Intraoperative relationships between regional myocardial distribution of bypass graft flow and the coronary collateral circulation

Abstract

The relationships between collateral coronary flow and the volume and regional distribution of graft blood flow were studied in 14 patients undergoing coronary artery bypass grafting. With the use of an electromagnetic flowmeter, graft flow was quantitated and the regional distribution of this flow was measured by radionuclide techniques. Two separate solutions containing macroaggregated human serum albumin particles labeled with 123 I and 99m Tc were injected into the bypass grafts. Specially designed sterile scintillation probes were used to count both radionuclides simultaneously to map the distribution of the macroaggregates over 53 areas covering the surface of the heart. Flow in milliliters per minute was calculated for each of the 53 regions by combining electromagnetic graft flow and the percentage distribution of the radioactivity. Injections were made into two separate grafts in two patients, into the same graft with an adjacent graft first open and then temporarily occluded in seven patients, into a graft with two sequential anastomoses in four patients, and into a single graft before and during reactive hyperemia in one patient. In nine patients, there was no evidence of collateral communication between the anterior, lateral, and posterior regions of the myocardium, regardless of the presence or absence of angiographically visualized collateral vessels. In three patients, there was clear demonstration of an area of common perfusion over the apex of the heart, supplied by both the anterior and posterior coronary arteries. Only two patients had collateral flow between closely adjacent regions of the anterolateral left ventricle and neither had angiographically demonstrable collateral vessels. In four patients with sequential anastomoses to adjacent areas of myocardium, both the total volume and the distribution of flow were improved by grafting both areas. From these data, we have concluded that (I) bypass graft flow is distributed to localized regions of myocardium, (2) collateral blood flow rarely occurs between adjacent areas of myocardium, (3) sequential or multiple grafts are beneficial in completely revascularizing adjacent areas of underperfused myocardium, and (4) concepts of coronary collateral blood flow and function derived from experimental animals may not apply to patients, and human data are necessary for application to the clinical situation.