Advantages of beta blockers versus antiarrhythmic agents and calcium antagonists in secondary prevention after myocardial infarction

Abstract

Patients who have sustained greater than or equal to 1 myocardial infarcts are at high risk for sudden death or reinfarction; the risk is highest for those with lowest ventricular ejection fraction, continuing myocardial ischemia and asymptomatic high-density and complex premature ventricular contractions. At present, beta blockers when given prophylactically are the only agents that reduce the incidence of sudden death and reinfarction in survivors of myocardial infarction (MI) in the first 2 years. The beneficial effect was shown to correlate with a reduction in heart rate, the effect being absent or deleterious with beta blockers with marked sympathomimetic activity. The effects of beta blockers on ventricular fibrillation appeared to be dissociated from those on premature ventricular contractions. Trials with calcium antagonists indicate that these drugs had no effect or increased the mortality rate. The divergent effect of beta blockers and calcium antagonists is unexplained but may be due in part to a lack of bradycardiac effect of calcium antagonists; there were no differences in effect among different calcium antagonists. Data from trials involving class I antiarrhythmic agents indicate that agents acting by depression of cardiac conduction are either devoid of effect or produce a modest increase in mortality. Results of the Cardiac Arrhythmia Suppression Trial, employing the newer class I agents flecainide and encainide, were used to determine whether the suppression of premature ventricular contractions in the survivors of acute MI reduces mortality. Flecainide and encainide suppressed premature ventricular contractions greater than 80%, but resulted in an increased mortality rate undoubtedly due to a marked proarrhythmic effect. Whether these data can be extrapolated to all class I agents is uncertain. Preliminary data with class III antiarrhythmic agents suggest that these agents, especially amiodarone, similarly to beta blockers, have the potential to reduce mortality in survivors of MI. Evolving data suggest that in the secondary prevention of morbid events in the survivors of acute MI, the focus must shift away from antiarrhythmic agents that delay conduction and toward beta blockers and antifibrillatory actions resulting from a prolongation of refractoriness.