Transitory immunologic response after implantation of the DeBakey VAD continuous-axial-flow pump

Body mass index-dependent immunological profile changes after left ventricular assist device implantation

Purpose

Infection is a common complication following left ventricular assist device (LVAD) implantation. Patients with obesity are particularly at risk due to their high percentage of adipose tissue and the resulting chronic inflammatory state and resulting immunological changes. This study investigated changes of immunological parameters in relation to body mass index (BMI) during the first year after LVAD implantation.

Methods

Blood samples were obtained prior to LVAD implantation and at 3 (1st FU), 6 (2nd FU) and 12 mo (3rd FU) after LVAD implantation. Patients were divided into three groups (normal weight: BMI of 18.5-24.9 kg/m2; n=12; pre-obesity: 25.0-29.9 kg/m2; n=15; obesity: ≥ 30.0 kg/m2; n=17) based on their BMI at the time of LVAD implantation. Flow cytometric analyses for CD4+ and CD8+ T cells, regulatory T cells (Tregs), B cells as well as dendritic cells (DCs) were performed.

Results

After LVAD implantation, obese patients (0.51 ± 0.20%) showed a higher proportion of overall DCs than normal-weight (0.28 ± 0.10%) and pre-obese patients (0.32 ± 0.11%, p<0.01) at 3rd FU. The proportion of BDCA3+ myeloid DCs was lower in obese patients (64.3 ± 26.5%) compared to normal-weight patients (82.7 ± 10.0%, pnormal-weight vs. obesity=0.05) at 2nd FU after LVAD implantation. The analysis of BDCA4+ plasmacytoid DCs revealed a reduced proportion in pre-obese (21.1 ± 9.8%, pnormal-weight vs. pre-obesity=0.01) and obese patients (23.7 ± 10.6%, pnormal-weight vs. obesity=0.05) compared to normal-weight patients (33.1 ± 8.2%) in the 1st FU. T cell analysis showed that CD4+ T cells of obese patients (62.4 ± 9.0%) significantly increased in comparison to pre-obese patients (52.7 ± 10.0%, ppre-obesity vs. obesity=0.05) and CD8+ T cells were lower in obese patients (31.8 ± 8.5%) than in normal-weight patients (42.4 ± 14.2%; pnormal-weight vs. obesity=0.04) at the 3rd FU. Furthermore, we observed significantly reduced proportions of Tregs in pre-obese patients compared to normal-weight and obese patients at 2nd FU (p=0.02) and 3rd FU (p=0.01) after LVAD implantation.

Conclusion

This study reported changes of the innate and adaptive immune system of pre-obese and obese compared to normal-weight patients one year after LVAD implantation. DCs and their subsets, CD8+ T cells and Tregs were affected immune cell populations that indicate immunological changes which might increase the incidence of postoperative infection.

Development of malignancies and their outcomes in patients supported on continuous-flow left ventricular assist devices-a systematic review

Background

With increased use of continuous-flow left ventricular assist devices (CF-LVAD), development of malignant tumors in this population is not uncommon. We sought to evaluate malignancies in CF-LVAD patients and evaluate the outcomes of treatment strategies.

Methods

Overall, 18 articles consisting of 28 patients were identified who developed malignancies after CF-LVAD placement. Patient-level data were extracted for systematic review.

Results

Median patient age was 60 years [59-67] and 85.7% (24/28) were male. CF-LVAD was placed as bridge-to-transplant (BTT) in 60.9% (14/23) of patients. The three most common malignancy types were GI in 35.7% (10/28) of patients, lung in 21.4% (6/28) and skin in 10.7% (3/28). Median time from CF-LVAD implant to malignancy diagnosis was 6.9 [2.5-12.8] months. Metastatic disease occurred in 17.9% (5/28) over a median time of 5.0 [1.0-82.0] months from the diagnosis. Surgical resection of the malignancy was performed in 57.1% (16/28) of patients. Our results showed that while there was a significantly higher probability of survival among patients who underwent surgery versus those who did not, when only stage I and II patients were included in the analysis, this difference was no longer statistically significant. Three patients were relisted for heart transplant after surgical treatment, and two received the transplant.

Conclusions

Surgical management of malignancies in patients on CF-LVADs may improve survival and transplant eligibility status, therefore, a CF-LVAD should not always preclude surgical treatment.

Mechanical shear stress and leukocyte phenotype and function: Implications for ventricular assist device development and use

Heart failure remains a disease of ever increasing prevalence in the modern world. Patients with end-stage heart failure are being referred increasingly for mechanical circulatory support. Mechanical circulatory support can assist patients who are ineligible for transplant and stabilise eligible patients prior to transplantation. It is also used during cardiopulmonary bypass surgery to maintain circulation while operating on the heart. While mechanical circulatory support can stabilise heart failure and improve quality of life, complications such as infection and thrombosis remain a common risk. Leukocytes can contribute to both of these complications. Contact with foreign surfaces and the introduction of artificial mechanical shear stress can lead to the activation of leukocytes, reduced functionality and the release of pro-inflammatory and pro-thrombogenic microparticles. Assessing the impact of mechanical trauma to leukocytes is largely overlooked in comparison to red blood cells and platelets. This review provides an overview of the available literature on the effects of mechanical circulatory support systems on leukocyte phenotype and function. One purpose of this review is to emphasise the importance of studying mechanical trauma to leukocytes to better understand the occurrence of adverse events during mechanical circulatory support.

The Inflammatory Response to Ventricular Assist Devices

The therapeutic use of ventricular assist devices (VADs) for end-stage heart failure (HF) patients who are ineligible for transplant has increased steadily in the last decade. In parallel, improvements in VAD design have reduced device size, cost, and device-related complications. These complications include infection and thrombosis which share underpinning contribution from the inflammatory response and remain common risks from VAD implantation. An added and underappreciated difficulty in designing a VAD that supports heart function and aids the repair of damaged myocardium is that different types of HF are accompanied by different inflammatory profiles that can affect the response to the implanted device. Circulating inflammatory markers and changes in leukocyte phenotypes receive much attention as biomarkers for mortality and disease progression. However, they are seldom used to monitor progress during and outcomes from VAD therapy or during the design phase for new devices. Even the partial reversal of heart damage associated with heart failure is a desirable outcome from VAD use. Therefore, improved understanding of the interplay between VADs and the recipient's inflammatory response would potentially increase their uptake, improve patient lives, and fuel research related to other blood-contacting medical devices. Here we provide a review of what is currently known about inflammation in heart failure and how this inflammatory profile is altered in heart failure patients receiving VAD therapy.

Ventricular Assist Devices and Anesthesia

Ventricular assist devices (VADs) have revolutionized longterm care for patients with congestive heart failure. These patients represent about 1% of the adults in the United States, considering that heart failure is a contributing factor in more than 250,000 deaths annually. It has been estimated that about 60,000 patients per year in the United States could benefit from heart transplantation or long-term mechanical support. Because of the short supply of donor hearts for transplant, assist devices have become of great value. At least four assist devices are clinically available, and two other devices are being investigated. Because cardiopulmonary bypass is required for implantation of these devices, anesthetizing these critically compromised patients requires extensive monitoring, skillful anesthetic management, and expert postoperative care.

Attenuation in peripheral endothelial function after continuous flow left ventricular assist device therapy is associated with cardiovascular adverse events

BACKGROUND

Patients with heart failure (HF) have abnormal endothelial function. Although use of a continuous flow left ventricular assist device (CF-LVAD) results in significant hemodynamic improvement, the effects on systemic endothelial function are unclear.

METHODS AND RESULTS

Eighteen HF patients with CF-LVAD implantation were included in this prospective observational study. We measured reactive hyperemia index (RHI) before and after CF-LVAD implantation to evaluate sequential changes in endothelial function. Patients were followed clinically for the occurrence of adverse cardiovascular events, a composite of death, thrombosis, bleeding, HF, renal failure, and arrhythmia. Preoperative RHI was 1.77±0.39. Early in the postoperative period (7-14 days after operation) RHI significantly decreased to 1.19±0.31 (P<0.001, compared with preoperative RHI). At first and second follow-up (4-6 weeks and 3-7 months after operation) RHI remained lower at 1.48±0.50 (P=0.030) and 1.26±0.37 (P=0.002), respectively, compared with preoperative RHI. The decrease in early postoperative RHI relative to preoperative RHI was significantly associated with adverse cardiovascular events after CF-LVAD (age-adjusted risk ratio for 0.25 decrease in RHI, 1.35; 95% confidence interval: 1.13-1.62, P=0.001).

CONCLUSIONS

Peripheral endothelial function had a significant and persistent decline up to 5 months following implantation of CF-LVAD, and this decline was associated with adverse cardiovascular events. These findings may provide insight into some of the vascular complications following CF-LVAD in HF patients.

Are blood stream infections associated with an increased risk of hemorrhagic stroke in patients with a left ventricular assist device?

Blood stream infections (BSIs) are an important cause of morbidity and mortality in patients with left ventricular assist devices (LVADs). The aim of this study was to examine the correlation between hemorrhagic cerebrovascular accident (CVA) and BSI after implantation of LVAD for advanced heart failure (HF). This was a retrospective descriptive review of 87 patients with end-stage HF, who underwent implantation of HeartMate II continuous-flow LVAD over a 4 year period. Blood stream infections were diagnosed by serial blood cultures, and suspected neurological complications including CVAs were confirmed by neuroimaging. Extensive patient chart review was performed, and descriptive characteristics were analyzed using SPSS statistical software. The mean age of our study population was 62.3 ± 12.8 years, and the majority of our patients were males (n = 75, 86.2%). The baseline characteristics were comparable in the patients with and without CVAs. Patients with BSI had a much greater incidence of CVA compared to patients without BSI (n = 13, 43.3% vs. n = 5, 10.0%; p < 0.0001). There was an increased mortality in patients with BSI than those without (n = 57, 65.5% vs. n = 30, 34.5%; p = 0.003). The risk of all CVAs (hemorrhagic/ischemic) was eightfold (odds ratio [OR] = 7.9; 95% confidence interval [CI] = 2.4-25.5; p = 0.001] in patients with BSI. Patients with BSI had a >20-fold risk of hemorrhagic CVA (OR = 24; 95% CI = 2.8-201.1; p = 0.03). Advanced HF patients with LVAD support who developed BSI need urgent evaluation and close monitoring for suspected neurological complications, particularly hemorrhagic CVA.

Left ventricular assist device-related infections: past, present and future

Over the last decade, left ventricular assist device (LVAD) implantation has emerged as an alternative treatment strategy in patients with advanced heart failure irrespective of their transplant eligibility. However, success and applicability of this therapy is largely limited by high complication rates associated with these devices. Although superior outcomes have been achieved with the second-generation continuous-flow LVADs, device-related infections continue to be a prevalent complication in this patient population and contribute significantly to the financial burden of this therapy due to an increased need for hospitalizations and surgical interventions. Patient selection, device design and LVAD-induced immune system dysfunction appear to be major risk factors for the development of device-related infections. Improvements in device design and better patient selection strategies, particularly with respect to identifying individuals with genetic susceptibility to device-related infections, may further reduce this prevalent complication and improve outcomes in patients with advanced heart failure.

Management of allosensitized cardiac transplant candidates

Cardiac transplantation remains the best treatment in patients with advanced heart failure with a high risk of death. However, an inadequate supply of donor hearts decreases the likelihood of transplantation for many patients. Ventricular assist devices (VADs) are being increasingly used as a bridge to transplantation in patients who may not survive long enough to receive a heart. This expansion in VAD use has been associated with increasing rates of allosensitization in cardiac transplant candidates. Anti-HLA antibodies can be detected before transplantation using different techniques. Complement-dependent lymphocytotoxicity assays are widely used for measurement of panel-reactive antibody (PRA) and for crossmatch purposes. Newer assays using solid-phase flow techniques feature improved specificity and offer detailed information concerning antibody specificities, which may lead to improvements in donor-recipient matching. Allosensitization prolongs the wait time for transplantation and increases the risk of post-transplantation complications and death; therefore, decreasing anti-HLA antibodies in sensitized transplant candidates is of vital importance. Plasmapheresis, intravenous immunoglobulin, and rituximab have been used to decrease the PRA before transplantation, with varying degrees of success. The most significant post-transplantation complications seen in allosensitized recipients are antibody-mediated rejection (AMR) and cardiac allograft vasculopathy (CAV). Often, AMR manifests with severe allograft dysfunction and hemodynamic compromise. The underlying pathophysiology is not fully understood but appears to involve complement-mediated activation of endothelial cells resulting in ischemic injury. The treatment of AMR in cardiac recipients is largely empirical and includes high-dose corticosteroids, plasmapheresis, intravenous immunoglobulin, and rituximab. Diffuse concentric stenosis of allograft coronary arteries due to intimal expansion is a characteristic of CAV. Its pathophysiology is unclear but may involve chronic complement-mediated endothelial injury. Sirolimus and everolimus can delay the progression of CAV. In some nonsensitized cardiac transplant recipients, the de novo formation of anti-HLA antibodies after transplantation may increase the likelihood of adverse clinical outcomes. Serial post-transplantation PRAs may be advisable in patients at high risk of de novo allosensitization.

Reduced pulsatility induces periarteritis in kidney: role of the local renin-angiotensin system

OBJECTIVE

The need for pulsatility in the circulation during long-term mechanical support has been a subject of debate. We compared histologic changes in calf renal arteries subjected to various degrees of pulsatile circulation in vivo. We addressed the hypothesis that the local renin-angiotensin system may be implicated in these histologic changes.

METHODS AND RESULTS

Sixteen calves were implanted with devices giving differing degrees of pulsatile circulation: 6 had a continuous flow left ventricular assist device (LVAD); 6 had a continuous flow right ventricular assist device (RVAD); and 4 had a pulsatile total artificial heart (TAH). Six other calves were histologic and immunohistochemical controls. In the LVAD group, the pulsatility index was significantly lower (0.28 +/- 0.07 LVAD vs 0.56 +/- 0.08 RVAD, vs 0.53 +/- 0.10 TAH; P < 0.01), and we observed severe periarteritis in all cases in the LVAD group. The number of angiotensin II type 1 receptor-positive cells and angiotensin converting enzyme-positive cells in periarterial areas was significantly higher in the LVAD group (angiotensin II type 1 receptor: 350 +/- 139 LVAD vs 8 +/- 6 RVAD, vs 3 +/- 2 TAH, vs 3 +/- 2 control; P < .001; angiotensin-converting enzyme: 325 +/- 59 LVAD vs 6 +/- 4 RVAD, vs 6 +/- 5 TAH, vs 3 +/- 1 control; P < .001).

CONCLUSIONS

The reduced pulsatility produced by a continuous flow LVAD implantation induced severe periarteritis in the kidneys. The local renin-angiotensin system was up-regulated in the inflammatory cells only in the continuous flow LVAD group.

Human leukocyte antigen sensitization in ventricular assist device recipients: a lesser risk with the DeBakey axial pump

BACKGROUND

Previous reports, all concerning pulsatile devices, have indicated an increased risk of development of circulating antileukocyte antigen (HLA; human leukocyte antigen) antibodies during ventricular assist device (VAD) support. We investigated sensitization in patients implanted with the DeBakey VAD (MicroMed Technology, Inc, Houston, TX) axial flow pump as a bridge to heart transplantation.

METHODS

Inclusion criteria for this prospective study were the following. Patients implanted with the DeBakey VAD axial flow pump, without HLA antibodies prior to implantation, with a duration of support of at least one month. The HLA antibody testing for IgG and IgM class I and II antibodies was performed weekly during support, using both a complement dependant cytotoxicity assay and an enzyme-linked immunosorbent assay (ELISA). Retrospective cross match was performed for all patients transplanted. The occurrence of graft rejection was determined by regular endomyocardial biopsies after heart transplantation, graded according to the International Society for Heart and Lung Transplantation (ISHLT) guidelines. Additionally, the transfusion history was reviewed for all patients.

RESULTS

Fourteen patients were included representing 1,220 cumulative patient-days of support (mean duration time on support, 87 days). No patient developed detectable IgG antibodies to class I or II. One patient had a positive ELISA, corresponding to nonsignificant (6/30) class I IgM antibodies at 3 weeks postimplantation. Ten patients underwent successful heart transplantation, representing 156 cumulative months. No retrospective cross match was positive. The percentage of significant acute rejection episodes (ISHLT grade 3A or more) was 6% and 4.3% in the first 6 months and from 6 to 12 months, respectively. No vascular rejection was noted. The posttransplantation survival rate was 87% at 6 months and 75% at 1 year, respectively.

CONCLUSIONS

Patients implanted with the DeBakey VAD axial flow pump as a bridge to heart transplantation do not appear to be exposed to an increased risk of sensitization.

L'activation sanguine au cours de l'assistance circulatoire mécanique prolongée

Mechanical circulatory support has become an approved treatment option for patients with cardiogenic shock or end-stage heart failure. However, recipients of heart assist devices are prone to high incidences of bleeding, thrombo-embolic and infectious complications. The occurrence of these complications is favoured by systemic alterations of coagulation and fibrinolysis, inflammation and immune responses. Several studies have evaluated these pathophysiological changes in patients undergoing long term circulatory support with pulsatile devices. However, the systemic consequences of the more recently introduced rotary blood pumps remain largely unknown. The present review focuses on the systemic consequences of long term circulatory support with pulsatile and non-pulsatile devices.

Extensive Coagulation Monitoring in Patients After Implantation of the MicroMed Debakey Continuous Flow Axial Pump

Ventricular assist device (VAD) implantation is associated with impaired primary hemostasis and thromboembolic complications. Recently, a new generation of implantable continuous flow axial pumps was introduced into clinical application. To study the potential thrombogenic properties of this type of pump, we applied extensive platelet monitoring was applied. In our institution, 13 patients received the MicroMed DeBakey VAD as a bridge to transplantation. Routine coagulation tests (platelet count, activated partial thromboplastin time, prothrombin time, antithrombin III activity) and platelet function tests (whole blood aggregometry, thrombelastography, flow cytometry) were performed. No clinically relevant thromboembolic events were detected. No correlation was found between global function tests, platelet aggregation, and thrombelastography. No correlation was detected between platelet activation and hemolysis parameters. Platelet aggregation and coagulation index were significantly suppressed early after operation. A subsequent phase of hyper-aggregability, starting around day 6, suggested the initiation of antiaggregation therapy. Platelet activation markers were upregulated in the postoperative period but were returned to preoperative levels after initiation of aspirin. In contrast to routine coagulation monitoring, platelet function tests reflect in detail the coagulation status of blood pump recipients and the efficiency of antiaggregation therapy. Aspirin and dipyridamole therapy in addition to oral anticoagulation using phenprocoumon may contribute to platelet function and clot mechanics restoration and is, therefore, recommended for patients after VAD implantation.

HLA sensitization in ventricular assist device recipients: does type of device make a difference?

BACKGROUND

We sought to (1) characterize the temporal pattern of T-cell panel reactive antibody during ventricular assist device support, (2) identify predictors of higher T-cell panel reactive antibody during ventricular assist device support, and (3) determine whether device type remained a predictor after accounting for nonrandom device selection.

METHODS

Between December 1991 and August 2000, 239 patients received implantable ventricular assist devices, of whom 231 had T-cell panel reactive antibody measured. Panel reactive antibody was measured before implantation of the assist device, approximately 2 weeks after device implantation, irregularly thereafter depending on clinical events and length of support, and at transplantation. Longitudinal mixed modeling was used to characterize the temporal pattern of sensitization and its predictors during ventricular assist device support. To account for nonrandom factors in device selection when comparing HeartMate (Thermo Cardiosystems, Inc, Woburn, Mass) and Novacor (Baxter Healthcare Corp, Novacor Div, Oakland, Calif) devices, we propensity-matched patients according to baseline characteristics.

RESULTS

T-cell panel reactive antibody increased rapidly after implantation of the ventricular assist device and then immediately began to decrease. Predictors of higher T-cell panel reactive antibody during support with the assist device were a shorter interval from device implantation to T-cell panel reactive antibody measurement (P <.0001), female sex (P =.0004), younger age (P =.01), higher T-cell panel reactive antibody before device implantation (P =.03), more perioperative red blood cell transfusions (P =.006), and an earlier date of device implantation (P =.001). In matched patients, device type was not a predictor of higher T-cell panel reactive antibody during ventricular assist device support (P =.8).

CONCLUSIONS

HLA sensitization during ventricular assist device support is not constant but increases rapidly at implantation and then decreases. This temporal pattern of sensitization is influenced by patient factors and not by the type of device.

What price support? Ventricular assist device induced systemic response

Use of ventricular support systems has been associated with myriad systemic complications. Engendered by the blood-biomaterial interface of a unique host/device relationship, these complications include diverse humoral dyscrasias that frequently culminate in episodes of bleeding, hemolysis and thrombogenicity, heightened susceptibility to inflammation and infection, and transient immunal compromise. Recent endeavor in biocompatibility research has served to illustrate the critical role played by cellular, humoral, and neurohormonal components in regulating cytokine expression and has provided insight into the complexities involved in such biomechanical juxtapositions. The following is intended as a review of current literature attempting to address the many aspects of this host/device interaction and their consequences for the supported patient.

Sensitivity, ventricular assist devices, and the waiting game in heart transplantation: what's new?

Orthotopic heart transplantation became more successful with the introduction of cyclosporine in the late 1970s. Although congestive heart failure has become a significant public health issue and the proportion of patients with advanced heart failure has increased, the number of heart transplants performed has not increased substantially in the past decade. Transplant waiting times have been related to many different factors. Unfortunately, implantation of ventricular assist devices (VADS) may provoke antibody responses. These result in the sensitization of patients and increased waiting time prior to transplantation. The purpose of this article is to explore etiologies of waiting times for pre heart transplant and left ventricular assist device pre heart transplant candidates, explain new theories of sensitization, define current methods to detect sensitization, and discuss nursing care implications.

Ventricular Assist Devices as a Bridge to Transplant or Recovery

Ventricular assist devices have emerged as the standard of care in treating end-stage heart failure. Their success in bridging patients to transplantation is well documented. The data supporting their ability to bridge patients to recovery is sparser. However, as technology continues to advance, these devices will offer a high quality of life both in and out of the hospital setting, making them options for a broader spectrum of heart failure patients.

Ventricular assistance to bridge to transplantation

In 2001, 2202 heart transplants were performed in the United States, leaving 4137 patients waiting who suffer from 30% annual mortality. Status I, Class IV heart failure patients have a 66% 1-year mortality rate and a survival approximating our worst cancers. Left ventricular assist devices (LVADs) first successfully bridged a patient to transplantation in 1978. LVADs have since functioned primarily thus, minimizing end-organ damage and providing rehabilitation potential for individuals awaiting transplantation. In this role, their effectiveness is well-established: they gain time for patients awaiting donors, preserve end-organ function, and provide potential for a high quality of life in and out of the hospital. This success has been the result of numerous advances in VAD technology, which this article discusses.

Intractable ventricular tachycardia and bridging to heart transplantation with a non-pulsatile flow assist device in a patient with isolated left-ventricular non-compaction

Intractable ventricular tachycardia was investigated in a 51-year-old man with isolated left ventricular non-compaction during implantation of an automated internal cardioverter-defibrillator. Favorable bridging to cardiac transplantation was achieved with the DeBakey left ventricular assist device (LVAD).

Ventricular assist devices

PURPOSE OF REVIEW

Recent advances in technology as well as new indications for implantation have appeared in the field of ventricular assist devices. Progress has also been made in the understanding of the underlying mechanisms of myocardial recovery after ventricular assist device support.

RECENT FINDINGS

Technological progress includes the development of fully implantable pulsatile and continuous flow pumps, either axial flow or centrifugal, for left ventricular and total heart assistance. Among the new indications for ventricular assist device support, the most important is the use of the device as permanent treatment for end-stage cardiac failure patients. Increased knowledge has been acquired regarding the effects of mechanical assistance and of unloading of the heart on haemodynamics, as well as on the cellular, molecular and electrophysiological characteristics of the failing heart. All these findings suggest that depressed myocardial function can sometimes recover with ventricular assist device therapy. Ventricular assist device support, however, still carries a high rate of complications: the device itself can fail, bleeding and thromboembolism are common, immunity is disturbed and the incidence of infection remains high.

SUMMARY

In patients with end-stage heart failure, ventricular assist devices can be used as a bridge to transplantation or to recovery, but they are now also considered as a long-term myocardial replacement therapy. Which device is the most appropriate for each indication, however, remains to be defined. Even if the underlying mechanisms of myocardial recovery are progressively clarified, the use of ventricular assist devices as a bridge to recovery still has limited clinical success. Clinical trials with the fully implantable devices are in their early stages, but these pumps appear promising in terms of efficacy, reliability and complication rate, as well as being easy to implant. Because more patients will benefit from ventricular assist device placement in the future, anaesthesiologists must be prepared to manage patients undergoing ventricular assist device placement or presenting for noncardiac surgery while under ventricular assist device support.