Interactions between implantable cardioverter-defibrillators and class III agents

Causes of Failure to Capture in Pacemakers and Implantable Cardioverter-defibrillators

The number of patients with implantable electronic cardiac devices is continuously increasing. As more pacemakers and implantable cardioverter-defibrillators (ICDs) are being placed, a basic understanding of some troubleshooting for devices is becoming essential. Loss of capture can be an emergent presentation for an unstable patient and can be encountered intermittently in hospitalized patients. There are many causes for a loss of capture, with the timing of the implant having a high correlation with certain causes over others. The most common acute cause just after the insertion procedure is lead dislodgement or malposition. In comparison, an increase in the required threshold promoting a loss of capture can happen after months to years of insertion of the pacemaker or ICD. This change can be due to a cardiomyopathy, fibrosis medications, metabolic imbalance, lead fracture, or an exit block. Loss of capture can also occur from external electrical stimuli and inappropriate pacemaker or ICD settings. Further, there are also potential noncardiac causes, such as medications, electrolyte imbalance, and acidemia. A knowledge of these factors is essential for health care providers, given the morbidity and mortality that can potentially be associated with device-related issues, especially in patients who are dependent on the included pacing function.

Implantable Cardioverter Defibrillator Therapy and the Need for Concomitant Antiarrhythmic Drugs

Implantable cardioverter defibrillators (ICDs) are increasingly used for the prevention of sudden cardiac death in patients with life-threatening ventricular arrhythmias (VAs); however, there is a potential for severe and debilitating anxiety caused by symptoms associated with ICD therapy and anticipation of shocks. Anxiety is a psycho-logic stressor, including physiologic components that may lead to adrenergic excitation triggering new arrhythmias and ICD therapies. This often requires concomitant antiarrhythmic medication to reduce the frequency of shocks and symptomatic arrhythmias treated by anti-tachycardia pacing. Although published studies have documented the efficacy of currently available antiarrhythmics, they have limitations in patients with heart failure, may affect the defibrillation threshold, and/or have been associated with major side-effects. In conclusion, for the patient with an ICD experiencing symptomatic ventricular tachycardia (VTs) episodes or ICD shocks, there is a need for pharmacologic therapy to reduce the incidence of such events without affecting the performance of the ICD or causing major side-effects.

Chronic oral amiodarone but not dronedarone therapy increases ventricular defibrillation threshold during acute myocardial ischemia in a closed-chest animal model

Dronedarone, a recently approved antiarrhythmic drug, has been shown to have fewer side effects than amiodarone, particularly with regard to thyroid and neurologic events. Since the effects of either drug on ventricular defibrillation threshold during ischemia are unknown, the aim of this study was to compare the effects of dronedarone and amiodarone on defibrillation efficacy during ischemia in a closed-chest animal model. Dronedarone (30 mg·kg·d) and amiodarone (20 mg·kg·d) were administered orally for 3 weeks to 19 and 21 pigs, respectively. A control group (no treatment) comprised 19 pigs. A 2-lead endovascular defibrillation system was used. Each biphasic shock was delivered after 8 seconds of ventricular fibrillation. A step-up/step-down protocol was used to calculate mean defibrillation threshold before and 10 minutes after coronary artery occlusion using an angioplasty balloon in the left descending artery. At basal state, defibrillation threshold did not differ between the control (20.8 ± 4.8 J), amiodarone (21.2 ± 2 J), and dronedarone (19.5 ± 3 J) groups. After ischemia, the amiodarone group had a significantly higher defibrillation threshold than the control group (29.6 ± 3 J vs. 21.8 ± 5 J, respectively; P = 0.015), but the dronedarone (22.8 ± 4 J) and control groups had similar defibrillation threshold values. These data indicate that oral dronedarone treatment, unlike oral amiodarone, does not affect defibrillation threshold during ischemia in pigs.

Rapid correction of hypokalemia in a patient with an implantable cardioverter-defibrillator and recurrent ventricular tachycardia

We present the case of a 74-year-old man with non-ischemic dilatated cardiomyopathy and an implantable cardioverter-defibrillator presenting with a serum potassium of 2.6 mmol/L, recurrent unstable ventricular tachycardia, and multiple defibrillations. Administration of a rapid bolus of 20 mEq KCL solution via central venous access, followed by an additional total of 80 mEq (orally and intravenously [i.v.]) over the next 2 h, resulted in immediate resolution of his recurrent unstable dysrhythmia without toxic side effects. Guidelines for rapid correction of hypokalemia quote a maximum safe administration of 20 mEq i.v./h. In addition to discussing the clinical relevance and physiologic interactions of the variables leading to this patient's presentation, we discuss the successful termination of his sustained recurrent ventricular dysrhythmia by rapid potassium repletion above currently recommended rates. The patient we present is representative of a growing population, given medical and technological advances over the years. Potassium boluses may be reasonable in such circumstances, particularly in patients with ICDs.

Clinical study of the acute effects of intravenous nifekalant on the defibrillation threshold in patients with persistent and paroxysmal atrial fibrillation

BACKGROUND

Antiarrhythmic agents are considered to have significant effects on the defibrillation energy requirement, so this study investigated the effects of nifekalant on defibrillation.

METHODS AND RESULTS

Forty-two patients with persistent atrial fibrillation (AF) underwent electrical cardioversion via intracardiac electrode catheters prior to and after the intravenous administration of nifekalant. The success rate of the defibrillation and change in the defibrillation threshold using sequential incremental defibrillation energy deliveries was investigated. In addition, the parameters that could predict the beneficial effects of nifekalant were also assessed. Nifekalant significantly decreased the defibrillation energy requirement in 13 of the 42 cases, and nifekalant also converted AF to sinus rhythm with an identical energy to that of the last unsuccessful defibrillation in 21 of 42 cases. The success of defibrillation seemed to be dependent on significant prolongation of the intracardiac atrial electrogram intervals during AF by the nifekalant.

CONCLUSIONS

Intravenous nifekalant significantly improved the electrical defibrillation efficacy in patients with persistent AF that was resistant to defibrillation, without any serious adverse effects.

Amiodarone Therapy in Patients Implanted With Cardioverter-Defibrillator for Life-Threatening Ventricular Arrhythmias

BACKGROUND

Whether amiodarone can improve the patient's clinical outcome by reducing implantable cardioverter-defibrillator (ICD) therapy deliveries for ventricular tachycardia or fibrillation (VT/VF) has not been clearly evaluated.

METHODS AND RESULTS

A total of 507 patients with VT/VF due to organic heart disease who had ICDs implanted were enrolled in this study. The patients were divided into 3 groups: Amiodarone (n=247), Class I anti-arrhythmic drug (n=103) and CONTROL (n=157) groups, and the total cause mortality and arrhythmic event free survival rates were evaluated between the groups. The mean follow-up period was 38+/-27 months. The left ventricular ejection fraction was significantly decreased in the Amiodarone group (Amiodarone: 37+/-15%; Class I: 39+/-16%;

CONTROL

44+/-17%). The mortality and arrhythmic events were significantly higher in the Class I group than the Amiodarone group (p<0.05), but there was no significant difference between the Amiodarone and CONTROL groups (arrhythmic event free rate at 5 years: Amiodarone: 53%; Class I: 35%;

CONTROL

48%; 5 year survival: 86%, 74% and 77%, respectively). Side effects from amiodarone were found in 12% of the patients, but no fatal events were observed.

CONCLUSIONS

The present study could not demonstrate the benefit of amiodarone in ICD patients, probably due to a significant clinical bias exerted in selecting this drug.

Antiarrhythmic drugs in patients with implantable cardioverter-defibrillators

Antiarrhythmic drugs need to be initiated in up to 70% of patients with implantable cardioverter-defibrillators (ICDs) in order to treat atrial tachyarrhythmias, decrease the frequency of defibrillator shocks, and terminate ventricular arrhythmias along with antitachycardia pacing. trial fibrillation (AF) occurs in about 20% of patients with ICDs (the majority with congestive heart failure [CHF]). Antiarrhythmic drugs are initiated for this indication in 2-20% of the ICD population. Data from CHF-STAT (Congestive Heart Failure: Survival Trial of Antiarrhythmic Therapy; amiodarone vs placebo) and DIAMOND-AF (Danish Investigations of Arrhythmia and Mortality ON Dofetilide--rial Fibrillation; dofetilide vs placebo) support the approach that restoration and maintenance of sinus rhythm might be beneficial in CHF, even though no study has specifically addressed the CHF population with ICDs. Further clarification on potential benefits of rhythm control in CHF-associated AF will come from the AF-CHF (Atrial Fibrillation and Congestive Heart Failure) trial that is currently underway. The vast majority of patients with ICDs will have discharges of their devices during follow-up. Although class III antiarrhythmic drugs are widely considered to be effective for prophylaxis against frequent shocks, there are surprisingly few controlled studies that demonstrate this. In contrast to conflicting amiodarone data, sotalol has been found to be effective in preventing shocks from ICDs in prospective, randomized, placebo-controlled studies. A large study (SHIELD; SHock Inhibition Evaluation with azimiLiDe) has shown that azimilide significantly reduces ventricular tachyarrhythmia recurrence, thereby reducing the burden of symptomatic ventricular tachyarrhythmia. Other novel antiarrhythmic drugs, such as dofetilide or dronedarone, as well as different strategies (e.g. in the OPTIC [Optimal Pharmacological Therapy in Implantable Cardioverter] trial; beta-adrenoceptor antagonist therapy alone, amiodarone plus beta-adrenoceptor antagonist therapy, or sotalol alone) for the prevention of ICD shocks are under evaluation. The majority of antiarrhythmic drugs, including sotalol, dofetilide, and azimilide, have no effect on, or are even associated with a decrease in, defibrillation thresholds in humans. Amiodarone, in contrast, has been shown to be related to higher defibrillation thresholds at implant and during follow-up of monophasic devices. Potential cardiac (e.g. ventricular proarrhythmia, negative inotropic effect) and drug-specific non-cardiac adverse effects are a frequent cause for drug discontinuation and need to be considered when initiating and maintaining antiarrhythmic drug therapy. In conclusion, antiarrhythmic drugs are frequently used in ICD patients, the main indications being treatment of atrial tachyarrhythmias and prevention of ICD shocks. Despite potential adverse effects, antiarrhythmics can be administered safely, as long as ICD/drug interactions are appreciated. Controlled studies that will further define the role of concomitant antiarrhythmic drug utilization in patients with ICDs are underway.

Azimilide decreases recurrent ventricular tachyarrhythmias in patients with implantable cardioverter defibrillators

OBJECTIVES

This study evaluated the effects of azimilide dihydrochloride (AZ) on anti-tachycardia pacing (ATP) and shock-terminated events in patients with implantable cardioverter defibrillators (ICDs).

BACKGROUND

Animal studies have shown the effectiveness of AZ for therapy of supraventricular and ventricular tachycardia (VT). Azimilide dihydrochloride was investigated as adjunctive treatment for reducing the frequency of VT and, thus, the need for ICD therapies, including ATP and cardioversion/defibrillation (ICD shocks) in patients with inducible monomorphic VT.

METHODS

A total of 172 patients were randomized to daily treatment with placebo, 35 mg, 75 mg, or 125 mg of oral AZ in this dose-ranging pilot study of patients with ICDs. The majority of patients had a history of documented remote myocardial infarction and congestive heart failure New York Heart Association class II or III.

RESULTS

The frequency of appropriate shocks and ATP were significantly decreased among AZ-treated patients compared with placebo patients. The incidence of ICD therapies per patient-year among the placebo group was 36, and it was 10, 12, and 9 among 35 mg, 75 mg, and 125 mg AZ patients, respectively (hazard ratio = 0.31, p = 0.0001). Azimilide dihydrochloride was generally well tolerated and did not affect left ventricular ejection fraction or minimal energy requirements for defibrillation or pacing.

CONCLUSIONS

Azimilide dihydrochloride may be a safe and effective drug for reducing the frequency of VT and ventricular fibrillation in patients with implanted ICDs.

Rationale and patient selection for "hybrid" drug and device therapy in atrial and ventricular arrhythmias

Three quite different forms of direct antiarrhythmic therapy are available for the treatment of cardiac arrhythmias: antiarrhythmic drugs, cardiac ablation and implantable devices (pacemakers and defibrillators). None of these therapies is fully effective and consequently they are increasingly combined. This combination therapy is often described as "hybrid" a term that implies fundamental different qualities of treatment which together provide some form of synergism. The mechanisms for the initiation and perpetuation of most cardiac arrhythmias are complex and multiple. It is therefore not surprising that single therapies are not completely effective. Theoretically the use of multiple different therapies allows more specific mechanisms of arrhythmia to be directly addressed. However, this is largely a theoretical concept that has only been strictly evaluated in a small number of studies. Studies of multiple therapies are difficult to perform unless the combination therapy is regarded as a strategy which can be compared to baseline, conventional treatment or one or more single constituent therapies from the combination. Despite the lack of formal studies there is a very substantial clinical experience which testifies to the value of hybrid therapy for the management of both atrial fibrillation and ventricular tachycardia/fibrillation.

Interactions of antiarrhythmic drugs and implantable devices in controlling ventricular tachycardia and fibrillation

Implantable cardioverter defibrillators (ICDs) have proven highly successful in the treatment of life-threatening ventricular arrhythmias. Despite the efficacy of the ICD in terminating ventricular arrhythmias, antiarrhythmic drugs remain an important adjunct to ICD therapy. The use of antiarrhythmic drug therapy in combination with the ICD is synergistic in terms of beneficial effects, but also has the potential for some adverse interactions. Knowledge and recognition of these potential interactions is important for any physician managing patients with an ICD. This review summarizes the benefits and adverse effects of ICD in combination with antiarrhythmic drug therapy, and provides guidelines to ensure safe application of this hybrid therapy.

Mechanisms of antiarrhythmic drug actions and their clinical relevance for controlling disorders of cardiac rhythm

This review on antiarrhythmic drugs traces the evolution of the fundamental mechanisms of action of drugs that have been used to control disorders of cardiac rhythm. It describes the very earliest data from experimental studies that dealt with the effects of acute and chronic administration of drugs in whole animals combined with the measurements of the action potential duration and the effective refractory period in isolated tissues. Antiarrhythmic drugs were found to have properties consistent with the block of fast sodium channel conduction, adrenergic blockade, repolarization block, and the block of slow-channel mediated conduction especially in the atrioventricular node. Over the past 15 years, the attention has focused on atrial tissue with atrial fibrillation emerging as the most common arrhythmia in clinical practice. Drug-induced increases in refractoriness as a function rate and in wavelength (product of refractoriness and conduction velocity), and a reduction in numbers of wavelets have been found to be critical in the conversion of atrial fibrillation and maintenance of sinus rhythm. The continued development of newer pharmacologic agents is likely to lead to the resolution of the controversy regarding rhythm versus rate control in various clinical subsets of the arrhythmia by controlled clinical trials.

Management of atrial arrhythmias secondary to severe congenital heart disease with the Atrioverter

An atrial defibrillator was implanted in a patient with congenitally corrected transposition of the great arteries, associated cardiac abnormalities, and persistent atrial arrhythmias. During a 15-month follow-up, 14 of 20 spontaneous episodes of his arrhythmias were successfully treated with the device. Two of these episodes were converted to sinus rhythm during ambulatory use of the device. Successful use of the device required implantation of a third defibrillation lead in the persistent left-sided superior caval vein and rigid control of congestive heart failure. An atrial defibrillator may be a valid treatment option in patients with congenital heart disease crippled by atrial fibrillation.

Hybrid therapy for ventricular arrhythmia management

Optimum arrhythmia management has evolved to couple ICD therapy with catheter ablative and drug therapy to attempt to eliminate or reduce arrhythmia risk. No longer should the clinician approach such therapy as a choice among single alternative strategies only. Optimum patient management includes not only recognition of the indications and benefits of such hybrid therapy but also a complete understanding of potential pitfalls of such therapy.

Concomitant device and drug therapy: current trends, potential benefits, and adverse interactions

Antiarrhythmic drug therapy in patients with implantable cardioverter defibrillators (ICDs) has decreased over the last 10 years. This trend, primarily seen with class I agents, has occurred mainly in patients with a cardiac arrest. However, despite this overall decrease, antiarrhythmic drug therapy remains an important adjuvant to ICD therapy. In addition to primary prevention of ventricular tachycardia and supraventricular tachycardia, antiarrhythmic drug therapy may potentiate tachycardia rate slowing and make ventricular tachycardia more tolerated hemodynamically and possibly more amendable to pacing therapy. Some of the class III antiarrhythmic drugs may actually lower defibrillation threshold. Unfortunately, these drugs may have adverse interactions with ICDs. An increase in defibrillation threshold or rate-dependent increase in pacing threshold may interfere with the effectiveness of device therapy. Proarrhythmic effects of antiarrhythmic drugs may enhance the frequency of device use. The bradycardic effects of antiarrhythmic drug therapy may similarly enhance the requirements for persistent bradycardia pacing and lead to early battery depletion and other adverse consequences. An awareness of potential benefits and adverse effects of antiarrhythmic drug therapy along with careful electrophysiologic assessment are necessary for optimum combination drug and device therapy.

Evaluation of antiarrhythmic drug efficacy in patients with an ICD: unlimited potential or replete with complexity and problems?

There are a number of novel ways in which implantable cardioverter defibrillator (ICD) endpoints can be used in clinical trials to evaluate antiarrhythmic drugs. The advances in ICD technology (storage, retrieval, and accurate interpretation of ICD electrograms) expand the potential to include the use of an ICD endpoint as a clinical surrogate for sudden death. The ICD also provides the necessary safety net to test new drugs. The frequent need for antiarrhythmic drugs in patients already fitted with an ICD (e.g., for atrial fibrillation) necessitates knowledge of the drugs' effect on defibrillator threshold. There are interpretative problems and challenges associated with all types of ICD trials. A particular difficult issue is the degree to which the results of data on antiarrhythmic drug efficacy and safety acquired in the context of an ICD endpoint trial might be extrapolated to patient populations in which the device is not used. These and other challenging issues are discussed, with the goal of enhancing the design and interpretation of clinical trials featuring ICD endpoints.

Current antiarrhythmic drugs: an overview of mechanisms of action and potential clinical utility

Reorientation in drug therapy to control cardiac arrhythmias continues to evolve in the wake of ongoing refinements in techniques and indications for radiofrequency ablation and the use of implantable devices for atrial and ventricular arrhythmias. The role of sodium channel blockers continues to be questioned, and data from clinical trials indicate that the use of this class of drugs should be limited to control symptoms in patients who have arrhythmias and either no or minimal heart disease. The decline in the use of sodium channel blockers has led to greater use of beta blockers and complex Class III agents, such as sotalol and amiodarone, as both primary therapy and adjunctive therapy with implantable defibrillators in patients with cardiac disease of varying degrees of ventricular dysfunction. Success with these Class III agents in the context of their side effects has led to the synthesis and characterization of compounds with simpler ion channel-blocking properties. The need for such compounds stemmed from the observation that atrial fibrillation (AF) as an arrhythmia is, for the most part, still not amenable to curative therapy by interventional procedures. The isolated block of the rapid component of the delayed rectifier current (IKr) has been found to have either a neutral (e.g., dofetilide) or deleterious (e.g., d-sotalol) effect on mortality in survivors of myocardial infarction. Thus, the objective of drug development should be the appropriate match between the substrate and an antiarrhythmic drug. The so-called pure Class III agents have been shown to have beneficial antifibrillatory effects in patients with AF. They are effective in inducing acute chemical conversion, preventing paroxysmal AF, and maintaining sinus rhythm in patients with persistent AF restored to sinus rhythm with DC cardioversion. AF is a complex arrhythmia, undoubtedly a result of multifaceted derangement of atrial ionic currents. Attention has therefore focused on newer compounds that have the propensity to block more than one ion channel. Examples of such agents are tedisamil and azimilide, the latter having been studied extensively in humans. It is the first of the Class III agents that block both components (IKr and IKs) of the delayed rectifier current, which results in a spectrum of electrophysiologic properties that includes lack of rate or use dependency in terms of effect on repolarization and refractoriness of atrial and ventricular myocardium. Available but unpublished clinical data indicate that azimilide may be effective over a wide range of tachycardia cycle lengths with a low incidence of torsades de pointes. In these respects, its properties, at least in terms of its use in AF, resemble those of amiodarone. However, the drug has little or no effect on AV conduction, which precludes the modulation of ventricular response in patients relapsing to AF.

Sotalol: Current Status and Expanding Indications

BACKGROUND: The role of antiarrhythmic drug therapy continues to undergo major changes. The change is necessitated by the advent of invasive interventional procedures, such as catheter ablation of arrhythmias and the use of implantable devices for sensing and terminating life-threatening ventricular arrhythmias and symptomatically traublesome supraventricular arrhythmias. Many conventional and time-honored drugs, such as sodium channel blockers, have been found either to be ineffective or to have the potential to produce serious proarrhythmic reactions. Attention is therefore focused on compounds that prolong repolarization and reduce sympathetic stimulation. Two compounds, amiodarone and sotalol, have emerged as prototypes of drugs of the future. METHODS AND RESULTS: This review focuses on sotalol for controlling supraventricular and ventricular tachyarrhythmias. Sotalol is a major antiarrhythmic agent that combines potent class III action with nonselective beta-blocking properties. The drug's pharmacokinetics is simple. Its elimination half-life is 10-15 hours, the drug being excreted almost exclusively by the kidneys. Sotalol's pharmacokinetics allows development of optimal dosing for initiation of therapy relative to changes in creatinine clearance with further dose adjustment by monitoring the QT interval on the surface electrocardiogram. The compound exerts broad-spectrum antiarrhythmic actions in supraventricular and ventricular arrhythmias. It prevents inducible ventricular tachycardia (VT) and ventricular fibrillation (VF) in approximately 30% of patients with a higher figure for the suppression of spontaneously occurring arrhythmias documented on Holter recordings. CONCLUSIONS: The major role of sotalol is in the management of VT/VF often in conjunction with an implantable cardioverter/defibrillator, in which context it lowere the defibrillation threshold. Sotalol is superior to class I agents, especially in VT/VF and in survivors of cardiac arrest. Sotalol has emerged as a major antifibrillatory compound for the control of life-threatening ventricular arrhythmias as the main indication. Data have indicated its potential for the maintenance of stability of sinus rhythm in patients with atrial fibrillation and flutter after electrical conversion and in preventing their occurrence in a variety of clinical settings.