The effects of on-pump and off-pump coronary artery bypass grafting on intraoperative graft flow in arterial and venous conduits defined by a flow/pressure ratio

Abstract

Despite profound differences in the neurohumoral milieu in patients undergoing on-pump and off-pump coronary artery bypass grafting, it is uncertain how this affects graft blood flow. We prospectively recorded intraoperative transit-time flow measurements (MediStim BF 2004; MediStim AS, Oslo, Norway) in all internal thoracic artery, radial artery, and long saphenous vein conduits in patients undergoing off-pump and on-pump bypass grafting by a single surgeon. We calculated a flow/pressure ratio as a ratio of mean graft flow to mean arterial pressure for all the conduits just before chest closure. Transit-time flow measurements were recorded in 266 grafts (203 off-pump; 63 on-pump) in 100 patients (80 off-pump; 20 on-pump). Overall, mean graft flow (milliliters per minute) was higher for all grafts in the on-pump group despite a significantly lower mean arterial pressure compared with the off-pump group (P < .05). Consequently the flow/pressure ratio was greater for all grafts in the on-pump group (internal thoracic artery 0.55 vs 0.35, radial artery 0.61 vs 0.36, long saphenous vein 0.77 vs 0.55). Overall mean graft flow was significantly greater in the long saphenous vein than in the internal thoracic artery (P < .001) and radial artery (P = .001), but there was no significant difference in mean graft flow in internal thoracic artery or radial artery grafts within each group. In comparison with the off-pump group, the overall mean graft flow and flow/pressure ratio were significantly higher and mean arterial pressure significantly lower for all grafts in the on-pump group. These findings are probably a result of vasodilatation resulting from cardiopulmonary bypass and reactive hyperemia resulting from a period of ischemia. There was no difference in the mean graft flow and flow/pressure ratio of arterial grafts, which were significantly less than for long saphenous vein grafts. In patients with unstable angina and/or hemodynamic instability, in whom rapid and maximum restoration of myocardial perfusion is a priority, potentially lower graft flow in arterial grafts and off-pump surgery should be considered.