Hemodynamics of Aorta-to-Coronary Artery Bypass: Experimental and Analytical Studies

Abstract

Aorta-to-coronary artery vein bypass was accomplished in 15 dogs. Flow in the graft and proximal coronary artery was measured with an electromagnetic flowmeter. The partition of flow was found to be dependent on (I) the graft-to-artery diameter ratio (D g/D a) and (2) the degree of stenosis present in the proximal coronary artery. With an unobstructed proximal coronary artery, small grafts (D g/D a < 2.0) assumed a mean of 73.7% of the total flow to the distal coronary artery, while large grafts (D g/D a ≥ 2.0) carried 95.1% of the total flow. When a short, 50% stenosis was placed on the proximal coronary artery, the graft always carried more than 90% of the total flow. Simple calculations based on Poiseuille's law provide results which agree closely with the experimental data. These data imply that thrombosis of the proximal coronary segment may well be expected following aorta-to-coronary artery bypass due to the small amount of flow in this vessel. Experimental data and calculations show that the velocity of graft flow decreased as the D g/D a ratio increased. With a D g/D a ratio decrease from 3.0 to 1.5, the graft velocity rose by as much as 320%. This indicates that in clinical coronary bypass there may be considerable advantage in using a small-diameter bypass vessel (either distal saphenous vein or internal mammary artery) to insure a higher velocity flow through the graft.