Beta blockers after myocardial infarction--aspects on study design based on current knowledge.

Abstract

The beta-blocker trials published so far may be subdivided into three different categories: 1) retrospective, 2) prospective non-conclusive, 3) prospective conclusive studies. The retrospective studies suffer the weaknesses of the retrospective method and may only be used as supportive evidence. There have so far been four prospective studies producing positive results, three with alprenolol and one with practolol. The studies presented support the concept that practolol and alprenolol reduce the long-term mortality due to sudden death from ischemic heart disease after myocardial infarction. All the studies have been criticized on various grounds and a list of unanswered remaining issues may be made. Acute and long-term effects of betablockade need not be the same. Our knowledge about the necessary doses and plasma levels is incomplete. All the studies published so far cover a maximum period of two years. If the study observation periods were prolonged it is likely that at some time the relative benefit becomes less. Ideal treatment should be reserved for those patients likely to derive significant benefit from it. At the present time identification of such patients is not sufficiently precise. Whether or not the beta-blockers have an antiarrhythmic effect, for instance demonstrated on chronic PVC's, this information is of little value in interpreting the proper mechanism of the beta-blockers in acute ischemia and lethal arrhythmias. In order to contribute new knowledge future studies should involve sufficiently large numbers of representative groups of patients, a stratified study design and a beta-blocker with ancillary properties different from alprenolol.