Estimation of Perfused Coronary Capillary Surface Area in Patients Undergoing Coronary Arterial Bypass Grafting

We utilized indicator-dilution techniques to estimate the activity of capillary endothelium- bound angiotensin converting enzyme (ACE) in twelve patients (age: 47–72 yrs) undergoing coronary arterial bypass graft (CABG) surgery. Measurements were performed before and after graft connection in the coronary (C) vascular bed and, at the same time, similar measurements were performed in the pulmonary (P) vascular bed. The specific ACE substrate, 3H-benzoyl-Phe-Ala-Pro (40µCi or 2 nmol), was injected as a bolus into the root of aorta or central vein and immediately blood was withdrawn from the coronary sinus or radial artery catheter, for C and P measurements, respectively. The procedure did not produce noticeable changes in routinely monitored cardiopulmonary parameters. Plasma concentrations of surviving substrate (S) and product (P: 3H-benzoyl-Phe) were estimated and substrate metabolism (M=P/(S+P)), enzyme activity (v=ln(S+P)/S)) and the parameter Amax/Km (proportional to perfused capillary surface area) were calculated over the entire arterial outflow concentration curve. After CABG, coronary blood flow increased by 40.6% (354±32 to 498±42 ml/min), whereas pulmonary blood flow remained unchanged (4.9±0.2 to 5.2±0.3 1/min). Perfused pulmonary capillary surface area also remained unaltered. However, perfused coronary capillary surface area increased significantly 1.7-, 2.3-, 4.1- and 3.9-fold in patients receiving 2(n=3), 3(n=4), 4(n=3) and 5(n=2) grafts, respectively. Overall, transpulmonary M and v values remained unaltered, whereas transcoronary M and v values increased (49.3±3% to 77.2±1.4% and 0.67±0.12 to 1.43±0.14, respectively). This procedure can provide quantitative diagnosis of coronary occlusion and an index of reperfusion after CABG.