Left ventricular assist device implantation causes platelet dysfunction and proinflammatory platelet-neutrophil interaction

Platelet count in heart failure patients undergoing left ventricular assist device

AIMS

Left ventricular assist device (LVAD) implantation, a therapy for end-stage heart failure, is associated with platelet (PLT) activation. This study aims to evaluate the prognostic impact of PLT count in patients with LVAD implantation.

METHODS AND RESULTS

Data from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) registry were investigated, and patients were divided into three groups according to tertiles. The dynamic change of PLT counts and its associations with long-term outcomes were analysed. The primary outcome was long-term mortality. A total of 19 517 patients who received the first continuous-flow LVAD were identified from the INTERMACS registry. The PLT count underwent a dynamic change towards normalization after LVAD implantation. Compared with intermediate, both high (hazard ratio [HR], 1.09, 95% confidence interval [CI]: 1.01 to 1.17, P = 0.033) and low (HR, 1.18, 95% CI: 1.10 to 1.27, P < 0.001) pre-implant PLT counts were associated with an increased risk of 2 year mortality. Compared with intermediate, a high post-implant PLT count was associated with an increased risk of 4 year mortality (HR, 1.38, 95% CI: 1.26 to 1.52, P < 0.001). Besides, both pre- and post-implant PLT counts exhibit a U-shaped association with the risk of mortality.

CONCLUSIONS

LVAD implantation could improve the PLT count towards normalization. Abnormal pre-/post-implant PLT counts were independently associated with increased risks of long-term mortality.

Increased phagocytosis capacity of circulating neutrophils in patients on continuous flow ventricular assist device support

BACKGROUND

Neutrophils take part in the innate immune response, phagocytosis, and pro-inflammatory cytokine release. The phagocytic capacity of circulating neutrophils in patients on continuous flow (CF) ventricular assist device (VAD) has not been well studied.

METHODS

Blood samples from 14 patients undergoing CF-VAD implantation were collected and analyzed preoperatively (at baseline) and on postoperative days (POD) 3, 7, 14, and 28. Flow cytometry was used to assess the surface expression levels of CD62L, CD162, and macrophage antigen-1 (MAC-1) and neutrophil phagocytic capacity. Interleukin 1 (IL1), IL6, IL8, TNF-α, neutrophil elastase, and myeloperoxidase in plasma were measured using enzyme-linked immunosorbent assays.

RESULTS

Among the 14 patients, seven patients had preoperative bridge device support. Relative to baseline, patients with no bridge device had elevated leukocyte count and neutrophil elastase by POD3 which normalized by POD7. Neutrophil activation level, IL6, IL8, and TNF-α increased by POD3 and sustained elevated levels for 7-14 days postoperatively. Elevated neutrophil phagocytic capacity persisted even until POD28. Similar patterns were observed in patients on a preoperative bridge device.

CONCLUSIONS

Neutrophil activation and phagocytic capacity increased in response to VAD support, while inflammatory cytokines remain elevated for up to 2 weeks postoperatively. These findings may indicate that VAD implantation elicits circulating neutrophils to an abnormal preemptive phagocytotic phenotype.

Hemocompatibility and biophysical interface of left ventricular assist devices and total artificial hearts

ABSTRACT

Over the past 2 decades, there has been a significant increase in the utilization of long-term mechanical circulatory support (MCS) for the treatment of cardiac failure. Left ventricular assist devices (LVADs) and total artificial hearts (TAHs) have been developed in parallel to serve as bridge-to-transplant and destination therapy solutions. Despite the distinct hemodynamic characteristics introduced by LVADs and TAHs, a comparative evaluation of these devices regarding potential complications in supported patients, has not been undertaken. Such a study could provide valuable insights into the complications associated with these devices. Although MCS has shown substantial clinical benefits, significant complications related to hemocompatibility persist, including thrombosis, recurrent bleeding, and cerebrovascular accidents. This review focuses on the current understanding of hemostasis, specifically thrombotic and bleeding complications, and explores the influence of different shear stress regimens in long-term MCS. Furthermore, the role of endothelial cells in protecting against hemocompatibility-related complications of MCS is discussed. We also compared the diverse mechanisms contributing to the occurrence of hemocompatibility-related complications in currently used LVADs and TAHs. By applying the existing knowledge, we present, for the first time, a comprehensive comparison between long-term MCS options.

Bioprosthetic Total Artificial Heart Implantation Does Not Induce Chronic Inflammation

The Aeson total artificial heart (A-TAH) has been developed for patients at risk of death from biventricular failure. We aimed to assess the inflammatory status in nine subjects implanted with the A-TAH in kinetics over one year. Laboratory assessment of leukocyte counts, inflammatory cytokines assay, and peripheral blood mononuclear cell collection before and after A-TAH implantation. Leukocyte counts were not significantly modulated according to time after A-TAH implantation (coefficient of the linear mixed effect model with 95% CI, -0.05 (-0.71 to -0.61); p = 0.44). We explored inflammatory cytokine after A-TAH and did not observe, at any time, a modified profile compared to pre-implantation values (all p -values > 0.05). Finally, we compared the distribution of circulating immune cell subpopulations identified based on sequential expression patterns for multiple clusters of differentiation. None of the population explored had significant modulation during the 12-month follow-up (all p -values > 0.05). In conclusion, using a cytokine multiplex assay combined with a flow cytometry approach, we demonstrated the absence of inflammatory signals in peripheral blood over a period of 12 months following A-TAH implantation.

Platelets and the Cybernetic Regulation of Ischemic Inflammatory Responses through PNC Formation Regulated by Extracellular Nucleotide Metabolism and Signaling

Ischemic events are associated with severe inflammation and are here referred to as ischemic inflammatory response (IIR). Recent studies identified the formation of platelet–neutrophil complexes (PNC) as key players in IIR. We investigated the role of extracellular platelet nucleotide signaling in the context of IIR and defined a cybernetic circle, including description of feedback loops. Cybernetic circles seek to integrate different levels of information to understand how biological systems function. Our study specifies the components of the cybernetic system of platelets in IIR and describes the theoretical progression of IIR passing the cybernetic cycle with positive and negative feedback loops based on nucleotide-dependent signaling and functional regulation. The cybernetic components and feedback loops were explored by cytometry, immunohistological staining, functional blocking antibodies, and ADP/ATP measurements. Using several ex vivo and in vivo approaches we confirmed cybernetic parameters, such as controller, sensor, and effector (VASP phosphorylation, P2Y₁₂, ADORAs and GPIIb/IIIa activity), as well as set points (ADP, adenosine) and interfering control and disturbance variables (ischemia). We demonstrate the impact of the regulated platelet–neutrophil complex (PNC) formation in blood and the resulting damage to the affected inflamed tissue. Taken together, extracellular nucleotide signaling, PNC formation, and tissue damage in IIR can be integrated in a controlled cybernetic circle of platelet function, as introduced through this study.

Hemostasis Disturbances in Continuous-Flow Left Ventricular Assist Device (CF-LVAD) Patients—Rationale and Study Design

Left ventricular assist devices are a treatment option for end-stage heart failure patients. Despite advancing technologies, bleeding and thromboembolic events strongly decrease the survival and the quality of life of these patients. Little is known about prognostic factors determining these adverse events in this group of patients. Therefore, we plan to investigate 90 consecutive left ventricular assist device (LVAD) patients and study in vitro fibrin clot properties (clot lysis time, clot permeability, fibrin ultrastructure using a scanning electron microscope) and the calibrated automated thrombogram in addition to the von Willebrand factor antigen, fibrinogen, D-dimer, prothrombin time/international normalized ratio (PT/INR), and activated partial thromboplastin time (APTT) to identify prognostic factors of adverse outcomes during the course of therapy. We plan to assess the hemostasis system at four different time points, i.e., before LVAD implantation, 3–4 months after LVAD implantation, 6–12 months after LVAD implantation, and at the end of the study (at 5 years or at the time of the adverse event). Adverse outcomes were defined as bleeding events (bleeding in general or in the following subtypes: severe bleeding, fatal bleeding, gastrointestinal bleeding, intracranial bleeding), thromboembolic events (stroke or transient ischemic attack, pump thrombosis, including thrombosis within the pump or its inflow or outflow conduits, arterial peripheral thromboembolism), and death.

Neutrophil dysfunction due to continuous mechanical shear exposure in mechanically assisted circulation in vitro

OBJECTIVE

Leukocytes play an important role in the body's immune system. The aim of this study was to assess alterations in neutrophil phenotype and function in pump-assisted circulation in vitro.

METHODS

Human blood was circulated for four hours in three circulatory flow loops with a CentriMag blood pump operated at a flow of 4.5 L/min at three rotational speeds (2100, 2800, and 4000 rpm), against three pressure heads (75, 150, and 350 mm Hg), respectively. Blood samples were collected hourly for analyses of neutrophil activation state (Mac-1, CD62L, CD162), neutrophil reactive oxygen species (ROS) production, apoptosis, and neutrophil phagocytosis.

RESULTS

Activated neutrophils indicated by both Mac-1 expression and decreased surface expression of CD62L and CD162 receptors increased with time in three loops. The highest level of neutrophil activation was observed in the loop with the highest rotational speed. Platelet-neutrophil aggregates (PNAs) progressively increased in two loops with lower rotational speeds. PNAs peaked at one hour after circulation and decreased subsequently in the loop with the highest rotational speed. Neutrophil ROS production dramatically increased at one hour after circulation and decreased subsequently in all three loops with similar levels and trends. Apoptotic neutrophils increased with time in all three loops. Neutrophil phagocytosis capacity in three loops initially elevated at one hour after circulation and decreased subsequently. Apoptosis and altered phagocytosis were dependent on rotational speed.

CONCLUSIONS

Our study revealed that the pump-assisted circulation induced neutrophil activation, apoptosis, and functional impairment. The alterations were strongly associated with pump operating condition and duration.