[Myocardial metabolism during coronary perfusion at 10 degrees C with or without cardioplegia associated with potassium]

Abstract

Myocardial metabolism was studied during coronary perfusion at 10 degrees c with haemodiluted blood by sampling the coronary sinus blood of 20 patients undergoing aortic valve replacement. The patients were divided into four groups : Group 1 with continuous coronary perfusion at 10 degrees c ; Group 2 : continuous perfusion at 10 degrees c with Potassium cardioplegia ; Group 3 : discontinuous coronary perfusion at 10 degrees c ; Group 4 : discontinuous perfusion at 10 degrees c with Potassium cardioplegia. In groups 1 and 2, coronary blood flow remained constant at an average of 200 ml/mn. Cardioplegia did not affect the peripheral coronary resistances at this temperature. During coronary perfusion the average myocardial oxygen consumption was 1.38 vol/mn (Group 1) and 0.18 vol/mn (Group 2), p < 0.01. This reduced oxygen consumption results in a fall in the average amount of oxygen extracted from 4.8 p.100 (Group 1) to 1.2 p.100 (Group 2) p < 0.01. At the end of coronary perfusion lactic acid production was not observed in Groups 1 and 2. Ten minutes after coming off bypass, the percentage of oxygen extraction was nearly the same in both groups (Group 1 : 38.4 p.100 ; Group 2 : 43.2 p.100). Systemic arterial lactic acid levels tended to be higher than those of coronary sinus blood in both groups. With discontinuous coronary perfusion and an average period of myocardial anoxia of 45 mn, metabolic acidosis was observed, greater in Group 3 than in Group 4 (p < 0.05) when the aorta was unclamped. Ten minutes after the end of bypass, despite normal levels of oxygen extraction, myocardial lactate production was observed in both groups. The enzyme levels, in particular the CPK MB isoenzyme, in the coronary sinus blood, remained low throughout operation in all four groups. Deep, stable and constant myocardial hypothermia (10 degrees c) induced by coronary perfusion with haemodiluted blood, affords excellent myocardial protection ; it was not possible to show the complementary benefits of Potassium cardioplegia at such low temperatures.