Collagen induced thrombus formation at the apex of eccentric stenoses--a time course study with non-anticoagulated human blood.

Atherosclerotic plaque rupture may trigger the formation of mural thrombus. This thrombus formation is apparently affected by very high and complex shear conditions introduced by the luminal narrowing (stenosis) of the atheroma. To study the impact of such blood flow behaviour on thrombus formation we employed a model system where collagen-induced thrombogenesis is studied at the apex of well-defined eccentric stenoses. Thrombus formation in non-anticoagulated human blood drawn directly from an antecubital vein over the collagen coated stenosis apex for periods of 0.5, 1, 3 or 5 min was quantified by morphometry. The stenoses reduced the cross-sectional area of the blood flow channel by 60, 80 and 89%, which corresponded to apex wall shear rates of 2600, 10,500 and 32,000 s-1, respectively. Platelet-collagen adhesion decreased by increasing shear at the stenosis apex. The corresponding adhesion rates were highest at 1 min, then they gradually decreased upon prolongation of the perfusion time. The platelet thrombus volume increased in concert with increasing shear rate up to 10,500 s-1, whereas, at 32,000 s-1, the volume wa decreased. The corresponding growth rates and rates of thrombus occlusion at the apex levelled off at 3 min. Significant fibrin deposition was not observed before 3 min, and was most pronounced at 10,500 and 32,000 s-1. The plasma levels of fibrinopeptide A and beta-thromboglobulin increased in concert with increasing shear and perfusion time, particularly at the two highest shear conditions. Thus, hallmarks of thrombus formation at these stenoses with increasing shear are decreased platelet-collagen adhesion, and increased platelet-platelet interaction and fibrin deposition. A fibrin tail downstream to the collagen-attached platelet thrombus is regularly observed when thrombus occlusion exceeds 40%. However, the reduced thrombus growth at the most occlusive stenosis (89%) is presumably due to the high shear stresses which may reduce the rate of platelet incorporation into the thrombus and/or tear off thrombus fragments.