Compensatory subendocardial hyperkinesis in the cat is abolished during coronary insufficiency outside an acutely ischaemic region

OBJECTIVE: The aims were to determine (1) whether acute coronary occlusion provoked uniform hyperkinesis in remote non-ischaemic myocardium, and (2) how subsequent coronary stenosis affected such hyperkinesis. METHODS: Two pairs of ultrasonic crystals were placed in the anterior left ventricular midwall of nine pentobarbitone anaesthetised open chest cats. One pair (longitudinal) ran parallel to subendocardial fibres; the other pair (circumferential) was aligned with subepicardial and mid-myocardial fibres. Following circumflex coronary occlusion, subsequent hypoperfusion of the anterior wall was established by controlled constriction of a shunt line from the right subclavian artery to the left main coronary artery in two discrete steps. RESULTS: Following circumflex occlusion maximum systolic shortening of segments aligned to subendocardial fibres increased from 6.7(SEM 0.9)% to 11.5(1.4)% (p less than 0.001), whereas circumferential segment shortening was unchanged, at 12.2(0.8)% v 14.1(1.1)%. During mild shunt stenosis [delta P = 42(2) mm Hg] subendocardial tissue blood flow in the anterior wall decreased by 42(10)% (p less than 0.001), and longitudinal segment shortening decreased from 11.5(1.4)% to 6.9(1.1)% (p less than 0.001). Corresponding shortening of circumferential segments did not change. During severe shunt stenosis [delta P = 52(3) mm Hg] subendocardial tissue blood flow decreased further, and shortening of longitudinal segments approached zero value (p less than 0.001). CONCLUSIONS: Compensatory hyperkinesis of remote non-ischaemic myocardium following an acute coronary occlusion may depend mostly on augmented subendocardial contraction.