Pilot Assessment of Platelet Thrombus Area and Contractile Force in Pediatric Congenital Heart Surgery Patients Using a Microfluidic Device

OBJECTIVES

This work was designed to evaluate maximum platelet contractile force and thrombus area before and after cardiopulmonary bypass (CPB) in pediatric patients having congenital heart disease (CHD) surgery using a microfluidic device.

DESIGN

A prospective cohort study was designed.

SETTING

The work took place at an academic medical center.

PARTICIPANTS

Twenty pediatric CHD patients ≤8 years of age with expected CPB time >30 minutes were enrolled.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood was collected at baseline and post-CPB. Maximum platelet contractile force and thrombus area were evaluated in vitro using a microfluidic device (ATLAS PST). Post-CPB samples were supplemented with recombinant von Willebrand factor (rVWF) to explore the impact on contractile force and thrombus area. At baseline, the maximum thrombus area was 0.06 (0.05, 0.07), and the maximum force was 123.3 nN (68.4, 299.5). Linear mixed-effects regression models showed that the maximum thrombus area was larger post-CPB and post-CPB + rVWF compared with pre-CPB (estimated coefficient [Est] = 0.04, p = 0.002; Est = 0.09, p < 0.001, respectively). The maximum thrombus area was also larger post-CPB + rVWF compared with post-CPB (Est = 0.04, p = 0.001). Force was higher post-CPB + rVWF compared with pre-CPB (Est = 173.32, p = 0.044).

CONCLUSIONS

In pediatric CHD patients, microfluidic testing demonstrated that platelet thrombus area increased slightly after CPB, while platelet contractile force did not change. In vitro addition of rVWF further increased thrombus area, suggesting augmentation of primary hemostasis. Microfluidic assessment of platelet contractile force and thrombus area in pediatric CHD patients appears feasible and can demonstrate changes after CPB. Further studies are needed to determine its accuracy, clinical utility, and normal values for pediatric patients.

Investigation of von Willebrand factor multimer abnormalities before and after aortic valve replacement using the Hydragel-5 assay

BACKGROUND

Severe aortic stenosis (sAS) is associated with acquired von Willebrand syndrome (AVWS) by loss of high-molecular-weight multimers (HMWM) of von Willebrand factor (VWF), potentially resulting in perioperative bleeding. Analysis of VWF multimers remains challenging. Recently, the new, rapid Hydragel 5 assay has been developed, using electrophoretic protein separation for dividing VWF-multimers into low (LMWM), intermediate (IMWM), and HMWM, the hemostatically active part of VWF. Here, we evaluated its impact on predicting blood loss in presence of AVWS after surgical aortic valve replacement (SAVR).

METHODS

We prospectively examined 52 patients (age: 68 ± 7 years; 54 % male) admitted to SAVR. They were divided in two groups (A: normal VWF, n = 28; B: abnormal VWF, n = 24, defined as VWF-activity/antigen (VWF:Ac/Ag)-ratio < 0.7 and/or HMWM loss). Blood samples and echocardiographic data were collected before, seven days and three months after SAVR. Blood loss and transfusions were recorded.

RESULTS

Baseline characteristics and clinical data were similar in both groups. HMWM loss was present in 38.5 % of all patients. HMWM, the VWF:Ac/Ag- and HMWM/(IMWM+LMWM)-ratios were significantly decreased preoperatively in group B but normalized after SAVR. Bleeding, re-thoracotomy and transfusion rates were comparable. HMWM loss was inversely correlated with the peak aortic gradient (Pmax) and positively with the aortic valve area (AVA), while HMWM/(IMWM+LMWM)-ratio negatively correlated with the mean aortic gradient (Pmean).

CONCLUSION

HMWM and HMWM/(IMWM+LMWM)-ratio inversely correlate with severity of AS and normalize after SAVR. The Hydragel-5 assay's might be valuable for routine diagnostics to assess bleeding risk and postoperative normalization of AS and VWF abnormalities in SAVR patients.

Mitral regurgitation is associated with similar loss of von Willebrand factor large multimers but lower frequency of anemia compared with aortic stenosis

Background

Various cardiovascular diseases cause acquired von Willebrand syndrome (AVWS), which is characterized by a decrease in high-molecular-weight (large) von Willebrand factor (VWF) multimers. Mitral regurgitation (MR) has been reported as a cause of AVWS. However, much remains unclear about AVWS associated with MR.

Objectives

To evaluate VWF multimers in MR patients and examine their impact on clinical characteristics.

Methods

Moderate or severe MR patients (n = 84) were enrolled. VWF parameters such as the VWF large multimer index (VWF-LMI), a quantitative value that represents the amount of VWF large multimers, and clinical data were prospectively analyzed.

Results

At baseline, the mean hemoglobin level was 12.9 ± 1.9 g/dL and 58 patients (69.0%) showed loss of VWF large multimers defined as VWF-LMI < 80%. VWF-LMI in patients with degenerative MR was lower than in those with functional MR. VWF-LMI appeared to be restored the day after mitral valve intervention, and the improvement was maintained 1 month after the intervention. Seven patients (8.3%) had a history of bleeding, 6 (7.1%) of whom had gastrointestinal bleeding. Gastrointestinal endoscopy was performed in 23 patients (27.4%) to investigate overt gastrointestinal bleeding, anemia, etc. Angiodysplasia was detected in 2 of the 23 patients (8.7%).

Conclusion

Moderate or severe MR is frequently associated with loss of VWF large multimers, and degenerative MR may cause more severe loss compared with functional MR. Mitral valve intervention corrects the loss of VWF large multimers. Gastrointestinal bleeding may be relatively less frequent and hemoglobin level remains stable in MR patients.

The Role of the von Willebrand Factor Collagen-Binding Assay (VWF:CB) in the Diagnosis and Treatment of von Willebrand Disease (VWD) and Way Beyond: A Comprehensive 36-Year History

The von Willebrand factor (VWF) collagen binding (VWF:CB) assay was first reported for use in von Willebrand diagnostics in 1986, by Brown and Bosak. Since then, the VWF:CB has continued to be used to help diagnose von Willebrand disease (VWD) (correctly) and also to help assign the correct subtype, as well as to assist in the monitoring of VWD therapy, especially desmopressin (DDAVP). However, it is important to recognize that the specific value of any VWF:CB is predicated on the use of an optimized VWF:CB, and that not all VWF:CB assays are so optimized. There are some good commercial assays available, but there are also some "not-so-good" commercial assays available, and these may continue to give the VWF:CB "a bad reputation." In addition to VWD diagnosis and management, the VWF:CB found purpose in a variety of other applications, from assessing ADAMTS13 activity, to investigation into acquired von Willebrand syndrome (especially as associated with use of mechanical circulatory support or cardiac assist devices), to assessment of VWF activity in disease states in where an excess of high-molecular-weight VWF may accumulate, and lead to increased (micro)thrombosis risk (e.g., coronavirus disease 2019, thrombotic thrombocytopenic purpura). The VWF:CB turns 37 in 2023. This review is a celebration of the utility of the VWF:CB over this nearly 40-year history.

Perioperative diagnosis and impact of acquired von Willebrand syndrome in infants with congenital heart disease

Acquired von Willebrand syndrome (aVWS) has been reported in patients with congenital heart diseases associated with shear stress caused by significant blood flow gradients. Its etiology and impact on intraoperative bleeding during pediatric cardiac surgery have not been systematically studied. This single-center, prospective, observational study investigated appropriate diagnostic tools of aVWS compared with multimer analysis as diagnostic criterion standard and aimed to clarify the role of aVWS in intraoperative hemorrhage. A total of 65 newborns and infants aged 0 to 12 months scheduled for cardiac surgery at our tertiary referral center from March 2018 to July 2019 were included in the analysis. The glycoprotein Ib M assay (GPIbM)/von Willebrand factor antigen (VWF:Ag) ratio provided the best predictability of aVWS (area under the receiver operating characteristic curve [AUC], 0.81 [95% CI, 0.75-0.86]), followed by VWF collagen binding assay/VWF:Ag ratio (AUC, 0.70 [0.63-0.77]) and peak systolic echocardiographic gradients (AUC, 0.69 [0.62-0.76]). A cutoff value of 0.83 was proposed for the GPIbM/VWF:Ag ratio. Intraoperative high-molecular-weight multimer ratios were inversely correlated with cardiopulmonary bypass (CPB) time (r = -0.57) and aortic cross-clamp time (r = -0.54). Patients with intraoperative aVWS received significantly more fresh frozen plasma (P = .016) and fibrinogen concentrate (P = .011) than those without. The amounts of other administered blood components and chest closure times did not differ significantly. CPB appears to trigger aVWS in pediatric cardiac surgery. The GPIbM/VWF:Ag ratio is a reliable test that can be included in routine intraoperative laboratory workup. Our data provide the basis for further studies in larger patient cohorts to achieve definitive clarification of the effects of aVWS and its potential treatment on intraoperative bleeding.

Treatment Algorithm for Patients With von Willebrand Syndrome Type 2A and Congenital Heart Disease-A Treatment Algorithm May Reduce Perioperative Blood Loss in Children With Congenital Heart Disease

OBJECTIVES

In children with congenital heart disease (CHD), excessive perioperative bleeding is associated with increased morbidity and mortality, thus making adequate perioperative hemostasis crucial. We investigate the prevalence of acquired von Willebrand syndrome type 2A (aVWS) in CHD and develop a treatment algorithm for patients with aVWS and CHD (TAPAC) to reduce perioperative blood loss.

DESIGN

Retrospective cohort study.

SETTING

Single-center study.

PATIENTS

A total of 627 patients with CHD, undergoing corrective cardiac surgery between January 2008 and May 2017.

INTERVENTIONS

The evaluation of perioperative bleeding risk was based on the laboratory parameters von Willebrand factor (VWF) antigen, ristocetin cofactor activity, platelet function analyzer (PFA) closure time adenosine diphosphate, and PFA epinephrine. According to the bleeding risk, treatment was performed with desmopressin or VWF.

MEASUREMENTS AND MAIN RESULTS

aVWS was confirmed in 63.3 %, with a prevalence of 45.5% in the moderate and 66.3 % in the high-risk group. In addition, prevalence increased with ascending peak velocity above the stenosis (v max ) from 40.0% at less than or equal to 3 m/s to 83.3% at greater than 5 m/s. TAPAC reduced mean blood loss by 36.3% in comparison with a historical control cohort ( p &lt; 0.001), without increasing the number of thrombotic or thromboembolic events during the hospital stay. With ascending v max , there was an increase in perioperative blood loss in the historical cohort ( p &lt; 0.001), which was not evident in the TAPAC cohort ( p = 0.230).

CONCLUSIONS

The prevalence of aVWS in CHD seems to be higher than assumed and leads to significantly higher perioperative blood loss, especially at high v max . Identifying these patients through appropriate laboratory analytics and adequate treatment could reduce blood loss effectively.

Acquired von Willebrand Syndrome in Children

Acquired von Willebrand syndrome (AVWS) is a rare bleeding disorder caused by various underlying diseases or conditions and should be distinguished from the inherited type of von Willebrand disease. AVWS is associated with underlying diseases such as cardiovascular, autoimmune, malignant, proliferative disorders, or with mechanical circulatory support (MCS). AVWS was first reported in 1968 and most case reports describe AVWS in adults. However, AVWS can appear in pediatric patients occasionally as well. Because bleeding complications are rare in everyday life, AVWS may be underdiagnosed in pediatric patients. Therefore, the diagnosis should be suspected in a pediatric patient who is known for one of these underlying diseases or conditions and who presents with an onset of bleeding symptoms, especially before the child will undergo an invasive procedure. Here, we present an overview of the diagnostic analyses regarding AVWS and of the underlying diseases or conditions in which AVWS should be considered. Importantly, the patient's history should be investigated for bleeding symptoms (mucocutaneous or postoperative bleeding). As no single routine coagulation test can reliably confirm or exclude AVWS, the diagnosis may be challenging. Laboratory investigations should include analysis of von Willebrand factor (VWF):antigen, VWF:collagen-binding capacity, VWF:activity, and VWF multimeric analyses. For treatment, tranexamic acid, 1-desamino-8-D-arginine vasopressin, and VWF-containing concentrate can be used. AVWS disappears after the underlying disease has been successfully treated or the MCS has been explanted.

Acquired von Willebrand syndrome (AVWS) type 2, characterized by decreased high molecular weight multimers, is common in children with severe pulmonary hypertension (PH)

BACKGROUND AND OBJECTIVES

Emerging evidence suggests that increased degradation of von Willebrand factor and decrease in high molecular weight multimers occurs in patients with pulmonary hypertension (PH). However, the link between acquired von Willebrand Syndrome (AVWS) type 2 and PH remains poorly understood.

MATERIAL AND METHODS

We retrospectively evaluated the charts of 20 children with PH who underwent bilateral lung transplantation (LuTx) between 2013 and 2022. Von Willebrand variables were determined in 14 of these patients; 11 patients had complete diagnostics including multimer analysis.

RESULTS

We confirmed AVWS in 82% of the children studied (9 of 11 patients by multimer analysis). The two remaining patients had suspected AVWS type 2 because of a VWF:Ac/VWF:Ag ratio of <0.7. Platelet dysfunction or suspicion of VWD type 1 were found in two separate patients. All but one of the 14 children with severe PH had a coagulation disorder. Most patients (9 proven, 2 suspected) had AVWS type 2. Notably, 3 of 5 patients (60%) with normal VWF:Ac/VWF:Ag ratio >0.7 had abnormal VWF multimers, indicating AVWS type 2. Hemostatic complications were observed in 4 of 12 (33%) patients with VWS and 3 of 6 (50%) patients without diagnostics and therapy.

CONCLUSION

For children with moderate to severe PH, we recommend systematic analysis of von Willebrand variables, including multimer analysis, PFA-100 and platelet function testing. Awareness of the diagnosis "AVWS" and adequate therapy may help to prevent these patients from bleeding complications in case of surgical interventions or trauma.

Acquired von Willebrand syndrome is common in infants with systemic-to-pulmonary shunts: Retrospective case-series

BACKGROUND

Although acquired von Willebrand syndrome (aVWS) has been described in congenital heart disease before, anatomical features leading to aVWS with characteristic reduction or loss of high molecular weight von Willebrand multimers (HMWM) are not well known. This study assesses the prevalence and effects of aVWS in infants with systemic-to-pulmonary shunts (SPS).

METHODS

This retrospective single-center study analyzes diagnostic data of infants with complex congenital heart defects requiring palliation with SPS. During the study period between 12/15-01/17 fifteen consecutive patients were eligible for analysis. Results of von Willebrand factor antigen (VWF:Ag), collagen binding activity (VWF:CB) and von Willebrand factor multimer analysis were included.

RESULTS

In all 15 patients with SPS an aVWS could be found. Blood samples were collected between 5 and 257 days after shunt implantation (median 64 days). None of the patients demonstrated increased bleeding in everyday life. However, 6 out of 15 patients (40%) showed postoperative bleeding complications after SPS implantation. Following shunt excision multimeric pattern normalized in 8 of 10 (80%) patients studied.

CONCLUSIONS

This study shows that in patients undergoing SPS implantation aVWS might emerge. Pathogenesis can be explained by shear stress resulting from turbulent flow within the shunt. Knowledge of aVWS existence is important for the consideration of replacement therapy with von Willebrand factor containing products and antifibrinolytic treatment in bleeding situations. Implementation of methods for rapid aVWS detection is required to achieve differentiated hemostatic therapy and reduce the risk of complications caused by empiric replacement therapy.

Differential sialic acid content in adult and neonatal fibrinogen mediates differences in clot polymerization dynamics

Increased sialic acid in neonatal fibrinogen influences fibrin knob-hole interactions during polymerization.

Neonatal fibrin polymerization involves more B knob– and fewer A knob–mediated interactions compared with adults.

Neonates possess a molecular variant of fibrinogen, known as fetal fibrinogen, characterized by increased sialic acid, a greater negative charge, and decreased activity compared with adults. Despite these differences, adult fibrinogen is used for the treatment of bleeding in neonates, with mixed efficacy. To determine safe and efficacious bleeding protocols for neonates, more information on neonatal fibrin clot formation and the influence of sialic acid on these processes is needed. Here, we examine the influence of sialic acid on neonatal fibrin polymerization. We hypothesized that the increased sialic acid content of neonatal fibrinogen promotes fibrin B:b knob-hole interactions and consequently influences the structure and function of the neonatal fibrin matrix. We explored this hypothesis through analysis of structural properties and knob:hole polymerization dynamics of normal and desialylated neonatal fibrin networks and compared them with those formed with adult fibrinogen. We then characterized normal neonatal fibrin knob:hole interactions by forming neonatal and adult clots with either thrombin or snake-venom thrombin-like enzymes that preferentially cleave fibrinopeptide A or B. Sialic acid content of neonatal fibrinogen was determined to be a key determinant of resulting clot properties. Experiments analyzing knob:hole dynamics indicated that typical neonatal fibrin clots are formed with the release of more fibrinopeptide B and less fibrinopeptide A than adults. After the removal of sialic acid, fibrinopeptide release was roughly equivalent between adults and neonates, indicating the influence of sialic acid on fibrin neonatal fibrin polymerization mechanisms. These results could inform future studies developing neonatal-specific treatments of bleeding.

Acquired von Willebrand Syndrome

Acquired von Willebrand syndrome can occur in the setting of myeloproliferative neoplasms; plasma cell dyscrasias and other lymphoproliferative disorders; autoimmune conditions; and causes of increased shear forces, such as aortic stenosis or other structural heart disease and mechanical circulatory support. The depletion of von Willebrand factor, especially high-molecular-weight multimers, can lead to mucocutaneous bleeding and the formation of arteriovenous malformations, particularly in the gastrointestinal tract. Management focuses on correction of the underlying cause when possible, but may include intravenous immunoglobulins, von Willebrand factor concentrate, rituximab, or antiangiogenic therapy depending on the clinical context.

Risk Factors of Thrombotic Complications and Antithrombotic Therapy in Paediatric Cardiosurgical Patients

The development of cardiosurgical care for paediatric and neonatal patients is undergoing the rapid growth. Complex, multi-stage reconstructive operations and the use of invasive monitoring are associated with high risk of venous and arterial thrombosis.

The cardiac surgery patient is inherently unique, since it requires controlled anticoagulation during cardiopulmonary bypass. Moreover, the most cardiovascular pediatric patients require antithrombotic measures over the perioperative period. In addition to medication support with the use of various groups of antithrombotic agents, vascular access management is justified in order to minimize the risk of thromboembolic complications, which can affect both the functional status, and common and inter-stage mortality.

The purpose of this review was to systematize the available data on risk factors contributing to the development of thrombotic complications in patients with congenital heart disease.

An information search was carried out using Internet resources (PubMed, Web of Science, eLibrary.ru); literature sources for period 2015–2020 were analysed. As a result of the analysis of the literature data age-dependent features of the haemostatic system, and associated with the defect pathophysiology, and undergone reconstructive interventions were described. The issues of pathophysiology of univentricular heart defects and risk factors associated with thrombosis were also covered.

Moreover, aspects of intraoperative anti-thrombotic support are discussed, as well as measures to prevent thromboembolic complications in this population.

Coordinated actions of haematologists, cardiologists, anaesthesiologists, intensivists, and cardiac surgeons will allow achieving a fine balance between risks of bleeding and thrombosis in the population of paediatric patients undergoing cardiovascular surgery. 

Acquired von Willebrand Syndrome in Pediatric Extracorporeal Membrane Oxygenation Patients: A Single Institution's Experience

OBJECTIVES

1) Describe the prevalence of acquired von Willebrand syndrome in pediatric patients undergoing extracorporeal membrane oxygenation deemed to be at increased risk for the disease in our institution, 2) discuss the challenges of testing for acquired von Willebrand syndrome diagnosis, 3) describe the characteristics of the patient population found to have acquired von Willebrand syndrome and their outcomes, and 4) discuss the potential implications of acquired von Willebrand syndrome on bleeding complications.

DESIGN

Retrospective chart review.

SETTING

PICU and cardiovascular ICU in a single institution.

PATIENTS

All PICU and cardiovascular ICU extracorporeal membrane oxygenation patients 0-18 years old who underwent screening for acquired von Willebrand syndrome between January 2014 and December 2016.

INTERVENTIONS

Humate P administration to a small subset of acquired von Willebrand syndrome positive subjects.

MEASUREMENTS AND MAIN RESULTS

Laboratory data of identified patients were analyzed. The diagnosis of acquired von Willebrand syndrome was made based on decreased ristocetin cofactor activity to von Willebrand factor antigen ratio and/or abnormal multimer analysis. Clinical data were extracted from the chart and through the Pediatric Extracorporeal Membrane Oxygenation Outcome Registry to describe the demographics, comorbidities, and outcomes of this patient population. In the 2 years, 29 patients had laboratory testing performed for surveillance and in cases of clinical bleeding. Of these, 23 (79%) were positive by criteria. No significant difference in mortality rate was found between patients with acquired von Willebrand syndrome versus without. We also did not find a significant difference in the blood product utilization or bleeding complications between patients with acquired von Willebrand syndrome versus without. Humate P was administered in 39% of patients (9/23) who were positive for acquired von Willebrand syndrome, but no significant difference was seen in blood product utilization or bleeding complications between acquired von Willebrand syndrome patients receiving Humate P versus those who did not.

CONCLUSIONS

Acquired von Willebrand syndrome is a common but under recognized disorder in pediatric extracorporeal membrane oxygenation patients. The clinical implications of this disorder on bleeding and its potential treatments are still unclear.

Turbulent Flow Promotes Cleavage of VWF (von Willebrand Factor) by ADAMTS13 (A Disintegrin and Metalloproteinase With a Thrombospondin Type-1 Motif, Member 13)

Objective—

Acquired von Willebrand syndrome is defined by excessive cleavage of the VWF (von Willebrand Factor) and is associated with impaired primary hemostasis and severe bleeding. It often develops when blood is exposed to nonphysiological flow such as in aortic stenosis or mechanical circulatory support. We evaluated the role of laminar, transitional, and turbulent flow on VWF cleavage and the effects on VWF function.

Approach and Results—

We used a vane rheometer to generate laminar, transitional, and turbulent flow and evaluate the effect of each on VWF cleavage in the presence of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type-1 motif, member 13). We performed functional assays to evaluate the effect of these flows on VWF structure and function. Computational fluid dynamics was used to estimate the flow fields and forces within the vane rheometer under each flow condition. Turbulent flow is required for excessive cleavage of VWF in an ADAMTS13-dependent manner. The assay was repeated with whole blood, and the turbulent flow had the same effect. Our computational fluid dynamics results show that under turbulent conditions, the Kolmogorov scale approaches the size of VWF. Finally, cleavage of VWF in this study has functional consequences under flow as the resulting VWF has decreased ability to bind platelets and collagen.

Conclusions—

Turbulent flow mediates VWF cleavage in the presence of ADAMTS13, decreasing the ability of VWF to sustain platelet adhesion. These findings impact the design of mechanical circulatory support devices and are relevant to pathological environments where turbulence is added to circulation.

Acquired von Willebrand Syndrome Associated with Cardiovascular Diseases

The blood glycoprotein von Willebrand factor (VWF) plays an important role in hemostasis and thrombosis. VWF is produced and secreted as large multimers by endothelial cells and megakaryocytes. It is then cleaved in a sheer-stress dependent manner by a specific protease, ADAMTS13, into multimers consisting of 2–80 subunits. Among VWF multimers, high molecular weight (HMW) multimers play important roles in platelet aggregation. Therefore, their loss induces a hemostatic disorder known as von Willebrand disease (VWD) type 2A. Various cardiovascular diseases, such as aortic stenosis, hypertrophic obstructive cardiomyopathy (HOCM), and several congenital structural diseases, as well as mechanical circulatory support systems, generate excessive high shear stress in the bloodstream. These cause excessive cleavage of VWF multimers resulting in a loss of HMW multimers, known as acquired von Willebrand syndrome (AVWS), a hemostatic disorder similar to VWD type 2A. Bleeding often occurs in the gastrointestinal tract since a fragile angiodysplasia develops associated with these diseases. Radical treatment for AVWS is to remove the pathological high shear causing AVWS.

Acquired von Willebrand syndrome in congenital heart disease surgery: results from an observational case-series

Essentials Bleeding complications during congenital heart disease surgery in neonatal age are very common. We report the perioperative incidence of acquired von Willebrand syndrome (aVWS) in 12 infants. aVWS was detected in 8 out of 12 neonates and infants intraoperatively after cardiopulmonary bypass. Ten patients received von Willebrand factor concentrate intraoperatively and tolerated it well. SUMMARY: Background Cardiac surgery of the newborn and infant with complex congenital heart disease (CHD) is associated with a high rate of intraoperative bleeding complications. CHD-related anatomic features such as valve stenoses or patent arterial ducts can lead to enhanced shear stress in the blood stream and thus cause acquired von Willebrand syndrome (aVWS). Objective To evaluate the intraoperative incidence and impact of aVWS after cardiopulmonary bypass (CPB) in neonates and infants with complex CHD. Patients/Methods We conducted a survey of patients aged < 12 months undergoing complex cardiac surgery in our tertiary referral center. Twelve patients, whose blood samples were analyzed for aVWS before CPB and immediately after discontinuation of CPB on a routine basis, were eligible for the analysis. von Willebrand factor antigen (VWF:Ag), ristocetin cofactor activity (VWF:RCo), collagen binding activity (VWF:CB), VWF:multimers and factor VIII activity (FVIII:C) were determined. Results aVWS was diagnosed by VWF multimer analysis in 10 out of 12 patients (83%) prior to surgery and intraoperatively at the end of CPB in 8 out of 12 patients (66%). Ten patients received VWF/FVIII concentrate intraoperatively as individual treatment attempts during uncontrolled bleeding. They tolerated it well without intraoperative thrombotic events. One patient suffered a transient postoperative cerebral sinuous vein thrombosis. Conclusions aVWS is of underestimated incidence in complex CHD surgery. These data may offer a new approach to reduce the risk of severe bleedings and to achieve hemostasis during high-risk pediatric cardiac surgery by tailoring the substitution with von Willebrand factor concentrate.

Idiopathic pulmonary arterial hypertension - a unrecognized cause of high-shear high-flow haemostatic defects (otherwise referred to as acquired von Willebrand syndrome) in children

Acquired von Willebrand syndrome (AVWS) is reported in high-flow high-shear congenital cardiac disorders. We hypothesized that the narrowed pulmonary vasculature in idiopathic pulmonary arterial hypertension (IPAH) may induce AVWS. We conducted a cross-sectional evaluation of children with IPAH. Patients with bleeding symptoms and/or laboratory abnormalities (thrombocytopenia, anomalies in coagulation screening tests) were tested in-depth for haemostatic defects. Fourteen children were followed with IPAH of which 8 were eligible. Four children exhibited abnormal bleeding scores (International Society on Thrombosis and Haemostasis Bleeding Assessment Tool: 3-5). All 8 patients showed very prolonged platelet function analyser (PFA)-100 closure times. Six children demonstrated either mild thrombocytopenia or low-normal von Willebrand factor (VWF) antigen (VWF:Ag) or VWF activity [mean (range), in iu/dl: VWF:Ag: 70 (61-91); VWF activity: 57 (34-70)]. Average VWF collagen binding capacity (VWF:CB) was 64 iu/dl (range: 53-123 iu/dl), with low-normal VWF activity/VWF:Ag or VWF:CB/VWF:Ag ratios occurring in five patients. All children had normal multimers distribution patterns. One patient underwent a lung transplantation, with normalization of haemostatic abnormalities post-surgery. Overall, 8 out of 14 children with IPAH had mild to moderate bleeding symptoms and/or laboratory abnormalities in keeping with AVWS. Normalization of the haemostatic defects following lung transplantation and lack of family history of bleeding attests to the acquired nature of their defects.

Association of Preoperative Cell Counts With Outcomes After Operation for Congenital Heart Disease

BACKGROUND

We examined the association of preoperative cell count abnormalities, which have been shown to be associated with outcomes in adult cardiac patients, with morbidity and mortality after operation for congenital heart disease (CHD) in children.

METHODS

We performed a retrospective cohort study on 4,865 children undergoing cardiac operation from 2004 to 2014. Our exposures of interest were presence of preoperative lymphopenia (lymphocyte count ≤ 3,000 cells/μL), thrombocytopenia (platelet count < 150 × 10³/μL), and neutrophilia (neutrophil count ≥ 7,000 cells/μL). Our outcomes of interest were mortality status, postoperative length of stay (LOS), and occurrence of postoperative complications. We performed logistic and linear regressions to determine the associations of preoperative cell counts with mortality, LOS, and complications, adjusting for age, sex, race or ethnicity, presence of a genetic syndrome, and Society of Thoracic Surgeons and European Association for Cardio-Thoracic Surgery Congenital Heart Surgery Mortality category.

RESULTS

Overall mortality was 2.8%, median LOS was 6 days, and 7.6% of patients had postoperative complications. Lymphopenia was associated with increased odds of postoperative mortality (odds ratio 1.67, 95% confidence interval: 1.15 to 2.43, p = 0.007). Lymphopenia, thrombocytopenia, and neutrophilia were all associated with longer postoperative LOS. Lymphopenia and thrombocytopenia were associated with increased occurrence of postoperative sepsis, and neutrophilia was associated with need for postoperative mechanical circulatory support.

CONCLUSIONS

In children undergoing CHD operation, preoperative lymphopenia is associated with increased in-hospital mortality postoperatively. Preoperative lymphopenia, neutrophilia, and thrombocytopenia are associated with longer postoperative LOS and with development of postoperative complications. Preoperative cell counts may serve as important prognostic markers in preoperative planning for patients with CHD.

Acquired von Willebrand Syndrome in an Infant With Coarctation of the Aorta and Williams Syndrome

An infant with coarctation of the aorta and Williams syndrome was noted to have petechiae in cardiology clinic prior to planned surgical intervention. Workup revealed acquired von Willebrand syndrome secondary to the high shear force generated by the aortic coarctation. He was treated with intra- and postoperative Humate P; there were no postoperative bleeding complications. His acquired von Willebrand syndrome resolved postoperatively.

Pediatric Acquired von Willebrand Syndrome in Cardiopulmonary Disorders: Do Laboratory Abnormalities Predict Bleeding Risk?

There are conflicting reports on whether or not laboratory abnormalities in pediatric acquired von Willebrand syndrome (AVWS) predict bleeding manifestations in patients with cardiopulmonary disorders (CPD). We retrospectively reviewed charts of patients with AVWS and CPD (n=16) seen at Texas Children's Hospital from 2003 to 2012. The most common CPD were valve stenoses, ventricular septal defects, and pulmonary hypertension. All patients had loss of high molecular weight multimers. Fifteen (94%) patients presented with bleeding symptoms, with menorrhagia and epistaxis being the most common. Von Willebrand ristocetin cofactor activity (VWF:RCo), as well as the use of anticoagulant or antiplatelet medication, did not predict bleeding manifestations (P=0.70 and 0.84, respectively). VWF:RCo/VWF antigen (Ag) ratio of <0.7 was significantly associated with presence of bleeding symptoms. All patients who had complete repair of their cardiac defect experienced normalization of VWF multimers and VWF:RCo/Ag ratio, as well as bleeding symptom resolution. We conclude that increased bleeding risk is associated with low VWF:RCo/Ag ratio in pediatric AVWS due to CPD. However, other laboratory abnormalities such as VWF:RCo level and qualitative multimer analysis, do not appear to predict bleeding. Future studies exploring quantification of multimer loss may be helpful in further assessing bleeding risk associations.

Risk Factors, Prophylaxis, and Treatment of Venous Thromboembolism in Congenital Heart Disease Patients

Congenital heart disease (CHD) is a common condition in the pediatric population, affecting up to 1% of all live births (i.e., around 40,000 newborns/year in the United States). Although CHD does have a wide range of severity, by the age of 5 years approximately 80% of patients will require at least one surgical intervention to achieve a complete/palliative cardiac repair. Today, in light of their much-improved surgical survival, the care of these patients focuses on morbidity prevention and/or treatment. One such morbidity has been the increased frequency of thrombotic occlusions [e.g., cardioembolic arterial ischemic strokes; arterial, cardiac, and/or newly created shunt thrombosis; venous thromboembolism (VTE)]. Patients with CHD are at high risk of developing thrombosis due to the disruption of blood flow, CHD-related coagulopathy, inflammation, and/or platelet activation secondary to extracorporeal circulation support required during open-heart surgery or as a bridge to recovery, which can increase thrombus formation. In this article, we will discuss how the coagulation system is altered in patients with CHD in regard to the patient's anatomy, procedures they undergo to correct their congenital heart defect, and other risk factors that may increase their thrombotic risk, focusing on VTE. We will also discuss the most recently published reports pertaining to guidelines on prophylaxis and treatment of VTE in this population. Finally, we will briefly address the long-term VTE outcomes for patients with CHD.

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.