Is postsystolic shortening area always a marker of myocardial ischaemia?

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Abstract
Postsystolic shortening area has been shown to be a sensitive marker of myocardial ischaemia in a one-vessel model. We tested whether postsystolic shortening provoked by interaction between ischaemic and nonischaemic regions is reduced in a two-vessel model, one vessel occluded and one subjected to coronary artery stenosis. Regional function in the left ventricular anterior wall was studied by orthogonal sonomicrometry during left coronary underperfusion in 14 pentobarbital-anaesthetized cats with an acute circumflex coronary artery occlusion. Left coronary underperfusion in two discrete steps decreased subendocardial blood flow in the left ventricular anterior wall to on average 60% (P < 0.001) and 20% (P < 0.001) of control value, while subepicardial flow did not change. End-diastolic lengths of longitudinal segments increased markedly even during mild subendocardial underperfusion, whereas end-diastolic lengths of circumferential segments only increased during severe subendocardial underperfusion with concomitant increase of left ventricular end-diastolic pressure. Systolic shortening, pressure-length loop area and shortening velocity of circumferential segments did not change. In contrast, systolic shortening and total pressure-length loop area of longitudinal segments decreased progressively approaching zero values during severe coronary underperfusion. Shortening velocity of longitudinal segments also decreased progressively during experimental protocol whereas postsystolic shortening area did not change. postsystolic shortening area is not a marker of subendocardial ischaemia in a two-vessel model which indicates that postsystolic shortening is primarily a phenomenon related to model of ischaemia. End-diastolic lengthening is predominant in the longitudinal axis of the heart during subendocardial ischaemia.