Changes in myocardial contraction pattern during initial reperfusion.
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.
Rynning
S E
SE
Department of Surgery, University of Bergen, Haukeland Hospital, Norway.
Birkeland
S
S
Hexeberg
E
E
Grong
K
K
D000818:Animals; D002415:Cats; D003326:Coronary Circulation; D006439:Hemodynamics; D008297:Male; D009200:Myocardial Contraction; D017202:Myocardial Ischemia / Q000503:physiopathology; D015425:Myocardial Reperfusion; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology