Jr. Obrien et al., DECREASED PLATELET-FUNCTION IN AORTIC-VALVE STENOSIS - HIGH-SHEAR PLATELET ACTIVATION THEN INACTIVATION, British Heart Journal, 74(6), 1995, pp. 641-644
Objective-To elucidate the mechanism of the bleeding tendency observed
in patients with aortic valve stenosis. Design-A prospective study of
high and low shear platelet function tests in vitro in normal control
s compared with that in patients with severe aortic valve stenosis wit
h a mean (SD) systolic gradient by Doppler of 75 (18) mm Hg before and
at least 4 months after aortic valve replacement. Setting-District ge
neral hospital. Results-The patients showed reduced retention in the h
igh shear platelet function tests. (a) Platelet retention in the filte
r test was 53.6 (12.6)% in patients with aortic valve stenosis and 84.
8 (9.6)% in the controls (P < 0.001). (b) Retention in the glass bead
column test was 49.8 (19.2) in the patients and 87.4 (8.7) in the cont
rols (P < 0.001). (c) The standard bleeding time was longer in the pat
ients (P < 0.06). Results of the high shear tests (a, b, and c) after
aortic valve replacement were within the normal range. The platelet co
unt was low but within the normal range before surgery and increased p
ostoperatively (P < 0.01). There were no differences in the results of
standard clotting tests, plasma and intraplatelet von Willebrand's fa
ctor, or in aggregation tests using five between patients with aortic
valve stenosis and controls. Conclusions-The high shear haemodynamics
of aortic valve stenosis modify platelet function in vivo predisposing
to a bleeding tendency. This abnormality of platelet function is dete
ctable only in vitro using high shear tests. The abnormal function is
reversed by aortic valve replacement. High shear forces in vitro activ
ate and then inactivate platelets. By the same mechanisms aortic valve
stenosis seems to lead to high shear damage in vivo, resulting in a c
linically important bleeding tendency in some patients.