Idiopathic pulmonary arterial hypertension – a unrecognized cause of high‐shear high‐flow haemostatic defects (otherwise referred to as acquired von Willebrand syndrome) in children

Summary Acquired von Willebrand syndrome (AVWS) is reported in high‐flow high‐shear congenital cardiac disorders. We hypothesized that the narrowed pulmonary vasculature in idiopathic pulmonary arterial hypertension (IPAH) may induce AVWS. We conducted a cross‐sectional evaluation of children with IPAH. Patients with bleeding symptoms and/or laboratory abnormalities (thrombocytopenia, anomalies in coagulation screening tests) were tested in‐depth for haemostatic defects. Fourteen children were followed with IPAH of which 8 were eligible. Four children exhibited abnormal bleeding scores (International Society on Thrombosis and Haemostasis Bleeding Assessment Tool: 3–5). All 8 patients showed very prolonged platelet function analyser (PFA)‐100 closure times. Six children demonstrated either mild thrombocytopenia or low‐normal von Willebrand factor (VWF) antigen (VWF:Ag) or VWF activity [mean (range), in iu/dl: VWF:Ag: 70 (61–91); VWF activity: 57 (34–70)]. Average VWF collagen binding capacity (VWF:CB) was 64 iu/dl (range: 53–123 iu/dl), with low‐normal VWF activity/VWF:Ag or VWF:CB/VWF:Ag ratios occurring in five patients. All children had normal multimers distribution patterns. One patient underwent a lung transplantation, with normalization of haemostatic abnormalities post‐surgery. Overall, 8 out of 14 children with IPAH had mild to moderate bleeding symptoms and/or laboratory abnormalities in keeping with AVWS. Normalization of the haemostatic defects following lung transplantation and lack of family history of bleeding attests to the acquired nature of their defects.