Clinical safety profile of sotalol in the treatment of arrhythmias

Assessment of Dofetilide or Sotalol Tolerability in the Elderly

Background: Dofetilide and sotalol are potassium channel antagonists that require inpatient QTc monitoring during initiation, due to increased risk of fatal arrhythmias. Elderly patients are especially subject to an increased risk of fatal arrhythmias due to polypharmacy, comorbidities, and physiologic cardiac changes with aging. This study will describe the tolerability and risk factors associated with the initiation of sotalol or dofetilide in patients ≥80 years of age. Methodology: This is a multicenter, retrospective, descriptive study of patients ≥80 years old who were initiated on either dofetilide or sotalol between May 8, 2018 and July 31, 2021 at institutions within the Mayo Clinic Health System. The percentage of patients who received nonpackage insert recommended doses was identified. Incidence of and reasons for dose reductions or discontinuations due to safety-related events or clinical concerns during the initial loading period were collected. Results: The final analysis included 104 patients. The majority of patients (75%) received nonstandard initial doses of dofetilide or sotalol based on baseline estimated creatinine clearance or QTc. Overall, 39% (N = 41) of patients experienced a dose reduction or discontinuation due to a safety-related event or concern. Patients who received nonstandard initial doses of dofetilide or sotalol had 4.7 times greater odds of experiencing a safety-related event requiring dose reduction or discontinuation. Conclusion: Following package insert dosing in elderly patients increases safety and tolerability relative to more aggressive dosing of dofetilide or sotalol.

Protocol Development and Initial Experience With Intravenous Sotalol Loading for Atrial Arrhythmias

BACKGROUND

Oral sotalol is a class III antiarrhythmic commonly used for the maintenance of sinus rhythm in patients with atrial fibrillation (AF). Recently, the Food and Drug Administration (FDA) approved the use of IV sotalol loading, based primarily on modeling data for the infusion. We aimed to describe a protocol and experience with IV sotalol loading for elective treatment of adult patients with AF and atrial flutter (AFL).

METHODS

We present our institutional protocol and retrospective review of initial patients treated with IV sotalol for AF/AFL at the University of Utah Hospital between September 2020 and April 2021.

RESULTS

Eleven patients received IV sotalol for initial loading or dose escalation. All patients were male, aged 56-88 years (median 69). Mean QT interval (QTc) intervals increased from baseline (mean 384 ms) immediately after infusion of IV sotalol (mean change 42ms), but no patient required discontinuation of the medication. Six patients were discharged after 1 night; 4 patients were discharged after 2 nights; and 1 patient was discharged after 4 nights. Nine patients underwent electrical cardioversion prior to discharge (2 prior to load; 7 post-load on the day of discharge). There were no adverse events during the infusion or within 6 months of discharge. Persistence of therapy was 73% (8 of 11) at mean 9.9 weeks to follow up, with no discontinuations for adverse effects.

CONCLUSIONS

We employed a streamlined protocol that was successfully implemented to facilitate the use of IV sotalol loading for atrial arrhythmias. Our initial experience suggests feasibility, safety, and tolerability while reducing hospitalization duration. Additional data are needed to augment this experience as IV sotalol use is broadened across different patient populations.

Feasibility and Safety of Intravenous Sotalol Loading in Adult Patients With Atrial Fibrillation (DASH-AF)

BACKGROUND

Inpatient initiation of sotalol is recommended owing to its proarrhythmic effects. The DASH-AF (Feasibility and Safety of Intravenous Sotalol Administered as a Loading Dose to Initiate Oral Sotalol Therapy in Adult Patients With Atrial Fibrillation) trial evaluates the safety and feasibility of intravenous (IV) sotalol, achieving a steady state with maximum QTc prolongation within 6 hours instead of the traditional 5-dose inpatient oral (PO) titration.

METHODS

DASH-AF is a prospective, nonrandomized, multicenter, open-label trial consisting of patients who underwent IV sotalol loading dose to initiate rapid oral therapy for atrial arrhythmias. IV dose was calculated based on the target oral dose as indicated by baseline QTc and renal function. Patients' QTc (in sinus) was measured via electrocardiography at 15-minute intervals and after IV loading completion. Patients were discharged 4 hours after first oral dose. All patients were monitored via mobile cardiac outpatient telemetry for 72 hours. The control group was composed of patients admitted for the traditional 5 PO doses. Safety outcomes were assessed in both groups.

RESULTS

One hundred twenty patients from 3 centers were enrolled from 2021 to 2022 in the IV loading group (compared with type of AF- and renal function-matched patients in the conventional PO loading cohort). This study demonstrated no significant change in ΔQTc in both groups, with a significantly lower number of patients requiring dose adjustment in the IV arm compared with the PO arm (4.1% vs 16.6%; P = 0.003). This led to potential cost savings of up to $3,500.68 per admission.

CONCLUSIONS

The DASH-AF trial shows that rapid IV sotalol loading in atrial fibrillation/flutter patients for rhythm control is feasible and safe compared with conventional oral loading with significant cost reduction. (Feasibility and Safety of Intravenous Sotalol Administered as a Loading Dose to Initiate Oral Sotalol Therapy in Adult Patients With Atrial Fibrillation [DASH-AF]; NCT04473807).

Molecular determinants of pro-arrhythmia proclivity of d- and l-sotalol via a multi-scale modeling pipeline

Drug isomers may differ in their proarrhythmia risk. An interesting example is the drug sotalol, an antiarrhythmic drug comprising d- and l- enantiomers that both block the hERG cardiac potassium channel and confer differing degrees of proarrhythmic risk. We developed a multi-scale in silico pipeline focusing on hERG channel – drug interactions and used it to probe and predict the mechanisms of pro-arrhythmia risks of the two enantiomers of sotalol. Molecular dynamics (MD) simulations predicted comparable hERG channel binding affinities for d- and l-sotalol, which were validated with electrophysiology experiments. MD derived thermodynamic and kinetic parameters were used to build multi-scale functional computational models of cardiac electrophysiology at the cell and tissue scales. Functional models were used to predict inactivated state binding affinities to recapitulate electrocardiogram (ECG) QT interval prolongation observed in clinical data. Our study demonstrates how modeling and simulation can be applied to predict drug effects from the atom to the rhythm for dl-sotalol and also increased proarrhythmia proclivity of d- vs. l-sotalol when accounting for stereospecific beta-adrenergic receptor blocking.

"Second line medications" for supraventricular arrhythmias in children: In-hospital efficacy and adverse events during treatment initiation of sotalol and flecainide

INTRODUCTION

Sotalol and flecainide are used as second line agents in children for the treatment of supraventricular arrhythmias (SA) refractory to anti-beta adrenergic antiarrhythmics or digoxin. Efficacy and adverse events in this cohort have not been well described. Here, we report our institutional experience of second line treatment initiation for SA in children.

METHODS AND RESULTS

Utilizing an institutional database, 247 patients initiated on sotalol and 81 patients initiated on flecainide were identified. Congenital heart disease (CHD) was present in 40% of patients. Arrhythmia-free discharge on single or dual agent therapy (in combination with other antiarrhythmics) was 87% for sotalol and 91% for flecainide. Neither age, sex, dosing, presence of CHD nor arrhythmia subtype were associated with alterations in in-hospital efficacy. Compared to baseline, QTc intervals in sotalol patients (436 [416-452 ms] vs. 415 [400-431 ms], p < .01) and QRS intervals in flecainide patients (75 [68-88 ms] vs. 62 [56-71 ms], p < .01) were prolonged. Dose reduction or discontinuation due to QRS prolongation occurred in 9% of patients on flecainide. QTc prolongation resulting in dose reduction/discontinuation of sotalol was encountered in 9 patients (4%) and death with documented torsade de pointes in 2 patients (1%), with 9 of 11 patients having underlying CHD.

CONCLUSION

In children requiring second line agents for treatment of SA, both sotalol and flecainide appear to be highly efficacious. Although predominantly safe in otherwise healthy patients, electrocardiogram changes can occur and children with underlying cardiac disease may have an increased risk of adverse events and rhythm-related side effects during initiation.

Hydroxychloroquine and QTc prolongation in patients with COVID-19: A systematic review and meta-analysis

BACKGROUND

Among many drugs that hold potential in COVID-19 pandemic, chloroquine (CQ), and its derivative hydroxychloroquine (HCQ) have generated unusual interest. With increasing usage, there has been growing concern about the prolongation of QTc interval and Torsades de Pointes (TdP) with HCQ, especially in combination with azithromycin.

AIMS

This meta-analysis is planned to study the risk of QTc prolongation and Torsades de pointes (TdP) by a well-defined criterion for HCQ, CQ alone, and in combination with Azithromycin in patients with COVID-19.

METHODS

A comprehensive literature search was made in two databases (PubMed, Embase). Three outcomes explored in the included studies were frequency of QTc > 500 ms (ms) or ΔQTc > 60 ms (Outcome 1), frequency of QTc > 500 ms (Outcome 2) and frequency of TdP (Outcome 3). Random effects method with inverse variance approach was used for computation of pooled summary and risk ratio.

RESULTS

A total of 13 studies comprising of 2138 patients were included in the final analysis. The pooled prevalence of outcome 1, outcome 2 and outcome 3 for HCQ, CQ with or without Azithromycin were 10.18% (5.59-17.82%, I2 - 92%), 10.22% (6.01-16.85%, I2 - 79%), and 0.72% (0.34-1.51, I2 - 0%) respectively. The prevalence of outcome 2 in subgroup analysis for HCQ and HCQ + Azithromycin was 7.25% (3.22-15.52, I2 - 59%) and 8.61% (4.52-15.79, I2 - 76%), respectively. The risk ratio (RR) for outcome 1 and outcome 2 between HCQ + Azithromycin and HCQ was 1.22 (0.77-1.93, I2 - 0%) & 1.51 (0.79-2.87, I2 - 13%), respectively and was not significant. Heterogeneity was noted statistically as well clinically (regimen types, patient numbers, study design, and outcome definition).

CONCLUSION

The use of HCQ/CQ is associated with a high prevalence of QTc prolongation. However, it is not associated with a high risk of TdP.

Model-Informed Development of Sotalol Loading and Dose Escalation Employing an Intravenous Infusion

BACKGROUND

Sotalol is often employed to prevent recurrence of symptomatic atrial flutter/atrial fibrillation. Because sotalol can prolong the QT interval excessively causing ventricular arrhythmias, a 3-day in-hospital loading or dose escalation period is mandated with oral administration in the product label for patient safety. In patients with normal renal function, 3 days (five oral doses) are required to obtain steady state maximum sotalol concentration, which results in maximum QT prolongation. The aim of this study is to develop an intravenous to oral loading regime for sotalol therapy that reduces the 3-day in-hospital initiation or dose escalation with oral administration to 1 day without compromising patient safety.

METHODS

Using model-informed drug development techniques, simulations were developed for initiation and dose escalation of sotalol therapy by employing an intravenous loading dose followed by oral sotalol administrations.

RESULTS

In patients with normal renal function, an initial 1-h loading dose of intravenous sotalol followed by two oral doses in 24 h has been developed permitting attainment of three maximum serum concentrations reflecting maximum QT prolongation in a 1-day observation period. Dosing regimens for patients with impaired renal function are also developed.

CONCLUSIONS

In patients with normal renal function, using an intravenous loading dose followed by oral administrations permits safe initiation or dose escalation of sotalol in 1 day instead of the 3-day dosing regimen with oral administration.

Potentially Inappropriate Prescriptions in Heart Failure with Reduced Ejection Fraction (PIP-HFrEF)

Heart failure (HF) is a chronic debilitating and potentially life-threatening condition. Heart Failure patients are usually at high risk of polypharmacy and consequently, potentially inappropriate prescribing leading to poor clinical outcomes. Based on the published literature, a comprehensive HF-specific prescribing review tool is compiled to avoid medications that may cause HF or harm HF patients and to optimize the prescribing practice of HF guideline-directed medical therapies. Recommendations are made in line with the last versions of ESC guidelines, ESC position papers, scientific evidence, and experts' opinions.

Anti-arrhythmic therapy in athletes

The spectrum of arrhythmias that may be encountered in athletes ranges from isolated ectopic beats to ventricular tachycardia, usually in the context of a structurally normal heart. Anti-arrhythmic therapy in these individuals may be particularly challenging because of the young age, the hypervagotonic state, the desire to maintain a high physical performance, the reluctance to take medications and the need to avoid molecules included in the list of prohibited drugs of the World Anti-Doping Agency. Furthermore, the possible serious adverse effects of anti-arrhythmic drugs should be balanced against the benign nature of arrhythmias in patients with no underlying heart disease. The review summarizes the most common arrhythmias of athletes and the possible therapeutic options, including anti-arrhythmic drugs and non-pharmacological interventions. Eligibility criteria according to current guidelines are also addressed.

Substrates and potential therapeutics of ventricular arrhythmias in heart failure

Heart failure (HF) is a clinical syndrome characterized by ventricular contractile dysfunction. About 50% of death in patients with HF are due to fetal ventricular arrhythmias including ventricular tachycardia and ventricular fibrillation. Understanding ventricular arrhythmic substrates and discovering effective antiarrhythmic interventions are extremely important for improving the prognosis of patients with HF and reducing its mortality. In this review, we discussed ventricular arrhythmic substrates and current clinical therapeutics for ventricular arrhythmias in HF. Base on the fact that classic antiarrhythmic drugs have the limited efficacy, side effects, and proarrhythmic potentials, we also updated some therapeutic strategies for the development of potential new antiarrhythmic interventions for patients with HF.

Management of Atrial Fibrillation Post Bypass Surgery with Intravenous Sotalol: A Case Study

Intravenous sotalol has been available for many years outside of the United States, but has only recently become available in the US. The safety and feasibility of intravenous sotalol for the prevention of recurrent atrial fibrillation following bypass surgery has not been described. The present case study is of a patient with several other co-morbidities undergoing coronary artery bypass graft surgery, who post-operatively developed atrial fibrillation. The patient received intravenous sotalol and was then transitioned to oral sotalol. The patient remained hemodynamically stable, with normal QTc and without further atrial fibrillation or tachyarrhythmias in the post-operative period until discharge. Intravenous sotalol is a reasonable alternative to intravenous amiodarone in the post bypass surgery patient with better tolerability and safety profile.

Predictors of Pharmacological Therapy of Ectopic Atrial Tachycardia in Children

Ectopic atrial tachycardia (EAT) is a relatively common type of supraventricular tachycardia in the pediatric population, and it can be resistant to antiarrhythmic drugs and lead to tachycardia-induced cardiomyopathy (TIC) if not properly managed. The purpose of this study was to determine the predictors of the response to pharmacological therapy in children with EAT. From January 2009 to April 2014, 115 children were admitted to our hospital with a diagnosis of EAT and placed on antiarrhythmic drugs. We examined the clinical history, response to therapy, and follow-up of the children. The incidence of TIC secondary to EAT was 22.6% (n = 26) in children. Incessant EAT accounted for 44.3% of all patients. Control of EAT with antiarrhythmic therapy was achieved in 73.9% (n = 85) of the children. The combination of sotalol and propafenone performed well in controlling EAT in children [complete control in 35 (49.3%) of 71]. The mean time of conversion to sinus rhythm was 24 days, and the mean duration of therapy was 11 months in children with resolution. Multivariate predictors of the control of EAT were age at presentation (OR 0.289, P = 0.038) and tachycardia type (OR 0.276, P = 0.006). TIC occurs in 22.6% of children with EAT. Incessant EAT is more frequently complicated by TIC. Independent factors associated with a good response to pharmacological therapy include a younger age at presentation and non-incessant tachycardia in children with EAT.

Drugs That May Cause or Exacerbate Heart Failure: A Scientific Statement From the American Heart Association

Heart failure is a common, costly, and debilitating syndrome that is associated with a highly complex drug regimen, a large number of comorbidities, and a large and often disparate number of healthcare providers. All of these factors conspire to increase the risk of heart failure exacerbation by direct myocardial toxicity, drug-drug interactions, or both. This scientific statement is designed to serve as a comprehensive and accessible source of drugs that may cause or exacerbate heart failure to assist healthcare providers in improving the quality of care for these patients.

Risk prediction for adverse events during initiation of sotalol and dofetilide for the treatment of atrial fibrillation

BACKGROUND

Inpatient antiarrhythmic drug initiation for atrial fibrillation is mandated for dofetilide (DF) and is often performed for sotalol (SL), particularly if proarrhythmia risk factors are present. Whether low-risk patients can be identified to safely allow outpatient initiation is unknown.

METHODS

A single-center retrospective cohort study was performed on patients initiated with DF or SL. Risk factors for adverse events (AEs), defined as any arrhythmia or electrocardiogram change requiring dose reduction or cessation, were identified.

RESULTS

Of 329 patients, 227 (69%) received SL and 102 (31%) DF. The cohort had a mean age of 63 ± 13 years; 70% of patients were male and had a baseline QTc of 440 ± 37 ms. A total of 105 AEs occurred in 92 patients: QTc prolongation or ventricular tachyarrhythmia in 70 patients (67% of AEs), bradyarrhythmias in 35 patients (33% of AEs), with some experiencing both AE types. Ventricular arrhythmias were seen in 23 patients (7%) and torsades de pointes in one (0.3%). Total AE rates were similar between drugs (P = 0.09); however, DF patients had more QTc prolongation or ventricular arrhythmias (P = 0.001). In SL patients, there were no predictors for QTc prolongation or ventricular proarrhythmia. In DF patients, higher baseline QTc interval (odds ratio = 1.64/25 ms, P = 0.01) was an independent predictor of QTc prolongation or ventricular proarrhythmias. For patients without proarrhythmia risk factors, overall AE rate was 26%.

CONCLUSIONS

In conclusion, AEs are common during DF and SL initiation but rarely severe in hospitalized inpatients. Baseline QTc predicts AEs for DF patients only and AE are common even in "low-risk" patients. These results support in-hospital drug initiation for all DF and SL patients.

The efficacy and tolerability of commonly used agents to prevent recurrence of atrial fibrillation after successful cardioversion

A number of therapeutic strategies exist for the restoration and maintenance of sinus rhythm in patients presenting with atrial fibrillation. The acute success rate with electrical cardioversion is high. However, many patients relapse into atrial fibrillation. A major challenge faced by those who care for patients with atrial fibrillation is the long-term maintenance of sinus rhythm whilst avoiding treatment-related adverse effects. This review examines the efficacy and tolerability of conventional anti-arrhythmic drugs for the secondary prevention of atrial fibrillation in the post-cardioversion period.

Antiarrhythmic drugs for the maintenance of sinus rhythm: risks and benefits

Atrial fibrillation (AF) is the most common arrhythmia seen in clinical practice, and its complications impose a significant economic burden. The development of more effective agents to manage patients with AF is essential. While clinical trials show no major differences in outcomes between rate and rhythm control strategies, some patients with AF require treatment with antiarrhythmic drugs (AADs) to maintain sinus rhythm, reduce symptoms, improve exercise tolerance, and improve quality of life. Currently available AADs, while effective, have limitations including limited efficacy, adverse events, toxicity, and proarrhythmic potential. The 6 most commonly used AADs (amiodarone, disopyramide, dofetilide [USA but not Europe], flecainide, propafenone, sotalol) have proarrhythmic effects (fewer with amiodarone). Amiodarone is the most effective AAD, but its safety profile limits its usefulness. Recent advances in AAD therapy include dronedarone and vernakalant. Dronedarone, approved by the United States Food and Drug Administration and the European Medicines Authority and others, has been proven efficacious in maintaining sinus rhythm and reducing the incidence of hospitalization due to cardiovascular events or death in patients with AF. The intravenous formulation of vernakalant is approved in the European Union, Iceland, and Norway. Oral vernakalant is currently undergoing evaluation for preventing AF recurrence and appears to be effective with an acceptable safety profile. Treatment should be individualized to the patient with consideration of pharmacologic risks and benefits according to AF management guidelines. Accumulating efficacy and safety data for new and emerging AADs holds promise for improved AF management and outcomes.

Comparison of a Standard versus Accelerated Dosing Regimen for d,l-Sotalol for the Treatment of Atrial and Ventricular Dysrhythmias

BACKGROUND

The current recommended starting dose of sotalol is 80 mg orally twice per day, followed by a judicious increase in dosage every 3 days under continuous telemetry monitoring. We hypothesized that sotalol administered at a higher starting dose (120 or 160 mg twice daily) would allow a more rapid attainment of therapeutic response with an acceptable safety and comparable efficacy profile.

METHODS

Two hundred nine inpatients with various atrial and ventricular dysrhythmias were begun on either a standard starting dose (80 mg b.i.d.) or an accelerated dose (120 or 160 mg b.i.d.) of sotalol. In-hospital occurrences of drug-related adverse effects (proarrhythmic and others), drug efficacy, and length of hospitalization were retrospectively compared between the two groups.

RESULTS

Ten patients (9.3%) in the 80 mg b.i.d. starting dose group experienced a cardiac adverse effect of sotalol as compared to 15 patients (14.9%) in the accelerated dose group (P = 0.286). The mean amount of corrected QT (QTc) prolongation over baseline was not significantly different between the two groups at hospital discharge (22.5 ms vs 21.6 ms, P = 0.898). There was a trend toward more noncardiac side effects of sotalol in the accelerated dose group: 2 (1.9%) versus 7(6.9%), P = 0.092. The average length of hospital stay was similar in the two groups (6.8 days vs 7.4 days, P = 0.558).

CONCLUSION

Initiating sotalol at 120-160 mg orally twice per day marginally increases the risk of cardiac and non-cardiac side effects compared to the standard starting regimen of 80 mg b.i.d. Such an accelerated dosing regimen neither shortened hospitalization nor had any effect on treatment efficacy in this retrospective analysis.

Pharmacogenetic aspects of drug-induced torsade de pointes: potential tool for improving clinical drug development and prescribing

Drug-induced torsade de pointes (TdP) has proved to be a significant iatro-genic cause of morbidity and mortality and a major reason for the withdrawal of a number of drugs from the market in recent times. Enzymes that metabolise many of these drugs and the potassium channels that are responsible for cardiac repolarisation display genetic polymorphisms. Anecdotal reports have suggested that in many cases of drug-induced TdP, there may be a concealed genetic defect of either these enzymes or the potassium channels, giving rise to either high plasma drug concentrations or diminished cardiac repolarisation reserve, respectively. The presence of either of these genetic defects may predispose a patient to TdP, a potentially fatal adverse reaction, even at therapeutic dosages of QT-prolonging drugs and in the absence of other risk factors. Advances in pharmacogenetics of drug metabolising enzymes and pharmacological targets, together with the prospects of rapid and inexpensive genotyping procedures, promise to individualise and improve the benefit/risk ratio of therapy with drugs that have the potential to cause TdP. The qualitative and the quantitative contributions of these genetic defects in clinical cases of TdP are unclear because not all of the patients with TdP are routinely genotyped and some relevant genetic mutations still remain to be discovered. There are regulatory guidelines that recommend strategies aimed at uncovering the risk of TdP associated with new chemical entities during their development. There are also a number of guidelines that recommend integrating pharmacogenetics in this process. This paper proposes a strategy for integrating pharmacogenetics into drug development programmes to optimise association studies correlating genetic traits and endpoints of clinical interest, namely failure of efficacy or development of repolarisation abnormalities. Until pharmacogenetics is carefully integrated into all phases of development of QT-prolonging drugs and large-scale studies are undertaken during their post-marketing use to determine the genetic components involved in induction of TdP, routine genotyping of patients remains unrealistic. Even without this pharmacogenetic data, the clinical risk of TdP can already be greatly minimised. Clinically, a substantial proportion of cases of TdP are due to the use of either high or usual dosages of drugs with potential to cause TdP in the presence of factors that inhibit drug metabolism. Therefore, choosing the lowest effective dose and identifying patients with these non-genetic risk factors are important means of minimising the risk of TdP. In view of the common secondary pharmacology shared by these drugs, a standard set of contraindications and warnings have evolved over the last decade. These include factors responsible for pharmacokinetic or pharmacodynamic drug interactions. Among the latter, the more important ones are bradycardia, electrolyte imbalance, cardiac disease and co-administration of two or more QT-prolonging drugs. In principle, if large scale prospective studies can demonstrate a substantial genetic component, pharmacogenetically driven prescribing ought to reduce the risk further. However, any potential benefits of pharmacogenetics will be squandered without any reduction in the clinical risk of TdP if physicians do not follow prescribing and monitoring recommendations.

Electrophysiologic effects of SB-237376: a new antiarrhythmic compound with dual potassium and calcium channel blocking action

Combined potassium and calcium channel blocking activities are suggested to be the basis for antiarrhythmic efficacy with low proarrhythmic risk. The electrophysiologic effects of SB-237376 were investigated in single myocytes and arterially perfused wedge preparations of canine or rabbit left ventricles. The concentration-dependent prolongation of action potential duration (APD) and QT interval by SB-237376 was bell-shaped and the maximum response occurred at 1-3 microM SB-237376 inhibited rapidly activating delayed rectifier K current (I(Kr) ) with an IC50 of 0.42 microM and use-dependently blocked L-type Ca current (I (Ca,L) ) at high concentrations. The SB-237376 (3 microM) induced phase-2 early afterdepolarizations (EADs) in five of six rabbit wedge preparations but none of six canine wedge preparations. This is probably due to larger increases of APD, QT interval, and transmural dispersion of repolarization (TDR) in rabbits than dogs. Based on the drug effects on QT interval, TDR, and EAD in rabbit ventricular wedge preparations, a scoring system predicted lower proarrhythmic risk for SB-237376 than for dl-sotalol, a specific I blocker. In conclusion, SB-237376 increases APD, QT interval, and TDR mainly by I (Kr) inhibition. These effects are self-limited due to SB-237376-induced I(Ca,L) blockade at high concentrations, which may explain its lower proarrhythmic risk than dl-sotalol.

The importance of the QT interval: a review of the literature

OBJECTIVE

QT interval (QTi) prolongation is generally associated with increased risk of ventricular arrhythmias such as torsade de pointes (TdP) and death.

METHOD

Literature review based on publications identified by means of electronic and manual search.

RESULTS

It has recently become apparent that not only antiarrhythmic drugs such as sotalol and quinidine, but also a variety of non-antiarrhythmic drugs such as certain antihistamines, antimicrobial drugs, psychiatric drugs and cisapride, may have the ability to induce prolongation of the QTi and TdP. Special concern should be drawn to the coadministration of drugs that inhibit the metabolism of these drugs such as ketoconazole, itraconazol and erythomycin. Patients with congenital long QT syndrome, patients with heart disease, with hypokalemia or hypomagnesemia, and women have an increased risk. Every sign of dizziness or syncope should be regarded as a warning sign of possible arrhythmia in patients treated with drugs that potentially prolong the QTi.

CONCLUSION

Measurement of the QTi before and during treatment is generally recommended in high-risk patients.

Sinus node dysfunction and atrial tachycardia after the Fontan procedure: The scope of the problem

Similar to other atrial baffling procedures, the Fontan procedure exposes patients to ongoing morbidity and mortality. The development of the bradycardia-tachycardia syndrome can have adverse effects on already-marginal hemodynamics and ventricular function. Patients with Fontan physiology and sinus node dysfunction can be managed with antibradycardic pacemakers. Atrial arrhythmias after "completion Fontan" are difficult to treat and usually require either antiarrhythmic agents, antitachycardic pacemakers, or radiofrequency catheter ablation of the re-entrant circuit. Successful treatment of atrial flutter occurs in only 50% to 70% of patients. There is a high recurrence rate of atrial flutter with any of the accepted management strategies. Copyright 1998 by W.B. Saunders Company

The canine Purkinje fiber: an in vitro model system for acquired long QT syndrome and drug-induced arrhythmogenesis

Torsade de pointes is a rare but potentially fatal ventricular arrhythmia associated with drug-induced delayed repolarization and prolongation of the QT interval. To determine if the arrhythmogenic potential of noncardiac drugs can be assessed in vitro, we evaluated the effects of 12 drugs on the action potential duration (APD) of cardiac Purkinje fibers and compared results with clinical observations. APD changes in canine and porcine fibers were evaluated under physiologic conditions (37 degrees C, [K+]0 = 4 mM) using standard microelectrode techniques. Six of seven drugs associated with QT prolongation or torsade de pointes in man (cisapride, erythromycin, grepafloxacin, moxifloxacin, sertindole, and sotalol) affected concentration-dependent prolongation of the APD in canine fibers during slow stimulation (2-s basic cycle length), attaining greater than 15% prolongation at high concentrations (> or = 10-fold clinically encountered plasma levels). Each of five drugs not linked clinically to QT prolongation and torsade de pointes (azithromycin, enalaprilat, fluoxetine, indomethacin, and pinacidil) failed to attain 15% prolongation, with fluoxetine, indomethacin, and pinacidil abbreviating the APD. Drugs eliciting the greatest prolongation also demonstrated prominent reverse rate-dependent effects. The antihistamine terfenadine (linked to dose-dependent QT prolongation and torsade de pointes clinically) only minimally prolonged the APD in canine and porcine fibers (and exerted no effect on midmyocardial fibers from left ventricular free wall) at supratherapeutic concentrations. On the basis of concentration-dependent APD prolongation and reverse rate-dependent effects, this Purkinje fiber model detects six of seven drugs linked clinically to acquired long QT syndrome and torsade de pointes, and clears each of five drugs not associated with repolarization abnormalities (overall 92% accuracy), validating the utility of this Purkinje fiber model in the preclinical evaluation of QT prolongation and proarrhythmic risk by noncardiac drugs.

Supraventricular tachycardia

Supraventricular tachycardias (SVT) comprise those tachycardias that originate above the bifurcation of the bundle of His. They can be classified broadly as AV node dependent and AV node independent. The mechanism and clinical manifestation of SVTs, which is essential to their correct diagnosis, is reviewed. The therapeutic management of SVTs, including acute and chronic drug therapy and catheter ablation, is discussed also.

Meta-analysis of the Risk of Torsades de Pointes in patients treated with intravenous racemic sotalol

OBJECTIVE

Intravenous (IV) racemic sotalol is useful for the treatment of multiple tachydysrhythmias. The authors hypothesized that the risk of torsades de pointes (TdP) in patients treated with a single IV infusion of sotalol is lower than the 2-4% risk associated with chronic oral sotalol therapy.

METHODS

A MEDLINE search under the subject heading "sotalol" was made of all publications involving humans written in English or German from 1966 to October 1, 2000. A meta-analysis of all original reports including patients who were given a single infusion of at least 1.5 mg/kg or 100 mg of IV sotalol over 30 minutes or less was performed. Potential variables predictive of TdP were assessed. The primary outcome was the observation of TdP associated with IV sotalol infusion. Secondary measurements included hypotension, bradycardia, and worsening of congestive heart failure. All excluded studies and case reports were also examined for evidence of TdP associated with IV sotalol treatment.

RESULTS

The search included 1,005 publications. There were 37 reports in which 962 patients received IV sotalol and met the inclusion criteria. There was one report of self-terminating TdP lasting 10 seconds among the 962 patients included in the study. There was no report of TdP associated with only IV racemic sotalol administration in any of the excluded studies. If it is assumed that the risk of TdP is homogeneous in the population of patients treated with IV sotalol, then based on the 962 included patients, the rate of TdP is 0.1% (95% CI = 0.003% to 0.6%).

CONCLUSIONS

The overall risk of TdP in patients treated with a single infusion of IV sotalol is low compared with that in patients given chronic oral sotalol therapy.

The class III antiarrhythmic effect of sotalol exerts a reverse use-dependent positive inotropic effect in the intact canine heart

OBJECTIVES

We sought to study the rate related effects of sotalol on myocardial contractility and to test the hypothesis that the class III antiarrhythmic effect of sotalol has a reverse use-dependent positive inotropic effect in the intact heart.

BACKGROUND

Antiarrhythmic drugs exert significant negative inotropic effects. Sotalol, a beta-adrenergic blocking agent with class III antiarrhythmic properties, may augment contractility by virtue of its ability to prolong the action potential duration (APD).

METHODS

In 10 anesthetized dogs, measurements of left ventricle (LV) peak (+)dP/dt and simultaneous endocardial action potentials were made during baseline conditions and after sequential administration of esmolol and sotalol. In addition, electrical and mechanical restitution curves were constructed at a basic pacing cycle length of 600 ms by introducing a test pulse of altered cycle length ranging from 200 ms to 2,000 ms.

RESULTS

In the steady state pacing experiments, sotalol prolonged the APD in a reverse use-dependent manner; such an effect was not seen with esmolol. At cycle lengths exceeding 400 ms, LV (+)dP/dt was significantly higher with sotalol than it was with esmolol. There was a direct relation between APD and LV (+)dP/dt with sotalol (r = 0.46, p < 0.001), but there was no significant relation between APD and LV (+)dP/dt with esmolol (r = 0.27, p = NS). Results in the single beat (restitution) studies were qualitatively similar to the steady state results; APD (at cycle length >400 ms) and LV (+)dP/dt (at cycle length >600 ms) were significantly higher with sotalol than they were with esmolol.

CONCLUSIONS

The reverse use-dependent prolongation of APD by sotalol is associated with a positive inotropic effect.

Antiarrhythmic drug initiation in patients with atrial fibrillation

Antiarrhythmic drugs remain the mainstay of treatment of atrial fibrillation, but their potential proarrhythmic effects hamper their optimal use. Drug-induced tachyarrhythmias (ventricular tachycardia or atrial tachyarrhythmias with rapid ventricular response) are life-threatening and often cause syncope. Because these events tend to cluster shortly after drug initiation, it is common practice to routinely hospitalize patients for drug initiation under continuous electrocardiographic surveillance. The low incidence of serious proarrhythmia makes the cost-effectiveness of this practice controversial. Torsades de pointes, in particular, can be predicted by the presence of one or more of the following risk factors: female gender, structural heart disease, prolonged baseline QT interval, bradycardia, hypokalemia, previous proarrhythmic responses, and higher drug plasma levels. Proarrhythmia induced by class IC agents is seen almost exclusively in patients with structural heart disease and ventricular dysfunction. A variety of monitoring devices permit electrocardiographic monitoring of patients in the outpatient setting. Efficient clinical pathways for the safe initiation of antiarrhythmic drugs in patients with atrial fibrillation do not require universal hospital admission. In patients without structural heart disease, outpatient initiation of most antiarrhythmic drugs appears safe. In patients with significant structural heart disease, class IC drugs are contraindicated, and most other drugs should be initiated in the hospital under continuous monitoring. The incidence of severe proarrhythmia is very low when loading doses of amiodarone of 600 mg/d or less are given to outpatients with structural heart disease.

JTc prolongation with d,l-sotalol in women versus men

Women are at increased risk for torsades de pointes associated with a variety of drugs that prolong ventricular repolarization, but few data exist regarding possible sex differences in extent of repolarization changes with these medications. We sought to compare JTc interval responses in women and men during treatment with d,l-sotalol. The study cohort consisted of 1,897 patients (26% women) with available baseline and > or =1 on-drug electrocardiogram from a database involving patients exposed to oral d,l-sotalol without developing torsades de pointes. The mean lowest and highest daily d,l-sotalol dose, normalized for weight, was not significantly different between sexes. At each dosing extreme, on-drug JTc was significantly longer in women (p < or =0.0002). Statistically independent predictors of on-drug JTc included gender (p = 0.003), baseline JTc (p = 0.0001), dose (p = 0.0001), serum creatinine (p < or =0.03), and history of sustained ventricular tachyarrhythmias (p = 0.01). In both men and women, as baseline JTc increased, the drug-induced increment in JTc became progressively smaller. Thus, in response to d,l-sotalol, JTc intervals become longer in women than in men. This sex difference is independent of dose and not solely attributable to the known gender disparity in baseline JTc. The greater propensity of women to drug-induced torsades de pointes may represent the most extreme expression of a basic sex difference in the response to medications that prolong ventricular repolarization.

Interactions between implantable cardioverter-defibrillators and class III agents

Although implantable cardioverter-defibrillators (ICDs) can successfully terminate ventricular arrhythmias, antiarrhythmic drugs are often required to prevent recurrent events. Class III antiarrhythmic agents have emerged as the safest, most effective, and widely used agents in the 40-70% of ICD patients who require concomitant antiarrhythmic medication. Antiarrhythmic agents can influence the effectiveness of ICDs to terminate arrhythmias through their effect on defibrillation threshold. All class III agents share the ability to prolong ventricular refractoriness and those with "pure" class III activity consistently decrease defibrillation threshold in the normal canine heart model. Sotalol, amiodarone, and bretylium all have other Vaughan Williams class actions that influence their respective effects on defibrillation threshold. Sotalol has been associated with a decrease in defibrillation threshold in both animal and in clinical studies, whereas amiodarone has been associated with variable effects in animal models and an increase in defibrillation threshold in clinical studies. Additionally, antiarrhythmic agents may prolong ventricular tachycardia (VT) cycle length, which may affect the ability to pace terminate or cardiovert VT. Amiodarone has a moderate slowing effect on the VT cycle length. Finally, class III drugs also have proarrhythmic potential that may affect the defibrillator's function. Sotalol can be associated with dose-related torsade de pointes, whereas amiodarone may slow the VT cycle length below the tachycardia detection rate cutoff. In conclusion, class III pharmacotherapy can be safely administered in conjunction with ICD therapy as long as the interaction between these therapeutic modalities is appreciated.

Mechanisms and management of proarrhythmia

It is now well recognized that therapy with antiarrhythmic drugs can not only suppress cardiac arrhythmias, but also may increase their frequency or provoke new ones. Specific proarrhythmia syndromes, each with a distinct underlying mechanism and approach to therapy, have been described. The best-recognized examples are digitalis intoxication, proarrhythmia associated with sodium-channel block, and torsade de pointes occurring during QT-prolonging therapies. In the case of sodium-channel blockers, 2 forms of proarrhythmia are commonly recognized: slow atrial flutter with 1:1 atrioventricular conduction, and frequent ventricular tachycardia ([VT], most often found in patients with pre-existing VT reentrant circuits). In all cases, the best approach to therapy is to identify patients at risk (and thereby avoid therapy entirely), to recognize proarrhythmia when it occurs, to withdraw offending agent(s), and to use specific corrective therapies when available. Although most recognized episodes of proarrhythmia are thought to occur early in drug therapy, the increased mortality during chronic antiarrhythmic therapy demonstrated in large randomized trials suggests this phenomenon can also develop during long-term drug treatment. The recognition of proarrhythmia and the delineation of its underlying mechanisms should not only improve therapy with available drugs, but may also direct development of newer agents devoid of this potential.

Mortality in the Survival With ORal D-sotalol (SWORD) trial: why did patients die?

The Survival With ORal D-sotalol (SWORD) trial tested the hypothesis that the prophylactic administration of oral d-sotalol would reduce total mortality in patients surviving myocardial infarction (MI) with a left ventricular ejection fraction (LVEF) of < or = 40%. Two index MI groups were included: recent (6 to 42 days) and remote (> 42 days) with clinical heart failure (n = 915 and 2,206, respectively). The trial was discontinued when the statistical boundary for harm was crossed (RR = 1.65; p = 0.006). All baseline variables known to be associated with mortality risk (e.g., LVEF, heart failure class, age) as well as variables related to torsades de pointes (e.g., time from beginning of therapy, QTc, gender, potassium, renal function, dose of d-sotalol) were assessed for interaction of each variable with treatment assignment, computing RR and 95% confidence interval (CI) from Cox regression models. The d-sotalol-associated mortality was greatest in the group with remote MI and LVEFs of 31% to 40% (RR = 7.9; 95% CI 2.4 to 26.2). Most variables known to be associated with torsades de pointes were not differentially predictive of d-sotalol-associated risk, except female gender (RR = 4.7; 95% CI 1.4 to 16.5). These findings suggest that (1) most of the d-sotalol-associated risk was in patients remote from MI with a LVEF of 31% to 40%; comparable placebo patients had a very low mortality (0.5%); and (2) very little objective data supports torsades de pointes or any specific proarrhythmic mechanism as an explanation for d-sotalol-associated mortality risk.

Cost effectiveness of inpatient initiation of antiarrhythmic therapy for supraventricular tachycardias

This study assessed the cost effectiveness of inpatient antiarrhythmic therapy initiation for supraventricular tachycardias using a metaanalysis of proarrhythmic risk and a decision analysis that compared inpatient to outpatient therapy initiation. A MEDLINE search of trials of antiarrhythmic therapy for supraventricular tachycardias was performed, and episodes of cardiac arrest, sudden or unexplained death, syncope, and sustained or unstable ventricular arrhythmias were recorded. A weighted average event rate, by sample size, was calculated and applied to a clinical decision model of therapy initiation in which patients were either hospitalized for 72 hours or treated as outpatients. Fifty-seven drug trials involving 2,822 patients met study criteria. Based on a 72-hour weighted average event rate of 0.63% (95% confidence interval, 0.2% to 1.2%), inpatient therapy initiation cost $19,231 per year of life saved for a 60-year-old patient with a normal life expectancy. Hospitalization remained cost effective when event rates and life expectancies were varied to model hypothetical clinical scenarios. For example, cost-effectiveness ratios for a 40-year-old without structural heart disease and a 60-year-old with structural heart disease were $37,510 and $33,310, respectively, per year of life saved. Thus, a 72-hour hospitalization for antiarrhythmic therapy initiation is cost effective for most patients with supraventricular tachycardias.

Analysis of the treatment of spontaneous sustained stable ventricular tachycardia

OBJECTIVES

To determine the termination rate of spontaneous sustained stable ventricular tachycardia (SSSVT) as a function of the first and second therapeutic interventions used, and to determine factors associated with successful termination.

METHODS

A multihospital, retrospective analysis of the treatment of patients with SSSVT was performed. The setting included 2 urban county hospitals, 2 urban private hospitals, and a Veterans Affairs hospital. Cases were identified by discharge diagnosis and ECG characteristics, and confirmed by electrophysiology study or ECG criteria.

RESULTS

There were 40 cases of SSSVT identified. Excluding adenosine, 35 patients were treated with lidocaine as a first intervention. The rate of termination with lidocaine bolus was 17% (6 of 35) (95% CI 7-34%). Regarding the 35 patients initially treated with lidocaine, the odds of termination of SSSVT were 11 times greater in those without a history of previous myocardial infarction (MI) than in those with a history of MI (95% CI 0.96-551). Of the 29 patients who failed initial lidocaine treatment, 23 were treated with a second lidocaine bolus, with a termination rate of 18% (4 of 22) (95% CI 5-40%). Only 2 patients with sustained ventricular tachycardia had a concurrent MI, and the tachycardia was unresponsive to initial lidocaine bolus in both cases. Fifteen patients received adenosine with no tachycardia terminations and no significant adverse effects.

CONCLUSIONS

The rate of SSSVT termination with lidocaine was low, particularly in patients with a history of Mi.

Further observations to elucidate the role of interventricular dispersion of repolarization and early afterdepolarizations in the genesis of acquired torsade de pointes arrhythmias: a comparison between almokalant and d-sotalol using the dog as its own control

OBJECTIVES

We sought to further elucidate the role of early afterdepolarizations (EADs) and interventricular dispersion of repolarization (deltaAPD) in the genesis of acquired torsade de pointes (TdP) arrhythmias.

BACKGROUND

Administration of class III agents can be associated with TdP. We developed a dog model in which TdP can be reproducibly induced by pacing after d-sotalol. This model shows reproducible results over weeks.

METHODS

In 14 anesthetized dogs with chronic complete atrioventricular block, two separate experiments were performed in which d-sotalol (2 mg/kg body weight) or almokalant (0.12 mg/kg) was administered. Monophasic action potentials were simultaneously recorded from the endocardium of the right and left ventricle to register EADs and to measure the action potential duration (APD). DeltaAPD was defined as the APD of the left ventricle minus that of the right ventricle.

RESULTS

Baseline conditions were identical in the serially performed experiments. The cycle length and QT time increased by 16% and 26% after d-sotalol and by 15% and 31% after almokalant, respectively. After both drugs the action potential of the left ventricle prolonged more than that of the right ventricle, thereby increasing deltaAPD (almokalant [mean +/- SD]: 110 +/- 60 ms; d-sotalol: 80 +/- 45 ms, p < 0.05). The incidence of EADs (18 of 22 vs. 11 of 24, p < 0.05) and single ectopic beats (EBs) (1.5 +/- 2 vs. 24 +/- 32, p < 0.01) was more frequently observed after almokalant than after d-sotalol. Moreover, multiple EBs only occurred after almokalant. These beats interfered with the basic rhythm, leading to dynamic changes in left ventricular APD and to additional increases in deltaAPD. Spontaneous TdP was observed in 9 of 14 dogs after almokalant and could be increased to 12 of 14 with programmed electrical stimulation. After d-sotalol, TdP could only be induced by programmed electrical stimulation (5 of 14, p < 0.05).

CONCLUSIONS

In the same dog, almokalant induced more delay in repolarization, more EADs, multiple EBs and more ventricular inhomogeneity in APD than d-sotalol. These changes were related to a higher incidence of TdP and thereby confirm a strong association of the occurrence of EADs, multiple EBs and deltaAPD in the genesis of TdP. These findings also show the possible value of our model for evaluating the proarrhythmic potential of different drugs.

Mechanisms and medical management of patients with atrial flutter

Type I atrial flutter is due to reentrant excitation, principally in the right atrium. The standard ECG remains the cornerstone for its clinical diagnosis. Acute treatment should be directed at control of the ventricular response rate and, if possible, restoration of sinus rhythm. Radiofrequency catheter ablation therapy provides the best hope of cure, although atrial fibrillation may subsequently occur after an ostensibly successful ablative procedure. Alternatively, antiarrhythmic drug therapy to suppress recurrent atrial flutter episodes may be useful, recognizing that occasional recurrences are common despite therapy. Radiofrequency ablation of the His bundle ablation with placement of an appropriate pacemaker system may be useful in selected patients.

The side effect profile of class III antiarrhythmic drugs: focus on d,l-sotalol

Class III antiarrhythmic drugs have been under extensive clinical investigation as safer, more effective alternatives to class I drugs, which have recognized risks in selected populations. Class III drugs prolong the action potential duration of myocardial cells, resulting in a lengthening of the effective refractory period. This pharmacologic activity has antiarrhythmic properties, but it may induce a distinctive form of proarrhythmia known as torsades de pointes. Amiodarone and d,l-sotolol are class III drugs that have been available for many years. In addition to their ability to prolong refractoriness, these drugs have other pharmacodynamic properties. Recent antiarrhythmic drug discovery has focused on the identification and development of selective or so-called pure class III drugs that are devoid of additional actions. Investigators have hoped that these drugs would be as effective as sotalol and amiodarone but have fewer adverse effects. Accumulating data, however, indicate that complex compounds exhibiting antiadrenergic and other electrophysiologic properties may be superior to pure class III agents.

Impact of volume loading and load reduction on ventricular refractoriness and conduction properties in canine congestive heart failure

OBJECTIVES

This investigations was undertaken to examine the alteration of electrophysiologic properties, including refractoriness, strength-interval relations and conduction, with the development of heart failure and to characterize the impact of volume loading on these indexes in the cardiomyopathic setting.

METHODS

Electrophysiologic properties in eight dogs with pacing-induced dilated cardiomyopathy were compared with those in six control dogs before and after rapid infusion of 800 ml of intravenous saline.

RESULTS

The right ventricular (RV) and left ventricular (LV) effective refractory period (ERP) and absolute refractory period (ARP) were significantly longer in dogs with pacing-induced cardiomyopathy than in control dogs: RV ERP 181 +/- 11 ms versus 138 +/- 7 ms (mean +/- SD) (p < 0.0001) and anterior LV ERP 177 +/- 13 ms versus 128 +/- 11 ms (p < 0.0001), respectively; ARP 159 +/- 14 ms versus 114 +/- 7 ms (p < 0.0001) at the RV site and 153 +/- 12 versus 117 +/- 5 ms (p < 0.0001) at the anterior LV site. After volume loading in cardiomyopathic animals, posterior and anterior LV ERPs became prolonged to 178 +/- 5 ms (p = 0.004) and 189 +/- 14 ms (p = 0.065), respectively, shifting the strength-interval relation in the direction of longer S1S2 coupling intervals. Anterior LV monophasic action potential durations at 90% repolarization also became prolonged from 192 +/- 10 ms to 222 +/- 23 ms (p < 0.012) with volume loading. These findings were not altered by subsequent sodium nitroprusside. Local conduction times parallel and perpendicular to fiber orientation were not altered by development of cardiomyopathy or volume alterations.

CONCLUSIONS

The development of dilated cardiomyopathy results in significant prolongation of refractoriness and repolarization that is increased further by volume augmentation but is not reversed by pharmacologic load reduction. Although these abnormalities may contribute to the environment needed for a non-reentrant, triggered or stretch-mediated arrhythmogenic process in cardiomyopathic states, additional studies will be required to demonstrate such a focal mechanism conclusively.

Efficacy and safety of sotalol in patients with refractory atrial fibrillation or flutter

Sotalol's usefulness in treatment of atrial fibrillation and atrial flutter is unproven. This study evaluated (1) the efficacy of sotalol in preventing recurrences of paroxysmal atrial fibrillation or atrial flutter and controlling ventricular rate (in chronic atrial fibrillation or relapse of paroxysmal atrial arrhythmias), (2) the safety of sotalol, and (3) predictors of sotalol efficacy. Thirty-three patients, 28 with paroxysmal and five with chronic atrial fibrillation or atrial flutter, received an average dose of 265 +/- 119 mg of oral sotalol per day. During a 10 +/- 12 month follow-up, recurrence rate for paroxysmal arrhythmia was 64%, with a 50% recurrence at 4.6 months. For patients with chronic atrial fibrillation, ventricular rates were well controlled with sotalol administration (136 +/- 33 beats/min versus 88 +/- 23 beats/min; p = 0.04). No patient with chronic atrial fibrillation converted to sinus rhythm during the study. Side effects necessitated sotalol discontinuation in three patients. By multivariate analysis, younger age, higher ejection fraction, and absence of hypertension independently predicted sotalol efficacy.