Prophylactic antiarrhythmic therapy in acute myocardial infarction.

Safe, effective prophylaxis of arrhythmias in acute myocardial infarction (AMI) is an important clinical goal. Despite rescue squads, out-of-hospital ventricular fibrillation (VF) has a poor prognosis. Even in-hospital VF has an important morbidity and mortality. Successful prophylactic therapy may also prevent infarct size enlargement associated with tachyarrhythmias. Several antiarrhythmic drugs have been investigated. In 3 studies, mortality was significantly reduced, but all of these have serious methodologic flaws and the validity of their conclusions is debatable. More reliance can be placed on 2 other studies which suggested that VF was significantly reduced by prophylactic therapy. However, in one of these studies, which used high-dose intravenous lidocaine, an unusually high incidence of VF was observed in the placebo-treated patients. The second study, reporting the use of metoprolol in AMI, was based on retrospective subset analysis. The reduction in VF was seen from the fourth day onwards and not during the acute phase of infarction. The favorable results with high-dose intravenous lidocaine are the basis for widespread use of prophylactic arrhythmia therapy in AMI. Uncontrolled observations provide some corroboration of the benefit. However, the claimed efficacy for lidocaine remains scientifically poorly substantiated and the safety of the high-dose regimen is controversial. Effective prophylaxis of arrhythmias in AMI could have important clinical benefit. However, the strategy would entail administration of a drug to many patients not at risk of arrhythmias (those without AMI) and to a number of patients in whom the complications of infarction are destined to develop.(ABSTRACT TRUNCATED AT 250 WORDS)