Resolution of thromboemboli in patients with submassive acute pulmonary embolism and related prognostic factors.

PURPOSE: The proportion of resolution of acute pulmonary thrombi varies from 35 to 43 % in studies that used perfusion scintigraphy performed at variable time points. We examined factors which could predict clot resolution.

METHODS: A single-center prospective observational cohort study in patients with acute sub-massive PE Data collected at baseline were: age, BMI, history of previous venous thromboembolism (HVTE), Charlson's comorbidity score (CcS), plasma troponin-t and D-dimer levels, Pulmonary Embolism Severity Score (PESS) and tricuspid regurgitation jet velocity (TRJ). Ventilation/perfusion scintigraphy (V/Q scan) was done at baseline, after one week and after six months (m) of anticoagulant treatment. If V/Q scan was abnormal at 6 m, prolongation of treatment with 3 m was proposed. Patients with persistent abnormal V/Q scan received an angio-CT if no other reasons for anticoagulation were present.

RESULTS: During the study period 83 patients were admitted for PE. 31 patients were excluded, 5 lost to follow-up. 47 patients, 22 men and 25 women completed the study. Mean age was 61 year (range 22-83), mean BMI 27,1 (range 16,4-38,4). At 1 week 5/47 (10.6%) and at 6m 20/47 (42.5%) had normalized V/Q scan. Five other patients (3 with matched V/Q defects, 1 with a new defect and 1 with no V/Q scan) had normal angio-CT at 6 m. The remaining 22 patients had persistent V/Q mismatch at 6 m. 10/22 agreed for anticoagulation to be prolonged by 3m. V/Q normalised in one. In the remaining 9, V/Q defects persisted. 5/9 had an abnormal angio-CT. 6/22 had a normal angio-CT at 6 m. In 4/22 anticoagulation was continued for other reasons. Two had no reassessment. We found no correlation between the persistence of perfusion defects on V/Q scan and HVTE, BMI, CcS, troponin-t , D-dimer level, PESS, nor TRJ.

CONCLUSIONS: 42.5 % of patients with PE have still mismatched perfusion defects at V/Q after 6 m of treatment. Baseline characteristics do not predict normalisation of perfusion defects. The agreement between pulmonary scintigraphy and angio-CT in detecting residual thrombi seems poor.

CLINICAL IMPLICATIONS: The duration of anticoagulation treatment after acute PE can not be based on normalisation of V/Q images alone. Further study of the clinical significance and cause of persistent scintigraphic perfusion abnormalities should be performed.