Pathology of stent implantation in internal mammary artery

The internal mammary artery (IMA) is the most durable conduit for bypassing the left anterior descending (LAD) coronary artery in patients undergoing coronary artery bypass graft surgery (CABG). However, little is known about how the IMA reacts histologically to stent implantation. From CVPath stent registry (1048 lesions, 614 cases), we obtained 4 stent lesions (2 bare metal stents, 2 drug-eluting stents) involving IMA grafts. The mean age of our patients was 63 years and the duration of stent implantation in the IMA ranged from 5 days to 5 years. Stented arteries were dissected from hearts and embedded in plastic, segmented at 3 mm intervals, sectioned at 4-6 microns and stained with H&E and Movat pentachrome stains. Histological observations were performed. Majority of stents (3 of 4) were implanted in anastomosis between IMA and LAD while 1 stent was implanted in IMA body. One stent with duration of 5 days showed stent thrombosis while others were all patent with fully coverage by varying degrees of neointima. Foamy macrophage, lipid pool and calcification in neointima were observed in 1 stent with duration of 5 years but it was limited only to the distal LAD part within the stented segment. Overall, in this small pathologic series, the majorities of stents were implanted in IMA-to-LAD anastomosis site and demonstrated acceptable pathologic responses.