Hyperkinesis without the Frank-Starling mechanism in a nonischemic region of acutely ischemic excised canine heart.

To determine the essential mechanism of increased systolic wall motion, i.e., hyperkinesis, in a nonischemic region (NIR) during acute ischemia, we simultaneously evaluated global and regional function of the excised, cross-circulated canine left ventricle connected to a volume servo pump before and after coronary occlusion. Regional areas were determined with pairs of orthogonal subendocardial sonomicrometers in the ischemic region (IR) and NIR. After coronary occlusion with left ventricular end-diastolic and stroke volumes kept constant, the amount of systolic area shrinkage (delta A) in NIR increased by 33 +/- 41% (p less than .05), despite a decrease in end-diastolic regional area by 3 +/- 4% (p less than .05). Regional work obtained from the wall tension-regional area (T-A) loop in NIR decreased by 50 +/- 24% due to a similar decrease in afterload despite the presence of hyperkinesis, indicating regional systolic unloading. When left ventricular end-diastolic volume was subsequently increased with a constant stroke volume, delta A in NIR increased at the expense of a further decrease in delta A in IR. The end-systolic T-A relationship in NIR remained unchanged, whereas that in IR markedly shifted rightward, suggesting that the contractile state of NIR was constant. These results indicate that hyperkinesis in NIR during acute ischemia can occur without a utilization of the Frank-Starling mechanism or an enhancement of regional contractile state, and that the essential mechanism of this phenomenon is regional afterload reduction due to an intraventricular mechanical interaction between IR and NIR.