Fibrin Resistance to Lysis in Patients with Pulmonary Hypertension Other Than Thromboembolic

Rationale: Reportedly, fibrin isolated from patients with chronic thromboembolic pulmonary hypertension (CTEPH) is resistant to lysis. Persistence of regions within the fibrin b chain, which mediate cell signaling and migration, could trigger the organization of pulmonary thromboemboli into chronic intravascular scars. Objectives: Ascertain whether fibrin resistance to lysis occurs in patients with pulmonary hypertension (PAH) other than CTEPH, andinthosewithpriorpulmonaryembolism(PE)andno pulmonary hypertension. Methods: Fibrinogen was purified from 96 subjects (17 with CTEPH, 14 with PAH, 39 with prior PE, and 26 healthy control subjects) and exposed to thrombin to obtain fibrin clots. Plasmin-mediated cleavage of fibrin b chain was assessed hourly over a 6-hour period by polyacrylamide gel electrophoresis. Fibrin band intensity was measured by densitometry of stained gels. Data were normalized to the band intensity of the undigested protein. Measurements and Main Results: By 1 hour of digestion, fibrin band intensity had decreased by a median of 25% (interquartile range [IQR],20to27%)incontrolsubjects,andby15%(IQR,11to18%)in patients with prior PE (P , 0.0001). The 1-hour median reduction in band intensity was 2% (IQR, 1 to 3%) in CTEPH, and 4% (IQR, 2 to 7%) in PAH (P , 0.0001 vs. control subjects and PE). The decline in fibrinbandintensityremainedsignificantlydifferentamongthefour groups up to 6 hours (P , 0.0001). Conclusions: Fibrin resistance to lysis occurs in pulmonary hyperten