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Am J Physiol Heart Circ Physiol 266: H980-H986, 1994;
0363-6135/94 $5.00
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AJP - Heart and Circulatory Physiology, Vol 266, Issue 3 980-H986, Copyright © 1994 by American Physiological Society

ARTICLES

Changes in myocardial contraction pattern during initial reperfusion

S. E. Rynning, S. Birkeland, E. Hexeberg and K. Grong
Department of Surgery, University of Bergen, Haukeland Hospital, Norway.

The characteristics of hypercontraction during initial reperfusion were studied in 10 pentobarbitone-anesthetized cats. The left anterior descending coronary artery was occluded for 10 min followed by 1 h of reperfusion, and regional function was assessed by two cross-oriented pairs of sonomicrometers placed in the left ventricular anterior wall. At 1 min of reperfusion (hyperfunctional phase) there was an uniform contraction pattern with 90% recovery of ejection shortening in both circumferential and longitudinal segments. During initial hypercontraction, end-diastolic segment lengths remained unchanged, whereas end-systolic segment lengths decreased transiently. Inotropic stimulation during reperfusion in four additional animals also affected end-systolic lengths more than end-diastolic lengths. This suggests that the initial hyperfunctional phase is due to an inotropic stimulation of the stunned myocardium, most probably caused by intracellular Ca2+ overload. At 5 min of reperfusion a nonuniform contraction pattern had developed with 68% recovery of shortening in circumferential segments vs. 25% in longitudinal segments. The decreased performance in longitudinal segments was paralleled by a delayed start of contraction as well as a decreased velocity of contraction. Because longitudinal segment shortening is a sensitive parameter of subendocardial performance, our results indicate a brief transmural hypercontraction followed by increasing dysfunction (stunning) in the subendocardial layer.


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