The time relationship for recovery of mechanical function, the intramyocardial electrogram and coronary flow after brief periods of regional myocardial ischemia, was studied in conscious dogs. Total left vemtricular (LV) function was assessed with measurements of LV systolic and diastolic pressures, rate of change of LV pressure (dP/dt), and dP/dt/P. Regional LV function was assessed with measurements of regional segment length and velocity of shortening. An implanted hydraulic occluder on either the left anterior descending or circumflex coronary artery was inflated for 5- and 15-min periods on separate days. A 5-min occlusion depressed overall LV function transiently, but just before release of occlusion overall function had nearly returned to control. At this time regional function in the ischemic zone was still depressed to the point of absent shorteining or paradoxical motion during systole and was associated with marked ST segment elevation (+ 10 +/- 2.2 mV) at the site where function was measured. With release of occlusion and reperfusion the intramyocardial electrogram returned to normal within 1 min, and reactive hyperemia subsided by 5-10 min. In contrast to the rapid return to preocclusion levels for coronary flow and the electrogram, regional mechanical function remained depressed for over 3 h. A 15-min coronary occlusion resulted in an even more prolonged (greater than 6 h) derangement of function in the ischemic zone. Thus, brief periods of coronary occlusion result in prolonged impairement of regional myocardial function which could not have been predicted from the rapid return of the electrogram and coronary flow. These observations indicate that brief interruptions of coronary flow result either in a prolonged period of local ischemia or that alterations of mechanical induced by ischemia far outlast the repayment of the oxygen debt.
G R Heyndrickx, R W Millard, R J McRitchie, P R Maroko, S F Vatner
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