Pathophysiology and Natural History - Coronary Artery Disease

The incidence of previous coronary artery bypass surgery (CABS) in patients with acute myocardial infarction admitted to our hospital has risen from 2.3% to 11.2% in 6 years. We compared infarct size and the angiographically determined cause of infarction in 52 control patients and in 52 consecutive patients with acute myocardial infarction at least 2 months after they had undergone CABS. Baseline characteristics were similar in both groups except for a higher incidence of preexisting Q waves in the post-CABS group (22 vs 10; p < .05). Indexes of myocardial infarct size were smaller in the post-CABS group compared with those in control patients: peak creatine kinease (CK) level (IU/liter) 11 13 + 1094 (mean + SD) vs 1824 1932 (p < .01), peak CK-MB level (IU/liter) 173 + 230 vs 272 -+332 (p < .02), peak summed ST segment elevation (mm) 3.5 + 4.8 vs 8.2 + 9.9 (p < .005), and QRS score on days 7 to 10, 1.9 + 3.0 vs 4.3 + 3.4 (p < .001). Postinfarction left ventricular ejection fraction was higher in the post-CABS group (53 + 13%) compared with that in control patients (47 + 12%; p < .05). The incidence of total occlusion of the artery to the infarct zone was similar in the post-CABS and control patients (33 vs 27), as was the incidence of one-, two-, and three-vessel disease (artery plus graft). Collateral blood flow to the infarct zone was found in 27 postCABS patients and in 23 control patients. The cause of infarction in post-CABS and control patients was a lesion in a major artery proximal to all branches in seven vs 22 (p < .001), a lesion in a diagonal or marginal artery in 15 vs four (p < .01), and a lesion in a distal small vessel in eight vs one (p < .05). In addition, eight patients with graft and artery occlusion had an occluded native vessel before surgery. Thus patients who have undergone previous CABS have smaller myocardial infarcts and better residual left ventricular function due to the presence of less jeopardized myocardium lying distal to the infarctproducing lesion. Circulation 71, No. 4, 693-698, 1985. THE NUMBER of coronary bypass operations performed annually in the United States was estimated to be 70,000 in 1977 and 160,000 in 1981.' As the proportion of patients with coronary disease who have had coronary artery bypass surgery (CABS) increases, the proportion of such patients among hospital admissions for acute myocardial infarction is also likely to increase. At our institute the prevalence of previous CABS among patients admitted for myocardial infarcFrom the Department of Medicine, Montreal Heart Institute, and the University of Montreal Medical School, Montreal. Supported in part by grants from the Jean-Louis Levesque Foundation and the Montreal Heart Institute Research Fund. Address for correspondence: David D. Waters, M.D., Montreal Heart Institute, 5000 East, Belanger Street, Montreal, Quebec, HIT 1C8 Canada. Received Aug. 27, 1984; revision accepted Dec. 20, 1984. Presented in part at the 57th Annual Scientific Sessions of the American Heart Association, Miami, November 1984. Vol. 71, No. 4, April 1985 tion has increased from 2.3% between 1977 and 1980 to 6.7% in 1980 to 1982 and 11.2% in 1982 to 1984. Myocardial infarction occurring late after CABS is important not only because of its increasing frequency but also because infarct size may be smaller and prognosis better in these circumstances.2 The purpose of this study was to compare indexes of infarct size and angiographic findings early after infarction in 52 patients with infarction 2 or more months after bypass and in 52 control patients.