[The internal mammary artery as a graft material for coronary artery bypass surgery. Histopathologic and biochemical studies of its atherosclerotic changes].

To evaluate the usefulness of the internal mammary artery (IMA) as a graft material for coronary artery bypass surgery, 1) the whole length of 26 bilateral IMAs and 13 left anterior descending coronary arteries (LADs) harvested at autopsies were comparatively examined on atherosclerosis from the histological point of view, and 2) the lipid (total cholesterol, triglyceride and phospholipid) contents of 12 IMA segments and 11 LAD segments excised at other autopsies were also comparatively examined from the biochemical standpoint. 1) The histologic index of atherosclerotic involvement was expressed as intima-to-media ratio (R) representing the severity of the intimal thickening. The severity of atherosclerosis was graded from I to IV according to the R value. Of all 274 IMA sections grade IV (R greater than or equal to 3.0) atherosclerosis was found in only one section (1/26 IMAs, 3.8%). The mean R value of all IMAs (0.30 +/- 0.36) was approximately one tenth of that of all LADs (3.01 +/- 2.05) (p less than 0.01). The histologic examination for whole segments of the IMAs revealed that atherosclerosis of the IMA was equally slight in every part of the IMA with no laterality. On the other hand, atherosclerosis of the LAD was characteristically severer in the proximal segment of the artery than the distal segment. 2) The contents of total cholesterol, triglyceride and phospholipid of the IMA and the LAD were 5.5 +/- 1.8 (IMA) vs 17.8 +/- 13.6 (LAD) micro g/mg wet wt. (p less than 0.05), 90.4 +/- 90.3 (IMA) vs 114.4 +/- 117.2 (LAD) micro g/mg wet wt. and 7.4 +/- 3.9 (IMA) vs 11.2 +/- 3.9 (LAD) micro g/mg wet wt. (p less than 0.05) respectively. The lipid content of the IMA was significantly smaller than that of the LAD. 3) The low incidence of atherosclerosis of the IMA in contrast to frequent atherosclerosis of the LAD was proven histologically as well as biochemically in the present study. This is the first report to describe the histologic examination of atherosclerosis on the whole length of the IMA and the biochemical analysis for the lipid content of the IMA in Japanese population.