Relationship between epicardial S-T segment changes and myocardial metabolism during acute coronary insufficiency.

Canine left ventricular wall metabolites (ATP, creatine phosphate, glycogen, glucose, glucose-6-phosphate, and lactate) were assessed in the ischemic region of the wall after 17 minutes of ligation of the left anterior descending coronary artery at its midlevel. Variations in the degree of lactate accumulation were found between different sites in the same ischemic region and between the outer and the inner left ventricular wall at the same site. High levels of lactate were associated with S-T segment elevation in the epicardial electrocardiogram, but no lactate accumulation or only mild lactate accumulation was found at isoelectric sites. Lactate accumulation at isoelectric sites was higher in the outer wall than it was in the inner wall; the opposite tendency was observed at sites of S-T segment elevation. In addition to high lactate levels, sites of S-T segment elevation demonstrated a more pronounced depletion of ATP and creatine phosphate, indicating not only a marked anaerobic glycolysis but also a more pronounced overall anaerobic stress. No relationship was found, however, between the absolute magnitude of S-T segment elevation and the degree of lactate accumulation or ATP depletion at sites of S-T segment elevation within the ischemic region. The data obtained in this study demonstrate that during myocardial ischemia epicardial sites of S-T segment elevation are sites of pronounced subendocardial and epicardial ischemia and of anaerobic metabolism.