Ischaemia induced development of functional coronary collateral circulation in ponies

The response of coronary collaterals in nine ponies subjected to repeated reversible occlusions (2 min duration, 30 min interval) of the left anterior descending coronary artery was studied at rest. Each pony was instrumented with a Doppler flowmeter and hydraulic cuff occluder around the left anterior descending coronary artery, left ventricular subendocardial sonomicrometers, and a left ventricular micromanometer. Initial occlusions increased end diastolic myocardial segment length by 3% and decreased segment systolic shortening, stroke work, and velocity of shortening by 103%, 95%, and 79% respectively in the left ventricular apex. Left ventricular systolic and end diastolic pressure, peak positive dP/dt, and heart rate were not significantly changed by occlusion. After 421(70) (mean(SEM)) occlusions no sustained alterations in myocardial segment function occurred in response to occlusion. Thus the presence of a subendocardial plexus did not protect against a severe loss of myocardial segment function when the ponies were initially subjected to occlusions of the left anterior descending coronary artery. However, repeated reversible occlusions enhanced coronary collateral blood flow such that it was adequate to maintain left ventricular function in the absence of left anterior descending coronary artery flow. It is concluded that the pony is highly suitable for use in studies of coronary collateral circulation because of its coronary anatomical similarity to man and its capacity to develop functional collateralisation.