Comparative study of the postoperative flow in the saphenous vein and internal mammary artery bypass grafts

Postoperative coronary bypass flow was evaluated in two groups of randomly selected patients with grafts to the left anterior descending artery (LAD). Saphenous vein bypass grafts were placed in 27 patients and internal mammary artery grafts in 25 patients. Postoperative flow studies were performed in both groups with roentgendensitometric methods based on the transit time of radiopaque media along the graft plus the mean graft diameter. There was no significant difference between the two groups of patients for age, duration of symptoms, or the frequency of hypertension, diabetes mellitus, prior myocardial infarction, or cardiomegaly. Intraoperative bypass flows were 75+/-27 and 77+/-24 ml. per minute for the saphenous vein group (SVG) and internal mammary artery group (IMAG), respectively. There was no significant difference in the heart rate or mean aortic pressure at the time of the roentgendensitometric flow study. The mean graft diameters were 3.0+/-0.5 and 1.9+/-0.3 mm. for the SVG and IMAG, respectively (p less than 0.001). The ratios of graft diameter to LAD diameter were 1.9+/-0.3 and 1.2+/-0.2 for the SVG and IMAG, respectively (p less than 0.001). The roentgendensitometric postoperative flows were 68+/-27 ml. per minute in the SVG and 46+/-16 ml. per minute in the IMAG (p less than 0.01). The present study indicates that flow in significantly higher in saphenous vein than in internal mammary artery bypasses and that the difference in flow may in part be explained on the basis of the graft diameter.