REGIONAL MYOCARDIAL DIMENSIONS FOLLOWING CORONARY-ARTERY BYPASS GRAFTING IN PATIENTS - RELATIONSHIP OF FUNCTIONAL DETERIORATION TO GRAFT OCCLUSION

Abstract

The direct relationship between graft flow and regional midwall myocardial function was not documented in patients. The present study was designed to quantitate the effects of coronary artery bypass grafting on regional myocardial mechanics distal to a coronary artery obstruction. In 21 patients with subtotal or total occlusion of the left anterior descending (LAD) coronary artery underwent coronary artery bypass grafting. After completing the aortic and coronary anastomoses, 2 miniature ultrasonic dimension transducers (2.5 mm diameter) were positioned in the minor axis of the anterior left ventricular free wall and were allowed to move. The transducers were placed at midwall depth and areas of clinically apparent myocardial fibrosis were not utilized as sites of implantation. During control, 30 min following the termination of cardiopulmonary bypass, regional myocardial dimensions, pulmonary artery diastolic pressure, arterial pressure and heart rate were recorded with all saphenous vein grafts open and after 30 s of single vein graft occlusion. These measurements were repeated during atrial pacing at a rate of 128 .+-. 4 beats/min. Data equalled the standard error of the mean. During control graft occlusion resulted in a regional decrease in systolic excursion from 1.3 .+-. 0.1 to 1.0 .+-. 0.2 mm (P < 0.01), and decrease in the rate of shortening from 8.7 .+-. 0.2 to 6.2 .+-. 1.1 mm/s (P < 0.05) heart rate, mean arterial pressure and diastolic pulmonary artery pressure were unchanged. Graft occlusion with atrial pacing resulted in an exaggerated decrease in regional systolic excursion, from 1.2 .+-. 0.2 to 0.6 .+-. 0.2 mm (P < 0.01) and rate of shortening, from 9.4 .+-. 1.5 to 4.4 .+-. 0.2 mm/s (P < 0.01). For the group of patients studied, end-diastolic lengths were unchanged with graft occlusion during control and atrial pacing. Isolated patients demonstrated regional dyskinesia as evidenced by holosystolic bulging after graft occlusion. These studies in patients have documented for the 1st time that despite a constant preload, afterload and heart rate, regional myocardial function following coronary artery bypass grafting is dependent upon adequate graft flow especially during stress.