Remodeling leads to distinctly more intimal hyperplasia in coronary than in infrainguinal vein grafts

BackgroundFlow patterns and shear forces in native coronary arteries are more protective against neointimal hyperplasia than those in femoral arteries. Yet, the caliber mismatch with their target arteries makes coronary artery bypass grafts more likely to encounter intimal hyperplasia than their infrainguinal counterparts due to the resultant slow flow velocity and decreased wall stress. To allow a site-specific, flow-related comparison of remodeling behavior, saphenous vein bypass grafts were simultaneously implanted in femoral and coronary positions.MethodsSaphenous vein grafts were concomitantly implanted as coronary and femoral bypass grafts using a senescent nonhuman primate model. Duplex ultrasound-based blood flow velocity profiles and vein graft and target artery dimensions were correlated with dimensional and histomorphologic graft remodeling in large, senescent Chacma baboons (n = 8; 28.1 ± 4.9 kg) during a 24-week period.ResultsAt implantation, the cross-sectional quotient (Qc) between target arteries and vein grafts was 0.62 ± 0.10 for femoral grafts vs 0.17 ± 0.06 for coronary grafts, resulting in a dimensional graft-to-artery mismatch 3.6 times higher (P < .0001) in coronary grafts. Together with different velocity profiles, these site-specific dimensional discrepancies resulted in a 57.9% ± 19.4% lower maximum flow velocity (P = .0048), 48.1% ± 23.6% lower maximal cycling wall shear stress (P = .012), and 62.2% ± 21.2% lower mean velocity (P = .007) in coronary grafts. After 24 weeks, the luminal diameter of all coronary grafts had contracted by 63%, from an inner diameter of 4.49 ± 0.60 to 1.68 ± 0.63 mm (P < .0001; subintimal diameter: −41.5%; P = .002), whereas 57% of the femoral interposition grafts had dilated by 31%, from 4.21 ± 0.25 to 5.53 ±1.30 mm (P = .020). Neointimal tissue was 2.3 times thicker in coronary than in femoral grafts (561 ± 73 vs 240 ± 149 μm; P = .001). Overall, the luminal area of coronary grafts was an average of 4.1 times smaller than that of femoral grafts.ConclusionsAlthough coronary and infrainguinal bypass surgery uses saphenous veins as conduits, they undergo significantly different remodeling processes in these two anatomic positions.

Clinical RelevanceSaphenous vein grafts still represent the gold standard of bypass graft surgery. Although flow-dependent vein graft remodeling has been experimentally shown, there is limited clinical appreciation for the remodeling differences between coronary and infrainguinal vein grafts because the procedures are generally performed by two different clinical disciplines. Understanding the site-specific baseline response of vein grafts in both positions is a prerequisite for optimally strategizing therapeutic modalities aiming at the suppression of potentially detrimental remodeling processes such as neointimal hyperplasia or luminal encroachment.