Functional Impairment of Von Willebrand Factor in Hypertrophic Cardiomyopathy : Relation to Rest and Exercise Obstruction

Hypertrophic obstructive cardiomyopathy submits blood to conditions of high shear stress. High shear stress impairs von Willebrand factor (VWF) and promotes abnormal bleeding in aortic stenosis. We sought to evaluate VWF impairment and its relationships to baseline or exercise obstruction in hypertrophic cardiomyopathy (HCM). Outflow obstruction was evaluated by rest and exercise echocardiography in 62 patients with HCM (age 44+/-16 years, 40 males). HCM was considered obstructive in 28 patients with rest or exercise peak gradient >or=30 mm Hg. Blood was sampled to assess VWF. History of bleeding was recorded. Baseline median (25th to 75th percentile) peak gradient was 11 (5-62) mm Hg. Shear-induced platelet adhesion was impaired in patients with obstructive HCM. The ratio of VWF-collagen-binding activity to antigen and the percentage of high-molecular-weight multimers of VWF were lower in patients with obstructive HCM than in those with nonobstructive HCM (0.49 [0.43 to 0.59] versus 0.82 [0.73 to 1.03] and 5.0% [3.9% to 7.2%] versus 11.7% [10.8% to 12.5%], respectively; both P