Evaluation Of Platelet Reactivity In Patients With Abnormal Heart Valves

The reactivity of platelets from 57 patients was evaluated prior to removal of either an abnormal natural mitral or aortic valve or a degenerated porcine bioprosthetic valve. Thirty patients had aortic stenosis or insufficiency, 21 had mitral stenosis or insufficiency, and 6 underwent the removal of a long-term (4 to 7 years after insertion) Hancock porcine bioprosthetic valve. Transmission electron microscopy was used in a standardized in vitro method to evaluate these platelets. The degree of surface activation (cytoplasmic spreading by single platelets) and aggregate formation were both recorded. A hyperactive response was defined as >20% of the spread type platelet and/or an increased number of aggregates (>93 aggregates/100 single platelets). Hyperactive platelet populations were found in only 8% (6 of 72) of normal subjects. In contrast, 60% (18 of 30) of patients with aortic stenosis or insufficiency, 76%, (16 of 21) of patients with mitral stenosis or insufficiency, and 83%, (5 of 6) of patients with a degenerated porcine valve showed hyperactive platelets. The mean percentage of the spread type platelet for the various groups was 40, 38 and 30 respectively with corresponding mean values of 106, 124 and 102 for platelet aggregates. The reactivity of platelets from the normal group differed significantly from each group of patients with abnormal valves (P > 0.01). However, the level of platelet reactivity between the patient groups with abnormal valves did not differ significantly. Disturbed flow, high shear stresses and the exposure of potentially thrombotic materials are all features associated with abnormal natural heart valves as well as a degenerated bioprosthesis and may explain our finding of increased platelet reactivity in these patients.