Summary
High shear forces can induce structural changes in the shape of the von Willebrand
factor (VWF) molecule, making it more sensitive for ADAMTS-13, a specific VWF protease.
This leads to proteolysis of the highest-molecular-weight multimers, which are the
most effective in platelet-mediated hemostasis under conditions of high shear stress.
The use of cardiopulmonary bypass (CPB) is accompanied with high shear forces and
could therefore lead to diminished VWF activity. Therefore, we studied VWF activity
in patients undergoing myocardial revascularization. We enrolled 60 patients undergoing
coronary artery bypass graft (CABG) surgery with and without CPB (30 in each group).
ADAMTS-13 activity, VWF antigen (VWF:Ag) and propeptide levels were measured directly
before and after the procedure. VWF activity was determined using both the ristocetin
cofactor activity (VWF:Rcof) and collagen binding (VWF:CB) assays. VWF:Rcof and VWF:CB,
both corrected for VWF:Ag, were significantly increased after the procedure in the
off-pump group (p<0.001 and p=0.05, respectively), but not in the CPB group. Postoperative
VWF:Ag and VWF-propeptide levels significantly increased in both groups. ADAMTS-13
activity increased after both types of surgery after correction for hemodilution.
Postoperative VWF: Rcof levels correlated with postoperative D-dimer levels (p=0.025)
and were associated with early cognitive decline in the off-pump group (p=0.025).
Our data indicate that VWF activity is increased after off-pump CABG, but not after
CABG with CPB. Since release of VWF is comparable in both groups, shear stress-induced
proteolysis due to the use of CPB may be responsible for the decreased VWF activity.
Keywords
Von Willebrand factor - hypercoagulability - proteases / inhibitors - acquired coagulation
disorders