Bleeding and thrombosis associated with ventricular assist device therapy

Platelet deposition estimation: A novel method for emulating the pump thrombosis potential of blood pumps

Pump thrombosis potential exists in most blood pumps and limits their clinical use. To improve the pump thrombosis performance of blood pumps, a method for emulating the platelet deposition on the flow passage component surfaces inside blood pumps was presented and tested. The method emulates the blood platelet deposition, employing laser-induced fluorescence tracing technology. The blood pump was rotated in a mock circulation loop with deionized water filled with fluorescent particles. The component surfaces were then explored via laser. The fluorescent particles were induced by laser and imaged in a charge-coupled device (CCD) camera to show the distribution of fluorescent particles gathering on the blood pump component surfaces. The activated platelet deposition was emulated by fluorescent particle gathering. The experiment showed obvious particle gathering on the interface surfaces and cross-sectional surface (perpendicular to the flow). This platelet deposition estimation (PDE) method can be easily incorporated in the in vitro testing phase to analyze and decrease a pump's thrombosis potential before animal experimentation, thereby reducing the cost of blood pump development. This methodology of emulating blood platelet deposition indicates its potential for improving flow passage component structure and reducing device thrombosis of blood pumps.

Sequential Pattern Mining of Longitudinal Adverse Events After Left Ventricular Assist Device Implant

Left ventricular assist devices (LVADs) are an increasingly common therapy for patients with advanced heart failure. However, implantation of the LVAD increases the risk of stroke, infection, bleeding, and other serious adverse events (AEs). Most post-LVAD AEs studies have focused on individual AEs in isolation, neglecting the possible interrelation, or causality between AEs. This study is the first to conduct an exploratory analysis to discover common sequential chains of AEs following LVAD implantation that are correlated with important clinical outcomes. This analysis was derived from 58,575 recorded AEs for 13,192 patients in International Registry for Mechanical Circulatory Support (INTERMACS) who received a continuous-flow LVAD between 2006 and 2015. The pattern mining procedure involved three main steps: (1) creating a bank of AE sequences by converting the AEs for each patient into a single, chronologically sequenced record, (2) grouping patients with similar AE sequences using hierarchical clustering, and (3) extracting temporal chains of AEs for each group of patients using Markov modeling. The mined results indicate the existence of seven groups of sequential chains of AEs, characterized by common types of AEs that occurred in a unique order. The groups were identified as: GRP1: Recurrent bleeding, GRP2: Trajectory of device malfunction & explant, GRP3: Infection, GRP4: Trajectories to transplant, GRP5: Cardiac arrhythmia, GRP6: Trajectory of neurological dysfunction & death, and GRP7: Trajectory of respiratory failure, renal dysfunction & death. These patterns of sequential post-LVAD AEs disclose potential interdependence between AEs and may aid prediction, and prevention, of subsequent AEs in future studies.

Platelet adhesion emulation: A novel method for estimating the device thrombosis potential of a ventricular assist device

Device thrombosis inside ventricular assist devices remains a limitation to their long-term clinical use. Thrombosis potential exists in almost all ventricular assist devices because the device-induced high shear stress and vortices can activate platelets, which then aggregate and adhere to the surfaces inside the ventricular assist device. To decrease the device thrombosis potential of long-term use of ventricular assist devices, a methodology entitled platelet adhesion emulation for predicting the thrombosis potential and thrombosis position inside the ventricular assist devices is developed. The platelet adhesion emulation methodology combines numerical simulations with in vitro experiments by correlating the structure of the flow passage components within the ventricular assist device with the platelet adhesion to estimate the thrombosis potential and location, with the goal of developing ventricular assist devices with optimized antithrombotic performance. Platelet adhesion emulation is aimed at decreasing the device thrombus potential of ventricular assist devices. The platelet adhesion emulation effectiveness is validated by simulating and testing an axial left ventricular assist device. The blood velocity relative to the surfaces of the flow passage components is calculated to estimate the platelet adhesion potential, indicating the probability of thrombus formation on the surfaces. Platelet adhesion emulation experiments conducted in a mock circulation loop with pump prototypes show the distribution of platelet adhesion on the surfaces. This methodology of emulating the device thrombosis distribution indicates the potential for improving the component structure and reducing the device thrombosis of ventricular assist devices.

Platelets and Immune Responses During Thromboinflammation

Besides mediating hemostatic functions, platelets are increasingly recognized as important players of inflammation. Data from experiments in mice and men revealed various intersection points between thrombosis, hemostasis, and inflammation, which are addressed and discussed in this review in detail. One such example is the intrinsic coagulation cascade that is initiated after platelet activation thereby further propagating and re-enforcing wound healing or thrombus formation but also contributing to the pathophysiology of severe diseases. FXII of the intrinsic pathway connects platelet activation with the coagulation cascade during immune reactions. It can activate the contact system thereby either creating an inflammatory state or accelerating inflammation. Recent insights into platelet biology could show that platelets are equipped with complement receptors. Platelets are important for tissue remodeling after injury has been inflicted to the endothelial barrier and to the subendothelial tissue. Thus, platelets are increasingly recognized as more than just cells relevant for bleeding arrest. Future insights into platelet biology are to be expected. This research will potentially offer novel opportunities for therapeutic intervention in diseases featuring platelet abundance.

Acute kidney injury following left ventricular assist device implantation: Contemporary insights and future perspectives

Currently, an increasing number of patients with end-stage heart failure are being treated with left ventricular assist device (LVAD) therapy as bridge-to-transplantation, bridge-to-candidacy, or destination therapy (DT). Potential life-threatening complications may occur, specifically in the early post-operative phase, which positions LVAD implantation as a high-risk surgical procedure. Acute kidney injury (AKI) is a frequently observed complication after LVAD implantation and is associated with high morbidity and mortality. The rapidly growing number of LVAD implantations necessitates better approaches of identifying high-risk patients, optimizing peri-operative management, and preventing severe complications such as AKI. This holds especially true for those patients receiving an LVAD as DT, who are typically older (with higher burden of comorbidities) with impaired renal function and at increased post-operative risk. Herein we outline the definition, diagnosis, frequency, pathophysiology, and risk factors for AKI in patients with an LVAD. We also review possible strategies to prevent and manage AKI in this patient population.

Early signatures of bleeding and mortality in patients on left ventricular assist device support: novel methods for personalized risk-stratification

Background: Left ventricular assist devices (LVADs) provide support for patients with end-stage heart failure. The aims of this study were to determine whether baseline analysis and early trends in routine laboratory data, platelet activity, and thromboinflammatory biomarkers following LVAD implantation reveal trends that predict personalized risks of one-year gastrointestinal (GI) bleeding, stroke, pump thrombosis, drive-line infections and mortality in patients on LVAD support. Methods: We performed an observational study at the University of Kentucky with 61 participants who underwent first-time LVAD implantation. Blood was collected at baseline and post-op days 0, 1, 3 and 6 as well as clinical follow-up. Demographics, clinical characteristics, one-year adverse events and routine laboratory data were collected from electronic medical records. Platelet function and plasma biomarkers were profiled. Results: Evaluation of routine laboratory results revealed that sustained thrombocytopenia and increased mean platelet volume (MPV) were associated with development of GI bleeding and mortality. Platelet function at follow-up visit predicted one-year bleeding events. Thrombotic biomarker sCD40L strongly predicted one-year GI bleeding at baseline before implantation and within the first week following LVAD implant. Conclusions: Early trends in routine bloodwork and platelet function may serve as novel signatures of patients at risk to experience adverse events.

Between a rock and a hard place: a high-risk patient with resistance to multiple P2Y12 antagonists

Impaired response to P2Y12 receptor antagonists, such as clopidogrel and prasugrel, can have devastating consequences for patients that require prolonged or indefinite therapy with these agents, including those with a left ventricular assist device (LVAD). While loss-of-function (LOF) alleles in CYP2C19 have been elucidated as contributing to high on treatment platelet reactivity (HTPR) during clopidogrel therapy, genetic variations in the metabolic pathway of prasugrel have not been shown to elicit this same effect. Moreover, limited studies have assessed the effect of coexisting genetic variations in pharmacokinetic and pharmacodynamic pathways. Herein, we report a left ventricular assist device patient exhibiting high on treatment platelet reactivity during clopidogrel and prasugrel therapy. Genotyping revealed variants in pharmacokinetic (CYP2B6), and pharmacodynamic pathways, with multiple variants in P2Y12, the target receptor.

A Fully Magnetically Levitated Left Ventricular Assist Device - Final Report

BACKGROUND

In two interim analyses of this trial, patients with advanced heart failure who were treated with a fully magnetically levitated centrifugal-flow left ventricular assist device were less likely to have pump thrombosis or nondisabling stroke than were patients treated with a mechanical-bearing axial-flow left ventricular assist device.

METHODS

We randomly assigned patients with advanced heart failure to receive either the centrifugal-flow pump or the axial-flow pump irrespective of the intended goal of use (bridge to transplantation or destination therapy). The composite primary end point was survival at 2 years free of disabling stroke or reoperation to replace or remove a malfunctioning device. The principal secondary end point was pump replacement at 2 years.

RESULTS

This final analysis included 1028 enrolled patients: 516 in the centrifugal-flow pump group and 512 in the axial-flow pump group. In the analysis of the primary end point, 397 patients (76.9%) in the centrifugal-flow pump group, as compared with 332 (64.8%) in the axial-flow pump group, remained alive and free of disabling stroke or reoperation to replace or remove a malfunctioning device at 2 years (relative risk, 0.84; 95% confidence interval [CI], 0.78 to 0.91; P<0.001 for superiority). Pump replacement was less common in the centrifugal-flow pump group than in the axial-flow pump group (12 patients [2.3%] vs. 57 patients [11.3%]; relative risk, 0.21; 95% CI, 0.11 to 0.38; P<0.001). The numbers of events per patient-year for stroke of any severity, major bleeding, and gastrointestinal hemorrhage were lower in the centrifugal-flow pump group than in the axial-flow pump group.

CONCLUSIONS

Among patients with advanced heart failure, a fully magnetically levitated centrifugal-flow left ventricular assist device was associated with less frequent need for pump replacement than an axial-flow device and was superior with respect to survival free of disabling stroke or reoperation to replace or remove a malfunctioning device. (Funded by Abbott; MOMENTUM 3 ClinicalTrials.gov number, NCT02224755.).

Prothrombotic activity of cytokine-activated endothelial cells and shear-activated platelets in the setting of ventricular assist device support

BACKGROUND

We systematically analyzed the synergistic effect of: (i) cytokine-mediated inflammatory activation of endothelial cells (ECs) with and (ii) shear-mediated platelet activation (SMPA) as a potential contributory mechanism to intraventricular thrombus formation in the setting of left ventricular assist device (LVAD) support.

METHODS

Intact and shear-activated human platelets were exposed to non-activated and cytokine-activated ECs. To modulate the level of LVAD-related shear activation, platelets were exposed to shear stress patterns of varying magnitude (30, 50, and 70 dynes/cm², 10 minutes) via a hemodynamic shearing device. ECs were activated via exposure to inflammatory tumor necrosis factor-α (TNF-α 10 and 100 ng/ml, 24 hours), consistent with inflammatory activation recorded in patients on LVAD circulatory support.

RESULTS

Adhesivity of shear-activated platelets to ECs was significantly higher than that of intact/unactivated platelets, regardless of the initial activation level (70 dynes/cm² shear-activated platelets vs intact platelets: +80%, p < 0.001). Importantly, inflammatory activation of ECs amplified platelet prothrombinase activity progressively with increasing shear stress magnitude and TNF-α concentration: thrombin generation of 70 dynes/cm² shear-activated platelets was 2.6-fold higher after exposure and adhesion to 100 ng/ml TNF-α‒activated ECs (p < 0.0001).

CONCLUSIONS

We demonstrated synergistic effect of SMPA and cytokine-mediated EC inflammatory activation to enhance EC‒platelet adhesion and platelet prothrombotic function. These mechanisms may contribute to intraventricular thrombosis in the setting of mechanical circulatory support.

Design and rationale of haemodynamic guidance with CardioMEMS in patients with a left ventricular assist device: the HEMO-VAD pilot study

AIMS

We aim to study the feasibility and clinical value of pulmonary artery pressure monitoring with the CardioMEMS™ device in order to optimize and guide treatment in patients with a HeartMate 3 left ventricular assist device (LVAD).

METHODS AND RESULTS

In this single-centre, prospective pilot study, we will include 10 consecutive patients with New York Heart Association Class IIIb or IV with Interagency Registry for Mechanically Assisted Circulatory Support Classes 2-5 scheduled for implantation of a HeartMate 3 LVAD. Prior to LVAD implantation, patients will receive a CardioMEMS sensor, for daily pulmonary pressure readings. The haemodynamic information provided by the CardioMEMS will be used to improve haemodynamic status prior to LVAD surgery and optimize the timing of LVAD implantation. Post-LVAD implantation, the haemodynamic changes will be assessed for additive value in detecting potential complications in an earlier stage (bleeding and tamponade). During the outpatient clinic phase, we will assess whether the haemodynamic feedback can optimize pump settings, detect potential complications, and further tailor the clinical management of these patients.

CONCLUSIONS

The HEMO-VAD study is the first prospective pilot study to explore the safety and feasibility of using CardioMEMS for optimization of LVAD therapy with additional (remote) haemodynamic information.

Antithrombotic Strategies and Device Thrombosis

Despite improvements in left ventricular assist device (LVAD) technology, bleeding and thrombotic complications are major concerns that adversely influence morbidity and mortality. Current antithrombotic therapy recommendations for LVAD thrombosis prophylaxis are largely derived from clinical device trials that implement a one-size-fits-all strategy. Objective serial laboratory-based assessment of thrombogenicity is needed to balance the risk of bleeding and thrombotic complications. Finally, the newest-generation device, the HeartMate 3, has been associated with lower levels of shear and reduced hemolysis that may mitigate thrombotic event occurrences.

Controversies and Challenges of Ventricular Assist Device Therapy

Left ventricular assist device (LVAD) therapy has emerged as an increasingly vital facet of the treatment algorithm for advanced heart failure. Growing experience with LVAD support has led to substantial improvements in outcomes, with 1-year survival rates approaching that of cardiac transplantation. These therapeutic refinements have engendered growing interests in the potential for expanding the clinical indications for LVAD therapy to patients with less advanced heart failure. The primary obstacles to this evolution of care center largely on the prevention and/or management of the adverse events associated with LVAD therapy along with patient preference. Many programs also face the mounting difficulty of balancing quality outcomes with the increased volume of implants. During the recently assembled Users Meeting organized by St. Jude Medical, heart failure clinicians from nearly 50 LVAD implanting centers discussed these and other challenges and controversies impacting the field. The present review summarizes the key insights gleaned from this meeting.

Two-Year Outcomes with a Magnetically Levitated Cardiac Pump in Heart Failure

BACKGROUND

In an early analysis of this trial, use of a magnetically levitated centrifugal continuous-flow circulatory pump was found to improve clinical outcomes, as compared with a mechanical-bearing axial continuous-flow pump, at 6 months in patients with advanced heart failure.

METHODS

In a randomized noninferiority and superiority trial, we compared the centrifugal-flow pump with the axial-flow pump in patients with advanced heart failure, irrespective of the intended goal of support (bridge to transplantation or destination therapy). The composite primary end point was survival at 2 years free of disabling stroke (with disabling stroke indicated by a modified Rankin score of >3; scores range from 0 to 6, with higher scores indicating more severe disability) or survival free of reoperation to replace or remove a malfunctioning device. The noninferiority margin for the risk difference (centrifugal-flow pump group minus axial-flow pump group) was -10 percentage points.

RESULTS

Of 366 patients, 190 were assigned to the centrifugal-flow pump group and 176 to the axial-flow pump group. In the intention-to-treat population, the primary end point occurred in 151 patients (79.5%) in the centrifugal-flow pump group, as compared with 106 (60.2%) in the axial-flow pump group (absolute difference, 19.2 percentage points; 95% lower confidence boundary, 9.8 percentage points [P<0.001 for noninferiority]; hazard ratio, 0.46; 95% confidence interval [CI], 0.31 to 0.69 [P<0.001 for superiority]). Reoperation for pump malfunction was less frequent in the centrifugal-flow pump group than in the axial-flow pump group (3 patients [1.6%] vs. 30 patients [17.0%]; hazard ratio, 0.08; 95% CI, 0.03 to 0.27; P<0.001). The rates of death and disabling stroke were similar in the two groups, but the overall rate of stroke was lower in the centrifugal-flow pump group than in the axial-flow pump group (10.1% vs. 19.2%; hazard ratio, 0.47; 95% CI, 0.27 to 0.84, P=0.02).

CONCLUSIONS

In patients with advanced heart failure, a fully magnetically levitated centrifugal-flow pump was superior to a mechanical-bearing axial-flow pump with regard to survival free of disabling stroke or reoperation to replace or remove a malfunctioning device. (Funded by Abbott; MOMENTUM 3 ClinicalTrials.gov number, NCT02224755 .).

PTEN deficiency promotes pathological vascular remodeling of human coronary arteries

Phosphatase and tensin homolog (PTEN) is an essential regulator of the differentiated vascular smooth muscle cell (SMC) phenotype. Our goal was to establish that PTEN loss promotes SMC dedifferentiation and pathological vascular remodeling in human atherosclerotic coronary arteries and nonatherosclerotic coronary arteries exposed to continuous-flow left ventricular assist devices (CF-LVADs). Arteries were categorized as nonatherosclerotic hyperplasia (NAH), atherosclerotic hyperplasia (AH), or complex plaque (CP). NAH coronary arteries from CF-LVAD patients were compared to NAH coronaries from non-LVAD patients. Intimal PTEN and SMC contractile protein expression was reduced compared with the media in arteries with NAH, AH, or CP. Compared with NAH, PTEN and SMC contractile protein expression was reduced in the media and intima of arteries with AH and CP. NAH arteries from CF-LVAD patients showed marked vascular remodeling and reduced PTEN and α-smooth muscle actin (αSMA) in medial SMCs compared with arteries from non-LVAD patients; this correlated with increased medial collagen deposition. Mechanistically, compared with ApoE^–/– mice, SMC-specific PTEN-null/ApoE^–/– double-knockout mice exhibited accelerated atherosclerosis progression and increased vascular fibrosis. By microarray and validated quantitative RT-PCR analysis, SMC PTEN deficiency promotes a global upregulation of proinflammatory and profibrotic genes. We propose that PTEN is an antiinflammatory, antifibrotic target that functions to maintain SMC differentiation. SMC loss of PTEN results in pathological vascular remodeling of human arteries.

PTEN loss correlates with dedifferentiation of smooth muscle cells of human coronary arteries affected with atherosclerosis or exposed to continuous-flow left ventricular assist devices.

Argatroban and Bivalirudin for Perioperative Anticoagulation in Cardiac Surgery

Argatroban and bivalirudin are used as replacement anticoagulants for heparin. The authors review clinical studies for these drugs in the perioperative setting of cardiac surgical patients including extracorporeal management and mechanical support therapy.