Evidence in vivo of an intact endothelial function in internal mammary arteries before and after implantation as coronary grafts

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Abstract
To evaluate the effect of grafting on the endothelial function of the internal mammary artery (IMA) in patients with coronary artery disease, the response to acetylcholine was examined in native IMA and in IMA grafts, and was compared with the response in the coronary arteries. Fourteen patients were examined, including 6 patients with advanced coronary artery disease without previous surgery or angioplasty (group 1), and 8 patients with IMA grafts 3 to 35 months after surgery (group 2). Acetylcholine (7 to 700 nmol/min) was infused selectively into either the left anterior descending coronary artery and the native IMA, or into the graft on the left anterior descending coronary artery. The effect on vessel diameters was assessed by quantitative angiography. The segments evaluated in both groups did not show angiographic evidence of significant local atherosclerosis. Seventy-eight percent of the coronary artery segments in group 1 and 91% in group 2 were contracted by acetylcholine. Native IMA and IMA grafts were not contracted by acetylcholine. There was a marked difference in a the response of graft segments and the adjacent coronary segments in group 2 (acetylcholine, 700 nmol/min: 100.6% ± 12.9% of control vs. 64.3% ± 32.4%; P < 0.001). By use of acetylcholine as an indicator of endothelial dysfunction it was concluded that the native IMA had intact endothelial function, in contrast to the coronary arteries of the same patients. Several months after surgery, the IMA still showed no evidence of an impaired endothelium-dependent vascular response.