EFFECT OF CORONARY-BYPASS SURGERY ON ANAEROBIC MYOCARDIAL LACTATE METABOLISM DURING PACING-INDUCED ANGINA-PECTORIS

Myocardial lactate metabolism was studied by coronary sinus catheterization in nine patients before and 8-12 months after coronary bypasss surgery. Measurements were performed at rest and during atrial pacing increased to a heart rate which produced strong chest pain. The estimation of myocardial lactate extraction and release was facilitated by a constant rate infusion of C-14 lactate and coronary sinus blood flow (CSBF) was measured by thermodilution. Pre-operatively strong chest pain could be elicited in all patients and isotope data indicated a significant myocardial lactate release in all of them, although the net a-cs difference was negative in only half of them. After bypass surgery the maximum tolerable heart rate was increased by 23 beats min-1 and chest pain both at heart rate 110 beats min-1 and at the highest heart rate achieved was reduced or absent in eight of the nine patients. The increase in chest pain during pacing was quantitatively related to the increase in myocardial lactate release, and the correlation between these two variables followed the same course after the operation as it did before. It is concluded that the improvement in chest pain limited cardiac performance after bypass surgery is well correlated with the improvement in myocardial aerboic metabolism.