Influence of Different Antithrombotic Regimens on Platelet-Mediated Thrombin Generation in Patients with Left Ventricular Assist Devices

Omission of Antiplatelet Therapy in Patients With HeartMate 3 Left Ventricular Assist Devices: A Systematic Review and Meta-Analysis

The HeartMate 3 (HM3) left ventricular assist device has decreased thromboembolic events and minimized the risk of pump thrombosis. However, bleeding complications due to combined antithrombotic therapy with a vitamin K antagonist (VKA) and aspirin remain high. Only limited data on the safety of VKA monotherapy in HM3 patients are available. A systematic search on the main databases was performed. Observational data and randomized trials were eligible for this analysis. As primary endpoint, we analyzed hemocompatibility-related adverse events (HRAE). As secondary endpoints, we investigated the individual components of the primary endpoint. The analysis was carried out using the odds ratio (OR) as outcome measure. A random-effects model was fitted to the data. Five manuscripts fulfilled the inclusion criteria. These trials included 785 patients (381 on VKA monotherapy, 404 on VKA and aspirin). VKA monotherapy significantly reduced HRAE (OR: 0.11 [95% confidence interval {CI}: 0.02-0.59], p = 0.01, I2 = 87%). The reduction was driven by a decrease in bleeding complications (OR: 0.12 [95% CI: 0.02-0.62], p = 0.01, I2 = 86%) without increasing the rates of thromboembolic events (OR: 0.69 [95% CI: 0.26-1.81], p = 0.45, I = 0%). Vitamin K antagonist monotherapy is associated with a significant reduction of bleeding events without increasing the risk of thromboembolic complications in HM3 patients.

Whole-Exome Sequencing in a Family with an Unexplained Tendency for Venous Thromboembolism: Multicomponent Prediction of Low-Frequency Variant Deleteriousness and of Individual Protein Interaction

Whole-exome sequencing (WES) in families with an unexplained tendency for venous thromboembolism (VTE) may favor detection of low-frequency variants in genes with known contribution to hemostasis or associated with VTE-related phenotypes. WES analysis in six family members, three of whom affected by documented VTE, filtered for MAF < 0.04 in 192 candidate genes, revealed 22 heterozygous (16 missense and six synonymous) variants in patients. Functional prediction by multi-component bioinformatics tools, implemented by a database/literature search, including ClinVar annotation and QTL analysis, prioritized 12 missense variants, three of which (CRP Leu61Pro, F2 Asn514Lys and NQO1 Arg139Trp) were present in all patients, and the frequent functional variants FGB Arg478Lys and IL1A Ala114Ser. Combinations of prioritized variants in each patient were used to infer functional protein interactions. Different interaction patterns, supported by high-quality evidence, included eight proteins intertwined in the "acute phase" (CRP, F2, SERPINA1 and IL1A) and/or in the "fibrinogen complex" (CRP, F2, PLAT, THBS1, VWF and FGB) significantly enriched terms. In a wide group of candidate genes, this approach highlighted six low-frequency variants (CRP Leu61Pro, F2 Asn514Lys, SERPINA1 Arg63Cys, THBS1 Asp901Glu, VWF Arg1399His and PLAT Arg164Trp), five of which were top ranked for predicted deleteriousness, which in different combinations may contribute to disease susceptibility in members of this family.

Left ventricular assist devices promote changes in the expression levels of platelet microRNAs

Introduction

MicroRNAs (miRs) emerged as promising diagnostic and therapeutic biomarkers in cardiovascular diseases. The potential clinical utility of platelet miRs in the setting of left ventricular assist device (LVAD) support is unexplored.

Methods

We prospectively measured the expression levels of 12 platelet miRs involved in platelet activation, coagulation, and cardiovascular diseases in LVAD patients by quantitative real-time polymerase chain reaction. Data were longitudinally measured before LVAD implant and after 1, 6, and 12 months of LVAD support, and compared with those measured in healthy volunteers (controls). In silico analysis was also performed to identify pathways targeted by differentially expressed miRs.

Results

Data from 15 consecutive patients and 5 controls were analyzed. Pre-implant expression levels of platelet miR-126, miR-374b, miR-223, and miR-320a were significantly different in patients vs. controls. The expression levels of platelet miR-25, miR-144, miR-320, and miR-451a changed significantly over the course of LVAD support; in silico analysis revealed that these miRs are implicated in both cardiac- and coagulation-associated pathways. Furthermore, the patients who suffered from bleeding (n = 5, 33%) had significantly higher pre-implant expression levels of platelet miR-151a and miR-454 with respect to the patients who did not. The same miRs were also differentially expressed in bleeders following LVAD implantation early before the clinical manifestation of the events.

Discussion

This study provides a proof-of-concept evidence of significant modulation of platelet miRs expression driven by LVADs. The possible existence of a platelet miRs signature predictive of the development of bleeding events warrants further validation studies.

High platelet reactivity is a predictor of left ventricular remodelling in patients with acute myocardial infarction

AIMS

Acute myocardial infarction (AMI) is associated with left ventricular remodelling (LVR), which leads to progressive heart failure. Platelets play a pivotal role in promoting systemic and cardiac inflammatory responses during the complex process of myocardial wound healing or repair following AMI. This study aimed to investigate the impact of platelet reactivity immediately after primary percutaneous coronary intervention (PCI) on LVR in AMI patients with ST-segment (STEMI) and non-ST-segment elevation (NSTEMI).

METHODS AND RESULTS

This prospective, single-centre, observational study included 182 patients with AMI who underwent primary PCI (107 patient with STEMI and 75 patients with NSTEMI). Patients were administered a loading dose of aspirin plus prasugrel before the procedure, and platelet reactivity was assessed using the VerifyNow P2Y12 assay immediately after PCI. Echocardiography was performed before discharge and during the chronic phase (8 ± 3 months after discharge). LVR was defined as a relative ≥20% increase in left ventricular end-diastolic volume index (LVEDVI). LVR in chronic phase was found in 34 patients (18.7%) whose platelet reactivity was significantly higher than those without LVR (259.6 ± 61.5 and 213.1 ± 74.8 P2Y12 reaction units [PRU]; P = 0.001). The occurrence of LVR did not differ between patients with STEMI and patients with NSTEMI (21.5% and 14.7%; P = 0.33). The optimal cut-off value of platelet reactivity for discriminating LVR was ≥245 PRU. LVEDVI significantly decreased at chronic phase in patients without high platelet reactivity (<245 PRU) (from 49.2 ± 13.5 to 45.4 ± 15.8 mL/m² ; P = 0.02), but not in patients with high platelet reactivity (≥d245 PRU) (P = 0.06). Multivariate logistic analysis showed that high platelet reactivity was an independent predictor of LVR after adjusting for LVEDVI before discharge (odds ratio, 4.13; 95% confidence interval, 1.85-9.79).

CONCLUSIONS

High platelet reactivity measured immediately after PCI was a predictor of LVR in patients with AMI during the chronic phase. The role of antiplatelet therapy on inflammation in the myocardium is a promising area for further research.

Insights Into the Low Rate of In-Pump Thrombosis With the HeartMate 3: Does the Artificial Pulse Improve Washout?

While earlier studies reported no relevant effect of the HeartMate 3 (HM3) artificial pulse (AP) on bulk pump washout, its effect on regions with prolonged residence times remains unexplored. Using numerical simulations, we compared pump washout in the HM3 with and without AP with a focus on the clearance of the last 5% of the pump volume. Results were examined in terms of flush-volume (V_f, number of times the pump was flushed with new blood) to probe the effect of the AP independent of changing flow rate. Irrespective of the flow condition, the HM3 washout scaled linearly with flush volume up to 70% washout and slowed down for the last 30%. Flush volumes needed to washout 95% of the pump were comparable with and without the AP (1.3–1.4 V_f), while 99% washout required 2.1–2.2 V_f with the AP vs. 2.5 V_f without the AP. The AP enhanced washout of the bend relief and near-wall regions. It also transiently shifted or eliminated stagnation regions and led to rapid wall shear stress fluctuations below the rotor and in the secondary flow path. Our results suggest potential benefits of the AP for clearance of fluid regions that might elicit in-pump thrombosis and provide possible mechanistic rationale behind clinical data showing very low rate of in-pump thrombosis with the HM3. Further optimization of the AP sequence is warranted to balance washout efficacy while limiting blood damage.

Physiology of Continuous-Flow Left Ventricular Assist Device Therapy

The expanding use of continuous-flow left ventricular assist devices (CF-LVADs) for end-stage heart failure warrants familiarity with the physiologic interaction of the device with the native circulation. Contemporary devices utilize predominantly centrifugal flow and, to a lesser extent, axial flow rotors that vary with respect to their intrinsic flow characteristics. Flow can be manipulated with adjustments to preload and afterload as in the native heart, and ascertainment of the predicted effects is provided by differential pressure-flow (H-Q) curves or loops. Valvular heart disease, especially aortic regurgitation, may significantly affect adequacy of mechanical support. In contrast, atrioventricular and ventriculoventricular timing is of less certain significance. Although beneficial effects of device therapy are typically seen due to enhanced distal perfusion, unloading of the left ventricle and atrium, and amelioration of secondary pulmonary hypertension, negative effects of CF-LVAD therapy on right ventricular filling and function, through right-sided loading and septal interaction, can make optimization challenging. Additionally, a lack of pulsatile energy provided by CF-LVAD therapy has physiologic consequences for end-organ function and may be responsible for a series of adverse effects. Rheological effects of intravascular pumps, especially shear stress exposure, result in platelet activation and hemolysis, which may result in both thrombotic and hemorrhagic consequences. Development of novel solutions for untoward device-circulatory interactions will facilitate hemodynamic support while mitigating adverse events. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.

[Integral tests of the hemostasis system in assessing the efficiency of acetylsalicylic acid in patients with ischemic heart disease]

Despite the fact that acetylsalicylic acid (ASA) is the "gold" standard for the prevention of cardiovascular complications in patients with coronary heart disease (CAD), a number of patients still have risks of atherothrombosis. In the present study, the antithrombotic effect of ASA in patients with CAD was assessed in platelet-rich plasma (PRP) using integral tests of the hemostasis study: the T-TAS system (Total Thrombus-formation Analysis System) and the thrombin generation test (TGT). The study involved 34 patients with stable CAD (11 women, 23 men) and people (15 women, 18 men) in the control group. As a result of assessing the activity of thrombus formation using the T-TAS system, a significant decrease in the area under the curve (AUC10) was found in the group with CAD patients compared with the control (135.6 [88.0-222.3] and 260.5 [217.3-301.9], respectively, p.

Bleeding in patients with continuous-flow left ventricular assist devices: acquired von Willebrand disease or antithrombotics?

OBJECTIVES

To evaluate the competing pro-haemorrhagic contribution of acquired von Willebrand (vW) disease and antithrombotic therapy in patients implanted with continuous-flow left ventricular assist devices (LVADs).

METHODS

We compared the extent of vW factor (vWf) degradation [vWf antigen (vWf:Ag)] and a decrease of functional activity of large vWf multimers [vWf collagen binding (vWf:CB)] in LVAD patients who did and did not suffer from bleeding. Data were measured pre-implant, at short-term (t1: <3 months) and long-term (t2: >12 months) follow-up. The occurrence of primary bleeding events, as well as bleeding recurrence, was correlated with patient-specific vWf profile and antithrombotic regimen. Indeed, patients were discharged on warfarin (international normalized ratio: 2-2.5) and aspirin, with the latter withhold after a first bleeding episode.

RESULTS

Fifty-three patients were enrolled. The median follow-up was 324 (226-468) days. We recorded 25 primary bleeding events (47% of patients). All primary events occurred in patients on warfarin and aspirin. Both vWf:Ag and vWf:CB decreased significantly post-implant (P = 0.0003 and P < 0.0001), and patients showing pathological vWf:CB/vWf:Ag ratio (<0.7) increased progressively over the time of support (pre-implant = 26%, t1 = 58%, t2 = 74%; P < 0.0001). Of note, activity of large vWf multimers of bleeders was significantly lower at t2 with respect to non-bleeders (vWf:CB: 61 (36-115) vs 100 (68-121), P = 0.04; vWf:CB/vWf:Ag ratio: 0.36 (0.26-0.61) vs 0.58 (0.33-0.96), P = 0.04). Despite these marked differences in the vWf profile, following aspirin discontinuation only 3 patients had bleeding recurrence.

CONCLUSIONS

Aspirin contributes significantly to haemorrhagic events in the background of acquired vW disease; its discontinuation significantly reduces bleeding recurrence.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT03255928; ClinicalTrials.gov Identifier: NCT03255928.

Characterization of the competing role of surface-contact and shear stress on platelet activation in the setting of blood contacting devices

Supraphysiological shear stress and surface-contact are recognized as driving mechanisms of platelet activation (PA) in blood contacting devices (BCDs). However, the competing role of these mechanisms in triggering thrombogenic events is poorly understood. Here, we characterized the dynamics of PA in response to the combined effect of shear stress and material exposure. Human platelets were stimulated with different levels of shear stress (500, 750, 1000 dynes/cm²) over a range of exposure times (10, 20, and 30 min) within capillary tubes made of various polymeric materials. Polyethylene (PE), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), and polyether ether ketone (PEEK), used for BCDs fabrication, were investigated as compared to glass and thromboresistant Sigma™-coated glass. PA was quantified using the Platelet Activity State assay. Our results indicate that mechanical stimulation and polymer surface-contact both significantly contribute to PA. Notably, the contribution of the mechanical stimulus ranges between +36% and +43%, while that associated with polymer surface-contact ranges from +48% to +59%, depending on the exposure time. In more detail, our results indicate that: (i) PA increases with increasing shear stress magnitude; (ii) PA has a non-linear, time-dependent relationship to exposure time; (iii) PA is largely influenced by biomaterials, with PE and PEEK having respectively the lowest and highest prothrombotic potential; (iv) the effects of polymer surface-contact and shear stress are not correlated and can be studied separately. Our results suggest the importance of incorporating the evaluation of platelet activation driven by the combined effect of shear stress and polymer surface-contact for the comprehensive assessment, and eventually minimization, of BCDs thrombogenic potential.

Metabolomic profile of patients with left ventricular assist devices: a pilot study

Background

Metabolomic profiling has important diagnostic and prognostic value in heart failure (HF). We investigated whether left ventricular assist device (LVAD) support has an impact on the metabolomic profile of chronic HF patients and if specific metabolic patterns are associated with the development of adverse events.

Methods

We applied untargeted metabolomics to detect and analyze molecules such as amino acids, sugars, fatty acids and other metabolites in plasma samples collected from thirty-three patients implanted with a continuous-flow LVAD. Data were analyzed at baseline, i.e., before implantation of the LVAD, and at long-term follow-up.

Results

Our results reveal significant changes in the metabolomic profile after LVAD implant compared to baseline. In detail, we observed a pre-implant reduction in amino acid metabolism (aminoacyl-tRNA biosynthesis) and increased galactose metabolism, which reversed over the course of support [median follow-up 187 days (63-334 days)]. These changes were associated with improved patient functional capacity driven by LVAD therapy, according to NYHA functional classification of HF (NYHA class I-II: pre-implant =0% of the patients; post-implant =97% of the patients; P<0.001). Moreover, patients who developed adverse thromboembolic events (n=4, 13%) showed a pre-operative metabolomic fingerprint mainly associated with alterations of fatty acid biosynthesis and mitochondrial beta-oxidation of short-chain saturated fatty acids.

Conclusions

Our data provide preliminary evidence that LVAD therapy is associated with changes in the metabolomic profile of HF and suggest the potential use of metabolomics as a new tool to stratify LVAD patients in regard to the risk of adverse events.

Thrombotic Risk of Rotor Speed Modulation Regimes of Contemporary Centrifugal Continuous-flow Left Ventricular Assist Devices

Contemporary centrifugal continuous-flow left ventricular assist devices (LVADs) incorporate dynamic speed modulation algorithms. Hemocompatibility of these periodic unsteady pump operating conditions has been only partially explored. We evaluated whether speed modulation induces flow alterations associated with detrimental prothrombotic effects. For this aim, we evaluated the thrombogenic profile of the HeartWare ventricular assist device (HVAD) Lavare Cycle (LC) and HeartMate3 (HM3) artificial pulse (AP) via comprehensive numerical evaluation of (i) pump washout, (ii) stagnation zones, (iii) shear stress regimens, and (iv) modeling of platelet activation status via the platelet activity state (PAS) model. Data were compared between different simulated operating scenarios, including: (i) constant rotational speed and pump pressure head, used as reference; (ii) unsteady pump pressure head as induced by cardiac pulsatility; and (iii) unsteady rotor speed modulation of the LC (HVAD) and AP (HM3). Our results show that pump washout did not improve across the different simulated scenarios in neither the HVAD nor the HM3. The LC reduced but did not eliminate flow stagnation (-57%) and did not impact metrics of HVAD platelet activation (median PAS: +0.4%). The AP reduced HM3 flow stagnation by up to 91% but increased prothrombotic shear stress and simulated platelet activation (median PAS: +124%). Our study advances understanding of the pathogenesis of LVAD thrombosis, suggesting mechanistic implications of rotor speed modulation. Our data provide rationale criteria for the future design optimization of next generation LVADs to further reduce hemocompatibility-related adverse events.

Post-operative of bleeding, haemolysis and coagulation in mechanical circulatory support patients

There are unique complications arising from mechanical support devices but some of the long-term systemic haematological complications are indistinguishable from management problems affecting the care of other patients receiving intermediate to long term care in the cardiac ICU. The field of mechanical cardiac assist device (MCAD) is evolving. Despite major changes in design of these devices the most feared haematological complications have remained unchanged, namely haemolysis, pump thrombosis or thromboembolism. This review article gives an overview over the pathophysiology of MCAD related haematological complications, their management and where possible an outlook on future strategies to prevent such complications. The impact of MCAD on blood is discussed, starting with rheology, common pump mechanisms, current and future pump surface coating materials, anatomical considerations of the connection of the circuit and design of the circuit itself. Moreover, the duration of the cardiovascular support, impact of bleeding complications and other patient factors. This article also covers the impact of long term mechanical cardiac support on the properties of platelets, the anticoagulation strategies and a basic guide to the differential diagnosis of haemolysis is reviewed. The section on anaemia considers anaemia in the wider perioperative setting for patients in critical care having undergone cardiac surgery and also discusses transfusion alternatives.

Clinical Applications, Pitfalls, and Uncertainties of Thrombin Generation in the Presence of Platelets

Platelet-dependent thrombin generation is a helpful tool to assess ex vivo the interaction between platelets and plasma coagulation factors in the initiation, amplification, and inhibition of thrombin generation (TG). This review article discusses the most relevant available data on the clinical applications of fluorogenic TG, the most widely used TG assay, performed in the presence of platelets, i.e., in platelet-rich plasma. With respect to prothrombotic states, arterial hypertension and obesity were the most prominent cardiovascular conditions linked to increased platelet-dependent TG. In addition, platelet-associated hypercoagulability, assessed by the TG assay, has been shown in individuals with active cancer. In terms of bleeding, platelet-dependent TG has been applied to assess bleeding risk in individuals with hemophilia, von Willebrand disease, and Glanzmann thrombasthenia as well as in subjects with other congenital or acquired coagulation factor deficiencies. In addition to risk prediction, a role of the TG assay has been suggested in monitoring antiplatelet therapy in prothrombotic conditions and replacement therapy in bleeding diathesis. Finally, for the routine clinical use and as a biomarker of disease development and progression, better standardization and clinical validation of platelet-dependent TG are still needed.