Myocardial ischemia during cardiopulmonary bypass. The hazards of ventricular fibrillation in the presence of a critical coronary stenosis

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 one hour and 2 hours of fibrillation. Intramyocardial oxygen tension (Po2) and carbon dioxide tension (Pco2) were continuously monitored in the IAD-supplied myocardium by a mass spectrometer probe inserted at midmyocardial depth. Selective arterial-coronary venous lactate differences were determined at control, one hour, and 2 hours. At the end of the 2 hour period, vital dye injection defined the distribution of the LAD. Endocardial flow to the myocardium of the stenosed LAD was reduced by 50 per cent after one hour and by 70 per cent after 2 hours (p