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 reductions in coronary flow can produce subsequent proportionate reductions in myocardial function and O-2 consumption compatible with myocardial hibernation. Background. Acute studies indicate that myocardial energy utilization can be downregulated during moderate flow reduction. Whether this apparently beneficial adjustment persists into the reperfusion period is unsettled because most postischemic contractile dysfunction 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 similar 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 levels ([mean +/- SEM] 80 +/- 3.1% and 81 +/- 5.1% of control values, both p < 0.05) and then returned to control values within 24 h. Similar proportionate reductions occurred after as few as five cycles of brief total occlusion (79 +/- 5.1% and 83 +/- 1.6% of control values, both again p < 0.05); these persisted with additional occlusions and then returned to baseline values within 3 h. The absence of irreversible injury was documented histologically in both series, Sham animals (n = 5) showed no changes in regional function or O-2 consumption throughout similar experimental periods. Conclusions. Moderate decreases in coronary flow or repeated brief coronary occlusions can be followed by proportionate reversible reductions in regional systolic function and O-2 consumption compatible with the traditional definition of myocardial hibernation. These findings emphasize the complexity of myocardial responses to flow restriction and call attention to limitations in characterizing reversibly hypocontractile myocardium as simply hibernating or stunned. (C) 1997 by the American College of Cardiology.