endocardial mapping of ventricular tachycardia in the intact human ventricle. III. Evidence of multiuse reentry with spontaneous and induced block in portions of reentrant path complex

OBJECTIVES

This study was conducted to characterize the functional nature of the reentrant tract responsible for ventricular tachycardia due to ischemic heart disease.

BACKGROUND

A zone of slow conduction forming the return path is though to form a critical component of the reentrant mechanism in ventricular tachycardia. Despite its importance, detailed knowledge of the return path is rare in clinical studies.

METHODS

Multielectrode arrays were used intraoperatively to obtain unipolar and high gain bipolar recordings of left ventricular endocardium in patients undergoing map-directed surgical ablation of ventricular tachycardia. A total of 224 local electrograms were analyzed for each tachycardia.

RESULTS

Of 10 consecutive patients undergoing intraoperative cardiac mapping, detailed recording of the return tracts of eight ventricular tachycardias were obtained in three patients. The recordings demonstrated that return tracts can be complex and extensive, with multiple paths of entry and exit. Potential and actual alternate paths were observed. Spontaneous and induced block occurred within portions of the complex. Intermittent block in one of two paths of entry resulted in intermittent cycle length changes of the tachycardia without a change in configuration. Block in one exit path resulted in a shift to alternative exit paths, with dramatic changes in ventricular activation and tachycardia configuration. Termination of the tachycardia could result from block close to the entrant or exit portion of the return tract. Different tachycardias were seen to share common portions of a return tract.

CONCLUSIONS

These observations enlarge and extend our knowledge of the functional repertoire of complex reentrant tracts that occur in infarct-related ventricular tachycardia. The use of common portions of a reentrant tract by several tachycardias is confirmed. Utilization of alternate pathways can account for changes in configuration and cycle length. Spontaneous and induced block can occur at points of entry and exit in a reentrant tract and may identify optimal targets for ablation attempts. Further advances will require greater emphasis on diastolic activation mapping.

Does late revascularization alter the evolution of the signal-averaged electrocardiogram in patients with a recent transmural myocardial infarction?

BACKGROUND AND OBJECTIVES

Early infarct-related artery patency associated with thrombolytic therapy decreases the incidence of signal-averaged electrocardiogram (SAECG) derived late potentials following acute Q wave myocardial infarction. The purpose of this prospective study was to follow the development of SAECG abnormalities in patients with persistent occlusion of the infarct-related artery, and to compare the course of those who subsequently had successful late percutaneous transluminal coronary angioplasty and coronary artery bypass grafting surgery with the course of those who were not revascularized.

METHODS

Baseline (24 +/- 25 days after myocardial infarction) SAECG studies were acquired from 39 patients just before revascularization of the infarct-related artery (group 1) and from 32 nonrevascularized patients (group 2). Late potentials were found in 19 group 1 patients and in 13 group 2 patients (not significant). Follow-up studies were done 103 +/- 63 days after baseline acquisition.

RESULTS

There were no differences between the two groups in the change in filtered QRS (fQRS), in low amplitude signal duration under 40 microV (LAS), or in the root mean square voltage of the last 40 ms (RMS). No difference was found in the frequency of resolution of late potentials (21.0% in group 1 versus 38.5% in group 2). Patients in whom late potential resolution occurred had less abnormal LAS than patients with persistent late potentials, and less abnormal RMS. In addition, the magnitude of change in the fQRS, LAS and RMS was significantly greater in patients with late potential resolution than in those with late potential persistence.

CONCLUSIONS

Late revascularization of an occluded infarct-related artery does not appear to enhance resolution of late potentials compared with conservative medical therapy. Resolution occurs in patients with less severe SAECG abnormalities. This may reflect a difference in arrhythmogenic substrate.

The effects of unilateral stellate ganglion blockade on human cardiac function during rest and exercise

INTRODUCTION

Left-sided stellate ganglion predominance has been proposed as a mechanism responsible for lethal ventricular arrhythmias, due to heterogenous ventricular repolarization. To determine the cardiovascular effects of such asymmetric sympathetic ganglion innervation in man, studies were performed in 15 patients undergoing unilateral stellate ganglion blockade for the management of chronic arm pain.

METHODS AND RESULTS

Standard 12-lead ECGs, systemic blood pressure, body surface potential mapping, and radionuclide angiography were performed during rest and graded exercise before and after blockade. Successful unilateral blockade was accomplished in 13 of the patients, 11 of whom had right-sided blockade and two left-sided blockade. No significant changes due to blockade of stellate ganglia, including QT intervals, were detected during rest or graded exercise in standard ECGs. No cardiac rhythm disturbances occurred in these states. Body surface potential maps and arterial blood pressure were similar during resting supine and upright positions, as well as immediately after exercise before and after blockade. Unilateral ganglionic blockade did not modify resting or exercise cardiac ejection fractions.

CONCLUSION

Unilateral stellate blockade in man does not induce untoward cardiovascular effects during rest or exercise.

Endocardial mapping of ventricular tachycardia in the intact human heart. II. Evidence for multiuse reentry in a functional sheet of surviving myocardium

OBJECTIVE

The purpose of this study was to obtain improved detection and characterization of reentrant circuits in the infarcted human ventricle.

BACKGROUND

The return path of reentrant ventricular arrhythmias usually is not manifested in clinical mapping studies but is thought to be formed by isolated bundles of surviving myocytes whose presence is difficult to detect by standard recording techniques.

METHODS

We obtained simultaneous unipolar and high gain bipolar recordings using a left ventricular endocardial balloon array in 10 patients with chronic ischemic heart disease undergoing intraoperative mapping of ventricular tachycardia.

RESULTS

Three patients demonstrated seven separate ventricular tachycardias that utilized a return tract that was manifested on up to 20% of all left ventricular electrode sites. The recordings suggested an extensive sheet of surviving myocardial fibers with multiple entry and exit points allowing for different reentrant paths at different times all in the same heart. In one patient, five different ventricular tachycardias could be induced, four of which utilized such a sheet. Two of these tachycardias had the same exit point (site of origin) but two different entry points with a long and short return path resulting in long and short tachycardia cycle lengths. The same sheet sustained another tachycardia with one entry and two exit points resulting in two separate "sites of origin" on the endocardium. Such sheets also were seen to insert into the left bundle system. In one patient portions of the sheet could be detected epicardially.

CONCLUSION

The existence of such a structure of surviving myocardium with functional pleomorphism may account for unexplained changes in tachycardia cycle length, epicardial entrainment and spontaneous morphologic changes during ventricular tachycardia.

Ventricular tachycardia after surgical repair of tetralogy of Fallot: results of intraoperative mapping studies

OBJECTIVES

Four patients with previous repair of tetralogy of Fallot and ventricular tachycardia underwent map-guided surgery to ablate the arrhythmias.

BACKGROUND

Although patients with repaired tetralogy of Fallot are at increased risk of sudden death due to ventricular tachycardia, little is known of the origin and mechanism of this arrhythmia.

METHODS

A customized right ventricular balloon with 112 electrodes was used to record endocardial activation and, where possible, simultaneous epicardial recordings were obtained with a sock electrode array. Three patients had an aneurysm of the right ventricular outflow tract and one had a septal aneurysm. All had moderate to severe pulmonary valve insufficiency. Preoperative electrophysiologic study demonstrated inducible rapid (cycle length 180 to 300 ms) hemodynamically unstable monoform ventricular tachycardias.

RESULTS

Intraoperatively, five different tachycardias (two in one patient) were induced and mapped. The sites of earliest activation were located in the subendocardium of the right ventricular outflow tract in all, but they varied widely among the septum, free wall and parietal band and could not be identified by visible scar. All were due to a macroreentrant circuit initiated by a critical delay in activation beyond a functional arc of block. Two patients treated by cryoablation while the heart was beating and perfused at normal temperature had inducible ventricular tachycardia postoperatively. In the two subsequent patients, the application of cryoablation under anoxic cardiac arrest resulted in noninducibility of arrhythmia.

CONCLUSIONS

Ventricular tachycardia in tetralogy of Fallot in these four patients was caused by macroreentry in the right ventricular outflow tract. Surgical success depends on detailed mapping and cryoablation under anoxic cardiac arrest. In patients at risk of sudden death, map-directed surgery may offer distinct advantages over either implantable devices or drug therapy.

Simultaneous Unipolar and Bipolar Recording of Cardiac Electrical Activity

An analog mapping system using a true bipolar left ventricular balloon electrode array is described, which enables simultaneous unipolar and bipolar recordings. It is an adaptation of a previous clinical analog mapping system used in the investigation of ventricular arrhythmias. The bipolar balloon array consists of 112 electrode pairs, each having a 2-mm separation. The signals from the electrodes are sensed in parallel by separate unipolar and bipolar amplifier units, which then drive a common multiplexer bus. The bipolar recording unit consists of high quality instrumentation amplifiers with adjustable gain and exhibits a full bandwidth minimum common mode rejection of 78 dB. Using this combination, it is possible to record local cardiac micropotentials while still retaining the advantages of unipolar electrograms to track overall cardiac activation.