Claudia Heilmann

Non-surgical bleeding in patients with ventricular assist devices could be explained by acquired von Willebrand disease.

OBJECTIVE Outcomes after ventricular assist device (VAD) implantation have significantly improved during the last decade. However, bleeding episodes remain a serious complication of VAD support. This cannot be explained by the individual anticoagulation regimen alone in several cases, but may be symptomatic of acquired von Willebrand disease (VWD). The leading finding in acquired VWD (AVWD) is the loss of large multimers which results in diminished binding to collagen and to the platelets. We, therefore, analysed patients with two VAD types for laboratory parameters of VWD and compared them with patients after heart transplantation (HTX). MATERIALS AND METHODS Seven patients with a HeartMate II left-ventricular assist device and five patients who received a Thoratec biventricular assist device were included in this study. Eight HTX recipients served as controls. Analysis included international normalized ratio (INR), partial thromboplastin time (PTT), platelet count, von Willebrand factor (VWF) antigen, collagen binding capacity, ristocetin cofactor activity, the ratios of the latter two to the VWF antigen and presence of large VWF multimers. RESULTS The VAD and HTX groups did not differ with regard to age or time-point of analysis after surgery. INR and number of platelets were comparable in both groups, PTT was prolonged in VAD patients. Both VAD and HTX patients had elevated but comparable amounts of VWF antigen. However, large multimers were missing in all of 10 tested VAD patients. In contrast, five of six tested HTX recipients displayed normal multimer pattern. Indeed, collagen binding capacity and ristocetin cofactor activity (which measures binding of VWF to platelets) were lower in VAD patients compared to HTX recipients. Impaired coagulation associated with VADs was also reflected by the diminished ratios of collagen binding capacity and ristocetin cofactor activity to VWF antigen. A pathologic collagen binding ratio was found in all 10 tested VAD patients and one of the eight HTX patients, a reduced ristocetin cofactor activity ratio in 10 of 12 VAD and one of eight HTX patients. CONCLUSION Non-surgical postoperative bleeding after VAD implantation could be explained by an AVWD. Several pharmacologic treatment options (tranexamic acid, desmopressin, VWF-factor VIII concentrate, recombinant factor VIIa) may arise from our data. Improved VAD design could prevent this problem in the future.

Acquired von Willebrand syndrome in patients with extracorporeal life support (ECLS)

PurposeExtracorporeal life support (ECLS) is used for patients with refractory heart failure with or without respiratory failure. This temporary support is provided by blood pumps which are connected to large vessels. Bleeding episodes are a typical complication in patients with ECLS. Recently, several studies illustrated that acquired von Willebrand syndrome (AVWS) can contribute to bleeding tendencies in patients with long-term ventricular assist devices (VAD). AVWS is characterized by loss of the high molecular weight (HMW) multimers of von Willebrand factor (VWF) as a result of high shear stress and leads to impaired binding of VWF to platelets and to subendothelial matrix. Since ECLS and VAD share several features, we investigated patients with ECLS for AVWS.MethodsWe analyzed 32 patients with ECLS and 19 of them without support. To diagnose AVWS, ratios of ristocetin cofactor activity (VWF:RCo) and collagen binding capacity (VWF:CB) to VWF antigen (VWF:Ag) were employed in conjunction with multimeric analysis.ResultsReduced VWF:RCo/VWF:Ag ratios were identified in 28 ECLS patients. Furthermore, VWF:CB/VWF:Ag ratios were decreased in 31 patients. HMW multimers of VWF were missing in the same 31 patients. Thus, 31 of 32 ECLS patients presented with AVWS. Twenty-two of the 32 patients suffered from bleeding complications. Without support, AVWS was not detectable in any analyzed patient.ConclusionOur data indicate that AVWS is a typical disorder in patients with ECLS. We hypothesize that AVWS could contribute to aggravation of bleeding tendencies in ECLS patients.

Acquired von Willebrand syndrome in patients with ventricular assist device or total artificial heart.

Unexplained bleeding episodes are associated with ventricular assist devices (VAD) and can occur in part due to acquired von Willebrand syndrome (AVWS). AVWS is characterised by loss of high molecular weight (HMW) multimers of von Willebrand factor (VWF) and decreased ratios of collagen binding capacity and ristocetin cofactor activity to VWF antigen. Loss of multimers can occur as VWF is subjected to increased shear stress, which occurs in presence of VADs. We studied 12 patients who required mechanical support of their native heart for terminal cardiac insufficiency. Nine patients underwent placement of a VAD, while three underwent placement of a total artificial heart (TAH), which is connected directly to heart and large cardiac vessels without cannulas. Within one day of VAD implantation, four of five patients evaluated demonstrated loss of HMW multimers and impaired VWF function. AVWS was present within two weeks of implantation in eight of nine patients, and in all seven tested patients after >/=3 months. Patients with different VAD types developed varying severities of AVWS. After VAD explantation, HMW multimers were detectable and VWF function normalised in all patients. AVWS was not observed in the TAH patients studied. Our findings demonstrate that patients with an implanted VAD experience a rapid onset of AVWS that is quickly and completely reversed after device explantation. In addition, TAH patients do not develop AVWS. These results suggest that shear stress associated with exposure of blood to VAD cannulas and tubes may contribute to the development of AVWS.

Haemolysis in patients with ventricular assist devices: major differences between systems

INTRODUCTION Implantation of a ventricular assist device (VAD) is a seminal therapeutic option for patients with terminal cardiac failure. However, haemolysis remains a clinically relevant adverse effect of several VAD types. Lysed erythrocytes release lactate dehydrogenase (LDH) and haemoglobin. Free haemoglobin in plasma is bound by haptoglobin with high affinity. The complex is internalised by monocytes/macrophages and degraded. Any more released free haemoglobin is captured by haemopexin. This complex also undergoes lysosomal degradation in various cells. Only now, the excessive free haemoglobin can be measured in plasma. Here, we investigated haemolysis in patients supported by different VAD types. METHODS Five patients with an intracorporeal centrifugal left ventricular VAD (LVAD), 10 patients with an axial LVAD and seven patients with a paracorporeal biventricular assist device (BVAD) were analysed preoperatively and 3 days (3.0+/-0.4 days, early), 2 weeks (14+/-1 days, intermediate) and 2 months (62+/-5 days, later) after VAD implantation for haptoglobin, haemopexin, free haemoglobin in plasma, LDH, total haemoglobin, haematocrit and transfusion requirements. RESULTS Patients with a centrifugal LVAD displayed normal haptoglobin and haemopexin, low free haemoglobin and moderately increased LDH. In comparison, axial LVADs were accompanied by lower haptoglobin and haemopexin and higher free haemoglobin and LDH values. In contrast, BVADs led to an almost complete loss of haptoglobin and haemopexin and to high levels of free haemoglobin and LDH at each analysed time point. CONCLUSIONS While severe haemolysis accompanies BVAD support, erythrocyte damage is less pronounced in the axial LVAD examined and only slight in the intracorporeal centrifugal LVAD. Haemopexin, a scavenger of free haemoglobin, can be used, in combination with haptoglobin and free haemoglobin, to assess erythrocyte damage.

Acquired Von Willebrand syndrome is an early-onset problem in ventricular assist device patients,

OBJECTIVE Acquired Von Willebrand syndrome (AVWS) can contribute to bleeding complications in patients with ventricular assist devices (VADs). AVWS results from shear stress, which causes unfolding of the high-molecular-weight (HMW) multimers of Von Willebrand factor (VWF) with subsequent cleavage. Loss of the HMW multimers of VWF is the leading finding in AVWS. In consequence, binding of VWF to collagen and to platelets is impaired. The onset of AVWS after VAD implantation is not yet determined. We examined VAD patients for presence of an AVWS in the early, intermediate, and late phase after VAD implantation. METHODS Patients with a biventricular Thoratec-PVAD(®) (BVAD, n = 6) or a left-ventricular HeartMateII(®) (HMII, n = 11) were analyzed prior to VAD implantation and after 1, 3, 14, 30, and 60 days. Diagnosis of AVWS based on VWF:ristocetin cofactor activity/VWF:VWF antigen (VWF:RCo/VWF:Ag), collagen-binding capacity:VWF antigen (VWF:CB/VWF:Ag), and multimeric analysis. In addition, we analyzed the number of bleeding episodes, which required surgical intervention. RESULTS No patient had an AVWS prior to VAD implantation. An AVWS was identified already in the very early postoperative period, that is, in almost all patients on the first day and in all patients on the third day. The AVWS was also detected in the majority of patients in the further course. Nine of all 17 patients suffered bleeding complications and required a total of 25 interventions due to hemorrhages. Forty percent of re-interventions were carried out within the first 10 days after implantation; five of these were necessary within the first 24h. CONCLUSION The AVWS is present already in the early postoperative phase after VAD implantation. Therefore, reduced shear stress has to be an important feature of newly developed assist devices in the future.

Collateral growth: cells arrive at the construction site

Coronary artery disease (CAD) and peripheral artery occlusion disease are the most common diseases in the Western world which are treated by pharmacological and surgical therapies. However, patients in the endstage of the disease are not suitable candidates for bypass surgery. Alternative therapies that boost the endogenous collateralization are required. Two mechanisms are naturally activated after onset of ischemia: 1. angiogenesis, sprouting of capillaries, and 2. arteriogenesis, enlargement of small preexisting arterioles. In the first part of this review, we describe the sequence of events during the development of collateral vessels. The second part focuses on two types of cells which are crucial for the development of collateral circulation, and which migrate to the site of vessel growth via peripheral blood: monocytes/macrophages and endothelial progenitor cells. The role of these cells and the implications for their use in treating ischemic diseases of cardiac and sceletal muscle are discussed.

Polyurethane Scaffolds Seeded With Genetically Engineered Skeletal Myoblasts: A Promising Tool to Regenerate Myocardial Function

In animal models, intramyocardial injection of primary skeletal myoblasts is supposed to promote tissue regeneration and to improve cardiac function after myocardial infarction. The usage of genetically engineered myoblasts overexpressing the paracrine factors involved in tissue repair is believed to enhance these effects. However, cell therapy via injection is always accompanied by a high death rate of the injected cells. Here, we describe the construction of a growth factor-producing myoblast-seeded scaffold to overcome this limitation. Skeletal myoblasts were isolated and expanded from newborn Lewis rats. Cells were seeded on polyurethane (PU) scaffolds (Artelon) and transfected with DNA of VEGF-A, HGF, SDF-1, or Akt1 using the lipid-based Metafectene Pro method. Overexpression was verified by ELISA, RT-PCR (VEGF-A, HGF, and SDF-1) and Western blot analysis (Akt1). The seeded scaffolds were transplanted onto damaged myocardium of Lewis rats 2 weeks after myocardial infarction. Six weeks later, their therapeutic potential in vivo was analyzed by measurement of infarction size and capillary density. Primary rat skeletal myoblasts seeded on PU scaffolds were efficiently transfected, achieving transfection rates of 20%. In vitro, we noted a significant increase in expression of VEGF-A, HGF, SDF-1, and Akt1 after transfection. In vivo, transplantation of growth factor-producing myoblast-seeded scaffolds resulted in enhanced angiogenesis (VEGF-A, HGF, and Akt1) or a reduced infarction zone (SDF-1 and Akt1) in the ischemically damaged myocardium. In summary, we constructed a growth factor-producing myoblast-seeded scaffold which combines the beneficial potential of stem cell transplantation with the promising effects of gene-therapeutic approaches. Because this matrix also allows us to circumvent previous cell application drawbacks, it may represent a promising tool for tissue regeneration and the re-establishment of cardiac function after myocardial infarction.

Lymph Angiogenesis After Lung Transplantation and Relation to Acute Organ Rejection in Humans

BACKGROUND Acute rejection after kidney transplantation was found to be associated with increased recipient-derived lymph angiogenesis. However, the relation of lymph angiogenesis to acute rejection in lung transplantation has not yet been investigated. METHODS Transbronchial biopsies from 23 lung transplant recipients (47 + or - 15 years old, 15 male, 19 double lungs, 4 single lungs), taken at 14 and 90 days after transplantation were investigated. Immunohistostaining for PROX-1 (an lymphatic endothelial marker) and for vascular endothelial growth factor receptor (VEGFR) 1 and 2 (blood capillary markers) was performed. Biopsies with no sign of rejection (International Society for Heart and Lung Transplantation [ISHLT] grade A0, n = 27) were compared with biopsies with rejection grade A1/A2 (n = 19). RESULTS Biopsies with ISHLT rejection grade A1 or A2 showed a significantly higher density of PROX-1 marked lymphatics in comparison with biopsies of grade A0 at 14 days (p < 0.001) and at 90 days (p < 0.001) after transplantation, and in the collective comparison (all biopsies with ISHLT grade A1 or A2 versus all biopsies with grade A0, p < 0.001). For VEGFR-1 and VEGFR-2, no difference was found between ISHLT grade A1 or A2 compared with grade A0, neither at 14 or 90 days nor in the collective comparison. CONCLUSIONS Increased lymphatic angiogenesis after lung transplantation, demonstrated by increased density of the PROX-1 lymphatic endothelial marker, was associated with histologically evident acute organ rejection in humans. Although the exact role of lymphatic angiogenesis in acute organ rejection remains to be determined, further study of the interaction between the microvasculature and acute rejection seems warranted. Pending further investigation, analysis of PROX-1 density may develop into a new tool for rejection monitoring, supplementing conventional rejection grading.

Successful resuscitation after prolonged periods of cardiac arrest: A new field in cardiac surgery

OBJECTIVE Cardiopulmonary resuscitation is associated with high mortality and poor neurological recovery. Cardiopulmonary resuscitation can cause ischemia-reperfusion injury of the whole body and brain. We assessed the hypothesis that controlled reperfusion of the whole body with cardiopulmonary bypass would limit reperfusion injury after 15 minutes of normothermic cardiac arrest with better survival and neurological recovery. METHODS Eleven pigs were exposed to normothermic ischemia for 15 minutes by inducing ventricular fibrillation, followed by cardiopulmonary resuscitation (control group, n = 4) or 60 minutes of cardiopulmonary bypass (treatment group, n = 7). Conditions of reperfusion and the reperfusate were controlled with cardiopulmonary bypass. Animals were observed for up to 7 days, and neurological assessment (Neurological Deficit Score: 0, normal; 500, brain death), magnetic resonance imaging, and brain histology were performed. RESULTS All animals in the control group died after 20 minutes of cardiopulmonary resuscitation (n = 4). All (n = 7) survived in the treatment group. Clinically apparent neurological recovery occurred within 24 hours; 1 fully conscious pig could not walk. The Neurological Deficit Score was 98 +/- 31 in all animals (n = 7) after 24 hours and decreased to 0 after 48 hours in 4 of 5 eligible animals; 1 animal had a Neurological Deficit Score of 110 after 3 days. Brain histology revealed hypoxic and apoptotic neurons with an inconclusive correlation regarding neurological recovery. CONCLUSION Clinically apparent neurological recovery after a period of 15 minutes of cardiac arrest occurred with cardiopulmonary bypass instead of cardiopulmonary resuscitation for reperfusing the whole body. This approach contrasts with cardiopulmonary resuscitation, in which resuscitation has been reported as successful after only 3 to 5 minutes of cardiac arrest. Cardiopulmonary bypass might be a key to improve survival and neurological recovery after cardiac arrest.

Platelet dysfunction and acquired von Willebrand syndrome in patients with left ventricular assist devices

OBJECTIVES Unexplained bleeding events are a severe complication in patients with left ventricular assist devices (LVADs). Platelet dysfunction and acquired von Willebrand syndrome (AVWS) may contribute to bleeding tendencies. Yet, comprehensive data with respect to platelet function and AVWS in LVAD patients in terms of bleeding events are scarce. METHODS Thirty-nine HeartMate II patients were included in this study. Data of at least two time points were available for each patient. Platelet function was analysed via light transmission aggregometry in 19 patients without LVAD, 28 in early (≤14 days) and 30 in late postimplantation states (≥30 days). Von Willebrand factor (VWF) antigen, VWF collagen binding capacity and VWF multimeric analyses were performed in 26 patients without LVAD, 39 in early and 33 in late postimplantation states to diagnose AVWS. Bleeding complications were recorded for 39 patients in the early and 33 in the late postoperative period. RESULTS Platelet dysfunction was detectable in 18 of 19 without LVAD and in all patients following LVAD implantation. Platelet aggregation values did not change over time (without-early, P = 0.27, n = 14; early-late, P = 0.17, n = 21). AVWS was not diagnosed in patients without LVAD, except for one. On LVAD, 33 of 39 patients had AVWS in the early and all in the late period (n = 33). Bleeding events occurred in 44% of patients in the early and in 64% of patients in the late period. CONCLUSIONS According to our data, platelet aggregation is often impaired in LVAD patients even without an implanted LVAD. Additionally, appearance of AVWS seems to be closely linked to LVAD implantation.