Selective enhancement of function of stunned myocardium by increased flow.

Abstract

Although augmentation of flow does not improve the performance of normal myocardium, the hyperemic response after brief coronary occlusion is associated with transient hyperfunction in the previously ischemic region. In this study we assessed the effect of vasodilator-enhanced coronary blood flow on the systolic function of postischemic stunned myocardium. In 18 open-chest, anesthetized dogs the anterior descending artery was occluded for 5 min, followed by a 10 min period of reflow, repeated 12 times with a final 90 min recovery period. After the recovery period, either 0.06 mg/min dipyridamole (n = 6), 1 mg/min papaverine (n = 6), or 1.5 micrograms/kg/min nitroglycerin (n = 6) was infused intravenously for 15 min. Regional myocardial blood flow, which had returned to normal before administration of vasodilator, was increased 150% above baseline by dipyridamole and 80% by papaverine, but was unchanged by nitroglycerin. Segmental shortening decreased after repeated occlusions: from 17.5% to 0.9% in the group later treated with dipyridamole, from 18.6% to 6.7% in the papaverine group, and from 19.2% to-1.9% in the nitroglycerin group (p less than .005 for all groups). Segmental shortening increased to 8.8% after dipyridamole, 13.6% after papaverine, and 5.1% after nitroglycerin (p less than .05 for all groups), although the load-independent end-systolic pressure-length relationship (ESPLR) showed a significant shift to the left, reflecting enhanced performance, only after dipyridamole and papaverine. For all dogs combined, the percent improvement in ESPLR was correlated with the percent increase in flow (R = -.73, p less than .001). Performance was unchanged in the control region despite similar augmentation of flow.(ABSTRACT TRUNCATED AT 250 WORDS)