Electrophysiologic evaluation of sinus node function in patients with sinus node dysfunction

Methylxanthine Derivatives in the Treatment of Sinus Node Dysfunction: A Systematic Review

While the chronotropic effects of theophylline and aminophylline are well-known, their clinical application in the treatment of sinus node dysfunction has not been established in a review. The purpose of this systematic review is to evaluate the efficacy and safety of methylxanthines in the treatment of bradyarrhythmias associated with sinus node dysfunction. A systematic review was conducted in accordance with PRISMA guidelines on Embase, PubMed, MEDLINE, Cochrane Central, Web of Science, SciELO, Korean Citation Index, Global Index Medicus, and CINAHL through June 2023. A total of 607 studies were identified through the literature search. After applying the inclusion and exclusion criteria, 14 studies were included in this review. The causes of bradyarrhythmias involving the sinoatrial node included acute cervical spinal cord injury, coronavirus disease of 2019, carotid sinus syncope, chronotropic incompetence, heart transplant, and chronic sinus node dysfunction. Theophylline and aminophylline were shown to be effective for increasing heart rate and reducing the reoccurrence of bradyarrhythmias. The data on symptom resolution was conflicting. While many case studies reported a resolution of symptoms, a randomized controlled trial reported no significant difference in symptom scores between the control, theophylline, and pacemaker groups in the treatment of sick sinus syndrome. The incidence of adverse effects was low across all study designs. The data suggests methylxanthines may be useful as an alternative or bridge to nonpharmacologic pacing; however, dosing has yet to be established for various indications. Overall, methylxanthines proved safe and effective as a pharmacologic therapy for bradyarrhythmic manifestations of sinus node dysfunction.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Pharmacologic Approach to Sinoatrial Node Dysfunction

The spontaneous activity of the sinoatrial node initiates the heartbeat. Sino-atrial node dysfunction (SND) and sick sinoatrial (sick sinus) syndrome are caused by the heart's inability to generate a normal sinoatrial node action potential. In clinical practice, SND is generally considered an age-related pathology, secondary to degenerative fibrosis of the heart pacemaker tissue. However, other forms of SND exist, including idiopathic primary SND, which is genetic, and forms that are secondary to cardiovascular or systemic disease. The incidence of SND in the general population is expected to increase over the next half century, boosting the need to implant electronic pacemakers. During the last two decades, our knowledge of sino-atrial node physiology and of the pathophysiological mechanisms underlying SND has advanced considerably. This review summarizes the current knowledge about SND mechanisms and discusses the possibility of introducing new pharmacologic therapies for treating SND.

Asymptomatic bradycardia amongst endurance athletes

It is established that an intensive training results in a lower average resting heart rate. Management of bradycardia in an athlete can be difficult given the underlying mechanisms are not clearly understood. The authors reviewed the different mechanisms described in the literature, including recent advances in physiology regarding remodeling of ion channels, which may partially explain bradycardia in athletes. Sinus bradycardia amongst athletes, especially endurance focused athletes, is common but difficult to apprehend. The underlying mechanisms are observably of multifactorial origin and likely incompletely elucidated by the current body of knowledge.

Recommendations for the use of electrophysiological study: Update 2018

The field of cardiac electrophysiology has greatly developed during the past decades. Consequently, the use of electrophysiological studies (EPSs) in clinical practice has also significantly augmented, with a progressively increasing number of certified electrophysiology centers and specialists. Since Zipes et al published the Guidelines for Clinical Intracardiac Electrophysiology and Catheter Ablation Procedures in 1995, no official document summarizing current EPS indications has been published. The current paper focuses on summarizing all relevant data of the role of EPS in patients with different types of cardiac pathologies and provides up-to-date recommendations on this topic. For this purpose, the PubMed database was screened for relevant articles in English up to December 2018 and ESC and ACC/AHA Clinical Practice Guidelines, and EHRA/HRS/APHRS position statements related to the current topic were analyzed. Current recommendations for the use of EPS in clinical practice are discussed and presented in 17 distinct cardiac pathologies. A short rationale, evidence, and indications are provided for each cardiac disease/group of diseases. In conclusion, because of its capability to establish a diagnosis in patients with a variety of cardiac pathologies, the EPS remains a useful tool in the evaluation of patients with cardiac arrhythmias and conduction disorders and is capable of establishing indications for cardiac device implantation and guide catheter ablation procedures.

Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model

Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias.

Long-term follow-up of early repolarization pattern in elite athletes

BACKGROUND

Early repolarization pattern (ERP) is considered a benign variant of the electrocardiogram (ECG), more frequent in athletes. However, prospective studies suggested that ERP is associated with an increased risk of sudden cardiac death (SCD). The purpose of this study is to determine the prevalence, clinical characteristics, and long-term outcome of ERP in elite athletes during professional activity and after retirement.

METHODS AND RESULTS

A cohort of 299 white elite athletes recruited between 1960 and 1999 was retrospectively analyzed. Athletes were eligible if they had participated for at least 6 consecutive months in high competition and retired for a minimum of 5 years before inclusion. Clinical data and ECG were abstracted from the clinical records using a questionnaire, and outcomes after a mean follow-up of 24 years were registered. Among the 299 athletes, 66% were men with a mean age of 20 (SD 6.4) years. ERP was found in 31.4% of participants, and it was located in lateral ECG leads in 57.4% of cases, in inferior leads in 6.4%, and in both leads in the remaining 36.2%. After retirement, ERP still persisted in 53.4% of athletes. Predictive factors for the persistence were: left ventricular hypertrophy signs at the baseline ECG (odds ratio [OR] 4.35; 95% confidence interval [CI], 1.43-13.24; P = .010), sinus bradycardia after retirement (OR 2.56; 95% CI, 1.09-5.99; P = .031), and presence of ERP during the sportive career (OR 20.35; 95% CI, 8.54-48.51; P < .001). After a mean follow-up of 24 years, no episodes of SCD occurred.

CONCLUSIONS

A third of elite athletes presented ERP, and this persisted in 53.4% of cases after retirement. After a long follow-up period, no difference in outcome of SCD was seen.

Differential effects of variation in athletes training on myocardial morphophysiological adaptation in men: focus on ¹²³I-MIBG assessed myocardial sympathetic activity

PURPOSE

High intensity systematic physical training leads to myocardial morphophysiological adaptations. The goal of this study was to investigate if differences in training were correlated with differences in cardiac sympathetic activity.

METHODS

58 males (19-47 years), were divided into three groups: strength group (SG), (20 bodybuilders), endurance group (EG), (20 endurance athletes), and a control group (CG) comprising 18 healthy non-athletes. Cardiac sympathetic innervation was assessed by planar myocardial (123)I-metaiodobenzylguanidine scintigraphy using the early and late heart to mediastinal (H/M) ratio, and washout rate (WR).

RESULTS

Left ventricular mass index was significantly higher both in SG (P < .001) and EG (P = .001) compared to CG without a statistical significant difference between SG and EG (P = .417). The relative wall thickness was significantly higher in SG compared to CG (P < .001). Both left ventricular ejection fraction and the peak filling rate showed no significant difference between the groups. Resting heart rate was significantly lower in EG compared to CG (P = .006) and SG (P = .002). The late H/M ratio in CG was significantly higher compared to the late H/M for SG (P = .003) and EG (P = .004). However, WR showed no difference between the groups. There was no significant correlation between the parameters of myocardial sympathetic innervation and parameters of left ventricular function.

CONCLUSIONS

Strength training resulted in a significant increase in cardiac dimensions. Both strength and endurance training seem to cause a reduction in myocardial sympathetic drive. However, myocardial morphological and functional adaptations to training were not correlated with myocardial sympathetic activity.

Ethics in electrophysiology: who speaks for this man?

In this case, a patient who is incapable of participating in health-care decisions requires a pacemaker generator replacement. Because the pacemaker may no longer be necessary, the issues of surrogacy and surrogate decision-making are considered. Where there are no involved family members, each state has procedures for finding an appropriate ombudsman for the patient who can assist in healthcare choices.

Clinical predictors of cardiac events in patients with isolated syncope and negative electrophysiologic study

BACKGROUND

Patients with syncope or near syncope of unknown etiology represent a great challenge to cardiologists. An initial symptomatic episode triggers a series of diagnostic analysis which remain unsatisfactory when negative. More invasive tools such as electrophysiologic testing yield only partial answers to risk stratification while the complementary implantable holter diagnostics are not usually considered until a recurrent episode is documented.

OBJECTIVE

This study targets predictors of significant cardiac rhythmic events in patients with a reported episode of syncope or near syncope presenting with negative diagnostics and electrophysiologic study results (EPS). A significant cardiac rhythmic event was defined as a combined end-point of (1) symptomatic AV block; (2) symptomatic conduction abnormalities requiring pacemaker therapy; (3) symptomatic sustained ventricular arrhythmia; and (4) sudden death.

METHODS

All patients undergoing EPS after a first episode of syncope or presyncope between January 1997 and December 2001 were included for analysis. The study population consisted of 329 pts (42.6% women), 21 to 96 years old (mean 70+/-15 years) referred for an EP study for syncope or near syncope.

RESULTS

Of the 329 patients who underwent EPS, 305 (92.7%) had follow-up data. The population, mean age 70 (+/- 15 years) and composed of 42% women, presented with hypertension (51.5%), diabetes mellitus (14.4%), hypercholesterolemia (30%), tobacco use (35%), a familial history of coronary heart disease (22%), history of stroke (4%), history of MI (12%), history of atrial fibrillation (10%), structural heart disease (17.4%), left ventricular ejection fraction 61 (+/- 11%) and ECG abnormalities (37%). These anomalies included right (RBBB) or left (LBBB) bundle branch blocks, left anterior fascicular block (LAFB), left posterior fascicular block (LPFB), bifascicular block (RBBB+LAFB) and traces of myocardial infarction. The mean follow-up was 31+/-20 months with 5% of patients recording significant cardiac rhythmic events (15/305): AV block requiring pacemaker therapy in 7 patients, sinus dysfunction in 4, sudden death in 3 and ventricular tachycardia in 1. Univariate analysis reveals structural heart disease, ECG abnormalities and LVEF associated with the risk of significant cardiac rhythmic events defined by the combined end-point. Multivariate analysis using a Cox model found that the only independent predictor of events was an ECG abnormality. The long-term risk of significant event in the subset with ECG abnormalities is of 10.6% (12/113). If unexplained syncope recurrence was included in the combined end-point, ECG abnormality and LVEF were both determinants with a 13.3% (15/113) risk of a arrhythmic events analysis in the subset of patients presenting with ECG abnormalities and Cox model found ECG abnormality as the only independent predictor of event.

CONCLUSIONS

This study demonstrated that an ECG abnormality is the only predictive variable associated with a significant arrhythmic event in patients with a lone episode of syncope or near syncope and a negative EPS.

Serial measures of sinoatrial and atrioventricular nodal function in ambulatory patients

We hypothesized that the outpatient assessment of SA and AV nodal (SAN, AVN) function could be a useful tool to determine the effectiveness of drugs and other treatments. We sought to examine the reproducibility, safety and ease of acquiring serial measurements of these parameters. Ten patients with permanent pacemakers underwent low current chest wall stimulation while their device was programmed to unipolar atrial triggered mode. Measurements at multiple conditioning drive train frequencies were obtained for: sinus nodal recovery time (SNRT); corrected sinus nodal recovery time (CSNRT); SA conduction time (SACT); AVN block cycle length (AVNBCL); and AVN effective refractory period (AVNERP). AVN function curves were also constructed. All studies were repeated after 2 weeks. Measures of sinus nodal and AVN function did not show significant differences between the two studies. The following co-efficients of correlation were obtained: SNRT800, r = 0.79; CSNRT800, r = 0.71; SNRT600, r = 0.71; CSNRT600, r = 0.44; SACT, r = 0.75; AVNBCL, r = 0.98; AVNERP800, r = 0.55; and AVNERP600, r = 0.99. AVN function curves did not significantly differ between week 1 versus week 2 at conditioning drive trains of either 800 ms or 600 ms. These data suggest that serial noninvasive electrophysiological measures of AVN and SAN function are reproducible over 2 weeks. Using data in this study, estimates of the sample size necessary for the evaluation of the effects of investigational drugs on the SAN and AVN in future studies are possible.

Syncope: current diagnosis and treatment

The patient with syncope often poses a formidable diagnostic challenge. A large number of underlying causes must be considered, ranging in severity from benign to life-threatening. A careful, systematic clinical evaluation beginning with a history, physical examination, and ECG will establish the diagnosis in most patients, and the judicious use of specialized testing will confirm or uncover the cause in many of the remaining cases. Further basic and clinical research into the pathogenesis and treatment of neurocardiogenic syncope, the role of HUT testing in neurally mediated syncope, and the optimal use of EPS in patients with cardiac disease will markedly improve our management of these patients in the future.

Electrophysiologic evaluation of sinus node function and atrioventricular conduction in patients with prolonged ventricular asystole during obstructive sleep apnea

In 15 patients with ventricular asystole of 8.5 +/- 3.5 seconds (range 5.0 to 16.8) occurring exclusively during obstructive sleep apnea, electrophysiologic study of sinus node function and atrioventricular conduction before and after administration of intravenous atropine (0.02 mg/kg) was performed. Electrophysiologic parameters of sinus node function were normal in 12 of 15 patients (80%) and atrioventricular (AV) nodal function was normal in 7 patients (47%). Almost all abnormal findings of sinus node function and AV nodal function were reversible by administration of atropine. The HisPurkinje system function was normal in 6 patients (40%). Prolonged HV intervals (57 to 73 ms) were found in 9 patients (60%). Intra- or infra-His block was not observed in any patient. In summary, electrophysiologic parameters of sinus node function and AV conduction were normal or only slightly abnormal in all 15 study patients, which suggests that prolonged ventricular asystole during obstructive sleep apnea is not due to fixed or anatomic disease of the sinus node or the AV conduction system.

Clinical effects and pharmacokinetics of a single oral dose of pirmenol hydrochloride

To establish the clinical efficacy of a single oral dose of pirmenol, we evaluated electrophysiologic and hemodynamic effects simultaneously after drug administration, performing electrophysiologic testing in 20 patients with ECG-documented paroxysmal supraventricular tachycardia (PSVT) before and after a single oral 200-mg dose of pirmenol. Hemodynamic measurements were made with a Swan-Ganz catheter in the first 10 consecutive patients. In a different series of patients, we administered a single 200-mg oral dose of pirmenol to evaluate its acute termination effect in 7 patients with PSVT and 9 with paroxysmal atrial fibrillation. Pirmenol prolonged the refractory period of the retrograde conduction system in patients with or without an accessory pathway, and supraventricular tachycardia was no longer inducible at 60 min in 11 patients [8 of 11 with atrioventricular (AV) reentrant tachycardia and 3 of 5 with AV nodal reentrant tachycardia]. Pirmenol increased the heart rate (p < 0.01) and total systemic resistance (p < 0.05), and reduced the stroke volume index (p < 0.01), all significantly. The plasma concentration of pirmenol at 1 h after administration was 0.75 +/- 0.48 microgram/ml. A single oral dose of pirmenol during tachyarrhythmia successfully restored sinus rhythm in 4 of 7 (57%) patients with PSVT and 4 of 9 (44%) patients with paroxysmal atrial fibrillation. A single oral dose of pirmenol was well tolerated as episodic treatment in patients with supraventricular tachyarrhythmias.

Invasive electrophysiological evaluation of patients with sleep apnoea-associated ventricular asystole-methods and preliminary results

Twelve patients (aged 48 +/- 12 y) with ventricular asystole of >3 s due to complete atrioventricular (AV) block (n = 8), sinoatrial (SA) block or sinus node arrest (n = 3) or both (n = 1) associated with obstructive sleep apnoea underwent invasive electrophysiological evaluation of sinus node function and AV conduction properties before and after administration of atropine (0.02 mg kg-1). Ventricular asystole lasted for 5.9 +/- 2.8 s (range 3.1-13 s). Sinus node function was assessed by measurement of sinus node recovery time, sinoatrial conduction time, and the response of sinus rate to atropine. Parameters of AV-conduction assessment included AH- and HV-intervals, AV- and VA-Wenckebach periods, and effective refractory period of the AV node before and after atropine. Sinus node function was normal in 11 of the 12 study patients and moderately abnormal in 1 patient. AV-nodal function was normal in 8 patients and moderately abnormal in 4 patients. A slightly prolonged HV-interval (59-63 ms) was present in 6 patients. Intra- or infra His block was not observed in any patient. In conclusion, normal or only moderately abnormal electrophysiological findings in patients with sleep apnoea-associated ventricular asystole suggest that a neurally mediated cardioinhibitory reflex may cause ventricular asystole in these patients. This sleep apnoea-triggered 'vasovagal' reflex may unmask pre-existing mild to moderate structural abnormalities of the AV conduction system.

The value of the clinical history in the differentiation of syncope due to ventricular tachycardia, atrioventricular block, and neurocardiogenic syncope

BACKGROUND

The present study was undertaken to identify and quantitate the symptoms associated with neurocardiogenic syncope, syncope due to ventricular tachycardia, and syncope resulting from atrioventricular block.

PATIENTS AND METHODS

Eighty patients referred for evaluation of syncope in whom a diagnosis of neurocardiogenic syncope, atrioventricular block, or ventricular tachycardia was established were studied. Each patient was interviewed using a standard questionnaire. The clinical histories were then compared to identify which variables best differentiated the cause of syncope.

RESULTS

The clinical histories of patients with syncope due to ventricular tachycardia and atrioventricular block were similar. Only age, the duration of prodromal symptoms, diaphoresis prior to syncope, and fatigue following syncope differed. In contrast, the clinical history in patients with neurocardiogenic syncope differed greatly from that obtained in patients with syncope due to atrioventricular block or ventricular tachycardia. Features of the clinical history that were predictive of syncope due to atrioventricular block or ventricular tachycardia were male sex, age > 54 years, < or = 2 episodes of syncope, and a duration of warning of < or = 5 seconds. Features of the clinical history predictive of syncope not due to ventricular tachycardia or atrioventricular block were palpitations, blurred vision, nausea, warmth, diaphoresis, or lightheadedness prior to syncope, and nausea, warmth, diaphoresis, or fatigue following syncope.

CONCLUSIONS

The results of this study identify and compare the features of the clinical history obtained in patients with syncope due to ventricular tachycardia, atrioventricular block, and neurocardiogenic syncope and demonstrate that the clinical history is of value in distinguishing patients with these three causes of syncope.

Electrophysiologic study in chronic Chagas' heart disease

Cardiac arrhythmias are common in chagasic patients. Electrophysiologic study is an invasive procedure for the investigation of sinus node function, atrioventricular node conduction and intraventricular (His-Purkinje) conduction and the mechanism of tachycardias. It is useful in elucidating syncope, dizziness and tachycardiac palpitations that remain unexplained by non-invasive diagnostic methods. It is fundamental in directing non-pharmacological therapy, especially in "sudden death" survivors. Chagasic patients may benefit from electrophysiologic study after a critical clinical evaluation.

Parasympathetic overactivity and its evaluation in patients with sinus nodal dysfunction

In 17 controls, and 17 patients with sinus nodal dysfunction, an electrophysiologic study was made of sinus nodal function and atrioventricular nodal conduction in the basal state. The study was then repeated in all patients after atropine. The heart rate, mean sinus cycle length, variations of sinus cycle length, sinus node recovery times, sinuatrial conduction time, AH interval, and atrioventricular nodal Wenckebach threshold were significantly different in patients from those of controls. All these parameters changed significantly in patients after atropine, and were comparable to those of controls except for the atrioventricular nodal Wenckebach threshold. Atropine failed to increase the heart rate beyond 90 beats per minute in 10 of 17 patients (sensitivity of 59%) or by at least 30% above the resting heart rate only in 4 of them (sensitivity of 24%). The variations of sinus cycle length, and their standardized value, could detect sinus nodal dysfunction with sensitivities of 59 and 47%, respectively. From our results, we conclude that there is parasympathetic overactivity in patients with sinus nodal dysfunction. Because of their very low sensitivities, the atropine test and variations of sinus cycle length were not useful in identifying sinus nodal dysfunction noninvasively. The normal response of the heart rate to atropine does not exclude sinus nodal dysfunction, but atropine may help to differentiate abnormalities intrinsic and extrinsic to the sinus node during the electrophysiologic study.

Electrophysiologic abnormalities in patients with hypertrophic cardiomyopathy. A consecutive analysis in 155 patients

Electrophysiologic studies (EPS) were performed in 155 patients with hypertrophic cardiomyopathy (HCM). Indications for EPS were cardiac arrest in 22 patients, syncope in 55 patients, presyncope in 37 patients, asymptomatic ventricular tachycardia (VT) in 24 patients, palpitations in 10 patients, and a strong family history of sudden cardiac death in seven patients. Thirty-five (23%) patients had significant resting left ventricular outflow tract obstruction. Electrophysiologic abnormalities were present in 126 (81%) patients. A high prevalence of abnormal sinus-node function (66%) and His-Purkinje (HV) conduction (30%) was noted. The most commonly induced supraventricular arrhythmias were atrial reentrant tachycardia and atrial fibrillation (10% and 11% of patients, respectively). Accessory atrioventricular pathways were present in seven (5%) patients. Programmed ventricular stimulation (PVS) induced nonsustained ventricular tachycardia in 22 (14%) patients and sustained ventricular arrhythmia in 66 (43%) patients. Sustained ventricular arrhythmia was polymorphic VT in 48 (73%) patients, monomorphic VT in 16 (24%) patients, and ventricular fibrillation in two (3%) patients. Induction was with two premature stimuli in 19 (29%) patients and three premature stimuli in 47 (71%) patients. Of 17 cardiac arrest survivors with sustained ventricular arrhythmia, 16 (94%) patients required three premature stimuli for arrhythmia induction. Sustained ventricular arrhythmia was induced at a right ventricular site in 51 (77%) patients and at a left ventricular site in 15 (23%) patients. Univariate analysis showed a significant (p less than 0.05) association between inducibility of sustained ventricular arrhythmia and VT on Holter in patients with a history of cardiac arrest or syncope but not in patients with presyncope or asymptomatic patients. Multivariate logistic regression analysis revealed that the following were significantly associated with inducibility of sustained ventricular arrhythmia: clinical presentation (cardiac arrest more than syncope more than presyncope more than asymptomatic patients, p = 0.0002; chronic or inducible atrial fibrillation, p = 0.002; and male gender, p = 0.04). In contrast, there was no clinical correlate of induced nonsustained VT.(ABSTRACT TRUNCATED AT 400 WORDS)

Natural history of patients with unexplained syncope and a nondiagnostic electrophysiologic study

The purpose of this study was to define the natural history of 99 patients with unexplained syncope who underwent an electrophysiologic test that either was entirely normal or demonstrated nonspecific abnormalities that were nondiagnostic (inducible polymorphic ventricular tachycardia or ventricular fibrillation, a mildly prolonged sinus node recovery time of less than 2 s, a His-ventricular interval of 55 to 99 ms or supraventricular tachycardia not associated with hypotension). The mean age (+/- SD) of the patients was 56 +/- 19 years; structural heart disease was present in 47 patients and absent in 52. Complete follow-up was available in 95 patients. During 20 +/- 11 months of follow-up, 2 patients (2%) died suddenly, 19 patients (20%) had recurrent syncope and 74 patients (78%) had no further episodes of syncope. Among the 19 patients who continued to have syncope after the electrophysiologic testing, the cause of syncope was established clinically in 4 and was found to be high degree atrioventricular (AV) block (2 patients) or sinus node dysfunction (2 patients). No clinical or laboratory findings distinguished patients who had sudden death or syncope during follow-up from patients who did not. In conclusion, in patients with unexplained syncope who undergo an electrophysiologic test that is nondiagnostic 1) the incidence of sudden death is low (2%); 2) the remission rate of syncope is high (80%); 3) the electrophysiologic test may be documented to have been falsely negative in greater than or equal to 20% of patients who continue to have syncope, syncope in these patients being caused by AV block or sinus node dysfunction; and 4) patients at risk of sudden death or recurrent syncope, or both, cannot be readily identified prospectively.

Effect of nifedipine on the sick sinus syndrome

The effect of nifedipine (N) on sinus node (SN) function was studied in 15 patients (9 males, 6 females) sixty-two to seventy-six (mean 68.1 +/- 11) years old, with sick sinus syndrome (SSS). SSS was characterized electrophysiologically by a prolonged corrected sinus node recovery time (CSNRT greater than 535 msec) and/or prolonged sinoatrial conduction time (SACT greater than 125 msec), assessed by applying premature atrial stimulation. Ten mg N was given sublingually, and CSNRT and SACT were again evaluated sixty minutes after N administration, and again ten minutes after 1.5 mg atropine (A) was given IV. Heart rate increased significantly after N (p less than 0.005), systolic blood pressure (SBP) diminished significantly (p less than 0.005), and CSNRT and SACT shortened significantly (p less than 0.005, p less than 0.005) and became normal in 7 and 5 patients respectively. After A administration, a further significant increase of heart rate (p less than 0.005) and decrease of CSNRT (p less than 0.005) and SACT (p less than 0.005) were observed. CSNRT and SACT became normal in 8 and 7 patients respectively. SBP remained stable.

The electrophysiological effects of intravenous magnesium on human sinus node, atrioventricular node, atrium, and ventricle

The effects of intravenously (IV) administered magnesium chloride (MgCl) on electrophysiologic and electrocardiographic variables were studied in 13 patients undergoing a routine electrophysiologic assessment for clinical indications. An infusion of 12 mmol of MgCl was given during a 10-min period and relevant electrophysiologic variables were determined before and after the infusion. Serum Mg levels increased from 0.78 +/- 0.03 (mean +/- SEM) before to 1.52 +/- 0.08 ms after the infusion (p less than 0.0001). Magnesium treatment caused a significant prolongation in PR interval (from 151 +/- 8 to 174 +/- 8 ms, p less than 0.001) as well as in QRS duration (from 90 +/- 4 to 101 +/- 6 ms, p less than 0.05). Likewise, intra-atrial (PA) as well as atrioventricular (AV) nodal (AH) conduction times were significantly prolonged (from 33 +/- 3 to 46 +/- 3 ms, p less than 0.01, and from 85 +/- 6 to 94 +/- 6 ms, p less than 0.05, respectively). Mean effective and functional atrial refractory periods increased (from 228 +/- 8 to 256 +/- 10 ms, p less than 0.01 and from 292 +/- 9 to 320 +/- 11 ms, p less than 0.01, respectively), as did mean AV node functional refractory period (from 399 +/- 29 to 422 +/- 27 ms, p less than 0.02). No significant change occurred with regard to sinus node function (as estimated from heart rate, sinus node recovery time, and calculated sinoatrial conduction time) or ventricular refractoriness. It is concluded that IV Mg has several electrophysiologic effects that may be beneficial in the treatment/prevention of supraventricular tachyarrhythmias.

Effect of pacing cycle length and autonomic blockade on sinus node refractoriness

Sinus node (SN) refractoriness can be measured indirectly by observing the return responses after the introduction of progressively earlier atrial premature beats. The SN effective refractory period (ERP) is defined as the longest premature interval resulting in an interpolated atrial return response. In the present study, SNERP was analyzed in 71 subjects--51 control persons and 20 patients with evidence of SN dysfunction. SNERP could be measured in 40 of 51 control subjects and was shown to prolong at shorter basic pacing cycle lengths. At a basic cycle length of 600 ms, SNERP was 330 +/- 40 ms, whereas at 500 ms it was 350 +/- 50 ms (p less than 0.05). At a basic cycle length of 600 ms, SNERP was measured in 31 control subjects and 7 patients with SN dysfunction. The values of 330 +/- 40 and 520 +/- 20 ms, respectively, in these 2 groups suggested that this method can be used to differentiate patients with SN dysfunction (p less than 0.001). In 12 control subjects, SNERP was measured before and after partial autonomic blockade with propranolol and atropine. SNERP shortened from 360 +/- 40 to 320 +/- 40 ms (p less than 0.05). It shortened with atropine and prolonged with propranolol. Thus, SNERP prolongs with a shorter basic pacing cycle length and is affected by autonomic manipulation, in a fashion analogous to the atrioventricular node.

Comparative cardiac effects of intravenous bolus of ipratropium bromide (itrop) and atropine sulfate in 22 patients

At the present time, there is no satisfactory pharmacological treatment for arrhythmia or conduction disorders induced by or aggravated by vagal hypertonia. The limited duration of action of the atropine derivatives currently available justifies the development of new compounds with expected longer acting duration. The aim of this study was to compare the effects of a single blind intravenous injection of ipratropium bromide to those of atropine sulfate in 22 patients. These patients were studied with continuous Holter recordings for three days. During the second and the third nights (patient sleeping), boluses of atropine (0.03 mg/kg) and of ipratropium bromide (0.03 mg/kg), respectively, were added to a continuous saline intravenous infusion. Accurate ECG analysis allowed determination of maximal heart rate peak, timing of maximal heart rate, variations in sinus cycle length, atrioventricular conduction, and durations of drug action. A nonsuggestive questionnaire was presented to patients to detect possible occurrence of side effects. The mean maximal heart rate rose significantly (p less than 0.001) for atropine (+46.2%) and for ipratropium bromide (+57.4%). The effects obtained with ipratropium bromide on the heart rate lasted nearly twice as long as those obtained with atropine (respectively, 120 +/- 38.4 min and 70 +/- 30 min- for the pharmacological half-life). Common minor muscarinic side effects (dryness of the mouth) were noted with the two drugs. In conclusion, this comparative intraindividual study confirmed the prolonged vagolytic effects of intravenous ipratropium bromide, which may be valuable in the treatment of patients with vagally mediated automaticity and conduction disturbances.

Reappraisal of atrioventricular junctional pacemaker automaticity in the sick sinus syndrome. Clinical significance and the role of autonomic chronotropic influences

Postpacing impulse recovery times of the junctional tissue (junctional automaticity) were determined by atrial or ventricular overdrive pacing in 27 patients with dysfunction of the sinus node. The maximum junctional recovery time (MJRT) could be measured in 22 patients and ranged from 1,630 to 9,730 ms (mean 3,860 +/- 2,077); the maximum corrected junctional recovery time (MJRTc) could be measured in 18 patients and ranged from 140 to 5,986 ms (mean 2,089 +/- 1,529). Autonomic influence on the JRTs was evaluated by intravenous administration of atropine (1.5 mg) alone or in combination with propranolol (5 to 6 mg). Of the seven patients in whom MJRTc and/or MJRT could be measured before and after drug intervention, the JRTs shortened in four and prolonged in three after combination of atropine and propranolol. Atropine alone shortened MJRT in all eight patients studied. Our data reveal that both vagal and catecholamine-dependent factors (especially vagal over-activity) are operative in the escape mechanism of the junctional tissue.

Atrial pacing to estimate total sinoatrial conduction time in children

No data exist concerning the total sinoatrial conduction time (TSACT) in children that compare values determined by the atrial extrastimulation technique (TSACTS) with those generated by the atrial pacing method (TSACTN). In this study, TSACT in 55 patients, age 0.2-18.5, was measured using both techniques. TSACTN was performed at a mean 90% (TSACTN-90) (n = 32) or a mean 95% (TSACTN-95 and (n = 38) of sinus cycle length (SCL). When data generated during determination of TSACTN-90 and TSACTS were compared, SCL and recovery cycle length (REC) were similar for both techniques. Likewise, TSACTS (128 +/- 40 ms) and TSACTN-90 (126 +/- 74 ms) were not significantly different. Coefficient of correlation was r = 0.82, p less than 0.001. Chi-square analysis demonstrated a strong association of normal and abnormal values between TSACTS and TSACTN-90. In contrast, when values generated during TSACTN-95 and TSACTS were compared, TSACTS exceeded TSACTN-95 (137 +/- 38 vs 105 +/- 58 ms; p less than 0.001). Values for SCL and REC were similar while correlation between TSACT determined by the two techniques remained strong (r = 0.82, p less than 0.001). Despite a good correlation between TSACTN-90 and TSACTS, individual differences in magnitude and direction were noted between the two techniques. In summary, TSACTN-90 approximates TSACTS in children. TSACTN-90 is preferable to TSACTN-95, probably due to more complete sinus node capture during atrial pacing. However, the behavior of the sinus node in response to extrastimuli (single or train) precludes favoring one technique over the other. More precise evaluation of sinoatrial conduction will require direct recording of sinus node activity.

Bedside evaluation of sinus bradycardia: usefulness of atropine test in discriminating organic from autonomic involvement of sinus automaticity

In 55 patients with persistent sinus bradycardia who underwent an electrophysiologic study of sinus node, both in the basal state and after autonomic blockade (propranolol, 0.2 mg/kg, and atropine, 0.04 mg/kg), an atropine test (0.02 mg/kg) was performed the following day. The 49 patients in whom sinus rate could be evaluated after atropine were subdivided into two groups--group I, 24 patients (age: 54 +/- 13 years) with normal intrinsic sinus automaticity (normal intrinsic heart rate and intrinsic corrected sinus node recovery time) and group II, 25 patients (age: 62 +/- 9 years) with abnormal intrinsic sinus automaticity. In group I, atropine increased sinus rate from 53.7 +/- 4 to 87.9 +/- 17 bpm (delta %: 65.5 +/- 33) and in group II from 51.6 +/- 5 to 73.9 +/- 14 bpm (delta %: 43.1 +/- 26). The discriminant threshold of sinus rate after atropine and its percent increase, obtained by discriminant analysis, was 80 bpm and +52%, respectively, with a misleading classification of 32% and 36%, respectively. The overall predictive accuracy of sinus rate after atropine was higher than the percent change in sinus rate (73% and 65%, respectively). These data evidence that the atropine test is not very helpful in discriminating between an organic and an autonomic involvement of sinus automaticity in patients with sinus bradycardia.

Impulse propagation from the SA-node to the ventricles

Normally the pacemaker of the mammalian heart is located in the sinus node. In the rabbit the sinus node can be subdivided into two regions, the center of the node where the impulse originates and the border zone through which the impulse is conducted towards the atrium. Conduction properties of both regions were investigated. It appeared that conduction velocity increases and refractoriness decreases when one goes from the nodal center towards the atrium. The tissue mass of the atrium is large in comparison to the sinus node and normally the resting membrane potential of atrial fibers is more negative than that of nodal fibers; consequently, a potential difference exists causing a current flow between both areas. Evidently this hyperpolarizing current flow depresses impulse formation in the border zone fibers which have better intrinsic pacemaker properties than fibers in the nodal center. If the impulse has reached the atrium it is conducted with a relatively high safety factor and will reach the AV node in principle without difficulty. The AV node, if deprived of sinus nodal dominance, develops spontaneous activity originating from the lower nodal fibers. Also in this structure, electrotonic depression by surrounding tissue causes deceleration of the pacemaker.

Electrophysiologic effects of d-sotalol in humans

Sotalol is a beta-adrenergic blocking agent that prolongs the duration of the cardiac action potential in humans, without affecting the upstroke velocity of depolarization. The dextrorotatory isomer, d-sotalol, retains these class III effects, but has little beta-blocking activity in vitro. d-Sotalol has not been studied extensively in humans. The electrocardiographic (ECG) and electrophysiologic effects of d- and d,l-sotalol were therefore assessed in a prospective randomized study of 20 patients. Each patient received either d-sotalol (1, 1.5 or 2 mg/kg body weight) or d,l-sotalol (1 mg/kg) by intravenous infusion. The QT and QTc intervals were prolonged and refractoriness increased in the atrium, atrioventricular (AV) node, His-Purkinje system and right ventricle after both d- and d,l-sotalol. After d-sotalol, the increases in both QT and QTc intervals and in atrial and ventricular effective refractory periods were dose dependent. Highly significant linear correlation was demonstrated between the plasma sotalol level and the change in QT (r = 0.86, p = 0.001) and QTc intervals (r = 0.79, p = 0.002), and between the plasma sotalol level and the effective refractory period of the right atrium (r = 0.75, p = 0.005) and ventricle (r = 0.70, p = 0.025). This study confirms that d-sotalol has effects consistent with class III properties. It demonstrates these effects in humans, and suggests that d-sotalol may prove to be a useful antiarrhythmic agent.