Expanding indications for the use of Class III agents in patients at high risk for sudden death

Amiodarone Offsets the Cardioprotective Effects of Ischaemic Preconditioning against Ischaemia/Reperfusion Injury

Both ischaemic preconditioning (IPC) and amiodarone protect against myocardial ischaemia. We examined whether a combination of IPC and amiodarone demonstrated an additive protective effect in isolated rat hearts ( n = 40). The controls (group I) were subjected to ischaemia/reperfusion injury; group II was subjected to cycles of IPC prior to ischaemia/reperfusion injury; group III was subjected to ischaemia in the presence of amiodarone (10−10 mol/l); and group IV was subjected to IPC followed by ischaemia in the presence of amiodarone (10−10 mol/l). Amiodarone produced the best preserved left ventricular end-systolic pressure and dP/dtmax, less developed ventricular stiffness, the shortest arrhythmia duration, and the smallest infarct size among the groups. All of the myocardial protective effects against ischaemia/reperfusion injury were diminished or abolished when IPC and amiodarone were applied sequentially.

Electrophysiological mechanisms of sophocarpine as a potential antiarrhythmic agent

AIM

To examine the electrophysiological effects of sophocarpine on action potentials (AP) and ionic currents of cardiac myocytes and to compare some of these effects with those of amiodarone.

METHODS

Langendorff perfusion set-up was used in isolated guinea pig heart, and responses to sophocarpine were monitored using electrocardiograph. Conventional microelectrode, voltage clamp technique and perforated patch were employed to record fast response AP (fAP), slow response AP (sAP) and ionic currents in guinea pig papillary muscle or rabbit sinus node cells.

RESULTS

Tachyarrhythmia produced by isoprenaline (15 μmol/L) could be reversed by sophocarpine (300 μmol/L). Sophocarpine (10 μmol/L) decreased the amplitude by 4.0%, maximal depolarization velocity (V(max)) of the fAP by 24.4%, and Na(+) current (I(Na)) by 18.0%, while it prolonged the effective refractory period (ERP) by 21.1%. The same concentration of sophocarpine could also decrease the amplitude and V(max) of the sAP, by 26.8% and 25.7%, respectively, and attenuated the Ca(2+) current (I(CaL)) and the K(+) tail current substantially. Comparison of sophocarpine with amiodarone demonstrated that both prolonged the duration and the ERP of fAP and sAP, both decreased the amplitude and V(max) of the fAP and sAP, and both slowed the automatic heart rate.

CONCLUSION

Sophocarpine could reverse isoprenaline-induced arrhythmia and inhibit I(Na), I(CaL), and I(Kr) currents. The electrophysiological effects of sophocarpine are similar to those of amiodarone, which might be regarded as a prospective antiarrhythmic agent.

Intravenous amiodarone treatment in horses with chronic atrial fibrillation

Six horses without underlying cardiac disease were presented because of atrial fibrillation of between 5 and 12 months duration. These horses received an intravenous amiodarone treatment of 5mg/kg/h for 1 h followed by 0.83mg/kg/h for 23h and subsequently 1.9mg/kg/h for 30h. During treatment, clinical signs were monitored and a surface ECG and an intra-atrial electrogram were recorded. Infusion was discontinued when sinus rhythm or side effects occurred. Four horses successfully cardioverted, of which one showed symptoms of hind limb weakness and weight shifting. Two horses did not cardiovert and showed similar side effects. In all horses, side effects disappeared within 6h after termination of treatment. Cardiac side effects, such as pro-arrhythmia, were not seen in any of the horses. Total bilirubin slightly increased in three horses and normalised within four days. It was concluded that amiodarone has the potential to treat naturally occurring chronic atrial fibrillation in horses, although further research is needed to refine the infusion protocol.

Acute effects of dronedarone on both components of the cardiac delayed rectifier K+ current, HERG and KvLQT1/minK potassium channels

Dronedarone is a noniodinated benzofuran derivative that has been synthesized to overcome the limiting iodine-associated adverse effects of the potent antiarrhythmic drug amiodarone. In this study, the acute electrophysiological effects of dronedarone on repolarizing potassium channels were investigated to determine the class III antiarrhythmic action of this compound. HERG and KvLQT1/minK potassium channels conduct the delayed rectifier potassium current IK in human heart, being a primary target for class III antiarrhythmic therapy. HERG and KvLQT1/minK were expressed heterologously in Xenopus laevis oocytes, and the respective potassium currents were recorded using the two-microelectrode voltage-clamp technique. Dronedarone blocked HERG channels with an IC50 value of 9.2 microM and a maximum tail current reduction of 85.2%. HERG channels were blocked in the closed, open, and inactivated states. The half-maximal activation voltage was shifted by -6.1 mV, and HERG current block by dronedarone was voltage-dependent, but not use-dependent. Dronedarone exhibited a weaker block of KvLQT1/minK currents (33.2% at 100 microM drug concentration), without causing significant changes in the corresponding current-voltage relationships. In conclusion, these data demonstrate that dronedarone is an antagonist of cloned HERG potassium channels, with additional inhibitory effects on KvLQT1/minK currents at higher drug concentrations, providing a molecular mechanism for the class III antiarrhythmic action of the drug.

Effects of amiodarone and dronedarone on voltage-dependent sodium current in human cardiomyocytes

Effect of Dronedarone on Cardiac Na Current.

INTRODUCTION

Amiodarone (AM) is a highly effective antiarrhythmic agent used in the management of both atrial and ventricular arrhythmias. Its noniodinated analogue dronedarone (SR) may have fewer side effects than AM. In this study, we compared the effects of AM and SR on the sodium current I(Na) in human atrial myocytes.

METHODS AND RESULTS

INa was studied with the whole-cell, patch clamp technique. Both AM and SR induced a dose-dependent inhibition of I(Na) recorded at -40 mV from a holding potential of -100 mV. AM inhibited I(Na) by 41%+/- 11% (n = 4) at 3 microM, and by 80%+/- 7% (n = 5) at 30 microM. SR produced more potent block, inhibiting INa significantly at only 0.3 microM (23%+/- 10%, n = 4) and completely (97%+/- 4%, n = 4) at 3 microM. Both AM and SR had only moderate effects on voltage-dependent properties of I(Na) (current-voltage relationship, availability for activation) and had no effect on the current decay kinetics.

CONCLUSION

Both AM and SR inhibit I(Na) significantly in single human atrial cells, showing that the two drugs have Class I antiarrhythmic properties. The acute effects of SR are more potent than those of AM. The study supports the idea that the iodinated form of the molecule has no part in the acute effect of AM on Na+ channels.

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.

Beneficial effects of amiodarone and dronedarone (SR 33589b), when applied during low-flow ischemia, on arrhythmia and functional parameters asssessed during reperfusion in isolated rat hearts

The effects of short-term amiodarone and dronedarone treatments on action potential characteristics and arrhythmia (ventricular tachycardia ) induced by reperfusion after global low-flow ischemia were studied in rat hearts. The actions of amiodarone and SR on recovery of coronary flow and contractile function were also determined. Isolated hearts were stabilized for 40 min and were then submitted to 25-min global low-flow ischemia (constant coronary flow, 0.3 ml/min) followed by 30 min of reperfusion at constant pressure. Drugs were applied only during ischemia: consequently, action potential duration (APD) tended to widen. During reperfusion, APD tended to recover or shorten, and the more complete the recovery, the less the arrhythmia. Despite its ability to widen APD during ischemia, amiodarone facilitated APD recovery during reperfusion. Moreover, APD shortening and ventricular tachycardia suppression exhibit a bell-shaped concentration-response relation, implying that the drugs affect ventricular tachycardia by a class III-independent action. These results point to an anti-ischemic action supported by improvement in function and inhibition of reactive hyperemia.

Analysis of the electrophysiological effects of ambasilide, a new antiarrhythmic agent, in canine isolated ventricular muscle and purkinje fibers

The aim of the study was to determine the in vitro rate-dependent cellular electrophysiological effects of ambasilide (10 and 20 microM/l), a new investigational antiarrhythmic agent, in canine isolated ventricular muscle and Purkinje fibers by applying the standard microelectrode technique. At the cycle length (CL) of 1000 ms, ambasilide significantly prolonged the action potential duration measured at 90% repolarization (APD(90)) in both ventricular muscle and Purkinje fibers. Ambasilide (10 microM/l) produced a more marked prolongation of APD(90) at lower stimulation frequencies in Purkinje fibers (at CL of 2000 ms = 56.0 +/- 16.1%, n = 6, versus CL of 400 ms = 15.1 +/- 3.7%, n = 6; p < 0.05), but, in 20 microM/l, this effect was considerably diminished (15.2 +/- 3.6%, n = 6, versus 7.3 +/- 5.1%, n = 6, p < 0.05). In ventricular muscle, however, both concentrations of the drug induced an almost frequency-independent lengthening of APD(90) in response to a slowing of the stimulation rate (in 20 microM/l at CL of 5000 ms = 19.0 +/- 1.5%, n = 9, versus CL of 400 ms = 16.9 +/- 1.4%, n = 9). Ambasilide induced a marked rate-dependent depression of the maximal rate of rise of the action potential upstroke (V(max)) (in 20 microM/l at CL of 300 ms = -45.1 +/- 3.9%, n = 6, versus CL of 5000 ms = -8.5 +/- 3.9%, n = 6, p < 0. 05, in ventricular muscle) and the corresponding recovery of V(max) time constant was tau = 1082.5 +/- 205.1 ms (n = 6). These data suggest that ambasilide, in addition to its Class III antiarrhythmic action, which is presumably due to its inhibitory effect on the delayed rectifier potassium current, possesses I/B type antiarrhythmic properties as a result of the inhibition of the fast sodium channels at high frequency rate with relatively fast kinetics. This latter effect may play an important role in its known less-pronounced proarrhythmic ("torsadogenic") potential.

Electrophysiological effects of dronedarone (SR33589), a noniodinated benzofuran derivative, in the rabbit heart : comparison with amiodarone

BACKGROUND

To overcome the side effects of amiodarone (AM), its noniodinated analogue, dronedarone (SR), was synthesized. In this study, its electrophysiological effects were compared with those of AM in rabbit hearts.

METHODS AND RESULTS

Five animal groups (n=7 each) for 3 weeks received daily oral treatment of 1 of these regimens: (1) control, vehicle only; (2) AM 50 mg/kg (AM50); (3) AM 100 mg/kg (AM100); (4) SR 50 mg/kg (SR50); and (5) SR 100 mg/kg (SR100). ECGs were recorded before drug and at 3 weeks of drug before euthanasia. Action potentials were recorded from isolated papillary muscle and sinoatrial node by microelectrode techniques. The short-term effects were studied in controls (n=5) at various concentrations of SR (0 to 10 micromol/L) in tissue bath. Action potential duration at 50% (APD(50)) and 90% (APD(90)) repolarization and upstroke dV/dt (V(max)) at various cycle lengths were compared by ANOVA with repeated measures. Compared with control, AM and SR increased RR, QT, and QTc intervals (P<0.0001 for all). Ventricular APD(50) and APD(90) were lengthened by 20% to 49% as a function of dose (P<0.005 to <0.0001) and cycle length (P<0.001). SR100 effects were greater than those of AM100 (P<0.002). V(max) was decreased by both AM100 (P<0.0001) and SR100 (P<0.01). Sinoatrial node automaticity was slowed in treated groups compared with that of the control group (P<0.0001 for all).

CONCLUSIONS

The electrophysiological effects of dronedarone are similar to those of AM but more potent, despite deletion of iodine from its molecular structure, a finding of importance for the development of future class III antiarrhythmic compounds.

Amiodarone: ionic and cellular mechanisms of action of the most promising class III agent

Amiodarone is the most promising drug in the treatment of life-threatening ventricular tachyarrhythmias in patients with significant structural heart disease. The pharmacologic profile of amiodarone is complex and much remains to be clarified about its short- and long-term actions on multiple molecular targets. This article reviews electrophysiologic effects of amiodarone based on previous reports and our own experiments in single cells and multicellular tissue preparations of mammalian hearts. As acute effects, amiodarone inhibits both inward and outward currents. The inhibition of inward sodium and calcium currents (I(Na), I(Ca)) is enhanced in a use- and voltage-dependent manner, resulting in suppression of excitability and conductivity of cardiac tissues especially when stimulated at higher frequencies and in those with less-negative membrane potential. Both voltage- and ligand-gated potassium channel currents (I(K), I(K,Na), I(K,ACh)) are also inhibited at therapeutic levels of drug concentrations. Acutely-administered amiodarone has no consistent effect on the action potential duration (APD). The major and consistent long-term effect of the drug is a moderate APD prolongation with minimal frequency dependence. This prolongation is most likely due to a decrease in the current density of I(K) and I(to). Chronic amiodarone was shown to cause a down-regulation of Kv1.5 messenger ribonucleic acid (mRNA) in rat hearts, suggesting a drug-induced modulation of potassium-channel gene expression. Tissue accumulation of amiodarone and its active metabolite (desethylamiodarone) may modulate the chronic effects, causing variable suppression of excitability and conductivity of the heart through the direct effects of the compounds retained at the sites of action. Amiodarone and desethylamiodarone could antagonize triiodothyronine (T3) action on the heart at cellular or subcellular levels, leading to phenotypic resemblance of long-term amiodarone treatment and hypothyroidism.

Antiarrhythmic agents for atrial fibrillation: focus on prolonging atrial repolarization

Atrial fibrillation (AF) has been the subject of considerable attention and intensive clinical research in recent years. Current opinion among physicians on the management of AF favors the restoration and maintenance of normal sinus rhythm. This has several potential benefits, including the alleviation of arrhythmia-associated symptoms, hemodynamic improvements, and possibly a reduced risk of thromboembolic events. After normal sinus rhythm has been restored, antiarrhythmic therapy is necessary to reduce the frequency of AF recurrence. In the selection of an antiarrhythmic agent, both efficacy and safety should be taken into consideration. Many antiarrhythmic agents have the capacity to provoke proarrhythmia, which may result in an increase in mortality. This is of particular concern with sodium-channel blockers in the context of patients with structural heart disease. Flecainide and propafenone are well tolerated and effective in maintaining sinus rhythm in patients without significant cardiac disease but with AF. Recent interest has focused on the use of class III antiarrhythmic agents, such as amiodarone, sotalol, dofetilide (recently approved), ibutilide (approved for chemical conversion of AF and atrial flutter), and azimilide (still to be approved) in patients with AF and structural heart disease. To date, amiodarone and sotalol still hold the greatest interest, and although controlled clinical trials with these agents have been few, a number are in progress and some have been recently completed. These agents are effective in maintaining normal sinus rhythm in patients with paroxysmal and persistent AF and are associated with a low incidence of proarrhythmia when used appropriately. Because of the relative paucity of placebo-controlled trials of antiarrhythmic agents in patients with AF, experience until recently has tended to dictate treatment decisions. Increasingly, selection of drug therapy is being based on a careful and individualized benefit-risk evaluation by means of controlled clinical trials, an approach that is likely to dominate the overall approach to the control of atrial fibrillation in the largest numbers of cases of the arrhythmia. Pharmacologic therapy is likely to be dominated by compounds that exert their predominant effect by prolonging atrial repolarization.

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.

Suppression of sustained ventricular tachyarrhythmias: a comparison of d,l-sotalol with no antiarrhythmic drug treatment

OBJECTIVES

This study evaluates the clinical efficacy of d,l-sotalol in patients with sustained ventricular tachyarrhythmias.

BACKGROUND

D,l-sotalol is an important antiarrhythmic agent to prevent recurrences of sustained ventricular tachyarrhythmias (VT/VF). However, evidence is lacking that an antiarrhythmic agent like d,l-sotalol can reduce the incidence of sustained ventricular tachyarrhythmias in comparison to no antiarrhythmic drug treatment.

METHODS

A prospective study was performed in 146 consecutive patients with inducible sustained ventricular tachycardia or ventricular fibrillation. In 53 patients, oral d,l-sotalol prevented induction of VT/VF during electrophysiological testing and patients were discharged on oral d,l-sotalol (sotalol group). In 93 patients, VT/VF remained inducible and a defibrillator (ICD) was implanted. After implantation of the device patients were randomly assigned to oral treatment with d,l-sotalol (ICD/sotalol group, n=46) or no antiarrhythmic medication (n=47, ICD-only group).

RESULTS

During follow-up, 25 patients (53.2%) in the ICD-only group had a VT/VF recurrence in comparison to 15 patients (28.3%) in the sotalol group and 15 patients (32.6%) in the ICD/sotalol group (p=0.0013). Therapy with d,l-sotalol, amiodarone or metoprolol was instituted in 12 patients (25.5%) of the ICD-only group due to frequent VT/VF recurrences or symptomatic supraventricular tachyarrhythmias. In nine patients, 17% of the sotalol group, an ICD was implanted after VT/VF recurrence, three patients (5.7%) received amiodarone. Total mortality was not different between the three groups.

CONCLUSIONS

D,l-sotalol significantly reduces the incidence of recurrences of sustained ventricular tachyarrhythmias in comparison to no antiarrhythmic drug treatment.

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.

Rate and time dependent effects of D-sotalol on the monophasic action potential after sudden increase of the heart rate

Experimental and clinical data suggests that almost all Class III antiarrhythmic agents diminish their ability to prolong cardiac repolarization at fast heart rates. However, only limited data exists about the time course of efficacy decay of Class III agents after sudden increase of the heart rate. In the present study, we assessed both rate and time dependent changes of the efficacy of d-sotalol in higher stimulation frequencies following an abrupt increase in heart rate. This might imitate the situation seen in the development of paroxysmal tachycardias. Monophasic action potentials were recorded from the right ventricular apex during sinus rhythm and constant stimulation with the paced cycle length (PCL) of 550 ms, 400 ms, and 330 ms in the baseline and 20 minutes after intravenous administration of d-sotalol (2.5 mg/kg) in seven patients with documented life-threatening ventricular tachyarrhythmias. D-sotalol significantly prolonged monophasic action potential duration at different steady-state heart rates (sinus rhythm: 21.1% +/- 3.6%; PCL 550 ms: 16.6% +/- 4.3%, 400 ms: 11.2% +/- 2.7%, 330 ms: 5.8% +/- 2.1%). The prolongation is significantly shorter in higher steady-state pacing, confirming a pronounced reverse-use dependent decrease of the efficacy of d-sotalol at faster stimulation frequencies. After the abrupt increase in heart rate, the beat-to-beat adaptation of the postdrug action potential prolongation exhibits only slight reverse-use dependent shortening. The decrease of the efficacy of d-sotalol is insignificant for the first 20 consecutive beats at the stimulation frequency of the PCL of 400 msec (from 16.6% at PCL of 550 ms to 14.6% at the 20th beat of the PCL of 400 ms), and for the first ten consecutive beats at the stimulation frequency of the PCL of 330 ms (from 16.8% at PCL of 550 ms to 12.3% at the 10th beat of the PCL of 330 ms). This slow decay of action potential prolongation after an abrupt increase in heart rate might contribute to the antiarrhythmic action of d-sotalol in cardiac tachyarrhythmias.

Spontaneous conversion and maintenance of sinus rhythm by amiodarone in patients with heart failure and atrial fibrillation: observations from the veterans affairs congestive heart failure survival trial of antiarrhythmic therapy (CHF-STAT). The Department of Veterans Affairs CHF-STAT Investigators

BACKGROUND

In a multicenter, double-blind, placebo-controlled study, the long-term effects of amiodarone on morbidity and mortality in patients with congestive heart failure (CHF) and atrial fibrillation (AF) were evaluated during a 4-year period.

METHODS AND RESULTS

Of 667 patients with CHF, 103 (15%) had AF at baseline. Of these, 51 were randomized to amiodarone and 52 to placebo. The group with sinus rhythm and the group in AF were comparable except for a higher proportion of AF in patients with nonischemic versus ischemic cardiomyopathy (41% versus 27%, P<0.005). The mean ventricular response (VR) during AF over 24 hours was reduced by amiodarone at 2 weeks (20%, P=0.001), at 6 months (18%, P=0.001), and at 12 months (16%, P=0.006). Maximal VR was reduced 22% (P=0.001) at 2 weeks, 19% (P=0.001) at 6 months, and 14% (P=0.001) at 12 months. Sixteen of 51 patients on amiodarone and 4 of 52 on placebo converted to sinus rhythm during the study (chi2=9.23, P=0.002). During follow-up, 11 of 268 patients in sinus rhythm on amiodarone at baseline and 22 of the 263 in sinus rhythm on placebo developed AF; the difference was significant (chi2=12.88, P=0.005). Analysis of total mortality during follow-up showed a significantly lower mortality rate (P=0. 04) in patients in AF at baseline who subsequently converted to sinus rhythm on amiodarone than in those who did not convert to sinus rhythm on the drug.

CONCLUSIONS

In patients with CHF, amiodarone has a significant potential to spontaneously convert patients in AF to sinus rhythm, with patients who convert having a lower mortality rate than those who do not. The drug prevented the development of new-onset AF and significantly reduced the VR in those with persistent AF.

Different Effects of Amiodarone and Quinidine on the Homogeneity of Myocardial Refractoriness in Patients With Intraventricular Conduction Delay

BACKGROUND: Increases in QT and JT dispersion have been suggested as indicative of a proarrhythmic potential as a result of heterogeneity in myocardial refractoriness, the reduction of which by antiarrhythmic agents might be associated with a beneficial effect on the development of serious ventricular arrhythmias. METHODS: To test the hypothesis that amiodarone reduces the heter-ogeneity of ventricular refractoriness to a significantly greater extent than quinidine in patients with intraventricular conduction defects under treatment for ventricular arrhythmias, the corrected and uncorrected QT and JT intervals and dispersions from 12-lead surface electrocardiograms were determined in 120 patients with intraventricular conduction defects with cardiac arrhythmias before and during treatment with amiodarone (n = 60) and quinidine (n = 60). RESULTS: Amiodarone increased QT from 403 +/- 50 ms to 459 +/- 47 ms (P <.001), with a similar increase in the corrected QT interval (QTc) (P <.001). Amiodarone reduced QT dispersion by 40% (P <.001), whereas quinidine increased by 18% (P <.001). The net effects of both drugs were similar for OTc. Amiodarone, but not quinidine, reduced heart rate significantly; amiodarone had no effect on the QRS; but quinidine increased if (P <.001). Quinidine as well as amiodarone increased the JT and JTc intervals significantly, but the effect of quinidine was qualitatively less striking. Amiodarone decreased the JT dispersion by 33% (P <.001) and JTc dispersion by 37% (P <.001). On the other hand, quinidine increased the corresponding values for JT and JTc by 18% (P <.001) and 21% (P <.001), respectively. The overall data on QT and JT dispersion indicate an improvement in the homogeneity of myocardial refractoriness with amiodarone treatment and the converse with quinidine treatment; this observation is consistent with a lower proarrhythmic propensity and mortality with amiodarone than with quinidine. Quinidine increased the QRS interval more than amiodarone, and the data indicate that in patients with intraventricular conduction defects, the monitoring of the JT interval might more accurately reflect changes in myocardial repolarization. CONCLUSIONS: Amiodarone and quinidine both increased the corrected and uncorrected QT and JT intervals; amiodarone decreased and quinidine increased the dispersion of these intervals, and these results suggested an improvement in the homogeneity of myocardial refractoriness as a result of amiodarone treatment and the converse as a result of quinidine treatment. Quinidine increased the QTS interval more than amiodarone, and the data indicate that in patients with intraventricular conduction defects, the monitoring of the JT interval might more accurately reflect changes in myocardial repolarization.

Antiarrhythmic drugs: a reorientation in light of recent developments in the control of disorders of rhythm

Numerous developments in our knowledge of arrhythmias during the past decade or so have had a major influence on antiarrhythmic drug therapy. It has become increasingly evident that arrhythmias merit treatment not only for the relief of symptoms, with improvement in quality of life, but also for the prolongation of survival by decreasing arrhythmic deaths. No longer can mere suppression of arrhythmias, symptomatic or asymptomatic, be equated with prolonged survival. We now know that antiarrhythmic drugs that act by blocking sodium channels can increase mortality and that the most important determinants of arrhythmia mortality are the degree and nature of ventricular dysfunction. To these considerations must be added the advances in nonpharmacologic approaches to controlling cardiac arrhythmias. There has been a shift to the use of implantable devices and of drugs with alternative modes of action, such as beta blockers and class III drugs (e.g., sotalol, amiodarone). However, the side-effect profiles of these 2 classes of compounds have led to the synthesis and characterization of agents that act simply by blocking > or = 1 membrane ion channels. The isolated block of the rapid component of the delayed rectifier potassium current (IKr) has been associated with potent antifibrillatory activity in the atria, with a neutral (e.g., with dofetilide) or deleterious (with d-sotalol) effect on mortality in postinfarct survivors. Therefore, the focus now is on compounds that can block > 1 ion channel (e.g., tedisamil and azimilide). Azimilide is the first of the class III agents that blocks both components of the delayed rectifier potassium current. The drug's overall action is associated with a spectrum of electrophysiologic properties that hold promise in the control of atrial and ventricular arrhythmias, with potential for improving survival in patients at risk for cardiac arrest.

Controlling cardiac arrhythmias: an overview with a historical perspective

During the past decade, several developments in our knowledge of antiarrhythmic drugs have had a major influence on our approach to their use. These developments may be summarized as follows: (1) it has become clear that arrhythmias merit treatment only for the relief of symptoms, with improved quality of life, and for prolongation of survival by reducing arrhythmic deaths; (2) suppression of arrhythmias--symptomatic or asymptomatic--may not necessarily decrease mortality, the net impact on mortality being agent-specific; (3) antiarrhythmic drugs have the propensity to decrease as well as to increase cardiac arrhythmias (producing proarrhythmias); (4) the most important determinant of arrhythmia mortality is the degree and nature of ventricular dysfunction; and (5) only controlled trials have the potential to establish the effect of treatment on mortality in patients with cardiac arrhythmias. To these considerations must be added the advances in nonpharmacologic approaches to controlling cardiac arrhythmias. These include catheter ablation of cardiac arrhythmias, certain surgical techniques that in selected patients offer prospects of cure, and the development of implantable ventricular and atrial cardioverter defibrillators, which allow the evaluation of drugs versus placebo against the background of the defibrillator. This is particularly germane in the case of life-threatening symptomatic ventricular arrhythmias such as sustained ventricular tachycardia and ventricular fibrillation. Antiarrhythmic drugs and implantable devices in the control of arrhythmias cannot be considered in isolation. Their role in mortality reduction needs to be defined alone as well as in combination by controlled clinical trials.

Sotalol Is More Powerful Than Propranolol in Suppressing Complex Ventricular Arrhythmias

BACKGROUND: Sotalol has combined type II and type III antiarrhythmic properties. Although the beta-blocking action of sotalol is thought to contribute to its antiarrhythmic actions, few data are available from direct comparative clinical trials with pure beta-blocking drugs. METHODS AND RESULTS: In this double-blind, randomized, multicenter, placebo-controlled, parallel study, we have compared the antiarrhythmic efficacy and safety of treatment with sotalol vs propranolol in 181 patients with organic heart disease and frequent (>30 ventricular premature complexes [VPCs]/h) repetitive ventricular premature complexes. Eighty-seven were randomized to receive sotalol and 94 received propranolol. The demographic and clinical characteristics of the two groups were identical, and the majority of patients had coronary artery disease or hypertensive heart disease. Most patients had a long-standing history (>5 years) of ventricular arrhythmias and, in a significant proportion, antiarrhythmic therapy with other drugs had failed in the past. After withdrawal of all antiarrhythmic drugs and 1 week of placebo, qualified patients were randomized to sotalol (320 mg/day) or propranolol (120 mg/day). patients not achieving adequate response were given higher doses of sotalol (640 mg/day) or propranolol (240 mg/day)At baseline, both groups had comparable frequency of total VPCs/hour (274/h and 255/h for sotalol and propranolol groups, respectively) which was reduced to 71 VPCs/h and 109/VPCs/h, respectively, at the end of phase 1. At final evaluation there was a significantly greater response to sotalol as demonstrated by 80% reduction in VPCs/hour with sotalol compared with only 50% reduction noted in the propranolol group. Adequate therapeutic response was also achieved in a significantly greater percentage of patients on sotalol compared with propranolol (56% vs 29%, P =.02). Sotalol was also superior to propranolol in suppressing the VT events/day during phase 1 (89% vs 78% reduction in VT events/day, P <.05). Sotalol was more effective than propranolol in all subgroups and in patients with heart rate <75 beats per minute. CONCLUSIONS: Sotalol is more powerful than propranolol in suppressing ventricular arrhythmias documented on Holter recordings. The superiority of sotalol appears to be related to its combined class II and class III antiarrhythmic actions.

Amiodarone: the expanding antiarrhythmic role and how to follow a patient on chronic therapy

Amiodarone was introduced as an antiarrhythmic compound in the early 1970s and was approved in the U.S. for the treatment of refractory ventricular arrhythmias in late 1984. Since that time the drug has become the most widely studied antiarrhythmic compound with expanding potential indications, including maintaining stability of sinus rhythm, secondary prevention in the survivors of myocardial infarction, and prolongation of survival in certain subsets of patients with congestive heart failure. Intravenous amiodarone was introduced in the U.S. in 1995 for the control of recurrent destabilizing ventricular tachycardia or ventricular fibrillation resistant to conventional therapy. The level of comfort in its use has risen considerably in the recent past. This has stemmed from the reasonably decisive evidence that class I agents increase mortality in patients with structural heart disease. In contrast, amiodarone either reduces mortality or its effect is neutral; this is consistent with its low to negligible proarrhythmic actions. The drug does not aggravate heart failure and it may even increase left ventricular ejection fraction and improve exercise capacity. Above all, it is becoming increasingly evident from wider experience and from controlled clinical trials that the side-effect profile of the drug is not as compelling an issue as it appeared to be when first used in much higher doses. Therefore, the overall objective of amiodarone therapy is to use the lowest dose that produces a defined therapeutic end point without causing serious side effects. Careful clinical surveillance in conjunction with monitoring of certain laboratory parameters and indices of efficacy at regular intervals permits the drug to be used effectively in a large number of patients who fail to respond to, or are intolerant of other antiarrhythmic compounds. Many experienced clinicians have begun to consider the use of amiodarone as first-line therapy in certain disorders of rhythm, especially in patients with severely compromised ventricular function.

Controlling Paroxysmal Atrial Fibrillation by a Combination of Amiodarone and Flecainide: Description of a Case With 15-Year Follow-up

A 77-year-old man with no known cardiac disease has had paroxysmal atrial fibrillation for 35 years with disabling symptoms and poor exercise tolerance when not in sinus rhythm, and he did not respond to conventional therapy. Fifteen years ago he was placed on amiodarone. His arrhythmia converted to atrial flutter with a flutter rate below 200 beats/min; DC cardioversion at 3 months led to transient sinus rhythm. At 5 months he converted spontaneously to sinus rhythm and had very few recurrences until 4 years later when he began to experience further frequent recurrences when the dose was reduced from 400 mg/day to 200 mg/day. Redosing at the higher dose led to skin discoloration; amiodarone was then replaced with sotalol, which the patient did not tolerate. After 9 months with efforts to rate control with various agents, amiodarone was reintroduced at 400 mg/day, which achieved full control, but to obviate the development of skin changes, flecainide was added at a dose of 100 mg twice a day, and the dose of amiodarone was gradually reduced to 200 mg/day. This combination regimen has produced no side effects or organ toxicity, although a degree of hypogonadism developed. It responded well to testosterone replacement. On the combination regimen, there have been no symptomatic arrhythmia recurrences over 8 years. Amiodarone and flecainide may have additive or synergistic effects in maintaining sinus rhythm in atrial fibrillation; the antiarrhythmic property of amiodarone is likely to minimize or nullify the proarryhthmic reactions of flecainide during combination therapy. This combination regimen may allow the extension of the use of flecainide in controlling refractory atrial flutter and fibrillation in patients with structural cardiac disease. The efficacy and safety of the combination regimen of the two drugs should be addressed in controlled clinical trials.

The coming of age of the class III antiarrhythmic principle: retrospective and future trends

Antiarrhythmic drug therapy is in a state of continuous flux. In the last decade or so, numerous experimental and clinical studies have revealed that drugs that act by delaying conduction, while markedly suppressing ventricular arrhythmias, have the proclivity to increase mortality in subsets of patients with significant cardiac disease. The adverse impact on mortality was confirmed by placebo-controlled randomized trials as well as meta-analysis of smaller randomized clinical trials. The latter indicated that beta blockers exert a beneficial effect on mortality. Benefit from drugs that lengthen repolarization, especially drugs that have the additional property of blocking sympathetic excitation, was also seen in relatively small numbers of patients. Sotalol and amiodarone fell into this category of antiarrhythmic drugs. There were 2 major consequences that stemmed from the results of these trials. First, the endpoint of clinical trials shifted to total mortality from surrogates such as defined degree of suppression of ventricular arrhythmias. Second, concern regarding increases in mortality produced by class I drugs engendered a shift in favor of drugs that prolong repolarization. Such a shift was bolstered by the growing body of data that established the efficacy of sotalol and amiodarone as potent agents for the control of life-threatening ventricular arrhythmias. They were both found to be superior to class I agents. The perception that the critical factor that mediates their efficacy is the homogeneous prolongation of repolarization has led to the synthesis and characterization of so-called pure class III agents, which include d-sotalol and other lKr blockers such as dofetilide, sematilide, E-4031, and almokalant, among numerous others. The increase in mortality produced by d-sotalol in patients with myocardial infarction and lowered ejection fraction and in patients with and without heart failure has led researchers to question how to design future antiarrhythmic molecules. In the search for an ideal antifibrillatory agent, should emphasis be placed on simple molecules such as pure class III agents or on those with more complex profiles, such as sotalol and amiodarone, which exhibit antiadrenergic actions and the ability to prolong cardiac repolarization? The available data are in favor of the latter approach.