Characterization of Von Willebrand Factor Multimer Structure in Patients With Severe Aortic Stenosis

An enhanced and rapid method for von Willebrand factor multimer analysis for mechanical circulatory device testing

BACKGROUND

Von Willebrand factor (VWF) is a critical glycoprotein in hemostasis and is an important factor in diagnosing bleeding disorders. Albeit the analysis of VWF is often compromised by inconsistent methodologies and challenges quantifying multimeric size. Current VWF multimer analysis methods are costly, time-consuming, and often inconsistent; thus, demanding skilled professionals. This study aimed to streamline and optimize the VWF multimer analysis technique, making it more efficient and reproducible, particularly for identifying or predicting mechanical circulatory support (MCS) induced bleeding disorders.

METHODS

Blood samples from healthy volunteers were exposed to high shear forces via a Medtronic HeartWare ventricular assist device. VWF multimers were analyzed using vertical-gel agarose electrophoresis and Western blotting. Differences in VWF distribution were determined using densitometry, and two methods of densitometric analysis were compared: proprietary software against open-source software.

RESULTS

Using the developed method: (i) protocol duration was accelerated from three days (in classical methods) to ~ eight hours; (ii) the resolution of the high molecular weight (HMW) VWF multimers were substantially improved; and (iii) densitometric analysis tools were validated. Additionally, the densitometry analysis using two software types showed a strong correlation between results, with the proprietary software reporting slightly higher HMW VWF percentages.

CONCLUSION

This methodology is recommended for affordable, accurate, and reproducible VWF multimer evaluations during MCS use and testing. Further research comparing this method with semi-automated methods would provide additional insight and improve inter-laboratory comparisons.

Prognostic Impact of High-Molecular-Weight von Willebrand Factor Multimer Ratio in Classical Low-Flow Low-Gradient Aortic Stenosis

INTRODUCTION

High-molecular-weight (HMW) von Willebrand factor (VWF) multimer deficiency occurs in classical low-flow, low-gradient (LF/LG) aortic stenosis (AS) due to shear force-induced proteolysis. The prognostic value of HMW VWF multimer deficiency is unknown. Therefore, we sought to evaluate the impact of HMW VWF multimer deficiency on clinical outcome.

METHODS

In this prospective research study, a total of 83 patients with classical LF/LG AS were included. All patients underwent dobutamine stress echocardiography to distinguish true-severe (TS) from pseudo-severe (PS) classical LF/LG AS. HMW VWF multimer ratio was calculated using densitometric Western blot band quantification. The primary endpoint was all-cause mortality.

RESULTS

Mean age was 79 ± 9 years, and TS classical LF/LG AS was diagnosed in 73% (n = 61) and PS classical LF/LG AS in 27% (n = 22) of all patients. Forty-six patients underwent aortic valve replacement (AVR) and 37 were treated conservatively. During a mean follow-up of 27 ± 17 months, 47 deaths occurred. Major bleeding complications after AVR (10/46; 22%) were more common in patients with HMW VWF multimer ratio <1 (8/17; 47%) in comparison to patients with a normal multimer pattern (2/29; 7%) at baseline (p = 0.003). In a multivariable Cox regression analysis, HMW VWF multimer deficiency was a predictor of all-cause mortality (HR: 3.02 [95% CI: 1.31-6.96], p = 0.009) in the entire cohort. This association was driven by higher mortality rates in the AVR group (multivariable-adjusted HR: 9.4; 95% CI 2.0-43.4, p = 0.004).

CONCLUSIONS

This is the first study to demonstrate the predictive value of HMW VWF multimer ratio for risk stratification in patients with classical LF/LG AS. HMW VWF multimer deficiency was associated with an increased risk of all-cause mortality and major bleeding complications after AVR.

Acquired Von Willebrand Deficiency in Adults With Aortic Stenosis: A Systematic Review

Von Willebrand factor (VWF) deficiency is associated with bleeding complications. The congenital type of Von Willebrand disease(VWD) is a very well-known bleeding disorder and sometimes may be associated with life-threatening hemorrhage. This systematic review is aimed at gathering further knowledge regarding the pathology of an acquired VWD form within a population of patients with aortic stenosis (AS) by shortlisting quality articles on this theme, through the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) 2020 guidelines. High shear stress caused by the stenotic valve cleaves VWF multimers, causing a relative state of deficiency. The condition returns to baseline immediately following surgical replacement of the valve. Results across eight studies reviewed by a majority concluded that in an AS patient with bleeding, the most likely cause is an acquired deficiency of VWF, associated with factors influencing blood flow and caused by the in-situ valve. However, several studies suggested otherwise/were misclassifications. This review highlighted the relationship between AS and acquired VWF deficiency and should be foreseen as an adverse complication, attracting further research and future theragnostic strategies for this condition.

High-molecular-weight von Willebrand Factor multimer ratio differentiates true-severe from pseudo-severe classical low-flow, low-gradient aortic stenosis

AIMS

Upon high wall shear stress, high-molecular-weight (HMW) von Willebrand Factor (VWF) multimers are degraded, thus, HMW VWF multimer deficiency mirrors haemodynamics at the site of aortic stenosis (AS). The aim of the present study was to analyse the role of HMW VWF multimer ratio for subcategorization of classical low-flow, low-gradient (LF/LG) AS.

METHODS AND RESULTS

Eighty-three patients with classical LF/LG AS were prospectively recruited and HMW VWF multimer pattern was analysed using a densitometric quantification of western blot bands. Patients were subclassified into true-severe (TS) and pseudo-severe (PS) classical LF/LG AS based on dobutamine stress echocardiography (DSE). Positive and negative predictive values (PPV/NPV) of HMW VWF multimer ratio for diagnosis of the TS subtype were calculated. HMW VWF multimer ratio in TS classical LF/LG AS was significantly decreased compared to PS classical LF/LG AS (0.86 ± 0.27 vs. 1.06 ± 0.09, P < 0.001). HMW VWF multimer deficiency occurred exclusively in the TS subtype with an optimal PPV of 1.000 and NPV of 0.379. HMW VWF multimer ratio showed a strong correlation with mean transvalvular pressure gradients during DSE (r = -0.616; P < 0.001). HMW VWF multimer ratio measured at baseline was higher compared to levels measured after DSE (0.87 ± 0.27 vs. 0.84 ± 0.31; P = 0.031) indicating DSE-induced increased proteolysis.

CONCLUSION

HMW VWF multimer ratio represents a valuable biomarker for classical LF/LG AS subclassification and mirrors haemodynamics during DSE. HMW VWF multimer ratio identifies the TS subtype without the use of other imaging techniques.

Differences in von Willebrand factor function in type 2A von Willebrand disease and left ventricular assist device-induced acquired von Willebrand syndrome

BACKGROUND

Patients with von Willebrand disease (VWD) type 2A or acquired von Willebrand syndrome (aVWS) as a consequence of implantation of left ventricular assist devices (LVAD) are both characterized by a loss of von Willebrand factor (VWF) function. Loss of VWF function is however more severe in VWD type 2A than in LVAD patients.

OBJECTIVES

To compare VWF function in patients with VWD type 2A and LVAD-induced aVWS to highlight the differences in VWF activity and to stress the importance of VWF multimer analysis for correct diagnosis of aVWS in LVAD patients.

PATIENTS/METHODS

Plasma samples from nine VWD type 2A, nine LVAD patients, and 20 healthy donors (HD) were analyzed for VWF function (VWF:CB/VWF:Ag and VWF:RCo/VWF:Ag) and loss of high molecular weight (HMW) VWF multimers.

RESULTS

A severely impaired VWF function was indeed confirmed in all VWD 2A patients. HMW VWF multimers were severely reduced compared to HD (0% [0, 12.29] vs 34.19% [31.68, 38.88] for HD, P < 0.001) and this loss was reflected by VWF:CB/VWF:Ag and VWF:RCo/VWF:Ag ratios <0.7. In contrast, VWF function was less affected in LVAD patients. Although HMW VWF multimers were reduced in all patients (20.31% [15.84, 21.71], vs 34.19% [31.68, 38.88] for HD, P < 0.001), six out of nine LVAD patients had normal VWF:CB/VWF:Ag or VWF:RCo/VWF:Ag ratios (>0.7).

CONCLUSIONS

VWF:CB/VWF:Ag or VWF:RCo/VWF:Ag analysis allows detection of impaired VWF function in VWD type 2A but not always in LVAD-induced aVWS patients. In contrast, VWF multimeric analysis allows detection of the loss of HMW VWF multimers in both groups of patients. Hence, performing VWF multimer analysis is crucial to detect aVWS in LVAD patients.