Randomized trials in coronary bypass surgery.

CORONARY artery bypass grafting is an effective treatment for increasing myocardial blood flow in selected patients with coronary artery disease. After this procedure, symptoms improve, coronary blood flow to the affected area is increased, and exercise tolerance is enhanced.1 In patients who have received maximal drug therapy and yet remain intolerably symptomatic, bypass surgery clearly adds a brilliant therapeutic advantage, at least for a few years. More than a year has elapsed since the initial results of the Coronary Artery Surgery (CASS) randomized trial were published in Circulation,'2, providing ample time for the medical community to assimilate the data collected from the 6 year follow-up of the 780 patients with proven coronary artery disease who were randomly assigned to either continued medical therapy or coronary bypass surgery on entry to the study that began recruitment in August 1975. Extensive followup data from the two other large randomized trials are now available, so that it should be possible to identify quite precisely what unanswered questions remain regarding the effectiveness of the operation. Does coronary artery bypass prolong life over the long term? Does it affect the rate of subsequent myocardial infarction? Are there clearly defined subsets among patients with chronic stable ischemic heart disease who may uniquely benefit from operation? When the primary end point of all-cause mortality in CASS was examined for the entire population equally and randomly assigned to surgical or medical therapy, cumulative survival after 6 years was 92% and 90%, respectively. These data permit the conclusion that there is no statistically significant survival advantage in embarking on prompt bypass surgery for patients with coronary disease similar to those in the CASS randomized population, although it is recognized that important differences in outcome in carefully defined subgroups may be hidden in analysis of the population as a whole. Such a conclusion is consonant with the