Evaluation of postoperative flow reserve in internal mammary artery bypass grafts

The internal mammary artery has been advocated for use in bypass grafting owing to its superior long-term patency when compared to saphenous vein grafts. Concern exists that the flow through the internal mammary artery may be inadequate during periods of peak myocardial demand. This flow was investigated in 24 consecutive patients with a mean proximal left anterior descending artery stenosis of 87.5% who were selected for coronary bypass using the internal mammary artery. Within 8 weeks of operation, all were evaluated by exercise thallium 201 scintigraphy. Thallium activity, expressed as a ratio of anteroseptal activity to posterolateral wall activity (or inferior wall activity if the posterolateral wall was deemed abnormal), was 0.97 +/- 0.15. A second group of 25 patients, with normal coronary arteries, was similarly evaluated. The mean septal to posterolateral wall thallium activity ratio for these control patients was 1.0 +/- 0.15. A third group of 26 patients who underwent single-vessel percutaneous transluminal coronary angioplasty of the left anterior descending artery and a fourth group of 28 saphenous vein graft recipients were compared by stress thallium scintigraphy. Thallium 201 activity for the vein graft group (0.96 +/- 0.19) was not significantly different from that for the mammary artery group, whereas the flows obtained with a single attempt at angioplasty were significantly inferior (p less than 0.05). The internal mammary artery provides excellent coronary flow at peak myocardial demand and compares favorably to angioplasty and saphenous vein grafting.