EFFECT OF DIFFERENTIAL SHEAR-STRESS ON PLATELET-AGGREGATION, SURFACE THROMBOSIS, AND ENDOTHELIALIZATION OF BILATERAL CAROTID-FEMORAL GRAFTSIN THE DOG

Purpose: The purpose of this study was to determine the effects of inc reased shear stress on the aggregability of platelets as they traverse a long, small-caliber (6 mm) Dacron graft in the dog and on the surfa ce thrombosis and endothelialization of such a graft. Methods: Each of nine dogs received bilateral carotid-femoral artery grafts, approxima tely 75 cm long, for 3 months; one graft of each pair had a distal fem oral arteriovenous fistula to produce a higher shear rate than the con tralateral graft. Platelet aggregation scores were determined on blood withdrawn from the external jugular vein and from the proximal and di stal ends of the grafts in each animal. Graft flow rates, which were u sed in the computation of shear stress, and luminal pressure gradients through grafts were measured during surgery and specimen retrieval. S pecimens were studied with light microscopy after hematoxylin and eosi n and immunocytochemical staining and by scanning electron and transmi ssion electron microscopy to evaluate the nature, composition, and thi ckness of the flow surface lining, as well as the transmural healing. Results: Two high-shear stress and two Low-shear stress grafts occlude d unilaterally; five dogs had bilaterally patent grafts, allowing comp arative analyses. All subjects had low platelet aggregability with asp irin. Platelet aggregation scores taken from proximal and distal ends of the grafts were not significantly different. The high-shear stress grafts had significantly more endothelial-like cell coverage (p < 0.03 71) than the low-shear stress grafts, less flow-surface thrombus (P < 0.0056), and a thinner surface lining (P < 0.0029), on both the neoint ima and pseudointima. Conclusions: In subjects with low platelet aggre gation scores, long Dacron grafts do not elevate platelet aggregabilit y of blood flowing through them. High-shear stress grafts have less fl ow surface thrombus, more endothelialization, and a thinner surface li ning than do low-shear stress grafts.