Summary
Atherosclerotic plaque rupture may trigger the formation of a 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 was 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 P-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.