Proteolysis of von Willebrand factor and shear stress-induced platelet aggregation in patients with aortic valve stenosis

Impact of transcatheter aortic valve implantation on circulating von Willebrand factor in patients with severe aortic stenosis

INTRODUCTION

Severe aortic stenosis (AS) can lead to degradation of high molecular weight (HMW) von Willebrand factor (VWF) which can result in haemostatic abnormalities. While studies have explored changes in VWF profiles before and after surgical aortic valve replacement (SAVR), the longer-term changes in VWF profiles pre- and post-transcatheter aortic valve implantation (TAVI) are less understood.

AIM

Our primary objective was to identify differences in VWF multimer profiles and VWF function pre-TAVI and 1-month post-TAVI. Our secondary objective was to correlate VWF markers with measures of AS severity.

METHODS

Adult patients with severe AS referred for TAVI at our institution were prospectively enrolled in this cohort study. Blood samples were collected for plasma analysis at three time points for all patients: 1 day pre-TAVI, 3 days post-TAVI, and 1-month post-TAVI. VWF antigen, activity, propeptide, collagen binding, multimers, and factor VIII coagulant activity were determined at each time point. Correlations between VWF parameters and severity of AS were assessed.

RESULTS

Twenty participants (15 males, five females) with severe AS were recruited for the study. There was a significant increase in HMW VWF between pre-procedure and 1-month post-TAVI (p < .05). There was a transient increase in VWF antigen levels and activity at 3-days post TAVI that decreased to pre-TAVI levels at 1-month. There were no statistically significant correlations between VWF markers and AS severity.

CONCLUSIONS

This is the first study to elucidate longer-term (>1 week) improvements in HMW VWF after a TAVI procedure in severe AS patients.

Effectiveness of aortic valve replacement in Heyde syndrome: a meta-analysis

AIMS

Heyde syndrome is the co-occurrence of aortic stenosis, acquired von Willebrand syndrome, and gastrointestinal bleeding. Aortic valve replacement has been demonstrated to resolve all three associated disorders. A systematic review and meta-analysis were performed to obtain best estimates of the effect of aortic valve replacement on acquired von Willebrand syndrome and gastrointestinal bleeding.

METHODS AND RESULTS

A literature search was performed to identify articles on Heyde syndrome and aortic valve replacement up to 25 October 2022. Primary outcomes were the proportion of patients with recovery of acquired von Willebrand syndrome within 24 h (T1), 24-72 h (T2), 3-21 days (T3), and 4 weeks to 2 years (T4) after aortic valve replacement and the proportion of patients with cessation of gastrointestinal bleeding. Pooled proportions and risk ratios were calculated using random-effects models. Thirty-three studies (32 observational studies and one randomized controlled trial) on acquired von Willebrand syndrome (n = 1054), and 11 observational studies on gastrointestinal bleeding (n = 300) were identified. One study reported on both associated disorders (n = 6). The pooled proportion of Heyde patients with acquired von Willebrand syndrome recovery was 86% (95% CI, 79%-91%) at T1, 90% (74%-96%) at T2, 92% (84%-96%) at T3, and 87% (67%-96%) at T4. The pooled proportion of Heyde patients with gastrointestinal bleeding cessation was 73% (62%-81%). Residual aortic valve disease was associated with lower recovery rates of acquired von Willebrand syndrome (RR 0.20; 0.05-0.72; P = 0.014) and gastrointestinal bleeding (RR 0.57; 0.40-0.81; P = 0.002).

CONCLUSION

Aortic valve replacement is associated with rapid recovery of the bleeding diathesis in Heyde syndrome and gastrointestinal bleeding cessation. Residual valve disease compromises clinical benefits.

Acquired von Willebrand syndrome: Five cases report and literature review

Acquired von Willebrand syndrome is a rare bleeding disorder with laboratory findings similar to those of inherited von Willebrand disease. Principal factors distinguishing acquired von Willebrand syndrome from the latter condition include lack of prior bleeding disorders, diagnosis at older age, negative family history and association with underlying conditions.

METHODS

Retrospective, monocentric descriptive case series of acquired von Willebrand syndrome diagnosed between 2010 and 2020. Diagnostic criteria included a recent history of bleeding, a negative family history and a presence of underlying disorders.

RESULTS

Five men were diagnosed with acquired von Willebrand syndrome. All of them presented with recent mucocutaneous bleeding. The biological phenotype was a type 2 von Willebrand disease in all cases, with decreased VWF:RCo/VWF:Ag and VWF:CB/VWF:Ag ratios (<0.7). Lymphoproliferative, autoimmune and cardiovascular diseases were the main underlying conditions identified. Screening for an anti-von Willebrand factor inhibitor was positive in two patients. Four patients received treatment for the underlying disorder. High-dose intravenous immunoglobulins were the most frequent treatment administrated. Improvement of plasma von Willebrand factor levels was observed in four cases.

CONCLUSION

Acquired von Willebrand syndrome is a rare but potentially serious disease. The diagnostic should be suspected in adults with unusual mucocutaneous bleeding associated with lymphoproliferative, myeloproliferative, autoimmune and cardiovascular disorders.

Comparison Between Intravenous and Intramuscular Octreotide in the Management of Heyde’s Syndrome

Heyde’s syndrome is defined as a triad of aortic stenosis, anemia due to angiodysplasia-related bleeding, and von Willebrand syndrome type 2A. It is a rare disease and a diagnostic challenge. Treatment modalities include symptomatic management, blood transfusions, aortic valve replacement, and medications such as octreotide. Here, we report the case of a patient who was resistant to symptomatic management, aortic valve replacement, as well as intravenous octreotide.

Circulating Monocyte Subsets and Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement (TAVR), as an alternative to open heart surgery, has revolutionized the treatment of severe aortic valve stenosis (AVS), the most common valvular disorder in the elderly. AVS is now considered a form of atherosclerosis and, like the latter, partly of inflammatory origin. Patients with high-grade AVS have a highly disturbed blood flow associated with high levels of shear stress. The immediate reopening of the valve during TAVR leads to a sudden restoration of a normal blood flow hemodynamic. Despite its good prognosis for patients, TAVR remains associated with bleeding or thrombotic postprocedural complications, involving mechanisms that are still poorly understood. Many studies report the close link between blood coagulation and inflammation, termed thromboinflammation, including monocytes as a major actor. The TAVR procedure represents a unique opportunity to study the influence of shear stress on human monocytes, key mediators of inflammation and hemostasis processes. The purpose of this study was to conduct a review of the literature to provide a comprehensive overview of the impact of TAVR on monocyte phenotype and subset repartition and the association of these parameters with the clinical outcomes of patients with severe AVS who underwent TAVR.

Recurrent gastrointestinal bleeding in a patient with Heyde syndrome with elevated factor VIII levels: A case report

Heyde syndrome is the association between gastrointestinal (GI) bleeding from intestinal angiodysplasia (IA) and aortic stenosis (AS). Although the course of disease progression that links AS and GI bleeding has not been determined, overlaps among AS, intestinal dysplasia, and acquired von Willebrand's syndrome is thought to result in GI bleeding. Proper repair of the aortic valve can result in significant improvement of GI bleeding and its recurrence. Herein, we are reporting this rare case, in which a patient with moderate AS on echocardiogram presents with recurrent GI bleeding from multiple IA in the setting of elevated factor VIII levels, to propose a theory that angiodysplasia could potentially develop due to intermittent, recurrent low-grade obstruction of submucosal veins at the level of the muscularis propria secondary to venous thrombosis related to elevated factor VIII levels.

Dynamic changes in platelets caused by shear stress in aortic valve stenosis

BACKGROUND AND OBJECTIVE:

Turbulent blood flow in patients with aortic valve stenosis (AS) results in morphological and functional changes in platelets and coagulation factors. The aim of this study is to determine how shear stress affects platelets and coagulation factors.

METHODS:

We retrospectively evaluated data from 78 patients who underwent AVR to treat AS between March 2008 and July 2017 at Kagoshima University Hospital.

RESULTS:

Platelet (PLT) count obviously decreased at three days after AVR, and increased above preoperative levels at the time of discharge. In contrast, platelet distribution width (PDW), mean platelet volume (MPV), and platelet large cell ratio (P-LCR) increased three days after AVR, then decreased to below preoperative levels. No differences were evident between groups with higher (HPPG > 100 mmHg) and lower (LPPG < 100 mmHg) peak pressure gradients (PPG) before AVR, whereas PLT count, PDW, MPV and P-LCR improved more in the HPPG group. Plateletcrit (PCT), which represents the total volume of platelets, increased after AVR due to decreased shear stress. High increasing rate of PCT was associated with lower PLT count, higher PDW and lower fibrinogen.

CONCLUSION:

Shear stress affects PLT count, PDW, and fibrinogen in patients with AS.

Von Willebrand factor in aortic or mitral valve stenosis and bleeding after heart valve surgery

OBJECTIVES

Low von Willebrand factor (VWF) increases the risk of bleeding. The objective was to assess the influence of VWF on bleeding after valvular surgery.

METHODS

We studied 82 consecutive patients in median age of 65.5 years with severe isolated aortic stenosis (AS, n = 62) or mitral stenosis (MS, n = 20), undergoing heart valve surgery in extracorporeal circulation. Preoperatively, we assessed VWF antigen (VWF:Ag) and activity (VWF:RCo), a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), and fibrinolysis inhibitors.

RESULTS

Compared with AS, MS patients were more frequently female (80 vs. 55%, p = 0.045) with atrial fibrillation (AF) (80 vs. 8%, p < 0.0001), with no difference in age or comorbidities. Median postoperative drainage was 420 ml for AS, and 425 ml for MS (p = 0.37). Patients with AS had lower VWF:RCo (125.8 [88.5-160.8] vs. 188.0 [140.3-207.3] IU/dl, p = 0.003) and VWF:Ag (135.8 [112.0-171.2] vs. 191.7 [147.3-236.4] IU/dl, p = 0.01) than MS patients. Mean VWF:RCo/Ag ratio was 0.88 ± 0.17, with no intergroup differences. ADAMTS13 levels and activity were similar in both groups. In AS, both VWF:RCo and VWF:Ag correlated inversely with maximal (r = -0.39, p = 0.0003 and r = -0.39, p = 0.0004, respectively) and mean (r = -0.40, p = 0.0004 and r = -0.39, p = 0.0006, respectively) transvalvular pressure gradients. There was no difference in perioperative bleeding between patients following mitral and aortic valve surgery, and bleeding was not associated with VWF:Ag or VWF:RCo.

CONCLUSIONS

In severe AS, VWF levels and activity correlate inversely with transvalvular pressure gradients, and are lower than in severe degenerative MS, but do not affect blood loss after valvular surgery in extracorporeal circulation.

Acquired von Willebrand syndrome: focused for hematologists

The acquired von Willebrand syndrome (AvWS) is a rare bleeding disorder with laboratory findings similar to those of inherited von Willebrand disease. However, unlike the inherited disease, AvWS occurs in persons with no personal and family history of bleeding and is often associated with a variety of underlying diseases, most frequently lymphoproliferative, myeloproliferative and cardiovascular disorders. After the presentation of a typical case, in this narrative review we discuss the more recent data on the pathophysiology, clinical, laboratory and therapeutic aspects of this acquired bleeding syndrome. We chose to focus particularly on those aspects of greater interest for the hematologist.

Pre-procedural abnormal function of von Willebrand Factor is predictive of bleeding after surgical but not transcatheter aortic valve replacement

Both transcatheter aortic valve implantation (TAVI) and surgical aortic valve replacement (SAVR) have been proven to effectively correct von Willebrand Factor (vWF) pathologies, however there is limited data simultaneously comparing outcomes of both approaches. We prospectively enrolled patients with severe aortic stenosis referred for TAVI (n = 52) or SAVR (n = 48). In each case, vWF antigen (vWF:Ag), vWF activity (vWF:Ac) and activity-to-antigen (vWF:Ac/Ag) ratio were assessed at baseline, 24 h and 72 h after procedure. VWF abnormalities were defined as reduced vWF:Ac/Ag ratio (< 0.8). Bleeding events in both arms were classified according to Valve Academic Research Consortium (VARC-2) definitions. Overall, there was no difference between patients referred for TAVI and SAVR in vWF:Ac (1.62 ± 0.52 vs 1.71 ± 0.64; p = 0.593), vWF:Ag (1.99 ± 0.81 vs 2.04 ± 0.81; p = 0.942) or vWF:Ac/Ag ratio (0.84 ± 0.16 vs 0.85 ± 0.12; p = 0.950). Pathological vWF:Ac/Ag ratio was found in 20 (38%) TAVI and 15 (31%) SAVR patients (p = 0.407). Normalization of vWF:Ac/Ag ratio at day 3 after procedure was achieved in 19 (95%) TAVI and 13 (87%) SAVR patients (p = 0.439). Similar prevalence of major or life-threatening bleedings (MLTB) after TAVI and SAVR in entire groups was observed (19% vs. 23%, p = 0.652). VWF abnormalities were associated with higher incidence of MLTB in SAVR (53% vs 9%, p < 0.001), but not TAVI (15% vs. 22%, p = 0.132). Accordingly, in receiver-operating characteristic curve analysis vWF:Ac/Ag ratio < 0.8 showed significant sensitivity and specificity for predicting MLTB in SAVR group (AUC 0.735, 95% CI 0.538–0.931, p = 0.019). We proved that abnormal function of vWF is corrected successfully after both TAVI and SAVR, but vWF abnormalities are predictive of MLTB only in surgical patients.

METALLOPROTEASE ADAMTS-13

Introduction. The signifi cance of ADAMTS-13 extends beyond its key role in the pathogenesis of thrombotic thrombocytopenic purpura (TTP); there is evidence of a relationship between a decrease in the ADAMTS-13 activity and thrombotic events in acute myocardial infarction and ischemic stroke.

Aim. To generalise available information on the structure and function of the metalloprotease ADAMTS-13.

General findings. The biological function of ADAMTS-13 consists in the cleavage of ultra-large von Willebrand factor (vWF) multimers. The fact that its defi ciency causes the development of TTP provides a basis for understanding the function of vWF–cleaving protease. ADAMTS-13 has a domain structure. The functional roles of most ADAMTS-13 domains, as well as the key role of the ADAMTS-13-vWF interaction in the regulation of haemostasis, are defi ned. The conformational activation of ADAMTS-13 by vWF constitutes an important aspect of its function. After getting into the bloodstream, ultra-large vWF multimers quickly adopt a closed conformation, which becomes very resistant to ADAMTS-13 proteolysis in the absence of shear stress. Ultra-large plasma vWF multimers regain their sensitivity to ADAMTS-13 after being exposed to high fl uid shear stress, which unfolds the central vWF-A2 domain. The unfolding of a vWF molecule under shear stress conditions reveals previously hidden exosites in domain A2, which gradually increase the binding affi nity between ADAMTS-13 and vWF. The mechanism underlying the production of autoantibodies against ADAMTS-13 is unknown and requires further study. The masking of cryptic epitopes in the closed conformation of ADAMTS-13 prevents the formation of autoantibodies. Early antigen recognition of ADAMTS-13 occurs through surface-exposed epitopes in the C-terminal domains. More detailed information on the mechanisms underlying the interaction between ADAMTS-13 and the vWF can improve the understanding of mechanisms involved in the regulation of the coagulation system.

Conflict of interest: the authors declare no confl ict of interest.

Financial disclosure: the study had no sponsorship.

Special considerations in the management of lower GI bleed by interventional radiology

Despite the rapid development of diagnostic and therapeutic modalities and techniques to manage LGIB patients from interventional radiology's standpoint, a successful localization of the bleeding site that leads to an effective embolotherapy remains a significant technical challenge. The interventional radiologist's decisions when managing patients with LGIB may significantly impact the clinical outcomes; therefore, management should be made based on careful and thorough considerations of factors such as etiology, locations, patient's comorbidities, and potential post-procedure complications, among others. The purpose of this paper is to review the management of LGIB by interventional radiology, focusing on a few challenging and common clinical situations that require special consideration by interventional radiologists.

Thrombotic microangiopathy in a very young infant with mitral valvuloplasty

BACKGROUND

Thrombotic microangiopathies (TMA) are microvascular occlusive disorders characterized by systemic or intrarenal platelet aggregation, thrombocytopenia, and red cell fragmentation. Post-operative TMA mostly occurs in adult patients with cardiovascular surgery, with the distinct pathophysiology from classical thrombotic thrombocytopenic purpura (TTP) although the exact pathophysiology remains unclear.

CASE PRESENTATION

A one-month-old infant developed TMA after the initial surgery of double outlet right ventricle. ADAM metallopeptidase with thrombospondin type 1 motif 13 (ADAMTS13) activity was sustained (64%) with the undetectable inhibitor. Von Willebrand factor (VWF) multimer analyses showed absent high-molecular weight multimers. Echocardiography disclosed severe mitral regurgitation. The mitral valve repair 32 days after the initial valvuloplasty led to prompt resolution of TMA. These suggested that TMA occurred in association with valvulopathy-triggered turbulent shear flow, mechanical hemolysis and endothelial damage. The consumption of large VWF multimers might account for the vascular high shear stress shown in Heyde syndrome.

CONCLUSION

The youngest case of post-operative TMA underscores the critical coagulopathy after the first surgical intervention for congenital heart disease.

A Case of Heyde Syndrome with Resolution of Gastrointestinal Bleeding Two Weeks After Aortic Valve Replacement

Patient: Female, 56

Final Diagnosis: Heyde syndrome

Symptoms: Anemia • gastrointesinal haemorrhage

Medication: —

Clinical Procedure: Colonoscopy • EGD • TAVR

Specialty: Gastroenterology and Hepatology

Outcomes in anticoagulated patients with atrial fibrillation and with mitral or aortic valve disease

Objective

To assess stroke/systemic embolism, major bleeding and other outcomes, and treatment effect of apixaban versus warfarin, in patients with atrial fibrillation (AF) and different types of valvular heart disease (VHD), using data from the Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation trial.

Methods

There were 14 793 patients with known VHD status, categorised as having moderate or severe mitral regurgitation (MR) (n=3382), aortic regurgitation (AR) (n=842) or aortic stenosis (AS) (n=324); patients with moderate or severe mitral stenosis were excluded from the trial. Baseline characteristics, efficacy and safety outcomes were compared between each type and no significant VHD. Treatment effect was assessed using an adjusted model.

Results

Patients with MR or AR had similar rates of stroke/systemic embolism and bleeding compared with patients without MR or AR, respectively. Patients with AS had significantly higher event rates (presented as rate per 100 patient-years of follow-up) of stroke/systemic embolism (3.47 vs 1.36; adjusted HR (adjHR) 2.21, 95% CI 1.35 to 3.63), death (8.30 vs 3.53; adjHR 1.92, 95% CI 1.41 to 2.61), major bleeding (5.31 vs 2.53; adjHR 1.80, 95% CI 1.19 to 2.75) and intracranial bleeding (1.29 vs 0.51; adjHR 2.54, 95% CI 1.08 to 5.96) than patients without AS. The superiority of apixaban over warfarin on stroke/systemic embolism was similar in patients with versus without MR (HR 0.69, 95% CI 0.46 to 1.04 vs HR 0.79, 95% CI 0.63 to 1.00; interaction P value 0.52), with versus without AR (HR 0.57, 95% CI 0.27 to 1.20 vs HR 0.78, 95% CI 0.63 to 0.96; interaction P value 0.52), and with versus without AS (HR 0.44, 95% CI 0.17 to 1.13 vs HR 0.79, 95% CI 0.64 to 0.97; interaction P value 0.19). For each of the primary and secondary efficacy and safety outcomes, there was no evidence of a different effect of apixaban over warfarin in patients with any VHD subcategory.

Conclusions

In anticoagulated patients with AF, AS is associated with a higher risk of stroke/systemic embolism, bleeding and death. The efficacy and safety benefits of apixaban compared with warfarin were consistent, regardless of presence of MR, AR or AS.

Clinical trial registration

ARISTOTLE clinical trial number NCT00412984.

von Willebrand factor abnormalities in aortic valve stenosis: Pathophysiology and impact on bleeding

Acquired von Willebrand syndrome (AVWS) may complicate severe aortic valve stenosis, due to a reduction in the haemostatically more efficient large von Willebrand factor (VWF) multimers. This study was designed to analyse the relevance of VWF abnormalities and haemorrhagic diathesis in severe aortic valve stenosis. Forty-one consecutive patients undergoing valve replacement were investigated: seven had minor bleeding symptoms in their recent history; 10 (24.3%) had a reduced VWF collagen binding (VWF:CB) to VWF antigen ratio, and 33 (80.5%) had a decrease in large VWF multimers. The shortage of large multimers was not associated with any accumulation of small VWF multimers (apparently ruling out any increased VWF proteolysis), nor was there any increase in VWF propeptide, which excludes a shorter VWF survival. The risk of developing VWF abnormalities was higher in patients with rheumatic valve disease than in degenerative cases (p=0.025) and in valves with <50% of residual endothelial cells (p=0.004). Bleeders differed from non-bleeders in that they had a higher mean transvalvular gradient and a more marked decrease in large VWF multimers. VWF abnormalities did not exacerbate peri-operative blood loss, however – a finding consistent with the full correction of these VWF abnormalities, seen already on the first postoperative day and persisting for up to six months after surgery. According to the data obtained in our cohort of patients VWF abnormalities are common in severe aortic stenosis, particularly in cases of rheumatic valve disease, but loss of the largest multimers does not seem to cause clinical bleeding in most patients.

Changes in von Willebrand factor-cleaving protease (ADAMTS-13) in patients with aortic stenosis undergoing valve replacement or balloon valvuloplasty

It was the objective of this study to determine whether reduced cleavage of von Willebrand factor (VWF) multimers following aortic valve replacement (AVR) is a consequence of reduced shear stress or postoperative changes in VWF cleavage protease (ADAMTS-13) activity. Aortic stenosis (AS) may be complicated by acquired von Willebrand disease. Aortic valve replacement (AVR) corrects the associated haematologic abnormalities. We enrolled 114 patients with severe AS scheduled for either balloon aortic valvuloplasty (BAV; n=64) or AVR (n=50). Haematologic assessments of VWF levels and activity and ADAMTS-13 were performed before and 24 hours after valve intervention. The VWF:RCo to VWF:Ag ratio, a surrogate for large VWF multimer activity, increased by 37% (p < 0.0001) after AVR and by 10% (p = 0.0002) after BAV. ADAMTS-13 activity significantly decreased after AVR (579 ± 127 to 468 ± 135 ng/ml; p<0.0001), but not after BAV (484 ± 153 to 529 ± 185 ng/ml; p = 0.10). By multivariable analysis, the change in VWF:RCo ratio after AVR was more strongly associated with the fall in ADAMTS-13 than with reduction of valve gradient; whereas the change in gradient better predicted the rise in VWF:RCo after BAV. In conclusion, both BAV and AVR reverse the haematological abnormalities of the acquired von Willebrand syndrome of AS and ADAMTS-13 levels decrease after AVR. These findings suggest that a portion of the haematologic benefit of AVR may be due to a postoperative decline in ADAMTS-13 rather than solely to relief of AS as previously thought.

Space and Time Resolved Detection of Platelet Activation and von Willebrand Factor Conformational Changes in Deep Suspensions

Tracking cells and proteins' phenotypic changes in deep suspensions is critical for the direct imaging of blood-related phenomena in in vitro replica of cardiovascular systems and blood-handling devices. This paper introduces fluorescence imaging techniques for space and time resolved detection of platelet activation, von Willebrand factor (VWF) conformational changes, and VWF-platelet interaction in deep suspensions. Labeled VWF, platelets, and VWF-platelet strands are suspended in deep cuvettes, illuminated, and imaged with a high-sensitivity EM-CCD camera, allowing detection using an exposure time of 1 ms. In-house postprocessing algorithms identify and track the moving signals. Recombinant VWF-eGFP (rVWF-eGFP) and VWF labeled with an FITC-conjugated polyclonal antibody are employed. Anti-P-Selectin FITC-conjugated antibodies and the calcium-sensitive probe Indo-1 are used to detect activated platelets. A positive correlation between the mean number of platelets detected per image and the percentage of activated platelets determined through flow cytometry is obtained, validating the technique. An increase in the number of rVWF-eGFP signals upon exposure to shear stress demonstrates the technique's ability to detect breakup of self-aggregates. VWF globular and unfolded conformations and self-aggregation are also observed. The ability to track the size and shape of VWF-platelet strands in space and time provides means to detect pro- and antithrombotic processes.

von Willebrand factor disruption and continuous-flow circulatory devices

Bleeding events remain a significant and frequent complication of continuous-flow left ventricular assist devices (VADs). von Willebrand factor (VWF) is critical to hemostasis by acting as a bridging molecule at sites of vascular injury for normal platelet adhesion as well as promoting platelet aggregation under conditions of high shear. Clinical and experimental data support a role for acquired von Willebrand disease in VAD bleeding episodes caused by shear-induced qualitative defects in VWF. Pathologic shear induces VWF unfolding and proteolysis of large multimers into smaller less hemostatic multimers via ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). This review outlines the pathobiology of VWF disruption in the context of VADs as well as current diagnostic and management strategies of the associated acquired von Willebrand disease.

Angiodysplasia in von Willebrand Disease: Understanding the Clinical and Basic Science

Severe and intractable gastrointestinal bleeding caused by angiodysplasia is a debilitating problem for up to 20% of patients with von Willebrand disease (VWD). Currently, the lack of an optimal treatment for this recurrent problem presents an ongoing challenge for many physicians in their management of affected patients. Over the past few years, studies have pointed to a regulatory role for the hemostatic protein, von Willebrand factor (VWF), in angiogenesis, providing a novel target for the modulation of vessel development. This article will review the clinical implications and molecular pathology of angiodysplasia in VWD.

Unusual Gastrointestinal Bleeding After Sutureless Aortic Valve Replacement: A Word of Caution

We report the clinical case of a male patient who presented, after an aortic valve replacement with a rapid deployment bioprosthesis, a Heyde-like syndrome, secondary to a moderate aortic paravalvular leakage. All the digestive and hematologic investigations confirmed the diagnosis. A redo surgery to fill the paravalvular gap was accomplished and the postoperative course was uneventful, with a normalization of the biological parameters. To our knowledge, this is the first described case of such a complication with the new generation of sutureless bioprosthesis.

Acquired von Willebrand syndrome in children with aortic and pulmonary stenosis

INTRODUCTION

This prospective study was planned to investigate the frequency and relationship of acquired von Willebrand syndrome (AVWS) with aortic and pulmonary stenosis in patients.

METHODS

A total of 84 children, ranging from two to 18 years of age, were enrolled in this study. Of these, 28 had isolated aortic stenosis, 32 had isolated pulmonary stenosis and 24 were healthy. Children with aortic and pulmonary stenosis associated with other congenital heart diseases were excluded. Children with hypothyroidism, renal or liver disease, malignancy or autoimmune disease were also excluded. Wholeblood count, blood group, factor VIII level, prothrombin time (PT), activated partial thromboplastin time (aPTT), von Willebrand factor antigen (VWF:Ag), ristocetin co-factor (VWF:RCo), and bleeding time using a platelet-function analyser (PFA-100) were performed in all patients. All of the children in the study underwent a detailed physical examination and echocardiographic evaluation.

RESULTS

A history of bleeding was positive in 18% of the aortic stenosis group, 9% of the pulmonary stenosis group, and 4% of the control group. Seven of 60 (12%) patients had laboratory findings that implied a diagnosis of AVWS, and two of these (28%) had a history of bleeding. The frequency of AVWS was 14% in patients with aortic stenosis and 9% in those with pulmonary stenosis.

CONCLUSION

AVWS is not rare in stenotic obstructive cardiac diseases. A detailed history of bleeding should be taken from patients with valvular disease. Even if the history is negative, whole blood count, PT and aPTT should be performed. If necessary, PFA-100 closure time and further tests should be planned for the diagnosis of AVWS.

In microfluidico: Recreating in vivo hemodynamics using miniaturized devices

Microfluidic devices create precisely controlled reactive blood flows and typically involve: (i) validated anticoagulation/pharmacology protocols, (ii) defined reactive surfaces, (iii) defined flow-transport regimes, and (iv) optical imaging. An 8-channel device can be run at constant flow rate or constant pressure drop for blood perfusion over a patterned collagen, collagen/kaolin, or collagen/tissue factor (TF) to measure platelet, thrombin, and fibrin dynamics during clot growth. A membrane-flow device delivers a constant flux of platelet agonists or coagulation enzymes into flowing blood. A trifurcated device sheaths a central blood flow on both sides with buffer, an ideal approach for on-chip recalcification of citrated blood or drug delivery. A side-view device allows clotting on a porous collagen/TF plug at constant pressure differential across the developing clot. The core-shell architecture of clots made in mouse models can be replicated in this device using human blood. For pathological flows, a stenosis device achieves shear rates of >100,000 s(-1) to drive plasma von Willebrand factor (VWF) to form thick long fibers on collagen. Similarly, a micropost-impingement device creates extreme elongational and shear flows for VWF fiber formation without collagen. Overall, microfluidics are ideal for studies of clotting, bleeding, fibrin polymerization/fibrinolysis, cell/clot mechanics, adhesion, mechanobiology, and reaction-transport dynamics.

Transport physics and biorheology in the setting of hemostasis and thrombosis

The biophysics of blood flow can dictate the function of molecules and cells in the vasculature with consequent effects on hemostasis, thrombosis, embolism, and fibrinolysis. Flow and transport dynamics are distinct for (i) hemostasis vs. thrombosis and (ii) venous vs. arterial episodes. Intraclot transport changes dramatically the moment hemostasis is achieved or the moment a thrombus becomes fully occlusive. With platelet concentrations that are 50- to 200-fold greater than platelet-rich plasma, clots formed under flow have a different composition and structure compared with blood clotted statically in a tube. The platelet-rich, core/shell architecture is a prominent feature of self-limiting hemostatic clots formed under flow. Importantly, a critical threshold concentration of surface tissue factor is required for fibrin generation under flow. Once initiated by wall-derived tissue factor, thrombin generation and its spatial propagation within a clot can be modulated by γ'-fibrinogen incorporated into fibrin, engageability of activated factor (FIXa)/activated FVIIIa tenase within the clot, platelet-derived polyphosphate, transclot permeation, and reduction of porosity via platelet retraction. Fibrin imparts tremendous strength to a thrombus to resist embolism up to wall shear stresses of 2400 dyne cm(-2) . Extreme flows, as found in severe vessel stenosis or in mechanical assist devices, can cause von Willebrand factor self-association into massive fibers along with shear-induced platelet activation. Pathological von Willebrand factor fibers are A Disintegrin And Metalloprotease with ThromboSpondin-1 domain 13 resistant but are a substrate for fibrin generation due to FXIIa capture. Recently, microfluidic technologies have enhanced the ability to interrogate blood in the context of stenotic flows, acquired von Willebrand disease, hemophilia, traumatic bleeding, and drug action.

Native valve disease in patients with non-valvular atrial fibrillation on warfarin or rivaroxaban

OBJECTIVE

To compare the characteristics and outcomes of patients with atrial fibrillation (AF) and aortic stenosis (AS) with patients with AF with mitral regurgitation (MR) or aortic regurgitation (AR) and patients without significant valve disease (no SVD).

METHODS

Using Rivaroxaban Once-Daily, Oral, Direct Factor Xa Inhibition Compared With Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF) data, we analysed efficacy and safety outcomes, adjusting hazard ratios (HRs) for potential confounders using Cox regression analysis.

RESULTS

Among 14 119 intention-to-treat ROCKET AF trial patients, a trial that excluded patients with mitral stenosis or artificial valve prosthesis, 214 had AS with or without other valve abnormalities, 1726 had MR or AR and 12 179 had no SVD. After adjusting for prognostic factors, the composite of stroke, systemic embolism or vascular death increased approximately twofold in patients with AS (AS 10.84, MR or AR 4.54 and no SVD 4.31 events per 100 patient-years, p=0.0001). All-cause death also significantly increased (AS 11.22, MR or AR 4.90 and no SVD 4.39 events per 100 patient-years, p=0.0003). Major bleeding occurred more frequently in AS (adjusted HR 1.61, confidence intervals (CI) 1.03 to 2.49, p<0.05) and MR or AR (HR 1.30, 1.07 to 1.57, p<0.01) than in no SVD, but there was no difference between AS and MR or AR (HR 1.24, 0.78 to 1.97). The relative efficacy of rivaroxaban versus warfarin was consistent among patients with and without valvular disease. Rivaroxaban was associated with higher rates of major bleeding than warfarin in patients with MR or AR (HR 1.63, 1.15 to 2.31).

CONCLUSIONS

We found that patients with AF and AS on oral anticoagulants may have distinctly different efficacy and safety outcomes than patients with MR or AR or no SVD.

TRIAL REGISTRATION NUMBER

NCT00403767; Post-results.

Increased bleeding risk in patients with aortic valvular stenosis: From new mechanisms to new therapies

Aortic stenosis (AS), the most prevalent acquired valvular disease in the adults that requires invasive treatment, coexists with coagulopathy, resulting in bleeding in approximately 20% of patients. In the current review, we summarize the available knowledge on the mechanisms underlying the bleeding tendency observed in AS, and discuss potential compensatory mechanisms preventing most patients with severe AS from experiencing bleeding. We offer an update on Heyde's syndrome and other types of bleeding, and study extensively their pathobiology, providing insights into the new emerging concepts on coagulation regulation in AS. The focus is given to the impact of valvular interventions on coagulation abnormalities in AS. Both surgical valve replacement and transcatheter aortic valve implantation are discussed. Finally, we discuss current treatment recommendations in AS related bleeding.

Risk Factors and Outcomes of Gastrointestinal Bleeding in Left Ventricular Assist Device Recipients

Increasing use of left ventricular assist devices (LVADs) has been accompanied by rising incidence of gastrointestinal bleeding (GIB). Objectives of this study were to determine the yearly incidence of GIB in LVAD recipients, compare outcomes of continuous-flow (CF) and pulsatile-flow LVAD eras, and investigate for risk factors. The Healthcare Cost and Utilization Project-Nationwide Inpatient Sample database from 2005 to 2010 was analyzed. Primary outcome of interest was incidence of GIB in LVAD recipients. Multivariate logistic regression model was used to examine independent associations of GIB with risk factors and outcomes. An estimated 8,879 LVAD index admissions and 8,722 readmissions in LVAD recipients over 6 years were analyzed. The yearly incidence of GIB after LVAD implantation increased from 5% in 2005 to 10% in 2010. On multivariate regression analysis, the odds of GIB was 3.24 times greater (95% confidence interval 1.53 to 6.89) in the era of CF LVADs than in the era of pulsatile-flow LVADs. Compared to their younger counterparts, in LVAD recipients aged >65 years, the adjusted odds of GIB was 20.5 times greater (95% confidence interval 2.24 to 188). GIB did not significantly increase the inhospital mortality but increased the inpatient length of stay. In conclusion, the incidence of GIB in LVAD recipients has increased since the use of CF LVADs has increased, leading to greater inpatient lengths of stay and hospital charges. Older recipients of CF LVADs appear to be at a greater risk of GIB.

Circulatory support devices: fundamental aspects and clinical management of bleeding and thrombosis

Circulatory support devices are increasingly being used to overcome cardiac or respiratory failure. Long-term devices are used either as a 'bridge to transplant' to support patients who are unable to wait any longer for a heart transplant, or, more recently, as 'destination therapy' for older patients suffering from end-stage heart failure and who have contraindications to heart transplantation. Short-term support devices for high-risk percutaneous coronary intervention, or as a 'bridge for decision' for patients suffering from refractory cardiogenic shock, have also been developed. The clinical benefit of such assist devices has been demonstrated in several important studies, but, unfortunately, thrombotic and bleeding complications are two major clinical issues in patients requiring these devices. Overcoming these issues is of major importance to allow the safe and broad use of these devices, and to consider them as true alternatives to heart transplantation. The present review focuses on thrombotic and bleeding complications, and describes how the risk of thrombosis and bleeding may vary according to the clinical indication, but also according to the type of device. We describe the current knowledge of the mechanisms underlying the occurrence of these complications, provide some guidance for choosing the most appropriate anticoagulation regimen to prevent their occurrence for each type of device and indication, and provide some recommendations for the management of patients when the complication occurs.

A case of Heyde syndrome: resolution following aortic valve replacement

Heyde syndrome is a triad of aortic stenosis, acquired coagulopathy, and anemia due to bleeding from intestinal angiodysplasia. Here we describe a case of this syndrome. An 80-year-old woman with severe aortic stenosis was referred to our department for an aortic valve replacement. She suffered from recurrent iron-deficiency anemia and required transfusions every 2 weeks. Gastroscopy and colonoscopy were normal with the exception of angiodysplasia without bleeding in the cecum. After aortic valve replacement her anemia was resolved. She was discharged on postoperative day 22. No transfusions were needed after the procedure. To date, her hemoglobin has remained stable at >10 mg/dL.

Factors predisposing to acquired von Willebrand syndrome during the course of polycythemia vera - retrospective analysis of 142 consecutive cases

INTRODUCTION

The aim of this study was to verify if PV patients with and without avWS differ in terms of their baseline clinical parameters.

MATERIAL AND METHODS

The study included 142 consecutive patients with PV. avWS was diagnosed on the basis of abnormally low levels of von Willebrand factor and other routine tests. Patients with and without concomitant avWS were compared in terms of their demographic characteristics, present and past medical histories and laboratory parameters.

RESULTS

Concomitant avWS was found in 17 PV patients (12.0%). Individuals with avWS have been diagnosed with PV at significantly younger age than those without, and significantly less often were in remission at the time of testing for bleeding disorders. Most of them (58.8%) presented with typical signs of bleeding disorder. Moreover, they showed significantly higher erythrocyte, leukocyte and platelet counts, abnormalities of coagulation profile corresponding to defects of primary hemostasis and abnormal values of all parameters used in the routine diagnosis of avWS.

CONCLUSIONS

Even every tenth patient with PV may develop avWS. Young age at diagnosis of PV and poor response to previous treatment of this condition are potential risk factors of avWS that should be considered during history taking. Sings of bleeding disorder observed in a person with PV necessitate evaluation for avWS.

High flow velocity through congenital cardiac lesions predicts preoperative platelet dysfunction

BACKGROUND

Platelet dysfunction resulting from abnormal fluid shear stress has been reported in adults with aortic stenosis. Blood flowing through a congenital heart defect at greater than normal velocity is subjected to increased shear stress. The primary aim was to determine whether peak flow velocity through congenital cardiac lesions predicts preoperative platelet dysfunction.

METHODS

The charts of 402 patients who underwent cardiopulmonary bypass and had preoperative platelet function analysis were evaluated. Platelet dysfunction was measured as a prolonged closure time (CT) in seconds with a platelet function analyzer. Echocardiography was used to determine peak velocity. The relationship between peak velocity and CT was analyzed using linear regression and Kaplan-Meier estimation.

RESULTS

The distribution of peak velocity was bimodal. The mean velocity of the lower group was 1.9 m/second and the higher group was 4.2 m/second. Univariate analysis showed age, weight, peak velocity, hematocrit, and Risk Adjustment for Congenital Heart Surgery score to be associated with prolonged CT. Using multivariable analysis, prolonged CT was significantly associated with peak velocity (p < 0.001). For each 1m/second increase in peak velocity the CT increased by over 9 seconds (p < 0.001). In addition, a median CT increase of more than 6 seconds was also associated with a 5 percentage point drop in hematocrit (p = 0.04).

CONCLUSIONS

Platelet dysfunction is associated with high blood flow velocity through congenital cardiac lesions. Lower preoperative hematocrit was associated with prolonged CT, which may suggest subclinical bleeding secondary to platelet dysfunction.

The CentriMag centrifugal blood pump as a benchmark for in vitro testing of hemocompatibility in implantable ventricular assist devices

Implantable ventricular assist devices (VADs) have proven efficient in advanced heart failure patients as a bridge-to-transplant or destination therapy. However, VAD usage often leads to infection, bleeding, and thrombosis, side effects attributable to the damage to blood cells and plasma proteins. Measuring hemolysis alone does not provide sufficient information to understand total blood damage, and research exploring the impact of currently available pumps on a wider range of blood cell types and plasma proteins such as von Willebrand factor (vWF) is required to further our understanding of safer pump design. The extracorporeal CentriMag (Thoratec Corporation, Pleasanton, CA, USA) has a hemolysis profile within published standards of normalized index of hemolysis levels of less than 0.01 g/100 L at 100 mm Hg but the effect on leukocytes, vWF multimers, and platelets is unknown. Here, the CentriMag was tested using bovine blood (n = 15) under constant hemodynamic conditions in comparison with a static control for total blood cell counts, hemolysis, leukocyte death, vWF multimers, microparticles, platelet activation, and apoptosis. The CentriMag decreased the levels of healthy leukocytes (P < 0.006), induced leukocyte microparticles (P < 10(-5) ), and the level of high molecular weight of vWF multimers was significantly reduced in the CentriMag (P < 10(-5) ) all compared with the static treatment after 6 h in vitro testing. Despite the leukocyte damage, microparticle formation, and cleavage of vWF multimers, these results show that the CentriMag is a hemocompatible pump which could be used as a standard in blood damage assays to inform the design of new implantable blood pumps.

Acquired von Willebrand syndrome in patients with a centrifugal or axial continuous flow left ventricular assist device

OBJECTIVES

The aim of this study was to determine whether differences in continuous flow left ventricular assist devices (LVADs) may lead to differences in the von Willebrand profile and the occurrence of bleeding and thromboembolic events.

BACKGROUND

The HeartMate II (Thoratec Corp., Pleasanton, California) and HeartWare Ventricular Assist Device (HVAD) (HeartWare, Inc., Framingham, Massachusetts) systems are the most frequently implanted LVADs worldwide. In all patients with an axial-flow HeartMate II, acquired von Willebrand syndrome (AvWS) due to the loss of large molecular weight multimers was found. The large molecular weight multimers of the von Willebrand factor (vWF) play a key role in primary hemostasis through interactions with platelets.

METHODS

This was a retrospective study of the vWF profile and incidence of bleeding and thromboembolic events in 102 patients receiving the HeartMate II (n = 51) and HVAD (n = 51). Between January 2003 and December 2010, vWF testing was performed in 102 of 175 consecutive patients after LVAD implantation.

RESULTS

AvWS was found in all patients, demonstrated by a decrease in the high molecular weight multimers of vWF to 30 ± 14% in HeartMate II patients and 34 ± 13% in patients with an HVAD. Significant predictors of vWF antigen included age (p = 0.011), number of days on the device (p = 0.035), C-reactive protein (p < 0.001), and blood group (p = 0.007). Bleeding and thromboembolic event rates were similar. However, lower fractions of vWF antigen and high molecular weight multimers did not correlate with the rate of bleeding complications or thromboembolic events.

CONCLUSIONS

AvWS developed in all patients after centrifugal or axial flow pump implantation. Different patterns of AvWS were seen between the devices as well as individually. However, the complication rates after implantation were similar.

Current management of von Willebrand disease and von Willebrand syndrome

PURPOSE OF REVIEW

Anesthesiologists frequently care for patients with altered hemostasis and coagulation. Where a clear history of familial and personal bleeding exists, a thoughtful plan can be developed in advance to manage the issue perioperatively. However, in some cases, it may not be known that the patient has a disorder until excessive bleeding is noted during or after surgery. Recognition of the issue and appropriate targeted therapy are the keys to successful management.

RECENT FINDINGS

With an estimated prevalence approaching 1% of the population, von Willebrand disease (vWD) is the most common hereditary bleeding diathesis, but the estimated prevalence of acquired vWD (often termed von Willebrand syndrome or vWS) is now believed to be significantly higher, especially in patients with malignancies, autoimmune diseases, cardiac valvular lesions, and in patients on mechanical circulatory support devices. Acquired vWD may also occur with certain medications.

SUMMARY

The mainstay of the diagnosis of vWD is laboratory testing. Preoperative clinical assessment and a high level of suspicion are often effective to alert the anesthesiologist to the possibility of vWS, thus allowing for appropriate testing and potential prophylaxis in elective situations, as well as appropriately targeted therapy of unexpected bleeding when a hemostatic derangement was not anticipated preoperatively.

Congenital cardiac lesions involving systolic flow abnormalities are associated with platelet dysfunction in children

BACKGROUND

Shear stress-induced platelet dysfunction (PD) is prevalent among adults with aortic stenosis. Our aim was to determine whether abnormal platelet function was associated with specific congenital cardiac lesions in children.

METHODS

The charts of 407 children who had undergone cardiopulmonary bypass and had preoperative platelet function analysis were evaluated. Patients were assigned to 1 of 11 different lesion categories. Platelet dysfunction (PD) was defined as prolonged closure time (CT) as measured with a platelet function analyzer. Odds ratio (OR) estimates for prolonged CT were calculated for each lesion category. Mean CTs were compared with Tukey-Kramer separated means testing. Analysis of variance modeling was used to determine association between hematocrit value and CT.

RESULTS

CT in patients with ventricular septal defects (VSD) and right ventricular outflow tract obstruction (RVOTO) lesions was prolonged. OR analysis found that patients with VSDs (OR, 2.46) or RVOTO (OR, 2.88) had at least a 95% probability of an abnormal CT. In contrast, patients with atrial septal defect (ASD), bidirectional Glenn procedure (BDG), and pulmonary insufficiency (PI) had a reduced probability of a prolonged CT (p < 0.05). A similar pattern was seen in parametric analysis comparing mean CTs across lesion categories. A lower preoperative hematocrit value was associated with prolonged CTs across all lesion types (p < 0.05).

CONCLUSIONS

PD was common in children with congenital cardiac lesions involving systolic flow abnormalities and was uncommon among children with lesions having diastolic abnormalities. Lower preoperative hematocrit values were associated with prolonged CTs, suggesting subclinical bleeding secondary to excessive platelet shearing.

Acquired von Willebrand's disease associated with epithelial myoepithelial carcinoma of the parotid salivary gland

This is the first case report of a patient with acquired von Willebrand's disease (AvWD) secondary to epithelial myoepithelial carcinoma (EMC) of the parotid salivary gland. This patient presented to haematology following an abnormal bleeding episode with von Willebrand factor Ristocetin cofactor (VWF:RCo) <5% and VWF:Ag 13%. He was diagnosed with AvWD. At the same time he was found to have a left parotid lump which was excised following a multidisciplinary team meeting. This was histologically reported as an EMC. Following excision, unusually this patient's AvWD did not resolve. Extensive investigation looking for other causes of the AvWD did not reveal any other potential cause; therefore, due to the similar timing of onset of both pathologies it is felt that the AvWD in this case is secondary to the EMC. This case report highlights the presentation, investigation and management of AvWD and parotid lumps as well as discussing proposed pathophysiological mechanisms for AvWD.

Antibody-based prevention of von Willebrand factor degradation mediated by circulatory assist devices

Haemorrhagic episodes in patients carrying circulatory assist devices represent a severe life-threatening clinical complication. These bleeding episodes may originate from a reduced functionality of von Willebrand factor (VWF), a multimeric protein pertinent to the formation of a haemostatic plug. It has been reported that the reduced functionality is due to increased proteolytic degradation by the enzyme ADAMTS13, a phenomenon that is facilitated by device-induced increases in shear stress to which VWF is exposed. Here, we have tested a series of VWF-derived protein fragments and monoclonal murine anti-VWF antibodies for their capacity to reduce shear stress-dependent degradation of VWF. Via direct binding experiments, we identified an anti-VWF antibody that partially blocked VWF-ADAMTS13 interactions (46 ± 14%). Epitope mapping experiments revealed that the antibody, designated mAb508, is directed against the distal portion of the VWF D4-domain (residues 2134-2301) and recognises a synthetic peptide encompassing residues 2158-2169. Consistent with its partial inhibition of VWF-ADAMTS13 interactions in binding assays, mAb508 reduced ADAMTS13-mediated VWF degradation in a vortex-based degradation assay by 48 ± 10%. In a HeartMateII-based whole blood-perfusion system, mAb508 was able to reduce degradation of high-molecular-weight (HMW)-VWF-multimers dose-dependently, with a maximal inhibition (83 ± 8%) being reached at concentrations of 10 μg/ml or higher. In conclusion, we report that partial inhibition of VWF-ADAMTS13 interactions using an anti-VWF antibody can prevent excessive degradation of HMW-VWF multimers. This strategy may be used for the development of therapeutic options to treat bleeding episodes due to shear stress-dependent VWF degradation, for instance in patients carrying circulatory assist devices.

Possible race and gender divergence in association of genetic variations with plasma von Willebrand factor: a study of ARIC and 1000 genome cohorts

The synthesis, secretion and clearance of von Willebrand factor (VWF) are regulated by genetic variations in coding and promoter regions of the VWF gene. We have previously identified 19 single nucleotide polymorphisms (SNPs), primarily in introns that are associated with VWF antigen levels in subjects of European descent. In this study, we conducted race by gender analyses to compare the association of VWF SNPs with VWF antigen among 10,434 healthy Americans of European (EA) or African (AA) descent from the Atherosclerosis Risk in Communities (ARIC) study. Among 75 SNPs analyzed, 13 and 10 SNPs were associated with VWF antigen levels in EA male and EA female subjects, respectively. However, only one SNP (RS1063857) was significantly associated with VWF antigen in AA females and none was in AA males. Haplotype analysis of the ARIC samples and studying racial diversities in the VWF gene from the 1000 genomes database suggest a greater degree of variations in the VWF gene in AA subjects as compared to EA subjects. Together, these data suggest potential race and gender divergence in regulating VWF expression by genetic variations.

Time course of acquired von Willebrand disease associated with two types of continuous-flow left ventricular assist devices: HeartMate II and CircuLite Synergy Pocket Micro-pump

BACKGROUND

Bleeding complications are frequent adverse events in patients supported with axial continuous-flow pumps. Previous retrospective studies demonstrated that bleeding events in patients with the HeartMate II (Thoratec Corp, Pleasanton, CA) were attributed to acquired von Willebrand syndrome. We sought to analyze the von Willebrand factor (VWF) profile in patients receiving a HeartMate II or a CircuLite (Saddle Brook, NJ,) device (Synergy Pocket Micro-pump) prospectively.

METHODS

Prospectively analyzed were 34 patients supported with left ventricular assist device (LVAD; 26 with HeartMate II and 8 with CircuLite). The control group comprised 20 patients who underwent heart transplantation (HTx). Blood samples were taken pre-operatively and at 14 days and 3, 6, 9, and 12 months post-operatively.

RESULTS

Patients with LVADs had a high incidence of bleeding complications. From the immediate post-operative phase throughout the entire observation, the VWF ristocetin cofactor activity (Rco)/antigen (Ag) ratio of patients with HeartMate II and CircuLite devices was consistently lower compared with HTx patients. No correlation was found between the individual VWF:Rco/Ag ratio and bleeding events or transfusion requirements. The VWF:Rco/Ag ratio normalized immediately in patients who received HTx.

CONCLUSIONS

Acquired von Willebrand syndrome was confirmed to occur immediately after the implantation of both types of LVAD and persisted up to 12 months. A lower VWF:Rco/Ag ratio was associated with larger transfusion requirements. Acquired von Willebrand syndrome resolves after LVAD explantation.

Heyde's syndrome

Gastrointestinal bleeding due to colonic angiodysplasia can be associated with calcified aortic stenosis. This association is referred to as Heyde's syndrome. Aortic valve replacement can prevent recurrent gastrointestinal bleeding in these cases. We describe the case of a 46-year-old woman with congestive heart failure related to aortic stenosis, and severe anemia, with multiple angiodysplasias on the ileum and colon. After aortic valve replacement, there were no further episodes of bleeding and her hemoglobin levels normalized.

Structure-function and regulation of ADAMTS-13 protease

ADAMTS-13, a plasma reprolysin-like metalloprotease, cleaves von Willebrand factor (VWF). Severe deficiency of plasma ADAMTS-13 activity results in thrombotic thrombocytopenic purpura (TTP), while mild to moderate deficiencies of plasma ADAMTS-13 activity are emerging risk factors for developing myocardial and cerebral infarction, pre-eclampsia, and malignant malaria. Moreover, Adamts13(-/-) mice develop more severe inflammatory responses, leading to increased ischemia/perfusion injury and formation of atherosclerosis. Structure-function studies demonstrate that the N-terminal portion of ADAMTS-13 (MDTCS) is necessary and sufficient for proteolytic cleavage of VWF under various conditions and attenuation of arterial/venous thrombosis after oxidative injury. The more distal portion of ADAMTS-13 (TSP1 2-8 repeats and CUB domains) may function as a disulfide bond reductase to prevent an elongation of ultra-large VWF strings on activated endothelial cells and inhibit platelet adhesion/aggregation on collagen surface under flow. Remarkably, the proteolytic cleavage of VWF by ADAMTS-13 is accelerated by FVIII and platelets under fluid shear stress. A disruption of the interactions between FVIII (or platelet glycoprotein 1bα) and VWF dramatically impairs ADAMTS-13-dependent proteolysis of VWF in vitro and in vivo. These results suggest that FVIII and platelets may be physiological cofactors regulating VWF proteolysis. Finally, the structure-function and autoantibody mapping studies allow us to identify an ADAMTS-13 variant with increased specific activity but reduced inhibition by autoantibodies in patients with acquired TTP. Together, these findings provide novel insight into the mechanism of VWF proteolysis and tools for the therapy of acquired TTP and perhaps other arterial thrombotic disorders.