Sex-specific differences in clot resolution 3 weeks after acute pulmonary embolism managed with anticoagulants—A substudy of the EINSTEIN-PE study

Background: It is unknown whether differences in clot structure and resolution contribute to the reported risk differences of recurrent venous thromboembolism (VTE) between men and women. Patients/Methods: We used data from the EINSTEIN-PE study, a randomized, multicenter, non-inferiority study in which patients 18 years and older with acute symptomatic pulmonary embolism (PE) were randomized to rivaroxaban or enoxaparin followed by a vitamin K antagonist. PE was diagnosed by computed tomography pulmonary angiography scan or high-probability ventilation/perfusion scintigraphy. Three weeks after randomization a follow-up scan was performed. An independent adjudication committee assessed the degree of vascular obstruction. Results and Conclusions: A total of 371 participants including 174 (46.9%) women and 197 (53.0%) men were included in the present analysis. At 3 weeks, there was no difference between men and women in complete clot resolution: 39.6% and 40.2%, respectively. The absolute reduction in pulmonary vascular obstruction at week 3 was also similar: 12.9% (95% confidence interval [CI]: 11.6–14.2) in men and 12.1% (95% CI: 10.4–13.7) in women, corresponding to a resolution ratio of 0.29 (95% CI: 0.24–0.33) and 0.35 (95% CI: 0.28–0.42), respectively. No differences in clot resolution were observed between men and women diagnosed with acute PE at 3 weeks after start of anticoagulant therapy. These findings suggest that the reported higher rate of VTE recurrence in men cannot be explained by decreased clot resolution.