Immunohistochemical comparison of traditional and modified harvesting of the left internal mammary artery

Abstract

The left internal mammary artery is the conduit of choice for coronary artery bypass grafting. In the traditional ("clipped-artery") harvesting technique, this artery is prepared as a pedicle; the distal part is clipped, cut, and covered with a papaverine-soaked cloth until anastomosis is performed. In modified ("nonclipped-artery") harvesting, the prepared artery is kept in situ and left connected to the systemic circulation until anastomosis. Better outcomes from use of the nonclip technique have been reported. In order to determine comparative endothelial integrity and endothelial nitric oxide synthase activity, we performed an immunohistochemical study of arterial graft segments that were procured by each technique. This cross-sectional study involved 40 patients who underwent elective coronary artery bypass grafting. The patients were randomized into 2 groups of 20. One group underwent traditional clipped-artery harvesting; the other group, modified nonclipped-artery harvesting. By immunohistochemical methods, we examined redundant segments taken from bifurcation levels of the arteries. The tunica media was thinner in the clipped arterial segments, a phenomenon that we attribute to high luminal pressure. Endothelial nitric oxide synthase immunostaining was absent in regions of denudation in the luminal endothelia of the clipped arteries; in contrast, pronounced immunostaining occurred in the endothelia of the nonclipped segments. We found that traditional harvesting disrupted the integrity of the luminal endothelia of the clipped arteries. In addition, the traditional procedure decreased nitric oxide production, as was revealed by immunostaining.

Keywords: Coronary artery bypass/methods; coronary disease/surgery; endothelium, vascular/physiology; graft occlusion, vascular; graft survival; immunohistochemistry; internal mammary-coronary artery anastomosis/adverse effects/methods; mammary arteries/transplantation; myocardial revascularization/methods; nitric oxide synthase/analysis/metabolism/type III; tunica media/enzymology/pathology.

Fig. 1 Hematoxylin & eosin-stained sections of arteries harvested by clip and nonclip techniques. A) The tunica media is thinner in the segments prepared by the clip technique, apparently due to high luminal pressure (orig. ×200). B) Tunica media thickness remains unchanged in segments harvested by the nonclip technique (orig. ×100)

Fig. 2 Immunohistochemical endothelial nitric oxide synthase (e-NOS) sections of arteries harvested by the clip and nonclip techniques (biotin-streptavidin stain, orig. ×400). A) In the clip technique, e-NOS immunostaining is absent in regions of denudation in the luminal endothelium. B) In the nonclip technique, e-NOS immunostaining is pronounced in the luminal endothelium (orig. ×400).

Fig. 3 Immunohistochemical endothelial nitric oxide synthase (e-NOS) sections of arteries harvested by the clip and nonclip techniques. A) In the clip technique, weak adventitial immunostaining of e-NOS is revealed in the vaso vasorum (arrow) (biotin-streptavidin stain, orig. ×200). B) In the nonclip technique, dense e-NOS immunostaining is revealed in the vaso vasorum (arrow) (orig. ×100).