MYOCARDIAL ISCHEMIA DURING CARDIOPULMONARY BYPASS - HAZARDS OF VENTRICULAR-FIBRILLATION IN PRESENCE OF A CRITICAL CORONARY STENOSIS

  • 1 January 1977
    • journal article
    • research article
    • Vol. 73  (5) , 746-757
Abstract
The effect of a critical coronary artery stenosis on myocardial blood flow and metabolism in the fibrillating heart was assessed by placing 10 dogs on cardiopulmonary bypass, venting the ventricle, inducing ventricular fibrillation and applying critical stenosis to the left anterior descending coronary artery (LAD). Endocardial and epicardial blood flows were measured by the radioactive microsphere technique prior to the application of the stenosis and after 1 h and 2 h of fibrillation. Intramyocardial O2 tension (PO2) and CO2 tension (PCO2) were continuously monitored in the LAD-supplied myocardium by a mass spectrometer probe inserted at midmyocardial depth. Selective arterial-coronary venous lactate differences were determined at control, 1 h and 2 h. At the end of the 2 h period, vital dye injection defined the distribution of the LAD. Endocardial flow to the myocardium of the stenosed LAD was reduced by 50% after 1 h and by 70% after 2 h (P < 0.05). Epicardial flow fell 40% after 1 h and 50% after 2 h (P < 0.05). Endocardial and epicardial flow in the distribution of the unstenosed circumflex coronary artery remained unchanged. Changes in myocardial PO2 and PCO2 in the LAD-supplied myocardium indicated the development of severe ischemia in all 10 dogs and suggested myocardial infarction in 5. There was a conversion from lactate extraction to lactate production during the 2 h period of ventricular fibrillation. The myocardium distal to a critical stenosis suffers a progressive reduction in flow during ventricular fibrillation which does not occur in regions supplied by unstenosed coronary arteries. Thus prolonged fibrillation in the presence of a flow-limiting coronary stenosis may play a role in the pathogenesis of myocardial infarction during coronary bypass surgery.