A prospective analysis of thrombotic events in the European collaboration study on low-dose aspirin in polycythemia (ECLAP).

Background: - The clinical course of polycythemia vera (PV) is often complicated by arterial and venous thrombosis. Current information on these vascular complications derives from very few prospective clinical trials and several retrospective studies. The purpose of this analysis is to report the incidence, clinical features and risk factors for thrombosis in a large number of patients prospectively followed in a multicountry European study.

Methods: - The European collaboration on low-dose aspirin in polycythemia vera (ECLAP) study is a multicenter project aimed at describing the natural history of PV. Overall, 1630 PV patients (57% males, median age at recruitment 65 years) were enrolled in the study. Five hundred and eighteen (32%) of these patients are entered into a parallel, double-blind, placebo-controlled, randomized clinical trial aimed at assessing the efficacy and safety of low-dose aspirin. The remaining 1112 (68%) are entered into an ongoing, observational, prospective, cohort study. The mean follow-up duration was 2.7 years (range 0-5.3).

Findings: - The cumulative incidence rate of cardiovascular events (i.e. cardiovascular death and non-fatal thrombotic events) was 5.5 events/100 persons per year. Thrombosis was the main cause of death. Age greater than 65 years and positive history of thrombosis were the two most important predictors of cardiovascular events. Smoking, hypertension and congestive heart failure were other significant risk factors for thrombosis. Platelet counts and myelosuppressive drugs were not associated with the risk of cardiovascular events. Antiplatelet therapy was the only variable associated with a lower risk of thrombosis.

Conclusion: - Cardiovascular events remain a major cause of mortality and morbidity in PV but the thrombotic risk seems to be more related to the patients' characteristics (age, previous thrombosis, cardiovascular risk factors) than to the disease itself. Thus, control of red cell mass and antithrombotic therapy appear to be effective treatments in limiting the risk of thrombosis.