Temporal sequence of dynamic contractile characteristics in ischemic and nonischemic myocardium after acute coronary ligation

The contractile characteristics of ischemic, border and nonischemic myocardium were studied In vivo for 4 hours with coronary ligation in 15 dogs utilizing Walton-Brodle strain gauge arches and “mercury in Silastic tubing” segment length gauges. In the ischemic zone, preejection tension fell precipitously by 17.3 ± 3.0 percent (mean ±1 standard error of the mean) (P < 0.02) within 15 seconds and 30.4 ± 5.1 percent (P < 0.001) within 1 minute. A gradual further decrease by 66.0 ± 6.3 percent of control values was seen after 4 hours. The rate of rise of tension ($\text{dT}\text{dt}$) showed similar changes. Tension during ejection also decreased abruptly and dramatically within the first 3 to 12 seconds after occlusion and exhibited a characteristic negative slope indicating aneurysmal bulging. A decrease from +10 ± 1.3 to ?4.3 ± 0.8 occurred In 15 seconds, although subsequently the negative slope diminished.Segment length similarly exhibited a continuous Increase in preejection lengthening over 10 to 30 minutes and segment shortening during ejection was replaced by segment lengthening during aneurysmal bulging. Phasic segment length showed increases of 22 percent in the first 15 seconds, 44 percent in 1 minute and 138 percent in 15 minutes, then a gradual decline for 4 hours. The border and nonischemic zones showed minimal and inconsistent changes.Therefore, the Ischemic myocardium is still able to generate tension, although at a progressively reduced level after coronary occlusion. Aneurysmal bulging takes place only during ejection. It becomes apparent 3 to 12 seconds after occlusion, Is maximal at 15 minutes and then decreases, probably as a result of reduced compliance. The data sugggest that the Ischemic zone is operating on a depressed lengthtension curve, but no significant changes are evident in the nonischemic and border zones of the left ventricle.