Post-treatment residual thrombus increases the risk of recurrent deep vein thrombosis and mortality

Background: Recurrent thromboembolic events after an initial deep vein thrombosis (DVT) are relatively frequent. Residual thrombus in the affected veins on ultrasound scan at the completion of anticoagulant therapy has been described as a recurrence risk factor, and may have utility in stratifying those patients at risk. Objectives: The aims of the study were to correlate the risk of recurrence of DVT with the results of ultrasound at completion of oral anticoagulant therapy. A secondary aim was to review the mortality in this population. Patients: A cohort of 316 DVT patients was included. The patients were divided into those with completely clear vessels on follow-up scan (45%) and those with residual thrombus identified (55%). Results: The cumulative incidence of recurrence was 10% by 2 years and 23% by 5 years. Patients with residual thrombus on follow-up ultrasound were at higher risk of recurrence (hazard ratio [HR] 2.2, 1.19-4.21; P = 0.012) which remained significant after multivariate adjustment for age, gender and malignancy (HR 2.2, 1.15-4.17; P = 0.018). During follow-up, the cumulative mortality was 12% at 2 years and 27% by 5 years. The risk of death was increased in patients with residual thrombus on follow-up scan (HR 3.9, 1.93-7.71; P < 0.001) and this risk persisted after multivariate analysis of age, gender and malignancy (2.8, 1.37-5.72; P = 0.005). The majority of deaths were due to malignancy (68%) however 10 (18%) died from vascular causes. There was a trend towards increased vascular death in the patients with residual thrombus on follow-up ultrasound scan, which did not reach significance (HR 4.1, 0.87-19.33; P = 0.13). Conclusions: Consistent with previous cohort studies, recurrence risk is increased in patients with residual thrombus on ultrasound. The increased risk of death in patients with residual thrombus, with a trend towards increased vascular death, may suggest that failure of thrombus resolution is a marker of more global vascular dysfunction.