The clinical significance of perioperative myocardial infarction (MI) after coronary artery bypass surgery is not known. Therefore, strategies for the risk stratification of these patients do not exist. This study was undertaken to define the effect of perioperative MI on prognosis after discharge from the hospital and to develop an approach to the risk stratification of these patients. prognosisl'2'6-8"12"14"16"18 and those showing no effect.3-5,9'10"13'17 It is generally agreed that perioperative MI increases in-hospitalFrom the

This study tested the hypothesis that myocardial tissue acidosis is responsible for maintenance of reduced arteriolar tone distal to a severe coronary arterial stenosis. Domestic swine (n=10) were instrumented with a coronary arterial stenosis that reduced vessel diameter 80%. Measurements of hemodynamic indexes were made 1) before stenosis, 2) at 5, 20, and 60 minutes after stenosis placement, and 3) after each of three, 20-minute NaOH infusions (0.05 M, 0.1 M, and 0.5 M) distal to the stenosis (group 1). Intracellular pH at the end of 30 minutes of 0.5 M NaOH infusion distal to the stenosis was measured in a second group (n=6) of swine (group 2). After stenosis placement in group 1, endocardial blood flow declined significantly, and evidence of regional acidosis (increased coronary venous Pco2 and decreased coronary venous pH) and ischemia (lactate production) developed. One hour later, evidence of acidosis persisted, though to a lesser extent. Myocardial oxygen and lactate metabolism exhibited similar patterns. Infusion of 0.5 M NaOH (0.38 ml/min) reduced (p < 0.01) distal zone epicardial blood flow but did not change endocardial flow. Regional myocardial oxygen extraction (75 ±8%, mean+SD) and consumption (8.2+±2.3 ml/min/100 g) also declined significantly (p<0.01) in response to 0.5 M NaOH infusion compared with 60 minutes after stenosis (86±4 and 12.4+2.8 ml/min/100 g respectively). The pH of coronary venous blood (7.41+0.05) was elevated (p <0.01) by 0.5 M NaOH above prestenosis (7.36+±0.03) and 60-minute poststenosis levels (7.33+±0.04). Measurement of intracellular pH (14C-DMO/3H-inulin technique) in group 2 animals showed that distal zone pH (7.00±0.11) after 0.5 M NaOH infusion was at a level similar to that in normal myocardium in a nonstenosed region of the heart. Thus, because endocardial blood flow was unchanged during 0.5 M NaOH infusion, even though pH of coronary venous blood reached systemic levels and intracellular pH increased significantly, tissue acidosis is probably not required for maintenance of arteriolar dilation distal to a severe coronary arterial stenosis. The data support the hypothesis that tissue acidosis capable of mediating acute changes in coronary arteriolar tone does not have a major role in the long-term maintenance of reduced vascular tone distal to a coronary arterial stenosis. (Circulation 1989;79:890-898