Antiarrhythmic agents for atrial fibrillation: focus on prolonging atrial repolarization

Antiarrhythmic and Proarrhythmic Properties of QT-Prolonging Antianginal Drugs

In recent years there has been a major reorientation of drug therapy for cardiac arrhythmias, its changing role, and above all, a radical change in the class of arrhythmia drugs because of their impact on mortality. The decline in the use of sodium-channel blockers has led to an expanding use of β-blockers and simple or complex class III agents for controlling cardiac arrhythmias. Success with these agents in the context of their side effects has spurred the development of compounds with simpler ion-channel blocking properties that have less complex adverse reactions. The resulting so-called pure class III agents, such as dofetilide or ibutilide, were found to have antifibrillatory effects in atrial fibrillation and flutter and in ventricular tachyarrhythmias. Such agents are effective and have diversity, but they have come into therapeutics with a price: the sometimes-fatal torsades de pointes. The drug amiodarone, a complex compound that was synthesized as an antianginal agent, has been an exception in this regard. Its therapeutic use is associated with a negligibly low incidence of torsades de pointes, even though the drug produces significant bradycardia and QT lengthening to 500 to 700 msec. Recent electrophysiologic studies suggest that this paradox is likely due to the differential block of ion channels in endocardium, epicardium, midmyocardial (M) cells, and Purkinje fibers in the ventricular myocardium. There is also clinical evidence suggesting that amiodarone reduces the “torsadogenic” effects of pure class III agents. Ranolazine was also synthesized for the development of antianginal properties that stem from a partial inhibition of fatty acid oxidation; it too has been found to have electrophysioloigic properties. These are somewhat similar to those of amiodarone on ion channels in endocardium, epicardium, M cells, and Purkinje fibers in the ventricular myocardium, but the drug does not prolong the QT interval to the same extent as amiodarone does. Thus, the drug produces modest increases in repolarization as judged by its effects on the action potential duration (APD) without the potential for the development of torsades de pointes. By virtue of its suppressant action on early afterdepolarizations and triggered activity in Purkinje fibers and M cells, the drug appears to have a powerful potential for reducing the torsadogenic proclivity of conventional class III antiarrhythmic compounds. The rationale for the therapeutic niche for amiodarone, and especially in the case of ranolazine, in the prevention of drug-induced torsades de pointes is discussed.

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.

Conversion efficacy of intravenous ibutilide compared with intravenous amiodarone in patients with recent-onset atrial fibrillation and atrial flutter

AIM

The aim of our study was to compare the efficacy and safety of ibutilide and amiodarone (intravenously) in converting recent-onset atrial fibrillation (AF) and atrial flutter (Af) to sinus rhythm (SR).

METHODS

The study was prospective, randomized and included 152 (103 men and 49 women) consecutive patients with AF or Af of 3-48 h duration. Ibutilide is a selective class III antiarrhythmic agent which when administered intravenously can terminate AF and Af. Amiodarone is also a class III antiarrhythmic agent that when given intravenously or orally has proved to be more effective than other agents in terminating AF and Af [B.N. Singh, F.V. Mody, B. Lopez, J.S. Sarma. Antiarrhythmic agents for atrial fibrillation: focus on prolonging atrial repolarization. Am J Cardiol 1999 Nov 4; 84: 161R-173R.]. Seventy-nine patients (56 with AF and 23 with Af) that consisted group A were treated with ibutilide. Seventy-three (52 with AF and 21 with Af) consisted group B and were treated with intravenous infusion of amiodarone.

RESULTS

The conversion rate of group A (ibutilide) was significantly higher than the conversion rate of group B (amiodarone) (80% vs. 57%, p=0.0054). As regards the kind of arrhythmia separately, for AF there wasn't significant difference (77% vs. 69%, p=ns) whereas for Af ibutilide was superior to amiodarone (87% vs. 29%, p=0.003). The conversion rates of ibutilide didn't differ for AF and Af (77% vs. 87%, p=ns).

CONCLUSIONS

Ibutilide is more effective than amiodarone in converting recent-onset Af to SR whereas both drugs are equally effective in converting recent-onset AF to SR.

Effect of a neuroprotective drug, eliprodil on cardiac repolarisation: importance of the decreased repolarisation reserve in the development of proarrhythmic risk

1. The aim of this study was to analyse the effects of eliprodil, a noncardiac drug with neuroprotective properties, on the cardiac repolarisation under in vitro circumstances, under normal conditions and after the attenuation of the 'repolarisation reserve' by blocking the inward rectifier potassium current (I(K1)) current with BaCl(2). 2. In canine right ventricular papillary muscle by applying the conventional microelectrode technique, under normal conditions, eliprodil (1 microm) produced a moderate reverse rate-dependent prolongation of the action potential duration (7.4+/-1.5, 8.9+/-2.1 and 9.9+/-1.8% at cycle lengths of 300, 1000 and 5000 ms, respectively; n=9). 3. This effect was augmented in preparations where I(K1) was previously blocked by BaCl(2) (10 microm). BaCl(2) alone lengthened APD in a reverse frequency-dependent manner (7.0+/-1.3, 14.2+/-1.6 and 28.1+/-2.1% at cycle lengths of 300, 1000 and 5000 ms, respectively; n=8). When eliprodil (1 microm) was administered to these preparations, the drug induced a marked further lengthening relative to the APD values measured after the administration of BaCl(2) (12.5+/-1.0, 17.6+/-1.5 and 20.5+/-0.9% at cycle lengths of 300, 1000 and 5000 ms, respectively; n=8). 4. In the normal Langendorff-perfused rabbit heart, eliprodil (1 microm) produced a significant QT(c) prolongation at 1 Hz stimulation frequency (12.7+/-1.8%, n=9). After the attenuation of the 'repolarisation reserve' by the I(K1) blocker BaCl(2) (10 microm), the eliprodil-evoked QT(c) prolongation was greatly enhanced (28.5+/-7.9%, n=6). In two out of six Langendorff preparations, this QT(c) lengthening degenerated into torsade de pointes ventricular tachycardia. 5. Eliprodil significantly decreased the amplitude of rapid component of the delayed rectifier potassium current (I(Kr)), but slow component (I(Ks)), transient outward current (I(to)) and I(K1) were not considerably affected by the drug when measured in dog ventricular myocytes by applying the whole-cell configuration of the patch-clamp technique. 6. The results indicate that eliprodil, under normal conditions, moderately lengthens cardiac repolarisation by inhibition of I(Kr). However, after the attenuation of the normal 'repolarisation reserve', this drug can induce marked QT interval prolongation, which may result in proarrhythmic action.

Atrial fibrillation: epidemiologic considerations and rationale for conversion and maintenance of sinus rhythm

Atrial fibrillation is now the most common cardiac arrhythmia for which a patient is hospitalized. Clinically, it presents in a form that is paroxysmal, persistent, or permanent and may be symptomatic or asymptomatic, occurring in the setting of either no cardiac disease ("lone atrial fibrillation") or, most often, in association with an underlying disease. Atrial fibrillation is associated with a 2-fold increase in mortality and, in the United States alone, causes over 75,000 cases of stroke per year. The annual prevalence of stroke is 5% to 7%, but the use of adequate anticoagulation can reduce this to less than 1%. Atrial fibrillation is a disorder of the elderly, with almost equal prevalence in men and women. In the United States, 80% of atrial fibrillation occurs in patients over the age of 65 years, and its prevalence tracks that of heart failure, which may be the cause, as well as the result, of the arrhythmia. Both conditions are increasing in epidemic proportions in the aging population. The most common causes of atrial fibrillation are hypertensive heart disease, coronary artery disease, and heart failure with a miscellany of lesser conditions, with about 10% lacking structural heart disease. Unlike other supraventricular arrhythmias, cure by the use of catheter ablation and surgical techniques has not been a reality except in a relatively small number of cases. However, restoration and maintenance of sinus rhythm remain the initial goal of therapy for most patients. Pharmacologic approaches remain the mainstay of therapy for rate control and anticoagulation as well as for maintenance of sinus rhythm following pharmacological or electrical conversion. The changing epidemiology of atrial fibrillation is highlighted, with the focus on its conversion by the use of newer and novel antifibrillatory agents relative to the mechanisms of the arrhythmia, to restore the stability of sinus rhythm.

Oral loading single dose flecainide for pharmacological cardioversion of recent-onset atrial fibrillation

The efficacy and safety of the single oral loading dose of flecainide for cardioversion of recent-onset atrial fibrillation was examined by reviewing the trials on the subject identified through a comprehensive literature search. Most of the trials used a single dose of 300 mg for oral loading. The success rate ranged from 57 to 68% at 2-4 h and 75 to 91% at 8 h after drug administration. The conversion time ranged from 110+/-82 to 190+/-147 min, depending on the duration of observation after drug administration, which in most trials was of 8 h. Single oral loading regimen of flecainide was significantly more efficacious than placebo, and was as efficacious as the single oral loading regimen of propafenone. Both the single oral loading and the intravenous loading regimens of flecainide were equally efficacious but the intravenous regimen resulted in an earlier conversion. Adverse effects reported were mild non-cardiac side effects, reversible QRS complex widening, transient arrhythmias and left ventricular decompensation. The transient arrhythmias were chiefly at the time of conversion and included appearance of atrial flutter and sinus pauses. No life-threatening ventricular arrhythmia or death was reported. The single dose oral loading regimen of flecainide appears to be effective for cardioversion of recent-onset atrial fibrillation with a relatively rapid effect within 2-4 h, and is free of serious complications in patients without structural heart disease. Patients with substantial structural heart disease were excluded from most of the trials.

Atrial fibrillation: the newest frontier in arrhythmia management

At least 2.3 million people in the United States have atrial fibrillation. Since the risk for developing atrial fibrillation increases with age, the number of people with atrial fibrillation is expected to rise sharply. Atrial fibrillation is a complex condition that adversely influences mortality, morbidity, quality of life, and use of health care resources. Knowledge generated from extensive research has led to innovative management strategies. As the number of individuals with atrial fibrillation increases and treatment options expand, nurses in a variety of settings will be challenged to respond to the multifaceted needs of this population. This review discusses the significance of atrial fibrillation and summarizes research findings influencing current management strategies. Pharmacologic therapies are reviewed and new technologies for atrial fibrillation treatment are introduced. Nursing assessment and treatment of patients' response to atrial fibrillation are discussed. Recommendations for patient education are offered. A plan describing specific nursing diagnoses, outcomes, interventions, and activities for care of patients with atrial fibrillation is presented.

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.

Significance and control of cardiac arrhythmias in patients with congestive cardiac failure

A wide spectrum of ventricular and supraventricular tachyarrhythmias occurs in the setting of congestive cardiac failure. However, the two most clinically significant are atrial fibrillation and ventricular tachycardia and fibrillation. In the past there has been much emphasis on premature ventricular contractions and more recently, on nonsustained ventricular tachycardia. For the most part, these arrhythmias are asymptomatic in heart failure. They are markers of sudden arrhythmic death but their suppression by antiarrhythmic drugs have not resulted in a reduction of total mortality. Two approaches have been used to this end. The first is the use of beta-adrenergic blocking drugs and antiarrhythmic agents such as amiodarone. Beta-blockers have been shown to significantly reduce sudden death as well as total mortality, while the effects of amiodarone have been less decisive. The prospective role of the implantable cardioverter defibrillator (ICD) is undergoing critical evaluation in patients with cardiac failure at high risk for sudden death. The elective role of the ICD is well established as first-line therapy in patients with heart failure resuscitated from sudden death and in those with sustained ventricular tachycardia in conjunction with conventional therapies for cardiac decompensation. The prevalence of atrial fibrillation rises as a function of severity of cardiac failure, but it is also in known that persistent atrial fibrillation with an uncontrolled ventricular response may induce heart failure. Controlled ventricular response may prevent congestive heart failure and improve left ventricular function. The two most common causes of atrial fibrillation in cardiac failure in Europe and America are ischemic heart disease and hypertension, while mitral valve disease remains the prevalent cause elsewhere. The choice of antiarrhythmic drugs for maintaining sinus rhythm is critical in the prevention of heart failure aggravation and proarrhythmic reactions of antiarrhythmic drugs. Amiodarone and dofetilide are most widely used in this context.

Prevention of and medical therapy for atrial arrhythmias in heart failure

A large proportion of heart failure patients suffer from atrial arrhythmias, prime amongst them being atrial fibrillation (AF). Ventricular dysfunction and the syndrome of heart failure can also be a concomitant pathology in up to 50% of patients with AF. However this association is more than just due to shared risk factors, research from animal and human studies suggest a causal relationship between AF and heart failure. There are numerous reports of tachycardia-induced heart failure where uncontrolled ventricular rate in AF results in heart failure, which is reversible with cardioversion to sinus rhythm or ventricular rate control. However the relationship extends beyond tachycardia-induced cardiomyopathy. Optimal treatment of AF may delay progressive ventricular dysfunction and the onset of heart failure whilst improved management of heart failure can prevent AF or improve ventricular rate control. Prevention and treatment of atrial arrhythmias, and in particular atrial fibrillation, is therefore an important aspect of the management of patients with heart failure. This review describes the incidence and possible predictors of AF and other atrial arrhythmias in patients with heart failure and discusses the feasibility of primary prevention. The evidence for the management of atrial fibrillation in heart failure is systematically reviewed and the strategies of rate versus rhythm control discussed in light of the prevailing evidence.

What niche will newer class III antiarrhythmic drugs occupy?

The decline in the use of sodium channel blockers has led to an expanding use of b-blockers and complex class III agents such as sotalol and amiodarone for controlling cardiac arrhythmias. Success with these agents in the context of their side effects has spurred the development of compounds with simpler ion channel-blocking properties with less complex adverse reactions. The resulting so-called pure class III agents were found to have antifibrillatory effects in atrial fibrillation (AF) and flutter, as well as in ventricular tachyarrhythmias. Pure class III compounds are effective in inducing acute chemical conversion of AF, in preventing paroxysmal AF, and in maintaining sinus rhythm in patients with persistent AF restored to sinus rhythm. Examples of such compounds are dofetilide, which selectively blocks IKr, and ibutilide, available only as an intravenous agent, which blocks the IKr and augments the inactivated Na+ current in atrial myocytes. Dofetilide and ibutilide have been introduced into clinical practice. Azimilide is the first of the class III agents that blocks both components (IKr and IKs) of the delayed rectifier current, which may confer certain electrophysiologic advantages. The potential therapeutic niche of ibutilide, dofetilide, and azimilide in the control of cardiac arrhythmias forms the basis of this review.

Amiodarone versus diltiazem for rate control in critically ill patients with atrial tachyarrhythmias

OBJECTIVE

To compare the rate-lowering effect of diltiazem and two amiodarone regimens in critically ill patients with recent-onset atrial tachyarrhythmias.

DESIGN

Prospective, randomized, controlled study.

SETTING

Medical cardiologic intensive care unit in a university hospital.

PATIENTS

Sixty critically ill patients (Acute Physiology and Chronic Health Evaluation [APACHE] III score 70 +/- 30, age 67 +/- 10 yrs).

INTERVENTIONS

Patients with atrial fibrillation (n = 57), atrial flutter (n = 2), or atrial tachycardia (n = 1, and a heart rate consistently >120 beats/min over 30 mins were randomly assigned to one of three intravenous treatment regimens. Group 1 received diltiazem in a 25-mg bolus followed by a continuous infusion of 20 mg/hr for 24 hrs, group 2 received amiodarone in a 300-mg bolus, and group 3 received amiodarone in a 300-mg bolus followed by 45 mg/hr for 24 hrs.

MEASUREMENTS AND MAIN RESULTS

The primary study end point was a >30% rate reduction within 4 hrs. The secondary study end point was a heart rate <120 beats/min (a patient was considered to have uncontrolled tachycardia if heart rate was >120 beats/min 4 hrs after study drug). The primary study end point was achieved in 14/20 (70%), 11/20 (55%), and 15/20 (75%) of patients in groups 1, 2, and 3, respectively (chi2 = 1.95, p =.38). Uncontrolled tachycardia was more frequently observed in group 2 (0/20, 9/29 [55%], and 1/20 [5%] of patients in groups 1, 2, and 3, respectively; chi2 = 17, p =.00016). In patients achieving tachycardia control, diltiazem showed a significantly better rate reduction (p =.0001 group 1 vs. group 3, p =.0001 over time; p =.0001 group 1 vs. group 2, p =.001 over time) when compared with the amiodarone groups. Premature drug discontinuation due to hypotension was required significantly more often in group 1 (6/20 [30%], 0/20, and 1/20 [5%] for groups 1, 2, and 3, respectively; chi2 = 10, p =.01).

CONCLUSION

Sufficient rate control can be achieved in critically ill patients with atrial tachyarrhythmias using either diltiazem or amiodarone. Although diltiazem allowed for significantly better 24-hr heart rate control, this effect was offset by a significantly higher incidence of hypotension requiring discontinuation of the drug. Amiodarone may be an alternative in patients with severe hemodynamic compromise.

Evaluation and management of cardiac arrhythmias in the elderly

Cardiac arrhythmias are common in elderly patients. Complete evaluation with detection of underlying structural heart disease and comorbidities is necessary. Prognosis is dependent on the presence of underlying heart disease, particularly the degree of ventricular dysfunction and the presence of comorbidities. Long-term prognosis is excellent in patients without underlying heart disease or severe comorbidities. Management and specific drug therapy in elderly patients with arrhythmias need to be individualized in reference to the underlying cardiac disorder, drug side effects, and the patient's comorbidities.

Effects of a new class III antiarrhythmic drug nibentan in a canine model of vagally mediated atrial fibrillation

Nibentan, a new class III antiarrhythmic drug, is highly effective in patients with atrial flutter and fibrillation. However, its mechanism of action remains unclear. The aim of this study was to investigate the effects of nibentan using a canine model of vagally sustained atrial fibrillation (AF). Nibentan was intravenously infused to anesthetized open-chest dogs during vagally induced AF. Cumulative doses of nibentan (0.063, 0.125, and 0.250 mg/kg) successfully terminated AF in 78, 88, and 100% as well as prevented AF reinduction in 11, 63, and 90% of cases, respectively. All doses of nibentan significantly and rate-independently increased atrial effective refractory period (AERP) with and without vagal stimulation. Activation mapping (224 epicardial electrodes) during AF showed that nibentan reduced the number of simultaneously occurring reentrant wavelets. Herewith the atrial excitation slowed down until conduction failure of reentrant wavelets led to arrhythmia termination. These changes in activation patterns can be accounted for by nibentan-induced increase of AERP (55 +/- 9%, 82 +/- 12%, and 90 +/- 6%; p < 0.01) and wavelength for reentry (47 +/- 7%, 68 +/- 12%, and 72 +/- 4%; p < 0.01) at rapid atrial rates in the presence of vagal stimulation. In conclusion, the high efficacy of nibentan against AF was associated with significant rate-independent increase in AERP and in wavelength, and might be in part explained by block of both delayed rectifier (I(K)) and muscarinic I(K,ACh) currents.