Critical importance of ensuring cardioplegic delivery with coronary stenoses

This study examines the relative importance of the duration of ischemia versus the adequacy of cardioplegic distribution and protection in hearts with coronary stenoses. Of 18 dogs on cardiopulmonary bypass, 12 underwent critical narrowing (greater than 90%) of the left circumflex artery (LCA) and total occlusion of the anterior descending coronary artery (LAD). In six dogs (control) the coronary arteries were patent. A 16 degrees C blood cardioplegic solution was given at 20 minute intervals of aortic clamping. In control dogs and in six dogs with stenoses, the aorta was clamped for 60 minutes. In the latter group, the stenoses were removed after 20 and 40 minutes to simulate sequential completion of grafts and better cardioplegic distribution. In the remaining dogs with stenoses, the aorta was clamped for only 30 minutes, with stenoses removed after the heart had been returned to the beating empty state for 30 minutes to simulate doing distal grafts with cardioplegic protection and proximal grafts during reperfusion (traditional technique). With sequential grafting, myocardial temperature was lower (16 degrees C versus 22 degrees C) and incidence of reperfusion fibrillation less than with the traditional technique. Despite a greater ischemic interval, sequential grafting with adequate cardioplegic distribution resulted in less lactate washout (5 +/- 15 versus 35 +/- 6 cc/100 gm/min), greater recovery of compliance, and higher stroke work indices (1.32 +/- 0.12 versus 0.75 +/- 0.15 kg-m/min). We conclude that the success of myocardial protection with potassium cardioplegia in hearts with coronary stenoses is related more to ensuring its distribution than to limiting the duration of ischemic arrest with the false assumption that the heart is reperfused adequately while proximal grafts are completed in the beating empty state.