Myocardial performance and collateral flow after transient coronary occlusion in exercising dogs

Fourteen dogs with prior constriction of the left circumflex (LCf) coronary artery were studied at rest and during treadmill running. Hemodynamics were measured before and after a 1-min LCf occlusion. Coronary and collateral flows were quantitated during occlusion both at rest and during exercise. Group I consisted of 4 dogs with resting collateral flow exceeding one-half (average 78%) of normal flow, and group II consisted of 10 dogs with collateral flows less than one-half (average 30%) of normal. At rest LCf occlusion caused no hemodynamic changes in group I, but stroke volume fell significantly in group II. During running, collateral flow after LCf occlusion doubled in group I, and there was only a small rise in left atrial pressure to 18 mmHg. In group II, collateral flow increased by 50% during running and actually decreased in 4 dogs. Significant cardiac failure developed as stroke volume halved, and left atrial pressure rose to an average 30 mmHg. Therefore exercise-induced depression of left ventricular function in the ischemic heart can be correlated to the amount of coronary collateral flow.