Reduction of coronary flow in the native circulation after bypass. Observations in a hydraulic model of the cardiovascular system.

The effects of aorta-coronary bypass upon flow in the native coronary artery were investigated in a hydraulic model of the cardiovascular system. An aorta-coronary bypass with a diameter identical to the coronary artery was used, since a graft diameter-to-coronary diameter ratio of one has been described as optimal. Stenoses of increasing severity were created in the simulated coronary artery. Aorta-coronary bypass eliminated the pressure gradients across the stenotic coronary segments. This caused a 50% reduction of flow in the normal or mildly stenotic native coronary artery. A higher percentage reduction of flow occurred in the bypassed artery when it was severely stenotic. Such a reduction of flow in patients may accelerate the atherosclerotic-thrombotic process and contribute to the high prevalence of occlusion of natural vessels following bypass. This disadvantageous hydraulic circumstance should be considered, particularly when bypass of mildly stenotic vessels is contemplated.