PB0277 - Rate of recurrent venous thromboembolism in infants with unprovoked venous thromboembolism

Background: Unprovoked venous thromboembolism (VTE) is rare in infants and few studies have evaluated the incidence of recurrent VTE in this population.

Aims: Describe the characteristics and management of infants with unprovoked VTE and determine the incidence of recurrent VTE.

Methods: We performed a single center, retrospective study including children age < 1 year with unprovoked VTE between 1/1/2003–8/1/2021. Patients were followed from index VTE until recurrent VTE or censoring (death or date of last contact). Analysis included descriptive statistics and estimated incidence of recurrent VTE with 95% confidence interval (CI). The Institutional Review Board exempted this study and the National Institutes of Health support HW.

Results: 43 infants met inclusion criteria (Table 1). We identified one recurrent VTE in 240.45 person-years (incidence rate = 4.16 [95% CI: 0.59 - 29.53] per 1000 person-years). This event was in a different anatomic location, 16.2 years after the index event in a patient with double inherited thrombophilia. The event occurred during an acute illness and anticoagulation dose reduction.

Therapeutic anticoagulation is summarized in Table 1. Documented reasons for not starting anticoagulation include concomitant or high risk for bleeding (13/23), unilateral renal vein thrombosis (2/23), minimal or no acute symptoms and/or thought to have occurred in-utero (8/23). Four patients remained on anticoagulation at the end of the study period or at censoring. Two patients were transitioned to low-dose anticoagulation for secondary prophylaxis; both had an inherited thrombophilia. The remaining seven patients with inherited thrombophilia did not receive long-term anticoagulation. No patients experienced major bleeding on anticoagulation, however two patients experienced clinically relevant non-major bleeding.

Conclusion(s): We demonstrated a low rate of recurrent VTE in children with a history of unprovoked VTE < 1 year old, with a median follow-up of 4.61 years (IQR: 1.34-8.88). Anticoagulation management varied and there were no observed, recurrent events after anticoagulation discontinuation.