Mechanical Heart Valves
The position of a mechanical valve influences the thrombosis risk with several studies showing that aortic valve replacements have a significantly lower risk of thrombosis than valves in the mitral position. A German study in 2005 of 2,735 patients with aortic valve, mitral valve or combined valve replacements reported 51 thromboembolic events with an incidence of 0.53% per patient-year for aortic valves versus 1.64% per patient year for mitral valves1.
An earlier study from Cannegeiter et al showed a
similar result with an incidence of 0.5 per
100 patient-years among patients with an aortic valve, 0.9 per 100 patient-years
among patients with a mitral valve, and 1.2 per 100 patient-years among those
with both an aortic and a mitral valve2.
Therefore all mechanical mitral
valve replacements are regarded as high risk.
An uncomplicated Aortic valve
however has a low thrombotic risk. The influence of other risk factors, other
than a prior stroke, remains uncertain but
it is reasonable to assume that the presence of atrial fibrillation, diabetes ,
heart failure or hypertension will have some influence on thrombotic risk.
Optimal Oral Anticoagulant Therapy in Patients with Mechanical Heart Valves. S.C. Cannegieter, et al. N Engl J Med 1995; 333:11