Postischaemic hypercontraction is enhanced in ischaemically injured canine myocardium

The aim was to identify the role of calcium flux in the pathogenesis of transient overshoot of regional myocardial contraction after brief ischaemia, ie, postischaemic hypercontraction.

Ten anaesthetised mongrel dogs were examined under open chest conditions. The left anterior descending coronary artery was initially occluded for 2 min and reperfused for 10 min. A further period of coronary occlusion of 15 min duration was followed by 15 min reperfusion to produce postischaemic regional dysfunction. A third occlusion of 2 min duration was followed by 10 min reperfusion to induce postischaemic hypercontraction. Coronary blood flow was measured using an ultrasonic transit time flow meter. Segment length was measured by ultrasonic microcrystals.

Postischaemic hypercontraction after 2 min coronary occlusion was exaggerated in ischaemically injured myocardium. The 10 dogs were divided into two groups, a control group (n = 5) and a verapamil treated group (n = 5), and were exposed to a final 2 min period of coronary occlusion with or without verapamil in the ischaemically injured myocardium. Postischaemic hypercontraction was attenuated in the verapamil treated group compared with the control group.

Exaggeration of postischaemic hypercontraction in ischaemically injured myocardium may be mediated by a trans-sarcolemmal calcium flux. Changes in calcium flux may play a role in the pathogenesis of this phenomenon in the normal myocardium.