Loss Of High Molecular Weight Von Willebrand Factor Multimers Research Articles

A noncanonical splicing variant c.875-5 T > G in von Willebrand factor causes in-frame exon skipping and type 2A von Willebrand disease

IntroductionA novel variant involving noncanonical splicing acceptor site (c.875-5 T > G) in propeptide coding region of von Willebrand factor (VWF) was identified in a patient with type 2A von Willebrand disease (VWD), who co-inherited with a null variant (p.Tyr271*) and presented characteristic discrepancy of plasma level of VWF antigen and activity, and a selective reduction of both intermediate-molecular-weight (IMWMs) and high-molecular-weight VWF multimers (HMWMs). Materials and methodsVWF mRNA transcripts obtained from peripheral leukocytes and platelets of the patients were investigated to analyze the consequence of c.875-5 T > G on splicing. The impact of the variant on expression and multimer assembly was further analyzed by in vitro expression studies in AtT-20 cells. The intracellular processing of VWF mutant and the Weibel-Palade bodies (WPBs) formation was evaluated by immunofluorescence staining and electron microscopy. ResultsThe mRNA transcript analysis revealed that c.875-5 T > G variant led to exon 8 skipping and an in-frame deletion of 41 amino acids in the D1 domain of VWF (p.Ser292_Glu333delinsLys), yielding a truncated propeptide. Consistent with the patient's laboratory manifestations, the AtT-20 cells transfected with mutant secreted less VWF, with the VWF antigen level in conditioned medium 47 % of wild-type. A slight retention in the endoplasmic reticulum was observed for the mutant. Almost complete loss of IMWMs and HMWMs in the medium and impaired WPBs formation in the cell, indicating truncated VWF propeptide lost its chaperon-like function for VWF multimerization and tubular storage. ConclusionsThe VWF splicing site variant (c.875-5 T > G) causes propeptide truncation, severely compromising VWF multimer assembly and tubular storage.

ADAMTS13 inhibition to treat acquired von Willebrand syndrome during mechanical circulatory support device implantation

BackgroundAcquired von Willebrand syndrome (aVWS) is common in patients with mechanical circulatory support (MCS) devices. In these patients, the high shear stress in the device leads to increased shear‐induced proteolysis of von Willebrand factor (VWF) by A Disintegrin And Metalloprotease with Thrombospondin type 1 repeats, number 13 (ADAMTS13). As a result, the high molecular weight (HMW) VWF multimers are lost, leading to a decreased VWF function and impaired hemostasis that could explain the bleeding complications that are frequently observed in these patients. To counteract this abnormal VWF degradation by ADAMTS13, we developed a novel targeted therapy, using an anti‐ADAMTS13 monoclonal antibody (mAb) that inhibits the shear‐induced proteolysis of VWF by ADAMTS13. MethodsHuman or bovine blood was circulated through in vitro MCS device systems with either inhibitory anti‐ADAMTS13 mAb 3H9 or 17C7 (20 μg/ml) or control anti‐ADAMTS13 mAb 5C11 or phosphate buffered saline (PBS). VWF multimers and function (collagen binding activity) were determined at different time points. Next, Impella pumps were implanted in calves and the calves were injected with PBS and subsequently treated with mAb 17C7. VWF, ADAMTS13, and blood parameters were determined. ResultsWe demonstrated that blocking ADAMTS13 could prevent the loss of HMW VWF multimers in in vitro MCS device systems. Importantly, our antibody could reverse aVWS in a preclinical Impella‐induced aVWS calf model. ConclusionHence, inhibition of ADAMTS13 could become a novel therapeutic strategy to manage aVWS in MCS device patients.

Inhibition of adamts13: a novel therapy to treat mechanical circulatory support-induced acquired von willebrand syndrome

Abstract Introduction Bleeding is the most frequent adverse event in patients with continuous flow mechanical circulatory support (CF-MCS) and has been linked to the occurrence of acquired von Willebrand syndrome (aVWS). MCS devices cause an increased shear-induced proteolysis of von Willebrand factor (VWF) by ADAMTS13, leading to aVWS. Hence, specifically blocking ADAMTS13 might be an efficient way to rescue the loss of HMW VWF multimers in CF-MCS patients. Purpose To investigate if blocking ADAMTS13, using an in-house developed inhibitory anti-ADAMTS13 monoclonal antibody (mAb), prevents the loss of high molecular weight (HMW) VWF multimers in in vitro CF-MCS systems and to determine the efficacy of this therapy in a CF-MCS calf model. Methods Human blood was perfused through in vitro CF-MCS systems (Heartmate II and Impella CP, axial flow heart pumps) in the presence of the inhibitory or control mAb (20 μg/mL). Bovine blood was perfused through an in vitro Impella 5.5 system with the inhibitory mAb (20 μg/mL) or PBS. Next, Impella 5.5 pumps were implanted in calves. One dose of the inhibitory mAb (600 μg/kg) or PBS was injected eight days after Impella implantation. Plasma samples were analysed for VWF multimers, VWF antigen (VWF:Ag) and VWF collagen binding activity (VWF:CB). Results A time-dependent decrease in HMW VWF multimers was observed in both in vitro CF-MCS systems in the presence of the control mAb, leading to a 70% reduction of HMW VWF multimers, 180 minutes (min) after blood perfusion (p=0.01 for HM II and p=0.0003 for Impella). This was also reflected by a severely decreased VWF:CB/VWF:Ag ratio (0.59±0.11 and 0.52±0.10 at 180 min versus 1.00±0.06 and 1.07±0.09 before perfusion, for the HM II (p=0.03) and Impella (p=0.001) respectively). Interestingly, blocking ADAMTS13 using the inhibitory mAb prevented the loss of HMW VWF multimers in both systems (p=0.50 for the HM II and p=0.06 for the Impella, 180 min after the start of perfusion). The preservation of HMW VWF multimers was also reflected by normal VWF:CB/VWF:Ag ratios (0.92±0.16 and 0.97±0.11 at 180 min versus 0.93±0.09 and 1.19±0.12 before perfusion for the HM II (p=0.75) and Impella (p=0.06) respectively). Blocking bovine ADAMTS13 using the inhibitory mAb could prevent the loss of HMW VWF multimers in the in vitro Impella 5.5 system, showing that the calf is a good preclinical animal model to study the in vivo effect of this novel therapy. Impella implantation in the calves led to a decrease in HMW VWF multimers (Figure 1A and B). Hence, this animal model represents the VWF laboratory features of MCS-induced aVWS. Moreover, the loss of HMW VWF multimers after pump implantation could be rescued after injection of the inhibitory mAb (Figure 1A and B). Conclusion Blocking ADAMTS13 rescues MCS-induced VWF proteolysis in calves. Hence, inhibiting ADAMTS13 function could become a promising therapeutic strategy to rescue aVWS-induced bleeding in MCS patients. Figure 1. Impella calf model Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Fund for Scientific Research Flanders

Diagnosis and Management of Acquired von Willebrand Disease in Heart Disease: A Review of the Literature.

The incidence of acquired von Willebrand syndrome (AvWS) in patients with heart disease is commonly perceived as rare. However, its occurrence is underestimated and underdiagnosed, potentially leading to inadequate treatment resulting in increased morbidity and mortality.In patients with cardiac disease, AvWS frequently occurs in patients with structural heart disease and in those undergoing mechanical circulatory support (MCS).The clinical manifestation of an AvWS is usually characterized by apparent or occult gastrointestinal (GI) or mucocutaneous hemorrhage frequently accompanied by signs of anemia and/or increased bleeding during surgical procedures. The primary change is loss of high-molecular weight von Willebrand factor multimers (HMWM). Whereas the loss of HMWM in patients with structural heart disease is caused by increased HMWM cleavage by von Willebrand factor (vWF)-cleaving protease, ADAMTS13, AvWS in MCS patients is predominantly a result of a high shear stress coupled with mechanical destruction of vWF itself.This manuscript provides a comprehensive review of the evidence regarding both diagnosis and contemporary management of AVWS in patients with heart disease.

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

BackgroundPatients 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. ObjectivesTo 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/MethodsPlasma 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. ResultsA 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). ConclusionsVWF: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.

Transcatheter aortic valve implantation leads to a restoration of von Willebrand factor (VWF) abnormalities in patients with severe aortic stenosis – Incidence and relevance of clinical and subclinical VWF dysfunction in patients undergoing transfemoral TAVI

BackgroundIn this study, we sought to analyze the incidence and relevance of von Willebrand factor (VWF) abnormalities in patients undergoing transcatheter aortic valve implantation (TAVI), especially on perioperative bleeding. Furthermore, we hypothesized that, similar to aortic valve surgery, TAVI results in a restoration of VWF abnormalities. Methods and resultsWe performed a prospective analysis of periinterventional VWF parameters in 74 patients (80±7years, female in 37.5%) undergoing transfemoral TAVI for severe symptomatic aortic valve stenosis. At baseline, VWF:Ag was 210±90IU/dl with a mean VWF activity of 166±106IU/dl; activity-to-antigen ratio was 0.85±0.45. Heyde's syndrome (severe aortic stenosis plus GI bleeding from angiodyplasia) was observed in 2/74 (2.7%). Whereas preprocedural loss of high-molecular-weight (HMW) VWF multimers was found in thirty-six patients (48.6%), none of the patients fulfilled criteria for possible acquired VW syndrome. After TAVI, an increase of both VWF:Ag and activity compared to baseline was observed (p<0.01). In patients with HMW multimer loss, post-interventional recovery of multimers occurred in all cases. In the two patients with Heyde's syndrome, a trend towards reduced VWF:Ag was seen, with loss of HMW multimers in one patient. Of interest, all patients suffering from periprocedural major bleeding (5/74; 6.8%) exhibited activity-to-antigen ratios <0.7, indicating subclinical VWF dysfunction. ConclusionWhereas clinically relevant VWF dysfunction is rare, loss of HMW VWF multimers is common in TAVI patients. Similar to surgery, TAVI leads to a restoration of this loss. Furthermore, VWF parameters may be useful parameter to evaluate risk of periprocedural bleeding.

Extracorporeal membrane oxygenation induces short-term loss of high-molecular-weight von Willebrand factor multimers.

High-molecular-weight (HMW) von Willebrand factor (vWF) multimers are crucial for primary hemostasis. Increased shear stress from ventricular assist devices can provoke premature degradation of HMW vWF multimers. Whether similar loss of vWF multimers occurs during extracorporeal membrane oxygenation (ECMO) is not clear. We conducted a prospective observational study in a clinical cohort of patients who required ECMO for intractable cardiac and/or respiratory failure. The primary end point was the quantity and quality of HMW vWF multimer bands before, during, and after ECMO support. To investigate further changes in primary hemostasis, we also measured vWF antigen activity (vWF:Ag), vWF ristocetin cofactor activity (vWF:RCo), and factor VIII in 38 patients who required ECMO support before initiation of ECMO (baseline), after 24 and 48 hours on ECMO, and 24 hours after termination of ECMO therapy. Compared with baseline, vWF:Ag and vWF:RCo decreased after 24 hours of ECMO (mean ± SD, vWF:Ag, 307% ± 152% to 261% ± 138%, P = 0.002; vWF:RCo 282% ± 145% to 157% ± 103%, P < 0.0001) and remained lower during ongoing support (vWF:Ag 265% ± 128%, P = 0.025; vWF:RCo 163% ± 94%, P < 0.0001). After termination of ECMO, vWF:Ag was greater than baseline (359% ± 131%, P = 0.004) and vWF:RCo was similar to baseline levels (338% ± 142%, P = 0.046). Compared with baseline, the calculated vWF:RCo/vWF:Ag ratio decreased after 24 hours on support (0.96 ± 0.23 to 0.61 ± 0.17, P ≤ 0.0001) and remained lower during 48 hours on ECMO (0.63 ± 0.18, P ≤ 0.0001). After termination of ECMO support (0.94 ± 0.19, P = 0.437), values rapidly returned to baseline. The number of HMW vWF multimers (n) decreased from baseline after 24 hours on ECMO (21 ± 1.4 to 14 ± 1.8, P ≤ 0.0001) and after 48 hours on ECMO (15 ± 2.1, P ≤ 0.0001). Twenty-four hours after termination of ECMO support, HMW vWF multimeric pattern had returned to baseline values (21 ± 1.8, P = 0.551). Loss of HMW vWF multimer bands occurred in patients undergoing ECMO support and resolved after the termination of ECMO. Although not detectable with coagulation screening tests, a vWF:RCo/vWF:Ag ratio <0.7 during ECMO was highly indicative for loss of HMW vWF multimers. Our findings may at least in part explain increased bleeding tendency during ECMO therapy. Administration of vWF concentrates may support restoration of primary hemostasis in patients with relevant bleeding during ECMO support.

The effect of shear stress on the size, structure, and function of human von Willebrand factor.

Clinical outcomes from ventricular assist devices (VADs) have improved significantly during recent decades, but bleeding episodes remain a common complication of long-term VAD usage. Greater understanding of the effect of the shear stress in the VAD on platelet aggregation, which is influenced by the functional activity of high molecular weight (HMW) von Willebrand factor (vWF), could provide insight into these bleeding complications. However, because VAD shear rates are difficult to assess, there is a need for a model that enables controlled shear rates to first establish the relationship between shear rates and vWF damage. Secondly, if such a dependency exists, then it is relevant to establish a rapid and quantitative assay that can be used routinely for the safety assessment of new VADs in development. Therefore, the purpose of this study was to exert vWF to controlled levels of shear using a rheometer, and flow cytometry was used to investigate the shear-dependent effect on the functional activity of vWF. Human platelet-poor plasma (PPP) was subjected to different shear rate levels ranging from 0 to 8000/s for a period of 6 h using a rheometer. A simple and rapid flow cytometric assay was used to determine platelet aggregation in the presence of ristocetin cofactor as a readout for vWF activity. Platelet aggregates were visualized by confocal microscopy. Multimers of vWF were detected using gel electrophoresis and immunoblotting. The longer PPP was exposed to high shear, the greater the loss of HMW vWF multimers, and the lower the functional activity of vWF for platelet aggregation. Confocal microscopy revealed for the first time that platelet aggregates were smaller and more dispersed in postsheared PPP compared with nonsheared PPP. The loss of HMW vWF in postsheared PPP was demonstrated by immunoblotting. Smaller vWF platelet aggregates formed in response to shear stress might be a cause of bleeding in patients implanted with VADs. The methodological approaches used herein could be useful in the design of safer VADs and other blood handling devices. In particular, we have demonstrated a correlation between the loss of HMW vWF, analyzed by immunoblotting, with platelet aggregation, assessed by flow cytometry. This suggests that flow cytometry could replace conventional immunoblotting as a simple and rapid routine test for HMW vWF loss during in vitro testing of devices.

Severity of VWF Multimer Loss Is Associated with Bleeding Tendency in Continuous Flow Left Ventricular Assist Device Recipients

AbstractAbstract 1122 Background:Continuous flow left ventricular assist device (CF-LVAD) recipients have increased tendency of post-surgical bleeding. We have previously described a universal loss of high molecular weight VWF multimers (HMWM), likely due to enhanced cleavage of the HMWM in CF-LVAD recipients. Among various VWF laboratory tests, VWF multimer analysis remains the reference method for detecting such an acquired VWF abnormality (AVWA). We hypothesize that the severity of AVWA is a predictor for bleeding tendency. In this study, using our in-gel VWF multimer electrophoresis method, we measured the severity of HMWM loss in CF-LVAD recipients by infra-red densitometry analysis and examined its association with other VWF activity test results and patients' bleeding tendency. Design:As part of an on-going prospective multicenter study, pre- and/or post-CF-LVAD implantation (7, 30 days and 5–7 months) blood samples were collected from 20 LVAD recipients during 2008 and 2009. Their clinically significant bleeding episodes were recorded. Plasma VWF antigen (VWF:Ag), VWF:Lx activity [Chen D, et al. J Thromb Haemost. 2011;9(10):1993–2002] and plasma VWF multimer analyses [Pruthi RK, et al. Thromb Res. 2010;126(6):543–9] were performed on all available plasma samples. VWF multimers were quantified by infra-red fluorescent densitometry analysis using Odyssey Infrared Imager version 2.0. VWF:multi ratio defined by density ratio between the high molecular weight multimer (HMWM, bands 11 and above) and low and intermediate molecular weight multimer (band 2 to 9) was calculated. Normal range of VWF:multi ratio was determined from 16 normal donor plasma and 4 pooled normal plasma. Statistical analyses including t-test and kappa test were employed. Result:The normal range of VWF:multi ratio is 0.4–0.76. The CV of VWF:multi ratio of a pooled normal plasma tested in 21 gel runs is 12%. Loss of VWF HMWM is present in three patients before CF-LVAD implantation and all patients after implantation. All samples with loss of HMWM show decreased VWF:multi ratio (<0.4). At a cut-off value of 0.4, the sensitivity and specificity of VWF:multi ratio for detecting HMWM loss are 100% and 95.5% respectively (n=67). Decrease of VWF:multi ratio is observed after implantation (0.41±0.07 pre- vs. 0.29±0.07 post-implantation, P<0.00001). In four patients who received heart transplantation, normalization of VWF multimer pattern and VWF:multi ratio (0.54±0.06) is observed. Ten patients had significant post-implantation bleeding episodes that are associated with significantly decreased VWF:multi ratio (0.26±0.04 bleeding vs. 0.32±0.09 non-bleeding, P=0.002) and VWF Lx/Ag ratio (0.72±0.10 bleeding vs 0.80±0.09 non-bleeding, P=0.001). At a cut-off of 0.26, VWF:multi ratio demonstrates a sensitivity of 64% and specificity of 85.7% for predicting clinically significant bleeding. The VWF:multi ratio shows moderate agreement with VWF:Lx/Ag ratio (Kappa value 0.42). Conclusions:Severity of VWF HMWM losses can be quantitatively measured by the new in-gel infra-red densitometry method (VWF:multi ratio). Severity of VWF HMWM losses defined by the VWF:multi ratios, along with VWF:Lx/Ag ratios are significantly associated with bleeding tendency in LVAD recipients. Disclosures:Milano:Thoratec: Consultancy.

Detection of Continuous Flow Left Ventricular Assist Device -Associated Acquired Von Willebrand Factor (VWF) Abnormality by An Automated Immunoturbidimetric VWF Activity Assay

Abstract▪2273▪This icon denotes a clinically relevant abstract Background:Continuous flow left ventricular assist device (CF-LVAD) recipients have high tendency of post-surgical gastrointestinal (GI) bleeding. We previously described the loss of high molecular weight VWF multimers (HMWM), due to either an accelerated clearance or enhanced cleavage of the HMWM, in most CF-LVAD recipients (Ann Thorac Surg. 90:1263–9). However, besides the tedious plasma VWF multimer analysis, neither VWF ristocetin cofactor nor collagen binding activity assay provides sufficient sensitivity for detecting such an acquired VWF abnormality (AVWA). In this study, we examined a new automated latex particle-enhanced immunoturbidimetric VWF activity assay (VWF:Lx) for its ability of detecting CF-LVAD-AVWA. We also analyzed the VWF pro-peptide (VWF:pp) to explored the potential mechanism of CF-LVAD-AVWA. Design:As part of an on-going prospective multicenter study, pre- and post-CF-LVAD implantation (7, 30 days and 5–7 months) blood samples were collected from 15 LVAD recipients (median age 52 years; 10 male and 5 female; 2008∼2009). Plasma VWF antigen (VWF:Ag), VWF:Lx activity, VWF:pp/Ag ratios were measured; and plasma VWF multimer analyses were performed on all available plasma samples. Standard statistical analyses were employed. Result:Loss of VWF HMWM was observed in 3 patients prior to CF-LVAD implantation and virtually all patients after surgery. VWF:Ag, VWF:Lx or VWF:pp/Ag ratios of the pre- and post-implantation samples were not significantly different (P> 0.1). However, VWF:Lx/Ag ratios of the post-implantation samples were significantly decreased (P<0.05). At a cut off of 0.8, the VWF:Lx/Ag ratio has a 90% sensitivity and specificity for detecting AVWA. Conclusions:VWF:Lx/Ag ratio has excellent sensitivity and specificity in detecting CF-LVAD-AVWA, and its impact on predicting post-surgical bleeding tendency in CF-LVAD recipients is being investigated. The distinct CF-LVAD-AVWA is most likely caused by enhanced cleavage, rather than clearance, of the HMWM.Table 1:Laboratory Characteristics of VWF in Pre- and Post-CF-LVAD Implantation Patient Plasma Samples.Laboratory Results (Mean±Standard Deviation)Pre-implantation (n=15)Day 7 Post (n=13)Day 30 Post (n=13)5–7 month Post (n=4)VWF:Ag (IU/dL)318 ± 178340 ± 136263.8 ± 122.7224 ± 78VWF:Lx (U/dL)258 ± 145246 ± 87102.5 ± 64.6165 ± 44VWF:Lx/Ag Ratio0.82 ± 0.120.74 ± 0.080.75 ± 0.060.76 ± 0.12VWF:pp/Ag Ratio1.04 ± 0.361.00 ± 0.300.99 ± 0.231.02 ± 0.10Samples with HMWM Loss (Present/Total)3/1510/1312/134/4Agreement between abnormal VWF:Lx/Ag ratio (<0.8) and VWF Multimer Analysis13/1511/1312/134/4 Disclosures:No relevant conflicts of interest to declare.

Mechanisms of Bleeding and Approach to Patients With Axial-Flow Left Ventricular Assist Devices

Axial-flow LVADs have become an integral tool in the management of end-stage heart failure. Consequently, nonsurgical bleeding has emerged as a major source of morbidity and mortality in this fragile population. The mechanisms responsible for these adverse events include acquired von Willebrand disease, GI tract angiodysplasia formation, impaired platelet aggregation, and overuse of anticoagulation therapy. Because of ongoing concerns for pump thrombosis and thromboembolic events, the thrombotic/bleeding paradigm has led to a difficult clinical dilemma for those managing patients treated with axial flow LVADs. As the field progresses, advances in the understanding of the pathological mechanisms underlying bleeding/thrombosis risk, careful risk stratification, and potential use of novel anticoagulants will all play a role in the management of the LVAD patient.

Acquired von Willebrand Syndrome in Continuous-Flow Ventricular Assist Device Recipients

Bleeding is a major cause of morbidity in recipients of continuous-flow left ventricular assist devices (CF-LVAD). A better understanding of the impact of CF-LVAD support on the hemostatic profile is necessary to establish better strategies for anticoagulation therapy and risk assessment for bleeding complications. A prospective multicenter study was conducted to characterize von Willebrand factor (vWF) profiles in patients undergoing CF-LVAD implantation. Blood samples were collected before and after CF-LVAD implantation from 37 patients between July 2008 and April 2009 at Duke University and the University of Minnesota. Blood samples were analyzed for vWF, platelet and collagen-binding ability. The presence of high-molecular-weight (HMW) vWF multimers were detected through gel electrophoresis, and deficiency was graded on a scale of 0 (normal) to 3 (severe loss). All 37 patients exhibited significant loss of HMW vWF multimers within 30 days of CF-LVAD implantation. Ten of the 37 patients experienced bleeding complications after CF-LVAD placement. All CF-LVAD recipients had acquired von Willebrand syndrome after LVAD placement, demonstrated by reduced or absent HMW vWF multimer levels. However, not all recipients had bleeding complications. These findings suggest that loss of HMW vWF multimers alone cannot predict bleeding risk. Further refinement of laboratory techniques and a larger follow-up is required to identify risk factors for bleeding in CF-LVAD recipients.