Peripheral embolization provides evidence for microvascular collaterals in hearts with chronic coronary artery occlusion.

Macroscopic collateral vessels are widely regarded as the primary source of blood flow to collateral-dependent myocardium. Microscopic coronary collateral vessels have also been described, but their functional significance is controversial. Experiments were conducted in 18 anesthetized dogs with chronic coronary artery occlusions. Indices of collateral function demonstrated that all hearts were well-collateralized. The previously occluded coronary artery was cannulated distal to the obstruction for measuring retrograde flow before and after injection of either 13 microns or 84 microns emboli. Mean arterial pressure and heart rate were not altered by coronary embolization. Embolization with 13 micron spheres caused retrograde flow to increase by 43% (n = 11), whereas embolization with 84 micron spheres had no effect on retrograde flow (n = 7). Retrograde flow dislodged occlusive 84 micron spheres, since these spheres were found in the retrograde flow, and since antegrade flow increased by 250% after retrograde flow diversion. These findings demonstrate that collateral vessels less than 84 micron diameter contribute significantly to perfusion of chronically collateral-dependent myocardium.