Speed Reduction Does Not Restore High Molecular Weight von Willebrand Multimers During HeartMate II Support: An In Vivo Study

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Acquired von Willebrand Syndrome (AVWS) in patients undergoing continuous-flow left ventricular assist device support is due to the loss of von Willebrand factor (vWF) high molecular weight multimers (HMWMs) by shear-mediated mechanisms. We investigated whether reducing speed in vivo would mitigate the shear effect. In outpatients (n = 6) with a HeartMate II, pump speed was decreased to 8,000 rpm for 6 hours. At baseline (9,140 ± 189 rpm), patients had an AVWS as evidenced by low vWF activity:antigen ratios (0.58 ± 0.13, normal >0.7) and reduced HMWMs. After 6 hours, there was no significant change in either the vWF activity:antigen ratio or the HMWMs. Decreasing pump speed does not ameliorate AVWS.

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