Clot resolution after 3 weeks of anticoagulant treatment of pulmonary embolism: Comparison of computed tomography and perfusion scintigraphy

Introduction: Little is known about the natural history of clot resolution in the initial weeks of anticoagulant therapy in patients with acute pulmonary embolism (PE). Aim: To assess clot resolution of acute PE with either computed tomography pulmonary angiography (CT-scan) or perfusion scintigraphy (Q-scan) after 3 weeks of anticoagulant treatment. Methods: This was a predefined safety analysis of the Einstein PE study, including PE patients, randomized to either enoxaparin with vitamin K antagonists or rivaroxaban. A similar scan as at baseline was repeated after 3 weeks. The percentage of pulmonary vascular obstruction (PVO) was calculated based on a weighted semi-quantitative estimation of obstruction. Clot resolution was assessed blindly by calculating the relative change after 3 weeks. Results: PE was diagnosed in 264 patients with CT-scan and in 83 with Q-scan. Baseline characteristics were comparable. At baseline, the mean PVO assessed with CT-scan (PVO-CT) and with Q-scan (PVOQ) were both 21% (Standard deviation (SD) 13%) (P = 0.9). The mean relative decrease in PVO after 3 weeks was 71% (SD) 33%) for PVO-CT, compared to 62% (SD 36%) for PVO-Q (P = 0.02), while complete resolution was observed in 44% (116/264; 95% CI 38-50%) and 31% (26/83; 95% CI 22-42%) with of CT-scan and Q-scan, respectively (P = 0.04). No difference in clot resolution between enoxaparin/ VKA and rivaroxaban was found. Conclusion: In patients with acute PE, only 3 weeks of anticoagulant treatment leads to complete clot resolution in a considerable proportion of patients and normalization is more often observed with CTscan than with Q-scan.