Comparison of the efficacy of propranolol and amiodarone in suppressing ventricular arrhythmias following myocardial infarction

Amiodarone versus other pharmacological interventions for prevention of sudden cardiac death

BACKGROUND

Sudden cardiac death (SCD) is one of the main causes of cardiac death. There are two main strategies to prevent it: managing cardiovascular risk factors and reducing the risk of ventricular arrhythmias. Implantable cardiac defibrillators (ICDs) constitute the standard therapy for both primary and secondary prevention; however, they are not widely available in settings with limited resources. The antiarrhythmic amiodarone has been proposed as an alternative to ICD.

OBJECTIVES

To evaluate the effectiveness of amiodarone for primary or secondary prevention in SCD compared with placebo or no intervention or any other antiarrhythmic drugs in participants at high risk (primary prevention) or who have recovered from a cardiac arrest or a syncope due to Ventricular Tachycardia/Ventricular Fibrillation, or VT/VF (secondary prevention).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), EMBASE (OVID), CINAHL (EBSCO) and LILACS on 26 March 2015. We reviewed reference lists of included studies and selected reviews on the topic, contacted authors of included studies, screened relevant meetings and searched in registers for ongoing trials. We applied no language restrictions.

SELECTION CRITERIA

Randomised and quasi-randomised trials assessing the efficacy of amiodarone versus placebo, no intervention, or other antiarrhythmics in adults. For primary prevention we considered participants at high risk for SCD. For secondary prevention we considered participants recovered from cardiac arrest or syncope due to ventricular arrhythmias.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the trials for inclusion and extracted relevant data. We contacted trial authors for missing data. We performed meta-analyses using a random-effects model. We calculated risk ratios (RR) for dichotomous outcomes with 95% confidence intervals (CIs). Three studies included more than one comparison.

MAIN RESULTS

We included 24 studies (9,997 participants). Seventeen studies evaluated amiodarone for primary prevention and six for secondary prevention. Only three studies used an ICD concomitantly with amiodarone for the comparison (all of them for secondary prevention).For primary prevention, amiodarone compared to placebo or no intervention (17 studies, 8383 participants) reduced SCD (RR 0.76; 95% CI 0.66 to 0.88), cardiac mortality (RR 0.86; 95% CI 0.77 to 0.96) and all-cause mortality (RR 0.88; 95% CI 0.78 to 1.00). The quality of the evidence was low.Compared to other antiarrhythmics (three studies, 540 participants), amiodarone reduced SCD (RR 0.44; 95% CI 0.19 to 1.00), cardiac mortality (RR 0.41; 95% CI 0.20 to 0.86) and all-cause mortality (RR 0.37; 95% CI 0.18 to 0.76). The quality of the evidence was moderate.For secondary prevention, amiodarone compared to placebo or no intervention (two studies, 440 participants) appeared to increase the risk of SCD (RR 4.32; 95% CI 0.87 to 21.49) and all-cause mortality (RR 3.05; 1.33 to 7.01). However, the quality of the evidence was very low. Compared to other antiarrhythmics (four studies, 839 participants) amiodarone appeared to increase the risk of SCD (RR 1.40; 95% CI 0.56 to 3.52; very low quality of evidence), but there was no effect in all-cause mortality (RR 1.03; 95% CI 0.75 to 1.42; low quality evidence).Amiodarone was associated with an increase in pulmonary and thyroid adverse events.

AUTHORS' CONCLUSIONS

There is low to moderate quality evidence that amiodarone reduces SCD, cardiac and all-cause mortality when compared to placebo or no intervention for primary prevention, and its effects are superior to other antiarrhythmics.It is uncertain if amiodarone reduces or increases SCD and mortality for secondary prevention because the quality of the evidence was very low.

Quantitative overview of randomized trials of amiodarone to prevent sudden cardiac death

BACKGROUND

Some randomized clinical trials of amiodarone therapy to prevent sudden cardiac death have had positive results and others have had negative results, but all were relatively small. This meta-analysis aimed to pool all trials to assess the effect of amiodarone on mortality and the impact of differences in patient population and study design on trial outcomes.

METHODS AND RESULTS

Fifteen randomized trials were identified, and outcome measures were combined by use of a random effects model. The effect of patient population and study design on total mortality was assessed by use of a hierarchical Bayes model. Amiodarone reduced total mortality by 19% (confidence limits, 6% to 31%; P<.01), with somewhat greater reductions in cardiac mortality (23%, P<.001) and sudden death (30%, P<.001). Mortality reductions were similar in trials enrolling patients after myocardial infarction (21%), with left ventricular dysfunction (22%), and after cardiac arrest (25%). There was a trend toward greater risk reduction in trials requiring evidence of ventricular ectopy (25%) than in the remaining trials (10%). The trials using placebo controls had considerably less risk reduction (10%) than trials with active controls (27%) or usual care controls (42%, posterior odds <0.02).

CONCLUSIONS

Amiodarone reduced total mortality by 10% to 19% in patients at risk of sudden cardiac death. Amiodarone reduced risk similarly in patients after myocardial infarction, with heart failure, or with clinically evident arrhythmia. The apparent inconsistencies among results of randomized trials appear to be due to small sample sizes and the type of control group used, not the type of patient enrolled.

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.

Amiodarone. An overview of its pharmacological properties, and review of its therapeutic use in cardiac arrhythmias

Amiodarone, originally developed over 20 years ago, is a potent antiarrhythmic drug with the actions of all antiarrhythmic drug classes. It has been successfully used in the treatment of symptomatic and life-threatening ventricular arrhythmias and symptomatic supraventricular arrhythmias. In patients with left ventricular dysfunction amiodarone does not usually produce any clinically significant cardiodepression and the drug has relatively high antiarrhythmic efficacy. Preliminary studies indicate that amiodarone may have a beneficial effect on mortality and survival in certain groups of patients with ventricular arrhythmias, an action probably related to both its antiarrhythmic and antifibrillatory effects. The adverse effect profile of amiodarone is diverse, involving the cardiac, thyroid, pulmonary, hepatic, gastrointestinal, ocular, neurological and dermatological systems. Interstitial pneumonitis and hepatitis are potentially fatal, but the vast majority of adverse events are less serious, and some may be dose dependent. Pretreatment monitoring, regular assessments and the use of minimum effective doses are, therefore, necessary. Thus, with appropriate monitoring to control its well recognised adverse effects amiodarone has an important place as an effective 'broad spectrum' antiarrhythmic drug which has, so far, been used when other treatments have proved ineffective. More recent preliminary data also suggest that it may also have a beneficial effect in the prevention of sudden death in some patients.

The value of oral amiodarone in the treatment of ventricular arrhythmias in heart disease

The antiarrhythmic properties of amiodarone at the ventricular level were discovered in the early 1970s. The unanimously recognised efficacy of amiodarone includes a weak negative inotropic effect and compensatory vasodilatory properties, making amiodarone particularly suitable for treating the potentially malignant arrhythmias associated with organic disease. In a review of 611 hospitalised patients on amiodarone, and 353 patients in whom the drug had been prescribed, over a 52-month period in our 60-bed department, we noted that amiodarone was prescribed in 53% of patients for arrhythmias and in 47% of patients for coronary insufficiency. Ventricular arrhythmias represented 13% of the rhythmic indications. These indications differ from those in the USA. The efficacy (70 to 90%) of amiodarone in ventricular extrasystoles has been shown in open studies. In coronary patients, the antiarrhythmic activity of amiodarone is superior to that of propranolol. However, there has been no controlled study because the need for a loading dosage, and the electrocardiographic effects render such studies difficult. After myocardial infarction, ventricular arrhythmias constitute a significant risk factor independently of prognosis; amiodarone may be useful in this indication, and studies of the European Myocardial Infarction Amiodarone Trial (EMIAT) type will examine its value here. Since 1973, it has been recognised that amiodarone can prevent ventricular tachycardia in 55 to 89% of patients in the clinical situation. After a long-standing controversy, the positive predictive value of programmed stimulation has finally been agreed on. In hypertrophic cardiomyopathy, retrospective studies suggest a reduction in mortality in patients treated with amiodarone. By contrast, the value of amiodarone in dilated cardiomyopathy requires more intensive investigation. We consider amiodarone to be indicated in ventricular arrhythmic complexes, particularly if they are associated with an ejection fraction of less than 35% and/or atrial fibrillation. The value of amiodarone in arrhythmias associated with heart failure needs to be evaluated. In conclusion, amiodarone is a powerful antiarrhythmic agent but, because of the possibility of dose- and duration-dependent side effects, evaluation of the risk: benefit ratio in each indication is needed.