The influence of the size of acute ischaemic myocardial lesions on coronary reserve and left ventricular function in the dog.

Acute ischaemic lesions of 5 and 15% of the left ventricular mass were produced in 10 dogs by ligations of branches of the left anterior descending coronary artery. Under maximal coronary dilatation by Dipyridamole and at constant aortic pressure, an ischaemic lesion of 15% caused reductions of blood flow in the left anterior descending coronary artery of 50% (p less than 0.05), , the R. circumflexus of 36% and of total myocardial blood flow (Argon method) by 44% (p less than 0.02). Parameters of left ventricular function, dp/dtmax and Vmax fell by 26 and 27% respectively (p less than 0.02). Ischaemic lesions of 5% LV mass were detected by 133 Xenon clearance estimations, but had no effect on any of the other variables measured. There was good agreement between estimations of total myocardial blood flow (Argon) and direct measurement of coronary flow with electromagnetic flowmeters (r = 0.957).