Myocardial blood flow following saphenous vein bypass surgery

Myocardial blood flow was measured by the 133Xe clearance technique in 21 patients 6 to 31 months after saphenous vein grafting for coronary arterial disease. Preoperative measurements were made in 16. All patients had improved symptomatically, and 20 had returned to work. Thirty of 39 grafts were entered and selective injections of 133Xe performed. Flow in the left coronary artery (LCA) was unchanged postoperatively in 9, increased in 5, and decreased in 1 (preoperative mean = 54 ml/100 g/min, SD +/- 16; postoperative mean = 65 ml/100 g/min, SD +/- 20). Flow in the right coronary artery (RCA) was unchanged postoperatively in 3, decreased in 9, and increased in 2 (preoperative mean = 46 ml/100 g/min, SD +/- 18; postoperative mean = 33 ml/100 g/min, SD +/- 12). Nine of 14 grafts to the left anterior descending coronary artery showed flow rates significantly greater than those in the corresponding LCA. Two of the 3 circumflex grafts showed flow rates significantly lower than those in the LCA. Four of 8 right grafts showed significantly higher flow rates than those in the corresponding RCA. These findings correlated well with the angiographic appearances. We conclude that saphenous vein grafting increases total myocardial blood flow. The data suggest that the coronary arteries and the grafts are supplying different regions of the myocardium, and that the graft regions were previously underperfused. There would appear to be little mixing of blood between artery and graft regions.