A functional estimate of overlap between adjacent coronary circulations in the dog.

We measured the functional overlap between the left arterior descending (LAD) and the rest of the coronary arteries in the dog heart. The measurements were performed by loading only the field of the LAD with 133Xe gas via a close-arterial injection during normal perfusion. The LAD perfusion was then interrupted and blood was allowed to flow retrograde from the distal LAD segment. This caused a condition of extremely low flow in the tissue perfused by the LAD. Examination of the washout kinetics revealed two distinct compartments. The slow compartment accounted for 97% of the injected Xenon and was assumed to represent the central ischemic field of the LAD. The fast component accounted for only 3% of the injected tracer and was assumed to include all regions of admixture between the LAD and other coronary vessels at the lateral borders. Thus, less than 3% of the LAD's field functionally communicates with the rest of the coronary circulation.