Reassessment of benefit-risk ratio and treatment algorithms for antiarrhythmic drug therapy after the cardiac arrhythmia suppression trial

Age-related electrophysiological and histological changes in rabbit hearts: age-related changes in electrophysiology

Because of the known higher incidence of cardiac arrhythmia in aged patients we tried to define the underlying arrhythmogenic substrate by quantifying those electrophysiological alterations in aged rabbit hearts, which are commonly believed to be arrhythmogenic, relating them to histological findings in the same hearts. This is the first investigation that analyses the effect of ageing on the epicardial excitation spreading. Isolated hearts from young (ten weeks) and old (1.5-2 years) white New Zealand rabbits were perfused according to the Langendorff-technique, submitted to epicardial potential mapping for 60 min and investigated histologically. Electrophysiological data in aged hearts showed a) a higher variability of the activation pattern, b) an increased dispersion of the epicardial potential duration; c) a prolongation of the AV-conduction time and of the duration of the epicardial activation signal, which was fractionated in aged hearts. Histological findings showed extensive incorporation of fat cells and connective tissue in ventricular and AV-node tissues, which may explain the prolonged conduction time, and a marked hypertrophy of the ventricular myocytes. The observed high dispersion, the broadened and fractionated epicardial activation signal and the enhanced variability of the activation patterns may be due to the observed long strands of collageneous tissue separating ventricular muscle fibres in aged hearts. These changes help to explain the enhanced susceptibility to arrhythmogenic stimuli with age.

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

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

Impact of the Food and Drug Administration approval of flecainide and encainide on coronary artery disease mortality: putting "Deadly Medicine" to the test

In his book Deadly Medicine and on television, Thomas Moore impugns the process of antiarrhythmic drug approval in the 1980s, alleging that the new generation of drugs had flooded the marketplace and had caused deaths in numbers comparable to lives lost during war. To assess these important public health allegations, we evaluated annual coronary artery disease death rates in relation to antiarrhythmic drug sales (2 independent marketing surveys). Predicted mortality rates were modeled using linear regression analysis for 1982 through 1991. Deviations from predicted linearity were sought in relation to rising and falling class IC and overall class I antiarrhythmic drug use. Flecainide came to market in 1986 and encainide in 1987. Combined class IC sales peaked in 1987 and 1988 (maximum market penetration, 20%, first quarter 1989). Results of the Cardiac Arrhythmia Suppression Trial (CAST) were disclosed in April 1989. Overall annual class I antiarrhythmic prescription sales actually fell slightly (-3% to -4%/yr) in the 2 years before CAST and then more abruptly (- 12%) in the year after CAST (1990). Sales of class IC drugs fell dramatically after CAST (by 75%). Coronary death rates (age adjusted) fell in a linear fashion during the decade of 1982 through 1991. No deviation from predicted rates was observed during the introduction, rise, and fall in class IC (and other class I) sales: rates were 126/100,000 in 1985 (before flecainide), 114 and 110 in 1987 and 1988 (maximum sales), and 103 in 1990 (after CAST). Deviations in death rates in the postulated range of 6,000 to 25,000 per year were shown to be excluded easily by the 95% confidence intervals about the predicted rates. Entry of new antiarrhythmic drugs in the 1980s did not lead to overall market expansion and had no adverse impact on coronary artery disease death rates, which fell progressively. Thus, the allegations in Deadly Medicine could not be confirmed.

Antiarrhythmic drug therapy for ventricular arrhythmias: current perspectives

Pharmacologic therapy for ventricular arrhythmias has undergone a remarkable change recently. Recognition of the importance of underlying structural heart disease on prognostic implications of ventricular arrhythmias has resulted in the refinement of the clinical classification of these arrhythmias. With refinement of techniques of risk stratification, it is now possible to identify patients ventricular arrhythmias at high risk for sudden death. Retrospective analyses of prior antiarrhythmic drug trials and new data from prospective randomized trials are now available and can more directly define the risks and benefits of antiarrhythmic therapy. Prevention of sudden death, reduction in total mortality, or improvement in symptoms remain the only benefits of antiarrhythmic drugs. With inclusion of total mortality as the major endpoint for assessment of pharmacologic interventions in high-risk patients, the potential for excess mortality due to antiarrhythmic agents is now recognized. The pharmacologic diversity of newly released antiarrhythmic agents and others under development has resulted in a re-evaluation of the traditional classification of these drugs. Multiple ongoing clinical trials will define the risks and benefits of antiarrhythmic therapy and other nonpharmacologic interventions in patients with ventricular arrhythmias.

Data-driven Decisions: The Importance of Clinical Trials in Arrhythmia Management

As a result of clinical trials, the measurement of arrhythmias has evolved over the past three decades. In the late 1960s, customary teaching was that ventricular premature depolarizations were dangerous and antiarrhythmic therapy, in hopes of reducing fatal consequences, became common place; however, following clinical trials such as CAST, IMPACT, and SWORD, we learned that, at least in postinfarct patients, arrhythmia suppression may lead to increased rather than reduced mortality. Such trials have led to a marked reduction in therapy of indiscriminate ventricular ectopy and have led to ongoing testing of specific subgroups identified as having particularly higher adverse prognostic risk. With the advent of cardiac monitoring and the confirmation that ventricular tachyarrhythmias are the most common cause for sudden death, their therapy, too, has evolved and matured, again aided by clinical trials. The ESVEM study prospectively examined the role of monitor-guided versus electrophysiologically guided drug therapy of ventricular tachyarrhythmias and confirmed that both approaches may have a role in reducing arrhythmic deaths-though the specific benefits of each technique remain somewhat unsettled. Both the ESVEM and CASCADE studies suggested that the most effective drugs for ventricular tachyarrhythmias are the class II/III drugs, sotalol and amiodarone, both appearing more effective than our older class I agents. These should now be viewed as the first-line drugs for these arrhythmias. The relative benefits of these two agents with respect to each other and to implantable cardioverter defibrillators, however, remains to be determined by further clinical trials, such as AVID and CIDS. The therapy of atrial tachyarrhythmias has similarly evolved with the aid of clinical observations. While rate control is required in all patients with atrial fibrillation, we have come to realize that the applications of antiarrhythmic drugs for the purpose of maintaining sinus rhythm must be used only selectively rather than uniformly. Both a meta-analysis by Coplen and colleagues and a report by the SPAF investigators suggested that with atrial arrhythmias, too, antiarrhythmic drug therapy may result in enhanced rather than reduced mortality in some circumstances. Additional clinical trials are needed to further elucidate the role of antiarrhythmic therapy of atrial fibrillation.

Risk factors for the development of specific noncardiovascular adverse effects associated with amiodarone

Noncardiovascular adverse effects associated with amiodarone result in substantial morbidity. Adverse effects involving the skin, liver, thyroid, and lungs have been reported in as many as 57%, 55%, 11%, and 13% of patients, respectively. Although risk factors for some amiodarone-induced adverse effects have been identified, risk factors for these specific side effects have not been systematically evaluated. Therefore, risk factors for development of amiodarone-induced dermatologic, hepatic, thyroid, or pulmonary adverse effects were identified using univariate analysis in 44 patients receiving the drug for supraventricular or ventricular arrhythmias (mean duration of therapy 99.5 +/- 110.8 weeks). Dermatologic side effects occurred in 4 (9.1%) patients. Patients who experienced dermatologic side effects were younger than patients who did not (mean age, 48.3 +/- 15.8 years versus 60.1 +/- 9.5 years, respectively; P = .03). Patients younger than 60 years of age were more likely to develop photosensitivity or blue-gray skin discoloration than those aged 60 or older (P = .05). Hepatic adverse effects occurred in 3 (6.8%) patients. Left ventricular ejection fraction was lower in those who developed hepatic adverse effects than in those who did not (15.0 +/- 4.0% versus 39.1 +/- 13.9%, P = .005). Adverse thyroid effects occurred in 6 (13.6%) patients; and pulmonary fibrosis occurred in 2 (4.5%) patients. No specific risk factors for adverse thyroid effects or pulmonary fibrosis were revealed. In conclusion, age less than 60 may be a risk factor for amiodarone-induced dermatologic adverse effects, whereas severely depressed left ventricular ejection fraction may be a risk factor for hepatic side effects associated with amiodarone.

Bridging the gap between basic and clinical electrophysiology: what can be learned from monophasic action potential recordings?

With rapid advances occurring in both basic and clinical electrophysiology, the gap between the two disciplines appears to be widening rather than narrowing. In most instances, we cannot apply the knowledge derived from cellular studies directly to clinical practice. Monophasic action potential (MAP) recording by contact electrode technique allows us to measure basic electrophysiological phenomena in the human heart and thus provides an important bridge between basic and clinical electrophysiology. MAP recordings produce the time course of cellular repolarization during cycle length changes and antiarrhythmic drug administration, lending insights into use dependency and reverse use dependency of antiarrhythmic drug effects in the clinical electrophysiology laboratory. The ability to deliver electrical stimuli at the MAP recording site further allows one to investigate drug-induced postrepolarization refractoriness. MAP recordings provide precise local activation times, important for mapping of abnormal ventricular activation, and detect areas of abnormal repolarization due to ischemia or scarring. MAP recordings are uniquely suited to detect early and delayed afterdepolarizations in the human heart, thereby helping to unravel the arrhythmia mechanisms in the long QT syndrome. By embedding the MAP electrode in a radiofrequency electrode, arrhythmogenic foci may be both detected and ablated. In many instances, MAP recordings are more accurate than ECG tracings in defining and distinguishing ventricular fibrillation and ventricular tachycardia. This can be of clinical importance during testing of the implantable cardioverter/defibrillator. An area of growing interest is stretch-activated arrhythmias. Here, MAP recordings are of particular value because no other method is available to record mechanically induced electrophysiological changes in the vigorously beating heart. It can be expected that MAP recordings will, in the future, provide this important bridge between "cell and bedside" also in atrial tachyarrhythmias, such as in atrial fibrillation and flutter.

A consensus report on antiarrhythmic drug use

During the past few years, a number of new antiarrhythmic agents have become available for use in the United States, encainide has been withdrawn from use, and others have had indications for use modified. Therefore, a meeting of arrhythmia specialists was convened in an attempt to develop guidelines for antiarrhythmic therapy. The resultant discussions and guidelines presented in this article address general issues such as the most important antiarrhythmic drug attributes, as well as therapy for particular arrhythmias such as premature ventricular contractions, ventricular tachycardia, ventricular fibrillation, ventricular ectopy, and supraventricular tachyarrhythmias.

Indications for antiarrhythmic suppression of ventricular arrhythmias: a definition of life-threatening ventricular arrhythmias

A surprising finding of the Cardiac Arrhythmia Suppression Trial (CAST), reported in 1989, is that well-tolerated and effective antiarrhythmic drugs may also be associated with an increase in mortality due to arrhythmia. Consequently, attention has been focused on the importance of the benefit-versus-risk assessment of such therapy. The benefits of antiarrhythmic therapy are reduction or elimination of arrhythmia-caused symptoms (both hemodynamic and nonhemodynamic) and of the associated risk of death. The risks of such treatment include not only noncardiac adverse effects and organ toxicity, but also early cardiac effects (proarrhythmia, heart failure, and conduction defects), as well as the newly recognized potential for late proarrhythmia or late arrhythmic death. Unfortunately, as the potential benefits of antiarrhythmic therapy increase in patients with poorer left ventricular function (owing to their being at greater risk for sudden death), the effectiveness of suppression decreases and the incidence of life-threatening complications increases. The impact of this benefit-risk profile is that the indication for most currently approved antiarrhythmic drugs needs to be limited to those patients with definite life-threatening ventricular arrhythmias that take the form of sustained ventricular tachyarrhythmias with associated hemodynamic symptoms. Broadening this indication to include patients with probable life-threatening or even possible life-threatening arrhythmias must await the availability of drugs with better benefit-risk profiles.

Comparative study on the proarrhythmic effects of some antiarrhythmic agents

BACKGROUND

A main side effect of antiarrhythmic drug therapy is the tendency of these drugs to promote arrhythmia within the therapeutic concentration range, i.e., the proarrhythmic activity of these drugs. However, a model for in vitro assessment, quantification, and comparison of proarrhythmic drug activities was still lacking, and only sparse data were available.

METHODS AND RESULTS

To analyze the arrhythmogenic risk of common antiarrhythmic drugs in a quantitative and comparative manner, isolated perfused rabbit hearts were treated with increasing concentrations of antiarrhythmic drugs corresponding to low, medium, and high therapeutic concentrations. For analysis of the epicardial activation process, an epicardial mapping (256 unipolar leads) was performed. For each electrode, the activation time was determined. From these data, the origins of epicardial activation ("breakthrough points" [BTP]) were determined. At each electrode, an activation vector (VEC) was calculated giving direction and velocity of the local excitation wave. The beat similarity of various heartbeats (under treatment) compared with control was evaluated by determination of the percentage of identical BTPs (deviation < or = 1 mm) and of similar VECs (deviation < or = 5 degrees). BTP and VEC were reduced by all antiarrhythmic agents tested (propafenone = flecainide > quinidine > ajmaline > procainamide > disopyramide > mexiletine = lidocaine > sotalol), indicating a more or less pronounced disturbance of the epicardial activation process. Treatment with propafenone, quinidine, and disopyramide and to a lesser extent sotalol prolonged the activation-recovery interval (ARI). ARI dispersion was greatly enhanced by flecainide and was reduced by sotalol. In addition, it could be shown that propranolol is able to reduce the proarrhythmic action of flecainide. This effect seemed to be due to a reduction of the flecainide-induced increase in ARI dispersion.

CONCLUSIONS

From the results of our study, we propose the following rank order of the arrhythmogenic risk: flecainide > propafenone > quinidine > ajmaline > disopyramide > procainamide > mexiletine, lidocaine > sotalol. Moreover, we conclude that propranolol given additionally may be helpful in reducing the proarrhythmic risk of flecainide.

Early and late proarrhythmia from antiarrhythmic drug therapy

Antiarrhythmic drug therapy is used with the hope of suppressing arrhythmias and therefore decreasing their associated symptoms or prolonging life. Unfortunately, many antiarrhythmic drugs have the opposite effect of exacerbating or provoking arrhythmias, a phenomenon that is termed proarrhythmia when such an event is specifically due to the drug in use. Early proarrhythmic events (within 30 days of initiation of drug use) have been reasonably well characterized and are predicted by either type of drug employed or the nature of the patient's cardiac disease and arrhythmia type. Late proarrhythmic events, as defined by placebo-controlled trials, have now been recognized as an increased risk of arrhythmic death in patients on antiarrhythmic drugs after many months of therapy. Initially, this late proarrhythmic event was identified with encainide and flecainide, but now several new studies have demonstrated that the risk of late proarrhythmia of comparable magnitude may be present in patients subjected to commonly used drugs, such as quinidine, mexelitine, etc. At present, only moricizine and the class II drugs (beta-adrenergic blockers) appear not to have this potential late proarrhythmic response. Therefore, before instituting antiarrhythmic drug therapy, the physician must be able to quantitate the degree of proarrhythmia and other risks of such therapy, as compared to their potential benefit, to define the proper indications for these agents.

Quinidine-related mortality in the short-to-medium-term treatment of ventricular arrhythmias. A meta-analysis

BACKGROUND

The interim results of the Cardiac Arrhythmia Suppression Trial requires physicians to use a higher threshold for employing antiarrhythmic agents in the treatment of benign or potentially lethal ventricular arrhythmias. Many have managed patients by switching to the traditional class I quinidine despite its known proarrhythmic tendency.

METHODS AND RESULTS

To evaluate the relation between quinidine therapy and mortality in patients with benign or potentially lethal ventricular arrhythmias, we performed a meta-analysis on four randomized double-blind active controlled parallel trials evaluating 1,009 patients in which quinidine (n = 502) was compared to flecainide (n = 141), mexiletine (n = 246), tocainide (n = 67), and propafenone (n = 53). All four trials had similar patient selection, protocols, and methodology (e.g., placebo lead-in and Holter monitoring) but varying lengths of drug exposure. A total of 12 deaths were reported on quinidine and four deaths on the other drugs: two on mexiletine, one on flecainide, and one on tocainide. The statistical analysis of the mortality rates was based on techniques for combining data across separate strata. Based on maximum likelihood estimation, the combined risk of dying on quinidine was statistically significantly higher compared to the other four drugs with a risk difference of 1.6%. The 95% confidence interval was 0-3.1% (p = 0.05). The likelihood ratio test for uniformity of the risk difference across strata showed the trials to be homogeneous (p = 0.88). There was one death recorded for the placebo lead-in period (2 weeks' exposure for 624 patients and 1 week for 385 patients), and seven deaths were reported within 2 weeks on active drug treatment--six on quinidine and one on mexiletine. Furthermore, proarrhythmia was reported in 20 patients on quinidine versus 11 patients on the four other drugs (p = 0.09).

CONCLUSIONS

These data suggest that quinidine may have an adverse effect on mortality as compared to other class I antiarrhythmic agents and that individualized patient selection for the use of this agent be carefully weighed relative to its potential for harm and benefit.