Introduction:
Bleeding episodes are frequently observed in patients being treated with mechanical circulatory support (MCS) and extracorporeal membrane oxygenation (ECMO). Acquired von Willebrand syndrome (avWS) is caused by high shear stress inside ECMO and MCS and contributes to the ECMO- and MCS-associated coagulopathy. avWS is characterized by loss of high molecular weight multimers of von Willebrand factor (vWF) and decreased collagen binding to vWF. avWS can be diagnosed using vWF multimer analysis, and by assessment of vWF levels and function. However, these diagnostic methods are elaborate and cannot provide quick results during acute bleeding. In this study we analyzed the management of MCS- and ECMO patients with suspected avWS with the aim to optimize diagnostic and therapeutic options.
Methods: 
Two patient groups, treated with either vv/vaECMO or impella left ventricular assist devices, were included in this study. In the first group 13 patients were retrospectively analyzed. In these patients avWS had been clinically suspected during the clinical course due to bleeding episodes on median day 6 of ECMO/impella treatment. vWF multimers had been measured to verify potential avWS.
In group two 11 patients were prospectively analyzed for the development of avWS during ECMO and impella treatment over time and the potential of diagnostic modalities. vWF-antigen, vWF:CBA and  vWF multimers were measured in blood samples before and 1h, 24 h and 48 h after device implantation. 
Results: In 12/13 group 1 patients avWS was retrospectively confirmed using vWF multimer analysis. During the initial bleeding phase, when results of vWF multimer analysis were not yet available, calculated treatment with vWF and/or vWF/FVIII concentrates was performed in 10/13 patients. DDAVP was administered in 5/13 patients. In group two all patients developed avWS within 48 hours after MCS/ECMO initiation. This was associated with bleeding in 50 % of the patients. The avWS detection rate of the VWF:CBA assay was higher than the detection rate using VWF multimer analysis. 
Conclusion: Due to heterogeneity of von Willebrand’s disease and assay limitations, none of the currently available laboratory procedures is sufficient to diagnose avWS rapidly during acute bleeding. Therefore, avWS-specific blood product application cannot be guided sufficiently.  Consequently, a Point of Care Test should be developed to improve early diagnosis and specific treatment of avWS.

05 - Acquired von Willebrand syndrome during mechanical circulatory support and extracorporeal membrane oxygenation: rapid onset and the demand for Point of Care Testing