Bleeding in continuous flow left ventricular assist device recipients: an acquired vasculopathy?

The Impact of Acute Exercise on Hemostasis and Angiogenesis Mediators in Patients With Continuous-Flow Left Ventricular Assist Devices: A Prospective Observational Pilot Study

Impaired primary hemostasis and dysregulated angiogenesis, known as a two-hit hypothesis, are associated with gastrointestinal (GI) bleeding in patients with continuous-flow left ventricular assist devices (CF-LVADs). Exercise is known to influence hemostasis and angiogenesis in healthy individuals; however, little is known about the effect in patients with CF-LVADs. The objective of this prospective observational study was to determine whether acute exercise modulates two-hit hypothesis mediators associated with GI bleeding in patients with a CF-LVAD. Twenty-two patients with CF-LVADs performed acute exercise either on a cycle ergometer for approximately 10 minutes or on a treadmill for 30 minutes. Blood samples were taken pre- and post-exercise to analyze hemostatic and angiogenic biomarkers. Acute exercise resulted in an increased platelet count ( p < 0.00001) and platelet function (induced by adenosine diphosphate, p = 0.0087; TRAP-6, p = 0.0005; ristocetin, p = 0.0009). Additionally, high-molecular-weight vWF multimers ( p < 0.00001), vWF collagen-binding activity ( p = 0.0012), factor VIII ( p = 0.034), angiopoietin-1 ( p = 0.0026), and vascular endothelial growth factor ( p = 0.0041) all increased after acute exercise. This pilot work demonstrates that acute exercise modulated two-hit hypothesis mediators associated with GI bleeding in patients with CF-LVADs.

Retinal microvascular remodeling associates with adverse events in continuous-flow left ventricular assist device-supported patients

BACKGROUND

Continuous-flow left ventricular assist device (cfLVAD) use is effective in supporting patients with end-stage heart failure (ESHF). Reduced flow pulsatility within the systemic circulation in cfLVAD-supported patients may lead to alterations within the microcirculation. Temporal changes in microvasculature in relation to adverse events in cfLVAD-supported patients have not been studied. We aimed to profile changes within retinal microvasculature and its association with adverse events.

METHODS

Retinal photography was performed using Topcon TRC-NW8 nonmydriatic fundus camera in cfLVAD-supported patients and ESHF control patients. Specific retinal measurements were evaluated using a validated semiautomated program. Demographic and adverse event data were documented.

RESULTS

Forty-eight patients were studied (n = 29 cfLVAD, n = 19 ESHF). There were significant trends in retinal arteriolar caliber (B = -0.53 µm, 95% confidence interval [CI]: -0.96 to -0.10, p = 0.016) and retinal fractal dimension parameters (B = 0.014, 95% CI: 0.001-0.002, p = 0.016) in linear mixed model regressions. Among cfLVAD patients, there was a significant association between the incidence of gastrointestinal bleeding and stepwise increases in retinal arteriolar-venular caliber ratio (hazard ratio: 3.03, 95% CI: 2.06-4.45, p = 0.005), a measure of arteriolar narrowing.

CONCLUSIONS

We have observed for the first time that alterations in retinal microvasculature in cfLVAD-supported patients may be associated with gastrointestinal bleeding. While understanding these temporal changes may predict future adverse events in cfLVAD-supported patients, further multicenter studies are required to confirm the associations observed.

Generation of Pulsatile Flow using Clinical Continuous Flow Pumps

Background

With the increasing use of mechanical circulatory support for long-term augmentation of cardiopulmonary function, the need for safer devices is apparent. Pump thrombosis and failure, inadequate ventricular unloading, progressive right-sided dysfunction, and end-organ hypoperfusion are seen with long-term mechanical circulatory support devices. Generation of pulsatile flow has been proposed to mitigate some of these risks by providing physiologic flow and pressure profiles to the vascular system and end-organs. Modification of continuous flow devices to provide pulsatility may prove a cheap and effective way to achieve physiologic flow; however, effective use of such a technique has yet to be demonstrated. This work aims to describe these efforts, as well as mechanical arguments regarding the challenges to be overcome in achieving this goal.

Methods

Prior literature and textbooks were used to develop the theoretical basis for the paper.

Results

Attempts at generating pulsatile flow with continuous flow devices have been marred by difficulty in mitigating viscous effects on oscillating mechanical systems. Currently available devices and research setups have been unable to generate truly physiologic pulsatile flow systems. New devices are needed that utilize various forms of positive displacement in order to generate true pulsatile flow that mimic native waveforms generated by the heart.

Conclusions

The mechanical challenges in generating pulsatile flow with continuous flow devices have precluded their widespread adoption in clinical practice. New pulsatile pumps are needed to achieve adequate physiologic pulsatility with improved side-effect profile.

Cellular and Molecular Mechanisms Activated by a Left Ventricular Assist Device

Left ventricular assist devices (LVADs) represent the final treatment for patients with end-stage heart failure (HF) not eligible for transplantation. Although LVAD design has been further improved in the last decade, their use is associated with different complications. Specifically, inflammation, fibrosis, bleeding events, right ventricular failure, and aortic valve regurgitation may occur. In addition, reverse remodeling is associated with substantial cellular and molecular changes of the failing myocardium during LVAD support with positive effects on patients' health. All these processes also lead to the identification of biomarkers identifying LVAD patients as having an augmented risk of developing associated adverse events, thus highlighting the possibility of identifying new therapeutic targets. Additionally, it has been reported that LVAD complications could cause or exacerbate a state of malnutrition, suggesting that, with an adjustment in nutrition, the general health of these patients could be improved.

von Willebrand Factor and Angiopoietin-2 are Sensitive Biomarkers of Pulsatility in Continuous-Flow Ventricular Assist Device Patients

Nonsurgical bleeding occurs in a significant proportion of patients implanted with continuous-flow ventricular assist devices (CF-VADs) and is associated with nonphysiologic flow with diminished pulsatility. An in vitro vascular pulse perfusion model seeded with adult human aortic endothelial cells (HAECs) was used to identify biomarkers sensitive to changes in pulsatility. Diminished pulsatility resulted in an ~45% decrease in von Willebrand factor (vWF) levels from 9.80 to 5.32 ng/ml (n = 5, p < 0.05) and a threefold increase in angiopoietin-2 (ANGPT-2) levels from 775.29 to 2471.93 pg/ml (n = 5, p < 0.05) in cultured HAECs. These changes are in agreement with evaluation of patient blood samples obtained pre-CF-VAD implant and 30-day postimplant: a decrease in plasma vWF level by 50% from ~45.59 to ~22.49 μg/ml (n = 15, p < 0.01) and a 64% increase in plasma ANGPT-2 level from 7,073 to 11,615 pg/ml (n = 8, p < 0.05). This study identified vWF and ANGPT-2 as highly sensitive to changes in pulsatility, in addition to interleukin-6 (IL-6), IL-8, and tumor necrosis-α (TNF-α). These biomarkers may help determine the optimal level of pulsatility and help identify patients at high risk of nonsurgical bleeding.

Update on Mechanical Circulatory Support

Mechanical circulatory support (MCS) devices provide temporary or intermediate- to long-term support for acute cardiopulmonary support. In the last 20 to 30 years, tremendous growth in MCS device usage has been seen. These devices offer support for isolated respiratory failure, isolated cardiac failure, or both. Initiation of MCS devices requires the input from multidisciplinary teams using patient factors and institutional resources to guide decision making, along with a planned "exit strategy" for bridge to decision, bridge to transplant, bridge to recovery, or as destination therapy. Important considerations for MCS use include patient selection, cannulation/insertion strategies, and complications of each device.

Effects of Pulsatility on Arterial Endothelial and Smooth Muscle Cells

Continuous flow ventricular assist device (CFVAD) support in advanced heart failure patients causes diminished pulsatility, which has been associated with adverse events including gastrointestinal bleeding, end organ failure, and arteriovenous malformation. Recently, pulsatility augmentation by pump speed modulation has been proposed as a means to minimize adverse events. Pulsatility primarily affects endothelial and smooth muscle cells in the vasculature. To study the effects of pulsatility and pulse modulation using CFVADs, we have developed a microfluidic co-culture model with human aortic endothelial (ECs) and smooth muscle cells (SMCs) that can replicate physiologic pressures, flows, shear stresses, and cyclical stretch. The effects of pulsatility and pulse frequency on ECs and SMCs were evaluated during (1) normal pulsatile flow (120/80 mmHg, 60 bpm), (2) diminished pulsatility (98/92 mmHg, 60 bpm), and (3) low cyclical frequency (115/80 mmHg, 30 bpm). Shear stresses were estimated using computational fluid dynamics (CFD) simulations. While average shear stresses (4.2 dynes/cm2) and flows (10.1 mL/min) were similar, the peak shear stresses for normal pulsatile flow (16.9 dynes/cm2) and low cyclic frequency (19.5 dynes/cm2) were higher compared to diminished pulsatility (6.45 dynes/cm2). ECs and SMCs demonstrated significantly lower cell size with diminished pulsatility compared to normal pulsatile flow. Low cyclical frequency resulted in normalization of EC cell size but not SMCs. SMCs size was higher with low frequency condition compared to diminished pulsatility but did not normalize to normal pulsatility condition. These results may suggest that pressure amplitude augmentation may have a greater effect in normalizing ECs, while both pressure amplitude and frequency may be required to normalize SMCs morphology. The co-culture model may be an ideal platform to study flow modulation strategies.

Endothelial Dysfunction-related Neurological Bleeds with Continuous Flow-Left Ventricular Assist Devices Measured by Digital Thermal Monitor

Endothelial dysfunction has been demonstrated in patients with Continuous Flow-Left Ventricular Assist Devices (CF-LVADs) but association with adverse events has not been shown. We used a noninvasive, operator-independent device called VENDYS® to assess vasodilatory function based on digital thermal measurements postrelease of a brachial artery occlusion in ambulatory patients with CF-LVAD (n = 56). Aortic valve opening and pulse perception were also documented before the test. Median duration of CF-LVAD support was 438 days. The VENDYS® test generates a vascular reactivity index (VRI). Outcomes for the CF-LVAD patients were compared between VRI < 1 and VRI ≥ 1. The bleeding events were driven primarily by a difference in neurologic bleeds. Multivariate analysis showed that VRI < 1 correlated with future bleeding events (HR: 5.56; P = 0.01). The C-statistic with the VRI dichotomized as above was 0.82. There was a trend toward a worse survival in patients with poor endothelial function. Endothelial vasodilatory dysfunction measured by a simple test utilizing digital thermal monitoring can predict adverse bleeding events in patients with CF-LVADs.

Increased bleeding risk with phosphodiesterase-5 inhibitors after left ventricular assist device implantation

Aims

Therapy with phosphodiesterase‐5 inhibitors (PDE5Is) after left ventricular assist device (LVAD) implantation has been associated with lower mortality and device thrombosis but increased risk for post‐operative and gastrointestinal bleeding. We aimed to evaluate the impact of long‐term PDE5Is on the overall bleeding risk after LVAD implantation.

Methods and results

We retrospectively included patients who received a continuous‐flow LVAD at our site and were prescribed with long‐term oral PDE5Is after discharge from the index hospitalization. The primary endpoint was the occurrence of bleeding at 12 month follow‐up. Secondary endpoints were all‐cause death and the combination of bleeding and all‐cause death. Our analysis included 109 patients of whom 75 (69%) received long‐term PDE5Is. Mean age was 56 years, and 85% were male. At 12 months, 19 (17%) patients experienced at least one bleeding event. Patients on PDE5Is had higher bleeding rates (23% vs. 6%, P = 0.03) and more bleeding events per patient‐year (0.32 vs. 0.06, P = 0.03) compared with patients not on PDE5Is. While overall bleeding incidence was excessively higher in the PDE5I group, there were no significant differences in the incidence of major bleeding (19% vs. 6%, P = 0.08) and gastrointestinal bleeding (11% vs. 3%, P = 0.18). Kaplan–Meier analysis revealed higher cumulative incidence of bleeding for the PDE5I group (log rank = 0.04) with no difference on all‐cause death (log rank = 0.67) and the combination of bleeding and all‐cause death (log rank = 0.13). Hospitalizations for bleeding and their duration were numerically higher in the PDE5I group (0.28 vs. 0.03, P = 0.07 and 2.4 vs. 0.2, P = 0.07, respectively).

Conclusions

Phosphodiesterase‐5 inhibitor treatment after LVAD implantation is associated with increased bleeding risk after LVAD implantation. The safety of long‐term PDE5Is in LVAD patients remains unclear and needs to be further clarified in prospective studies with randomized study design.

Novel Use of Tamoxifen to Reduce Recurrent Gastrointestinal Bleeding in Patients with Left Ventricular Assist Devices

Gastrointestinal bleeding (GIB) is a frequent complication in patients with continuous-flow left ventricular assist devices (LVAD). We retrospectively evaluated eight patients implanted with a HeartWare LVAD between July 2017 and June 2020 who experienced at least one episode of GIB and were started on tamoxifen 20 mg once daily for secondary prevention. Tamoxifen was associated with a significant decrease in major GIB from a median of 3 (IQR 1.4-7) events/patient-year pre-tamoxifen initiation to 0 (IQR 0-0.9) events/patient-year post-tamoxifen initiation (p = 0.02). Transfusion of packed red blood cells also decreased from 16.8 (IQR 9.9-30.6) units/patient-year pre-tamoxifen initiation to 1.5 (IQR 0-7.5) units/patient-year post-tamoxifen (p = 0.04). Tamoxifen was well tolerated and no thromboembolic complications were observed. This small cohort study suggests that tamoxifen is associated with reduced GIB and transfusion requirements, with no apparent increase in thrombotic risk. A larger, randomized study is warranted to confirm the results of this exploratory analysis. Graphical abstract.

Device-related epistaxis risk: continuous-flow left ventricular assist device-supported patients

BACKGROUND

The aim of this study was to analyze the effect of device-dependent factors on epistaxis episodes comparing patients supported with a continuous-flow left ventricular assist device (CF-LVAD) to patients under the same antithrombotic therapy.

METHODS

Patients who underwent CF-LVAD between 2012 and 2018 were reviewed retrospectively from the institutionally adopted electronic database. Patients who underwent mitral valve replacement (MVR) surgery receiving the same anticoagulant and antiaggregant therapy were included as a control group. Demographics, epistaxis episodes, and nonepistaxis bleeding between the two groups were compared.

RESULTS

A total of 179 patients met the inclusion criteria (61 patients CF-LVAD group, 118 patients MVR group). The median (range) follow-up periods for the study (CF-LVAD) and control (MVR) groups were 370 (2819) and 545.70 (2356) days, respectively. There was a significant difference for frequency of bleeding episodes per month between CF-LVAD and MVR groups (p = 0.003 < 0.05). The most common site of bleeding was the anterior septum in both groups (90.9% for the CF-MVR group and 100% for the MVR group). While 14 patients (23%) had nonepistaxis bleeding in the CF-LVAD group, only two patients (1.7%) had nonepistaxis bleeding in the MVR group. There were significant differences in nonepistaxis bleeding rates between the CF-LVAD and MVR groups (χ²=19.79, p < 0.001).

CONCLUSION

Both epistaxis and nonepistaxis bleeding rates were higher in the CF-LVAD group than in the MVR group. This suggests that the use of CF-LVAD support could directly increase the risk of hemorrhagic complications.

LEVEL OF EVIDENCE

2A (Etiology/Harm).

Outcome of patients receiving a continuous flow left ventricular assist device - a retrospective single center study

Objectives. We present the outcome of the first 80 patients receiving a continuous flow left ventricular assist device at Helsinki University Hospital between December 2011 and November 2018. Design. This was a single-center retrospective study. We describe our patient management in detail. The primary end-points were death, heart transplantation, or pump explant. Data was reported in accordance with the Interagency Registry for Mechanical Circulatory Support protocol. All patients receiving an assist device during the study period were included in the data analysis. Results. Mean patient age was 53 ± 12 years at implantation and 85% were male. Most patients suffered from dilated (48%), or ischemic (40%) cardiomyopathy. One-third of patients were bridged with venoarterial extracorporeal membrane oxygenation to assist device implantation. Implant strategy was bridge to transplant or bridge to decision in most patients (88%). Mean follow-up time on pump was 529 ± 467 days. Survival was 98, 92, 85, 79 and 71% at 1, 3, 12, 24 and 36 months, respectively. Most common causes of death were multi-organ failure, right heart failure, or stroke. Only three patients (4%) had suspected pump thrombosis, two of which resolved with medical treatment and one resulting in death. Pump exchange or explant were not performed in a single patient. Neurological events occurred in 18%, non-disabling stroke in 8%, and fatal stroke in 4% of the patients. The incidence of device-related infection was 10%. Conclusions. Survival rates were good, although one third of patients were bridged with temporary circulatory support. We report a high level of freedom from pump thrombosis, fatal stroke, and driveline infection.

Understanding risk factors and predictors for stroke subtypes in the ENDURANCE trials

BACKGROUND

Stroke is a devastating morbidity associated with left ventricular assist device (LVAD) support. We report a comprehensive analysis of stroke subtypes in the ENDURANCE destination therapy (DT) and ENDURANCE Supplemental (DT2) trials.

METHODS

Patients in the combined HeartWare LVAD (HVAD) cohorts of the DT and DT2 trials were included. Neurologic events included ischemic stroke (ischemic cerebrovascular accident [ICVA]), hemorrhagic stroke (hemorrhagic cerebrovascular accident [HCVA]), and transient ischemic attack (TIA). Peri-operative strokes were defined as occurring within 2 weeks of the implant.

RESULTS

A total of 604 patients received an HVAD in the DT (n = 296) and DT2 (n = 308) trials. Over 2 years, 178 (29.5%) had at least 1 cerebrovascular accident (CVA). Forty-four (7.3%) had HCVAs, 116 (19.2%) had ICVAs, and 44 (7.3%) had TIAs. Thirty (5.0%) had peri-operative stroke. In multivariable analysis, sub-therapeutic international normalized ratio (INR) values were independently associated with peri-operative stroke. Supra- and/or sub-therapeutic INR values, peripheral vascular disease, and presence of left ventricular thrombus were independently associated with ICVA. No aspirin and supra- and/or sub-therapeutic INR values were independently associated with TIA. No aspirin, supra- and/or sub-therapeutic INR values, and prior stroke and/or TIA were associated with HCVA. In further analysis, mean arterial pressure (MAP) was higher in the ICVA (86.8mm Hg, p = 0.002 4) and TIA (88.8mm Hg, p<0.0001) groups, but not in HCVA, than in the No-CVA group (81.4mm Hg). Time in therapeutic range for INR was 65.3% for the No-CVA group, 62.9% (p = 0.59) for HCVA, 65.1% (p = 0.97) for ICVA, and 63.2% (p = 0.62) for TIA.

CONCLUSIONS

Supra- and sub-therapeutic INR values at the time of CVA were associated with all stroke subtypes >14 days post-implant. MAP was higher among those with ICVA and TIA but not with HCVA compared to without CVA. Our study demonstrates the challenges of anti-thrombotic therapy and blood pressure management in LVAD population.

Novel Model to Predict Gastrointestinal Bleeding During Left Ventricular Assist Device Support

BACKGROUND

Gastrointestinal bleeding (GIB) is a leading cause of morbidity during continuous-flow left ventricular assist device (CF-LVAD) support. GIB risk assessment could have important implications for candidate selection, informed consent, and postimplant therapeutic strategies. The aim of the study is to derive and validate a predictive model of GIB in CF-LVAD patients.

METHODS AND RESULTS

CF-LVAD recipients at the Utah Transplantation Affiliated Hospitals program between 2004 and 2017 were included. GIB associated with a decrease in hemoglobin ≥2 g/dL was the primary end point. A weighted score comprising preimplant variables independently associated with GIB was derived and internally validated. A total of 351 patients (median age, 59 years; 82% male) were included. After a median of 196 days, GIB occurred in 120 (34%) patients. Independent predictors of GIB included age >54 years, history of previous bleeding, coronary artery disease, chronic kidney disease, severe right ventricular dysfunction, mean pulmonary artery pressure <18 mm Hg, and fasting glucose >107 mg/dL. A weighted score termed Utah bleeding risk score, effectively stratified patients based on their probability of GIB: low (0-1 points) 4.8%, intermediate (2-4) 39.8%, and high risk (5-9) 83.8%. Discrimination was good in the development sample (c-index: 0.83) and after internal bootstrap validation (c-index: 0.74).

CONCLUSIONS

The novel Utah bleeding risk score is a simple tool that can provide personalized GIB risk estimates in CF-LVAD patients. This scoring system may assist clinicians and investigators in designing tailored risk-based strategies aimed at reducing the burden posed by GIB in the individual CF-LVAD patient and healthcare systems.

Phase 3 DREAM-HF Trial of Mesenchymal Precursor Cells in Chronic Heart Failure

Advanced heart failure (HF) is a progressive disease characterized by recurrent hospitalizations and high risk of mortality. Indeed, outcomes in late stages of HF approximate those seen in patients with various aggressive malignancies. Clinical trials assessing beneficial outcomes of new treatments in patients with cancer have used innovative approaches to measure impact on total disease burden or surrogates to assess treatment efficacy. Although most cardiovascular outcomes trials continue to use time-to-first event analyses to assess the primary efficacy end point, such analyses do not adequately reflect the impact of new treatments on the totality of the chronic disease burden. Consequently, patient enrichment and other strategies for ongoing clinical trial design, as well as new statistical methodologies, are important considerations, particularly when studying a population with advanced chronic HF. The DREAM-HF trial (Double-Blind Randomized Assessment of Clinical Events With Allogeneic Mesenchymal Precursor Cells in Advanced Heart Failure) is an ongoing, randomized, sham-controlled phase 3 study of the efficacy and safety of mesenchymal precursor cells as immunotherapy in patients with advanced chronic HF with reduced ejection fraction. Mesenchymal precursor cells have a unique multimodal mechanism of action that is believed to result in polarization of proinflammatory type 1 macrophages in the heart to an anti-inflammatory type 2 macrophage state, inhibition of maladaptive adverse left ventricular remodeling, reversal of cardiac and peripheral endothelial dysfunction, and recovery of deranged vasculature. The objective of DREAM-HF is to confirm earlier phase 2 results and evaluate whether mesenchymal precursor cells will reduce the rate of nonfatal recurrent HF-related major adverse cardiac events while delaying or preventing progression of HF to terminal cardiac events. DREAM-HF is an example of an ongoing contemporary events-driven cardiovascular cell-based immunotherapy study that has utilized the concepts of baseline disease enrichment, prognostic enrichment, and predictive enrichment to improve its efficiency by using accumulating data from within as well as external to the trial. Adaptive enrichment designs and strategies are important components of a rational approach to achieve clinical research objectives in shorter clinical trial timelines and with increased cost-effectiveness without compromising ethical standards or the overall statistical integrity of the study. The DREAM-HF trial also presents an alternative approach to traditional composite time-to-first event primary efficacy end points. Statistical methodologies such as the joint frailty model provide opportunities to expand the scope of events-driven HF with reduced ejection fraction clinical trials to utilize time to recurrent nonfatal HF-related major adverse cardiac events as the primary efficacy end point without compromising the integrity of the statistical analyses for terminal cardiac events. In advanced chronic HF with reduced ejection fraction studies, the joint frailty model is utilized to reflect characteristics of the high-risk patient population with important unmet therapeutic needs. In some cases, use of the joint frailty model may substantially reduce sample size requirements. In addition, using an end point that is acceptable to the Food and Drug Administration and the European Medicines Agency, such as recurrent nonfatal HF-related major adverse cardiac events, enables generation of clinically relevant pharmacoeconomic data while providing comprehensive views of the patient's overall cardiovascular disease burden. The major goal of this review is to provide lessons learned from the ongoing DREAM-HF trial that relate to biologic plausibility and flexible clinical trial design and are potentially applicable to other development programs of innovative therapies for patients with advanced cardiovascular disease. Clinical Trial Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02032004.

Evaluation of flow-modulation approaches in ventricular assist devices using an in-vitro endothelial cell culture model

BACKGROUND

Continuous-flow ventricular assist devices (CF-VADs) produce non-physiologic flow with diminished pulsatility, which is a major risk factor for development of adverse events, including gastrointestinal (GI) bleeding and arteriovenous malformations (AVMs). Introduction of artificial pulsatility by modulating CF-VAD flow has been suggested as a potential solution. However, the levels of pulsatility and frequency of CF-VAD modulation necessary to prevent adverse events are currently unknown and need to be evaluated.

METHODS

The purpose of this study was to use human aortic endothelial cells (HAECs) cultured within an endothelial cell culture model (ECCM) to: (i) identify and validate biomarkers to determine the effects of pulsatility; and (ii) conclude whether introduction of artificial pulsatility using flow-modulation approaches can mitigate changes in endothelial cells seen with diminished pulsatile flow. Nuclear factor erythroid 2-related factor 2 (Nrf-2)-regulated anti-oxidant genes and proteins and the endothelial nitric oxide synthase/endothelin-1 (eNOS/ET-1) signaling pathway are known to be differentially regulated in response to changes in pulsatility.

RESULTS

Comparison of HAECs cultured within the ECCM (normal pulsatile vs CF-VAD) with aortic wall samples from patients (normal pulsatile [n = 5] vs CF-VADs [n = 5]) confirmed that both the Nrf-2-activated anti-oxidant response and eNOS/ET-1 signaling pathways were differentially regulated in response to diminished pulsatility. Evaluation of 2 specific CF-VAD flow-modulation protocols to introduce artificial pulsatility, synchronous (SYN, 80 cycles/min, pulse pressure 20 mm Hg) and asynchronous (ASYN, 40 cycles/min, pulse pressure 45 mm Hg), suggested that both increased expression of Nrf-2-regulated anti-oxidant genes and proteins along with changes in levels of eNOS and ET-1 can potentially be minimized with ASYN and, to a lesser extent, with SYN.

CONCLUSIONS

HAECs cultured within the ECCM can be used as an accurate model of large vessels in patients to identify biomarkers and select appropriate flow-modulation protocols. Pressure amplitude may have a greater effect in normalizing anti-oxidant response compared with frequency of modulation.

Tumor necrosis factor-α levels and non-surgical bleeding in continuous-flow left ventricular assist devices

BACKGROUND

Non-surgical bleeding (NSB) due to angiodysplasia is common in left ventricular assist device (LVAD) patients. Thrombin-induced angiopoietin-2 (Ang-2) expression in LVAD patients leads to altered angiogenesis and is associated with lower angiopoietin-1 (Ang-1) and increased NSB. However, the mechanism for decreased Ang-1, made by pericytes, is unknown and the origin of thrombin in LVAD patients is unclear. We hypothesized that high tumor necrosis factor-α (TNF-α) levels in LVAD patients induce pericyte apoptosis, tissue factor (TF) expression and vascular instability.

METHODS

We incubated cultured pericytes with serum from patients with heart failure (HF), LVAD or orthotopic heart transplantation (OHT), with or without TNF-α blockade. We performed several measurements: Ang-1 expression was assessed by reverse transcript-polymerase chain reaction (RT-PCR) and pericyte death fluorescently; TF expression was assessed by RT-PCR in cultured endothelial cells incubated with patient plasma with or without TNF-α blockade; and TF expression was assessed in endothelial biopsy samples from these patients by immunofluorescence. We incubated cultured endothelial cells on Matrigel with patient serum with or without TNF-α blockade and determined tube formation by microscopy.

RESULTS

Serum from LVAD patients had higher levels of TNF-α, suppressed Ang-1 expression in pericytes, and induced pericyte death, and there was accelerated endothelial tube formation compared with serum from patients without LVADs. TF was higher in both plasma and endothelial cells from LVAD patients, and plasma from LVAD patients induced more endothelial TF expression. All of these effects were reversed or reduced with TNF-α blockade. High levels of TNF-α were associated with increased risk of NSB.

CONCLUSIONS

Elevated TNF-α in LVAD patients is a central regulator of altered angiogenesis, pericyte apoptosis and expression of TF and Ang-1.