Extensive Coagulation Monitoring in Patients After Implantation of the MicroMed Debakey Continuous Flow Axial Pump

Baseline Thromboelastogram as a Predictor of Left Ventricular Assist Device Thrombosis

Left ventricular assist device (LVAD) pump thrombosis occurs in up to 8.4% of patients within 3-months postimplantation. Thromboelastography (TEG) could be used to signal hypercoagulability at LVAD implantation to predict patients at high risk for thrombosis. We sought to evaluate whether TEG maximum amplitude (MA) hypercoagulability (MA ≥69 mm) at the time of LVAD implantation predicts pump thrombosis. A single center, retrospective, nested case-control study was conducted using patients from January 1, 2005, to March 31, 2015. Each pump thrombosis case was matched to two control subjects based on age ± 5 years, sex, and duration of follow-up. A multivariable logistic regression analysis was performed on the matched sets; the odds ratio with 95% confidence interval (CI) was calculated to estimate the relative risk. Thirty-seven age- and sex-matched case-control sets were included for a total of 111 study participants. TEG-MA hypercoagulability occurred in 10.8% of the case group versus 6.8% of controls. There was no association between TEG-MA hypercoagulability and device thrombosis (odds ratio 1.71, 95% confidence interval 0.42-7.05, p = 0.46). Utilization of baseline TEG-MA hypercoagulability to detect individuals at risk for LVAD thrombosis is a novel concept. This study found no significant association between TEG-MA and LVAD thrombosis.

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.

Bleeding and thrombosis in chronic ventricular assist device therapy: focus on platelets

PURPOSE OF REVIEW

Left ventricular assist devices (LVADs) have markedly improved the survival for patients with advanced heart failure but are plagued with significant morbidity, including pump thrombosis and bleeding. Better understanding of the platelet, and its role in the balance of bleeding and thrombosis, stands to impact the frequency and treatment of these significant complications.

RECENT FINDINGS

In patients with LVADs, there is little consistency linking traditional biomarkers of platelet activation and clinical events. A number of innovative methods of assessing platelet functionality, including shedding of platelet receptors and formation of microparticle complexes as well as measuring mitochondrial membrane potentials, exist and appear to be clinically relevant. Acquired von Willebrand syndrome, while not explaining all bleeding events, is a central feature of mechanical support and offers a target for innovative therapies.

SUMMARY

Although the platelet is only one component of impacting thrombosis and bleeding in patients supported with LVADs, it plays a central role in mediating these two opposing forces. Innovations in understanding platelet physiology as well as manipulating genomic and receptor interactions for an individual patient will be critical if we are to decrease these serious adverse events in the future.

Thrombosis in continuous-flow left ventricular assist devices: pathophysiology, prevention, and pharmacologic management

Continuous-flow left ventricular assist devices reduce short-term mortality and improve quality of life in patients with end-stage heart failure. Unfortunately, device-related complications remain common, with many patients experiencing adverse events within the first year. New literature suggests that rates of device-related thrombosis may be increasing since 2011, which is particularly troublesome given that this pathology can result in a disabling stroke, organ damage, and death. In 2013, a group of practitioners in the field of mechanical circulatory support published a treatment algorithm based on their expert opinion. However, a comprehensive review of the pharmacotherapy of this condition is lacking. A search of the literature revealed 20 separate publications of case reports or case series describing outcomes associated with the use of drug therapy for suspected pump thrombosis. Each of these experiences was limited by small sample size, nonrandomized treatment allocation, and nonstandardized medication dosing. Data describing the outcomes of surgical versus medical management of device thrombosis are also sparse, with only three published reports identified. Based on the review of this limited literature, surgical management appears to be the preferred treatment modality, especially in those with organ hypoperfusion or hemodynamic instability. In patients ineligible for surgery, pharmacotherapy options remain limited. Use of all drug classes described in the literature for the HeartMate II device-fibrinolytics, glycoprotein IIb/IIIa inhibitors, and direct thrombin inhibitors-was hindered by either marginal efficacy or bleeding. Based on historical experience with unfractionated heparin in patients under HeartMate II support, we recommend this agent as a possible option for those with suspected pump thrombosis in lieu of surgical device exchange. For the HeartWare HVAD, limited data suggest that direct intraventricular administration of alteplase may be an acceptable treatment alternative. Additional research is clearly needed to further delineate the role of pharmacotherapy and to identify the optimal agent for managing this potentially life-threatening condition.

Coagulation management in patients undergoing mechanical circulatory support

The incidence of bleeding and thrombo-embolic complications in patients undergoing mechanical circulatory support therapy remains high and is associated with bad outcomes and increased costs. The need for anticoagulation and anti-platelet therapy varies widely between different pulsatile and non-pulsatile ventricular-assist devices (VADs) and extracorporeal membrane oxygenation (ECMO) systems. Therefore, a unique anticoagulation protocol cannot be recommended. Notably, most thrombo-embolic complications occur despite values of conventional coagulation tests being within the targeted range. This is due to the fact that conventional coagulation tests such as international normalised ratio (INR), activated partial thromboplastin time (aPTT) and platelet count cannot detect hyper- or hypofibrinolysis, hypercoagulability due to tissue factor expression on circulating cells or increased clot firmness, and platelet aggregation as well as response to anti-platelet drugs. By contrast, point-of-care (POC) whole blood viscoelastic tests (thromboelastometry/-graphy) and platelet function tests (impedance or turbidimetric aggregometry) reflect in detail the haemostatic status of patients undergoing mechanical circulatory support therapy and the efficacy of their anticoagulation and antiaggregation therapy. Therefore, monitoring of haemostasis using POC thromboelastometry/-graphy and platelet function analysis is recommended during mechanical circulatory support therapy to reduce the risk of bleeding and thrombo-embolic complications. Notably, these haemostatic tests should be performed repeatedly during mechanical circulatory support therapy since thrombin generation, clot firmness and platelet response may change significantly over time with a high inter- and intra-individual variability. Furthermore, coagulation management can be hampered in non-pulsatile VADs by acquired von Willebrand syndrome, and in general by acquired factor XIII deficiency as well as by heparin-induced thrombocytopenia. In addition, POC testing can be used in bleeding patients to guide calculated goal-directed therapy with allogeneic blood products, haemostatic drugs and coagulation factor concentrates to optimise the haemostasis and to minimise transfusion requirements, transfusion-associated adverse events and to avoid thrombo-embolic complications, as well. However, coagulation management in patients undergoing mechanical circulatory support therapy is somehow like navigating between Scylla and Charybdis, and development of protocols based on POC testing seems to be beneficial.

Pulsed or continuous flow in long-term assist devices: a debated topic

The end-stage cardiomyopathy is an increasing worldwide problem. Cardiac transplantation lacks sufficient donors to treat all patients, and there is thus debate about alternative strategies. The use of left ventricular assist devices for long-term support is increasing with a positive impact on patient survival. Although there is an ongoing debate regarding the risks and benefits of maintaining pulsatile flow during long-term ventricular assist device support, there has been a significant move towards implantation of continuous flow devices due to the lower surgical morbidity and better long-term reliability of these pumps. The following is a review of the literature on continuous and pulsatile flow for long-term support. Starting from the definition of flow, we analyze the current evidence and consider gastrointestinal complications.

Hematologic effects of continuous flow left ventricular assist devices

The extent of hematologic effects of the new continuous flow left ventricular assist devices (CF-LVAD) has not been studied. Recent clinical studies have demonstrated that hemolysis and thrombosis are not common during CF-LVAD support, however, the incidence of bleeding remains a concern. The rate of postoperative bleeding is similar to that of the prior generation pulsatile LVAD, but gastrointestinal bleeding due to angiodysplasia and arteriovenous malformations is more common and appears to be related to the blood flow rheology of these devices. New evidence suggests that acquired von Willebrand's disease develops in some patients due to the reduction in high molecular weight (HMW) multimers of von Willebrand's factor (vWF). Similar to acquired von Willebrand's disease seen in patients with aortic stenosis, the shear stress of the CF-LVAD may cause proteolysis of the HMW multimers of vWF. In addition to acquired von Willebrand's disease, there is activation of the fibrinolytic system and a loss of platelet numbers and function during CF-LVAD support. The hematologic responses during CF-LVAD support are constantly changing, and antiplatelet therapy may need to be adjusted accordingly. Considerable research is needed to better define the complex hematologic effects during CF-LVAD support. Screening of patients for angiodysplasia and von Willebrand's disease before CF-LVAD implant may allow for effective preemptive treatment. Because bleeding causes significant morbidity for this population, more effective treatment strategies need to be developed.

Recurrent device thrombi during mechanical circulatory support with an axial-flow pump is a treatable condition and does not preclude successful long-term support

The formation of pump thrombus after implantation of axial-flow ventricular assist devices has been described previously. We report a case of recurrent pump thrombus formation in a 63-year-old man who was bridged to heart transplantation with a MicroMed DeBakey ventricular assist device. He was treated with a low, dose-adjusted thrombolytic treatment protocol, and was subsequently successfully bridged to transplantation. Transient pump thrombus formation does not preclude safe long-term support with an axial-flow pump when diagnosed and treated appropriately.

Perioperative management of ventricular assist devices in children and adolescents

Ventricular assist devices are an integral part of therapy for patients with end-stage heart failure. Devices can either bridge to recovery or to transplantation. Options for ventricular assist devices include those that are centrifugal, pulsatile, and new rotary/axial devices. Care of the patient on a ventricular assist device is multifaceted, involving pharmacologic or mechanical support of the right ventricle, management of systemic vascular resistance, and manipulation of the hematologic system to avoid bleeding or thrombosis. In addition, care of these patients involves support of all end organs and avoidance of infectious complications. Care of these patients is complex, requiring a highly integrated team for optimal outcome.

The DuraHeart VAD, a Magnetically Levitated Centrifugal Pump The University of Vienna Bridge-to-Transplant Experience

BACKGROUND

The clinical application of the DuraHeart (Terumo Heart Inc, USA) has begun in Europe as a clinical trial of a third-generation implantable centrifugal blood pump. Four successful clinical implants are presented.

METHODS AND RESULTS

Four male patients had end-stage left heart failure and received a DuraHeart VAD as a left ventricular assist device for bridge-to-transplantation. The pump showed good performance with flow rates of 4.9+/-0.5 L/min after gradual weaning of extracorporeal circulation. The pump flow was then maintained at 6.1+/-0.5, 5.5+/-0.3, 5.5+/-0.1, 5.7+/-0.1, 5.5, 6.4 and 6.5 L/min at the 1st, 4th, 8th, 12th, 16th, 20th and 24th postoperative week, respectively. No significant elevation of mean plasma-free hemoglobin was detected. The patients were discharged on the 18th, 42nd, 41st and 31st postoperative day, respectively, and all were successfully transplanted on the 202nd, 84th, 128th and 96th postoperative day, respectively. At the time of transplant surfaces of the removed pumps were free from thrombus formation, although intraventricular pannus growth was observed around the inflow cannulae in all patients.

CONCLUSION

The DuraHeart VAD showed stable and sufficient circulatory support for the bridge-to-transplant procedure in this cohort of 4 patients.

High level of cerebral microembolization in patients supported with the DeBakey left ventricular assist device

OBJECTIVE

Microembolic signals detected by transcranial Doppler ultrasonography have been demonstrated to be clinically relevant in patients supported with pulsatile left ventricular assist devices. We prospectively investigated the quantity of microembolic signals in patients supported with the continuous-flow DeBakey left ventricular assist device (MicroMed DeBakey VAD; MicroMed Technology, Inc, Houston, Tex) including the refined Carmeda BioActive Surface system (Carmeda AB, Stockholm, Sweden).

METHODS

Twenty-three patients (20 male) aged 14 to 62 years supported with DeBakey left ventricular assist devices (n = 6 with Carmeda) were enrolled in this study. Microembolic signal monitorings were performed twice weekly by insonating the middle cerebral artery for 20 minutes without and 20 minutes with oronasal application of oxygen (6 L/min). Evidence of clinically manifest thromboembolic events was based on regular questionnaires, clinical examinations, and results of diagnostic procedures.

RESULTS

Despite a low incidence of thromboembolic complications (0.24 per 100 left ventricular assist device days), 20 patients (87%) showed circulating microemboli. Overall, microembolic signals were found in 175 of 499 transcranial Doppler ultrasonographic examinations (35.1%), with mean counts of 81.2 +/- 443 (range 0-5042 signals/h). Both microembolic signal prevalence (25% vs 34%, P = .01) and absolute signal counts (46.5 vs 104, P < .01) significantly declined with oxygen delivery. There was no significant correlation between the individual microembolic signal activity and the incidence of clinical thromboembolism or the intensity of antihemostatic treatment. Patients supported with the Carmeda device did not show reduced rates of clinical thromboembolization or cerebral microemboli.

CONCLUSION

In patients with DeBakey left ventricular assist devices, a high load of clinically silent microemboli can be detected within the cerebral arteries despite a low incidence of embolic complications. It needs to be investigated whether such continuous, presumably gaseous microembolization causes cognitive or neuropsychologic deficits.