PROPORTIONATE REVERSIBLE DECREASES IN SYSTOLIC FUNCTION AND MYOCARDIAL OXYGEN-CONSUMPTION AFTER MODEST REDUCTIONS IN CORONARY FLOW - HIBERNATION VERSUS STUNNING

Objectives. This study sought to determine whether modest short-term r eductions in coronary flow can produce subsequent proportionate reduct ions in myocardial function and O-2 consumption compatible with myocar dial hibernation. Background. Acute studies indicate that myocardial e nergy utilization can be downregulated during moderate flow reduction. Whether this apparently beneficial adjustment persists into the reper fusion period is unsettled because most postischemic contractile dysfu nction has been presumed to represent stunned or irreversibly injured myocardium. Methods. Responses of regional myocardial function and O-2 consumption were assessed in chronically instrumented dogs after simi lar to 50% reductions in flow for 2 h (n = 8) or repeated 2-min total coronary occlusions (n = 6). Results. When unrestricted perfusion was restored after sustained partial occlusions, regional function and O-2 consumption stabilized at proportionate, systematically decreased lev els ([mean +/- SEM] 80 +/- 3.1% and 81 +/- 5.1% of control values, bot h p < 0.05) and then returned to control values within 24 h. Similar p roportionate reductions occurred after as few as five cycles of brief total occlusion (79 +/- 5.1% and 83 +/- 1.6% of control values, both a gain p < 0.05); these persisted with additional occlusions and then re turned to baseline values within 3 h. The absence of irreversible inju ry was documented histologically in both series, Sham animals (n = 5) showed no changes in regional function or O-2 consumption throughout s imilar experimental periods. Conclusions. Moderate decreases in corona ry flow or repeated brief coronary occlusions can be followed by propo rtionate reversible reductions in regional systolic function and O-2 c onsumption compatible with the traditional definition of myocardial hi bernation. These findings emphasize the complexity of myocardial respo nses to flow restriction and call attention to limitations in characte rizing reversibly hypocontractile myocardium as simply hibernating or stunned. (C) 1997 by the American College of Cardiology.