Effects of afterload elevation on the ischemic myocardium in isolated, paced canine heart with partial coronary stenosis

Abstract

The effect of afterload elevation on the ischemic myocardium was examined in an isolated, paced canine heart with a partial coronary stenosis. The coronary blood flow of the left circumflex coronary artery was reduced to approximately one-third of the values before stenosis. The left circumflex coronary stenosis produced a decrease in global ventricular function, a decrease in systolic shortening and deviation of the ST-segment of the epicardial electrocardiogram and an increase in myocardial carbon dioxide (CO 2) tension of the ischemic region. Then, afterload elevation with constant preload decreased the myocardial CO 2 tension and improved the ST-segment deviation of the ischemic myocardium. Mechanical function, estimated by the relation between mean aortic pressure and systolic shortening, also improved with elevation of mean aortic pressure. In contrast, afterload elevation combined with preload elevation did not improve ischemic injury, as estimated by myocardial CO 2 tension, and did not improve ST-segment deviation or mechanical function despite an increase in left circumflex coronary flow. These results suggest that the elevation of afterload pressure under constant preload improves ischemia produced by a partial coronary stenosis due to increased coronary blood supply; however, the preload elevation counterbalances the beneficial effects of afterload elevation.