Nonmechanical Factors Affecting Aortocoronary Vein Graft Flow

To study aortocoronary vein graft flow, hemodynamic measurements were made in 17 patients with 22 grafts while on cardiopulmonary bypass during ventricular fibrillation and sinus rhythm and 15 minutes after termination of cardiopulmonary bypass. When compared with graft flow to the stable working heart, flow to the nonworking heart in sinus rhythm was reduced 50%. When fibrillating, the nonworking heart received 33% more flow than when in sinus rhythm but still significantly less flow than the working heart. All hemodynamic parameters measured, including flow in 12 grafts, remained stable between 15 minutes and 60 minutes following cardiopulmonary bypass. In contrast, heart rate and flow in 10 grafts fell within five minutes after 1 mg of propranolol was given intravenously. Although it was still reduced, heart rate had begun to rise 30 minutes after propranolol, but graft flow did not begin to return toward predrug control levels until over 60 minutes after drug administration. Further reduction in aortocoronary vein graft flow after heart rate had started to increase supports the possibility of a direct propranolol action reducing myocardial oxygen consumption in addition to its bradycardiac effect. This study shows the sensitivity of intraoperative vein graft flow to physiological and pharmacological factors and the need to standardize the technique and timing of flow measurements if their value for predicting long-term graft patency is to be determined.