Thrombotic response to mechanical circulatory support devices

Cardiovascular mechanical circulatory support (MCS) device use triggers thrombosis and hemostatic disorders, which may become fatal if thrombi occlude circulation or cause embolic complications. Consequently, antithrombotic medications are administered, which often cannot eliminate thrombosis and further compromise patient survival by introducing an additional risk of severe bleeding events. MCS thrombosis is induced and affected by the combined interplay of patient pathology, the foreign artificial biomaterial's surface properties, and pathological flow conditions. From a device design perspective, the latter 2 may be controlled for and redesigned to minimize the thrombotic response. This review examines how MCS thrombosis is affected by the biomaterial properties of surface roughness and topography, chemistry and charge, wettability, and bioactive coatings and the hemodynamic flow properties of margination, low flow and coagulation, high flow and platelet activation, von Willebrand factor activation, and hemolysis. For each property, we explain its well-established underlying biological, chemical, or physical effects on thrombosis and highlight current and proposed design strategies that could reduce MCS thrombosis. We review the potential reasons thrombosis still complicates MCS devices and postulate that an improved understanding of the dominant thrombotic process occurring at specific regions of devices and mechanistic insights into the combined effects of material properties with flow are still required. Together, we provide a guide for potential biomaterial and flow design changes to reduce thrombosis in MCS, emphasizing that novel biomaterials and device geometries should be tested under operationally and clinically relevant flow conditions to develop safer future-generation devices with reduced thrombotic responses.

Understanding the role of vascular stretch on modulation of VWF and ANGPT-2 in continuous flow left ventricular assist device (CF-VAD) patients

Non-surgical bleeding is a common complication in patients on continuous flow left ventricular assist device (CF-VAD) support. This study investigates how the transition from cyclic to constant stretch following CF-VAD implantation affects endothelial biosynthesis and release of Von Willebrand factor (VWF) and angiopoietin-2 (ANGPT-2), two molecules that play an essential role in the development of non-surgical bleeding. Human aortic endothelial and umbilical vein endothelial cells (HAECs and HUVECs) were cultured within a uniaxial stretch device that mimics stretch associated with both normal pulsatile and CF-VAD conditions. Following 72 hours of stretch, transcriptional regulation, intracellular accumulation, and secretion of VWF and ANGPT-2 were evaluated using molecular expression profiling and immunofluorescence microscopy. Constant stretch associated with CF-VADs upregulates transcriptional levels of VWF and ANGPT-2 in HAECs and HUVECs compared to physiological cyclic stretch (p < 0.05). Transcriptional increases in both VWF and ANGPT-2 in HAECs also resulted in increased intracellular protein levels of VWF and ANGPT-2 measured using ELISA, western blots and immunofluorescence microscopy, whereas in HUVECs, the intracellular increase was evident only with western blots and immunofluorescence microscopy. Finally, constant stretch appears to promote ANGPT-2 release and inhibit release of VWF from both HAECs and HUVECs compared to cyclic stretch. Our study found that constant stretch upregulates the production of both VWF and ANGPT-2. However, while the release of ANGPT-2 is elevated under constant stretch, the release of VWF declines, resulting in elevated extracellular levels of ANGPT-2, but not VWF.

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.

Early Postoperative Changes in Von Willebrand Factor Activity Are Associated With Future Bleeding and Stroke in HeartMate 3 Patients

Hemocompatibility-related adverse events (HRAEs), particularly gastrointestinal bleeding, remain a frequent complication after left ventricular assist device (LVAD) implantation. The current study sought to describe and analyze whether early (<60 days) postoperative von Willebrand factor (VWF) activity assays predict the risk of gastrointestinal bleeding and stroke. A prospective single-center study including 74 HeartMate 3 device recipients between 2016 and 2023 was undertaken. The postoperative trajectory of the VWF profile was analyzed using linear mixed-effect models and Cox models were used to quantify associations between an early postoperative dip (≤0.7) in VWF activity assay measurements and late outcomes. Preoperatively, the mean VWF:Activity (Act)/Antigen (Ag) and VWF:Collagen Binding (CB)/Ag ratios were 0.94 (95% confidence interval [CI] = 0.81-1.02) and 0.95 (95% CI = 0.80-1.03), respectively, decreasing to 0.66 (95% CI = 0.57-0.73) and 0.67 (95% CI = 0.58-0.74) within 40 days ( p < 0.05). In patients with VWF:CB/Ag and VWF:Act/Ag ratios ≤0.7 significantly more gastrointestinal bleeding (hazard ratio [HR]: 2.53; 95% CI = 1.1-5.8, and HR: 3.7; 95% CI = 1.5-9.2, respectively) and hemorrhagic stroke events (HR: 3.5; 95% CI = 1.6-7.6 and HR: 4.9; 95% CI = 2.1-11.7, respectively) were observed throughout the entire late (>60 days) postoperative period. In patients with VWF:Act/Ag ratio ≤0.7 less ischemic stroke events were observed (HR: 0.11; 95% CI = 0.01-0.85). In conclusion, VWF:Act/Ag and VWF:CB/Ag ratios ≤0.7 in the early postoperative phase can be used as biomarkers to predict HRAEs during long-term LVAD support.

Apixaban in bridge to transplant and destination LVAD - rationale and study design: the ApixiVAD trial

AIMS

Use of novel anticoagulation in mechanical circulatory support is controversial. We report the rationale and design of the ApixiVad pilot trial, a pilot study testing the safety of apixaban as an anticoagulant in patients bridged to transplant (BTT) or for destination (DT) with Heartmate 3 (HM3) left ventricular assist device (LVAD).

METHODS AND RESULTS

Apixaban has been used in small non-randomized cohorts in LVAD patients and shown to be effective in ex vivo studies. The ApixiVAD study examines apixaban use in a multicentre, international, open-label, randomized, controlled trial aiming to include 50 BTT or DT HM3 patients with a 1:1 randomization ratio. This event-driven study has a maximum follow-up period of 24 months with interim analysis at 6 months. The primary outcome is death, thromboembolic events and major bleeding, including operative bleeding and immediate transplant outcomes. The secondary outcome focuses on patients' quality of life related to anticoagulation. This investigator-driven pilot study is not powered to determine the non-inferiority of apixaban. An increase in primary outcome in the apixaban group of 20% will be considered a signal of harm.

CONCLUSIONS

A positive outcome in the ApixiVAD study would provide the basis for future, larger, pivotal anticoagulation trials in LVAD patients.

An ISHLT consensus statement on strategies to prevent and manage hemocompatibility related adverse events in patients with a durable, continuous-flow ventricular assist device

Life expectancy of patients with a durable, continuous-flow left ventricular assist device (CF-LVAD) continues to increase. Despite significant improvements in the delivery of care for patients with these devices, hemocompatability-related adverse events (HRAEs) are still a concern and contribute to significant morbility and mortality when they occur. As such, dissemination of current best evidence and practices is of critical importance. This ISHLT Consensus Statement is a summative assessment of the current literature on prevention and management of HRAEs through optimal management of oral anticoagulant and antiplatelet medications, parenteral anticoagulant medications, management of patients at high risk for HRAEs and those experiencing thrombotic or bleeding events, and device management outside of antithrombotic medications. This document is intended to assist clinicians caring for patients with a CF-LVAD provide the best care possible with respect to prevention and management of these events.

The Role of the von Willebrand Factor Collagen-Binding Assay (VWF:CB) in the Diagnosis and Treatment of von Willebrand Disease (VWD) and Way Beyond: A Comprehensive 36-Year History

The von Willebrand factor (VWF) collagen binding (VWF:CB) assay was first reported for use in von Willebrand diagnostics in 1986, by Brown and Bosak. Since then, the VWF:CB has continued to be used to help diagnose von Willebrand disease (VWD) (correctly) and also to help assign the correct subtype, as well as to assist in the monitoring of VWD therapy, especially desmopressin (DDAVP). However, it is important to recognize that the specific value of any VWF:CB is predicated on the use of an optimized VWF:CB, and that not all VWF:CB assays are so optimized. There are some good commercial assays available, but there are also some "not-so-good" commercial assays available, and these may continue to give the VWF:CB "a bad reputation." In addition to VWD diagnosis and management, the VWF:CB found purpose in a variety of other applications, from assessing ADAMTS13 activity, to investigation into acquired von Willebrand syndrome (especially as associated with use of mechanical circulatory support or cardiac assist devices), to assessment of VWF activity in disease states in where an excess of high-molecular-weight VWF may accumulate, and lead to increased (micro)thrombosis risk (e.g., coronavirus disease 2019, thrombotic thrombocytopenic purpura). The VWF:CB turns 37 in 2023. This review is a celebration of the utility of the VWF:CB over this nearly 40-year history.

Gastrointestinal Bleeding in Patients Supported with Left Ventricular Assist Devices: The Journey from Bridging to Destination

End-stage heart failure is a prevalent and fatal cardiovascular disease. Almost 1 in 4 cases of mortality in the United States is attributed to heart failure. Left ventricular assist devices (LVADs) have emerged as a safe destination therapy or bridge to transplant. Despite remarkable results, LVAD is associated with significant adverse events, such as gastrointestinal bleeding (GIB). In this review, we aimed to understand the incidence and prevalence, pathophysiologic mechanisms, predictors, diagnostic mechanisms, management, and preventative measures of GIB in patients with an LVAD. GIB is a common adverse event in patients with an LVAD with an incidence of 15% to 25%. The exact pathogenesis of GIB is poorly understood. However, different mechanisms of bleeding have been described, such as arteriovenous malformations, acquired von Willebrand syndrome, coagulopathy, and treatment with antithrombotic therapy. Upper GIB is the most common site of GIB in patients with an LVAD. The management of GIB in patients with LVAD includes ensuring hemodynamic stability, holding or reversing antithrombotic therapy, and investigating and controlling the source of GIB through diagnostic and interventional endoscopic and radiologic means. Prophylactic medication use (e.g., danazol, octreotide, and bevacizumab) can decrease the risk of GIB in patients with an LVAD by decreasing arteriovenous malformations. Despite that the overall risk of GIB has decreased with new advancements in LVAD technology, further studies are needed regarding predictors, risk stratification, and optimal antithrombotic therapy to minimize the morbidity and mortality in patients with an LVAD. In conclusion, prompt diagnosis and management in a multidisciplinary team approach are crucial and lifesaving in such a life-threatening condition.

Neurologic Complications in Patients With Left Ventricular Assist Devices

Left ventricular assist device (LVAD) use has revolutionised the care of patients with advanced heart failure, allowing more patients to survive until heart transplantation and providing improved quality for patients unable to undergo transplantation. Despite these benefits, improvements in device technology, and better clinical care and experience, LVADs are associated with neurologic complications. This review provides information on the incidence, risk factors, and management of neurologic complications among LVAD patients. Although scant guidelines exist for the evaluation and management of neurologic complications in LVAD patients, a high index of suspicion can prompt early detection of neurologic complications which may improve overall neurologic outcomes. A better understanding of the implications of continuous circulatory flow on systemic and cerebral vasculature is necessary to reduce the common occurrence of neurologic complications in this population.

Effect of Angiotensin II Antagonism on Gastrointestinal Bleeding in Patients With Left Ventricular Assist Devices: A Systematic Review and Meta-Analysis

The importance of medical therapy to ameliorate the incidence and impact of left ventricular assistance device-related gastrointestinal bleeding has been highlighted recently with several single-center studies. Electronic databases were searched for studies that compared the incidence of gastrointestinal bleeding for those people on left ventricular assist support with and without angiotensin II inhibition. Angiotensin II inhibition was associated with a lower incidence of gastrointestinal bleeding (pooled RR 0.58, 95% confidence interval (CI): 0.34-0.98; p = 0.04], with a trend toward toward lower incidence with arteriovenous malformation-associated gastrointestinal bleeding (pooled RR 0.50, 95% CI: 0.25-1.03; p = 0.06).

Optimal Tests to Minimise Bleeding and Ischaemic Complications in Patients on Extracorporeal Membrane Oxygenation

Patients supported with extracorporeal membrane oxygenation (ECMO) experience a very high frequency of bleeding and ischaemic complications, including stroke and systemic embolism. These patients require systemic anticoagulation, mainly with unfractionated heparin (UFH) to prevent clotting of the circuit and reduce the risk of arterial or venous thrombosis. Monitoring of UFH can be very challenging. While most centres routinely monitor the activated clotting time and activated partial thromboplastin time (aPTT) to assess UFH, measurement of anti-factor Xa (anti-Xa) level best correlates with heparin dose, and appears to be predictive of circuit thrombosis, although aPTT may be a better predictor of bleeding. Although monitoring of prothrombin time, platelet count and fibrinogen is routinely undertaken to assess haemostasis, there is no clear guidance available regarding the optimal test.Additional tests, including antithrombin level and thromboelastography, can be used for risk stratification of patients to try and predict the risks of thrombosis and bleeding. Each has their specific role, strengths and limitations. Increased thrombin generation may have a role in predicting thrombosis. Acquired von Willebrand syndrome is frequent with ECMO, contributing to bleeding risk and can be detected by assessing the von Willebrand factor activity-to-antigen ratio, while the platelet function analyser can be used in urgent situations to detect this, with a high negative predictive value. Tests of platelet aggregation can aid in the prediction of bleeding.To personalise management, a selection of complementary tests to collectively assess heparin-effect, coagulation, platelet function and platelet aggregation is proposed, to optimise clinical outcomes in these high-risk patients.

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.

Five-year outcomes of patients supported with HeartMate 3: a single-centre experience

OBJECTIVES

The HeartMate 3 left ventricular assist device was first implanted in 2014 and received the Conformité Européenne mark in 2015. Since then, several trials demonstrated its high haemocompatibility associated with good survival and low adverse events rates. Herein, we report our institutional experience with patients supported with HeartMate 3 for 5 years.

METHODS

This prospective cohort study included patients receiving a HeartMate 3 implantation in 2014 as part of the HeartMate 3 Conformité Européenne Mark clinical trial. Patients had follow-up visits every 3 months while on left ventricular assist device support, and all patients completed the 5-year follow-up. The primary end point was survival at 5 years. Secondary end points included adverse events, health status and quality of life.

RESULTS

Eight patients (men: 75%) aged 59 years (min-max: 52-66 years) were enrolled. At 5 years, survival was 100%. Patients remained on support for a median time of 1825 days (min-max: 101-1825 days); 2 patients successfully received cardiac transplants. No right heart failure, haemolysis, pump thrombosis, pump malfunction or neurological events occurred in any patients. A driveline infection was observed in 6 patients (0.25 events/patient-year). Compared to baseline, a significant improvement in quality of life and in New York Heart Association functional class was noted after the implant and for the whole follow-up time. A slight decline in kidney function and in the 6-min walk test results occurred after 3 years.

CONCLUSIONS

This study reports the longest single-centre follow-up of the HeartMate 3, showing excellent haemocompatibility over time with high survival and low complication rates at 5 years.

Device-induced platelet dysfunction in patients after left ventricular assist device implantation

BACKGROUND

Non-surgical bleeding (NSB) is a major complication after left ventricular assist device (LVAD) implantation. It has been reported that non-physiological shear stress caused by LVADs could alter platelet receptor expression, which leads to bleeding disorders caused by coagulation dysfunctions.

OBJECTIVES

Because bleeding diathesis could be multifactorial, we focused on the combined characterization of platelet receptor expression patterns and oxidative stress to compare patients with NSB and patients without coagulation disorder in a monocentric, prospective study.

METHODS

Blood samples were obtained from LVAD patients with NSB (bleeder group, n = 19) and without NSB (non-bleeder group, n = 20). The platelet receptors platelet endothelial cell adhesion molecule-1 (PECAM-1), glycoprotein (GP)Ibα, P-selectin, CD63, and GPIIb/IIIa, as well as the production of intraplatelet reactive oxygen species (ROS) were quantified by flow cytometry. Aggregation capacity was evaluated by aggregometry.

RESULTS

The surface expression level of P-selectin and GPIbα on platelets was decreased in bleeders (P-selectin: 465 ± 72 U; GPIbα: 435 ± 41 U) compared to non-bleeders (P-selectin: 859 ± 115 U, P < .01; GPIbα: 570 ± 49 U, p = .04). Additionally, the mean fluorescence intensity of ADP-stimulated P-selectin and PECAM-1 expressing platelets were reduced in bleeders (P-selectin: 944 ± 84 U; PECAM-1: 6722 ± 419 U) compared to non-bleeders (P-selectin: 1269 ± 130 U, P = .04; PECAM-1: 8542 ± 665 U, P = .03). Bleeders showed a higher amount of ROS formation in platelets (88.0 ± 2.6%) than non-bleeders (81.5 ± 2.1%, P = .05).

CONCLUSIONS

These findings suggested that changes of three platelet receptors (GPIbα, P-selectin, and PECAM-1) and elevated oxidative stress may play a role in patients with bleeding complications following LVAD implantation. These results might help to explain the high incidence of spontaneous hemorrhage during LVAD support through an altered platelet function.

Association between digoxin use and gastrointestinal bleeding in contemporary continuous flow left ventricular assist device support

BACKGROUND

Assess the association between digoxin use and gastrointestinal bleeding (GIB) in a multicenter continuous flow left ventricular assist device (LVAD) cohort.

METHODS

Patients implanted with continuous flow LVADs with data on GIB and digoxin use from two centers were included in the analysis (n = 649). GIB events were captured up to 2 years of follow-up. Digoxin use was defined as digoxin prescribed at discharge or within the first 3 months after LVAD implantation. A negative binomial regression model was performed to determine the association between digoxin use and number of GIB events over the follow-up period.

RESULTS

Mean age of the cohort was 57 years (±14) and 45% (293/649) were bridge to transplant (BTT). Digoxin was prescribed in 33% of patients. Digoxin use was associated with an unadjusted 32% reduction in the incidence of rate of all cause GIB (IRR 0.68, 95% CI 0.46-0.99, p = 0.049). After adjusting for age, sex, Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profile, renal function, and implanting center there was still a 34% reduction in the incidence rate (IRR 0.67, 95% CI 0.45-0.99, p = 0.048). When limiting the analysis to those with likely arteriovenous malformation associated GIB, the association strengthened (unadjusted: IRR 0.48, 95 % CI 0.26-0.89, p = 0.02, adjusted: IRR 0.47, 95 % CI 0.25-0.9, p = 0.022).

CONCLUSIONS

In this multicenter study, inclusive of contemporary devices, digoxin use was associated with reduced GIB events. Prospective data will be required to confirm this association.

A real-life experience with HeartMate III

BACKGROUND

The HeartMate III (HM3) left ventricular assist device (LVAD) is the most recent LVAD to receive CE Mark and the Food and Drug Administration approval. It is a fully magnetically levitated pump with no reported haemolysis, pump thrombosis or pump failure in the first in-man study (a previous stody). It has now received market approval in the European Union, United States of America, and Australia. We reviewed our real-life experience with the device, to assess outcomes over the medium term.

METHODS

We conducted a retrospective review of prospectively collected data for 33 consecutive patients implanted with a HM3 LVAD between November 2014 and October 2018 at The Alfred Hospital, Melbourne, Australia.

RESULTS

Of the 33 patients, 31 remained alive at the census date, with only two early deaths and 11 patients transplanted. There were no pump thromboses, but there were three cases of clot ingestion (two on the right and one on the left). Seven patients required permanent biventricular assist device support. The duration of HM3 support at the time of census was a median of 196 (interquartile range, 118-386) days.

CONCLUSION

This series demonstrates excellent results of the HM3 LVAD in an uncensored, real-life, consecutive group of patients in a single institution.