Effects of Coronary Bypass Graft Occlusion

High-fidelity recordings of left ventricular (LV) pressure and its corresponding first derivative (dP/dt), electrocardiogram, and systemic arterial pressure were obtained intraoperatively following insertion of aortocoronary saphenous vein bypass grafts in eight men. During sequential 3-min periods, the bypass grafts were, in turn, open, occluded by vascular clamps, and opened by releasing the clamps. Peak dP/dt averaged 1342 mm Hg/sec before graft occlusion, fell to 1223 mm Hg/ sec during occlusion, and rose following release of occlusion to 1373 mm Hg/sec. LV end-diastolic pressure (LVEDP) averaged 14.5 mm Hg before, 17.6 mm Hg during, and 16.1 mm Hg after graft occlusion. Arterial systolic and diastolic pressure and heart rate showed little change (P > 0.05) throughout the experiments. Left ventricular performance as gauged by peak dP/dt/LVEDP decreased an average of 25% (P <0.001) during graft occlusion and returned to control levels following release of occlusion. Total vein graft blood flow, measured immediately before the occlusion experiments, averaged 164 ml/min. Good correlation was lacking between vein graft blood flow and performance changes during graft occlusion in individual patients. Aortocoronary vein bypass grafts are capable of participating directly in the mechanical events of the cardiac cycle. Acute graft occlusion can impair, while restoration of graft flow can improve, left ventricular performance.