Von Willebrand factor ratio as a risk factor for bleeding in aortic valve stenosis replacement surgery

Objective Patients with aortic valve stenosis (AVS) often undergo valve replacement by thoracotomy. Since this is a major surgical procedure, sufficient hemostasis is required to avoid postoperative complications. Increased shear stress as a result of stenosis can reduce platelet function and von Willebrand factor (VWF). A VWF ratio (VWF:RCo/VWF antigen) below 0.7 may be associated with the loss of the largest VWF multimers and consequently with reduced VWF functionality. This study focuses on the evaluation of primary hemostasis in patients undergoing AVS and valve replacement surgery.

Material and Methods 60 patients with AVS were included in this study. A categorization of the patients into “more bleeding” group and “less bleeding” group was performed based on the postoperative blood loss. In addition, the severity of stenosis (mild/moderate, severe) was determined by the peak aortic velocity. Clinical characteristics, e. g. hemostasis data and platelet function, were evaluated before and five days after surgery.

Results The “more bleeding” group had twice as much mean postoperative chest tube blood loss as the “less bleeding” group (15.5%; 780.7±220 mL vs. 6.5%; 387.1±190 mL; percent p = 0.016, volume p = 0.035). Furthermore, blood loss was associated with both severity of stenosis (p = 0.05) and VWF ratio (p = 0.033). The risk of higher blood loss increased in patients with a low VWF ratio (OR = 2.448; 95 % CI:1.1093-9.140; p = 0.064) and in patients with severe stenosis (OR = 7.0; 95 % CI: 1.8391-58.39; p = 0.050). The “more bleeding” group had more cases of severe stenosis (93.3 % vs 66.7 % p = 0.050) and significantly lower VWF ratio (0.6±0.19 vs. 0.41±0.23; p = 0.021). After surgery, a significant reduction in shear stress (102.3±23.6 vs. 31.3±6.0 p<0.0001) and a significant increase in VWF ratio (0.56±0.2 vs. 0.70±0.2 p = 0.001) could be observed. Platelet function measured by light transmission aggregometry (LTA) showed no significant correlation with increased blood loss.

Conclusion Patients with AVS may have an increased risk of postoperative bleeding if their VWF ratio is below 0.7. However, reduced platelet function (assessed by LTA) showed no association with increased bleeding in this collective. Further investigations are necessary to study e. g. platelet-VWF or platelet-collagen interaction.

Publication History

Article published online:
18 June 2021