Summary
Unexplained bleeding episodes are associated with ventricular assist devices (VAD)
and can occur in part due to acquired von Willebrand syndrome (AVWS). AVWS is characterised
by loss of high molecular weight (HMW) multimers of von Willebrand factor (VWF) and
decreased ratios of collagen binding capacity and ristocetin cofactor activity to
VWF antigen. Loss of multimers can occur as VWF is subjected to increased shear stress,
which occurs in presence of VADs. We studied 12 patients who required mechanical support
of their native heart for terminal cardiac insufficiency. Nine patients underwent
placement of a VAD, while three underwent placement of a total artificial heart (TAH),
which is connected directly to heart and large cardiac vessels without cannulas. Within
one day of VAD implantation, four of five patients evaluated demonstrated loss of
HMW multimers and impaired VWF function. AVWS was present within two weeks of implantation
in eight of nine patients, and in all seven tested patients after ≥3 months. Patients
with different VAD types developed varying severities of AVWS. After VAD ex-plantation,
HMW multimers were detectable and VWF function normalised in all patients. AVWS was
not observed in the TAH patients studied. Our findings demonstrate that patients with
an implanted VAD experience a rapid onset of AVWS that is quickly and completely reversed
after device explantation. In addition, TAH patients do not develop AVWS. These results
suggest that shear stress associated with exposure of blood to VAD cannulas and tubes
may contribute to the development of AVWS.
Keywords
Acquired coagulation disorders - von Willebrand disease - surgery