Right atrial versus right ventricular HeartWare HVAD position in patients on biventricular HeartWare HVAD support: A systematic review

Effect of RVAD Cannulation Length on Right Ventricular Thrombosis Risk: An In Silico Investigation

Left ventricular assist devices (LVADs) have been used off-label as long-term support of the right heart due to the lack of a clinically approved durable right VAD (RVAD). Whilst various techniques to reduce RVAD inflow cannula protrusion have been described, the implication of the protrusion length on right heart blood flow and subsequent risk of thrombosis remains poorly understood. This study investigates the influence of RVAD diaphragmatic cannulation length on right ventricular thrombosis risk using a patient-specific right ventricle in silico model validated with particle image velocimetry. Four cannulation lengths (5, 10, 15 and 25 mm) were evaluated in a one-way fluid-structure interaction simulation with boundary conditions generated from a lumped parameter model, simulating a biventricular supported condition. Simulation results demonstrated that the 25-mm cannulation length exhibited a lower thrombosis risk compared to 5-, 10- and 15-mm cannulation lengths due to improved flow energy distribution (25.2%, 24.4% and 17.8% increased), reduced stagnation volume (72%, 68% and 49% reduction), better washout rate (13.0%, 11.6% and 9.1% faster) and lower blood residence time (6% reduction). In the simulated scenario, our findings suggest that a longer RVAD diaphragmatic cannulation length may be beneficial in lowering thrombosis risk; however, further clinical studies are warranted.

The Future of Durable Mechanical Circulatory Support: Emerging Technological Innovations and Considerations to Enable Evolution of the Field

The field of durable mechanical circulatory support (MCS) has undergone an incredible evolution over the past few decades, resulting in significant improvements in longevity and quality of life for patients with advanced heart failure. Despite these successes, substantial opportunities for further improvements remain, including in pump design and ancillary technology, perioperative and postoperative management, and the overall patient experience. Ideally, durable MCS devices would be fully implantable, automatically controlled, and minimize the need for anticoagulation. Reliable and long-term total artificial hearts for biventricular support would be available; and surgical, perioperative, and postoperative management would be informed by the individual patient phenotype along with computational simulations. In this review, we summarize emerging technological innovations in these areas, focusing primarily on innovations in late preclinical or early clinical phases of study. We highlight important considerations that the MCS community of clinicians, engineers, industry partners, and venture capital investors should consider to sustain the evolution of the field.

Current and future options for adult biventricular assistance: a review of literature

In cardiogenic shock various short-term mechanical assistances may be employed, including an Extra Corporeal Membrane Oxygenator and other non-dischargeable devices. Once hemodynamic stabilization is achieved and the patient evolves towards a persisting biventricular dysfunction or an underlying long-standing end-stage disease is present, aside from Orthotopic Heart Transplantation, a limited number of long-term therapeutic options may be offered. So far, only the Syncardia Total Artificial Heart and the Berlin Heart EXCOR (which is not approved for adult use in the United States unlike in Europe) are available for extensive implantation. In addition to this, the strategy providing two continuous-flow Left Ventricular Assist Devices is still off-label despite its widespread use. Nevertheless, every solution ensures at best a 70% survival rate (reflecting both the severity of the condition and the limits of mechanical support) with patients suffering from heavy complications and a poor quality of life. The aim of the present paper is to summarize the features, implantation techniques, and results of current devices used for adult Biventricular Mechanical Circulatory Support, as well as a glance to future options.

Durable biventricular assist device support for 1212 days as a bridge to heart transplantation

Experience with durable biventricular assist devices (BiVADs) as a bridge to heart transplantation (HTx) is limited, particularly in women. A 41-year-old woman with biventricular failure complicated by cardiogenic shock underwent durable concurrent BiVAD implantation and was supported for 1212 days as a bridge to HTx. During BiVAD support, she experienced bacteremia (day 1030 of support), appropriately managed with intravenous antibiotics. She is alive and well, 1479 days from BiVAD implantation and 267 days from orthotopic HTx. Strategies contributing to successful prolonged support include concurrent BiVAD implantation, aggressive cardiac rehabilitation, diet management for weight loss and frequent interval surveillance.

Biventricular assist devices and total artificial heart: Strategies and outcomes

In contrast to the advanced development of the left ventricular assist device (LVAD) therapy for advanced heart failure, the mechanical circulatory support (MCS) with biventricular assist device (BVAD) and total artificial heart (TAH) options remain challenging. The treatment strategy of BVAD and TAH therapy largely depends on the support duration. For example, an extracorporeal centrifugal pump, typically referred to as a temporary surgical extracorporeal right ventricular assist device, is implanted for the short term with acute right ventricular failure following LVAD implantation. Meanwhile, off-label use of a durable implantable LVAD is a strategy for long-term right ventricular support. Hence, this review focuses on the current treatment strategies and clinical outcomes based on each ventricle support duration. In addition, the issue of heart failure post-heart transplantation (post-HT) is explored. We will discuss MCS therapy options for post-HT recipients.

Bridge to transplantation from mechanical circulatory support: a narrative review

Objective

To highlight recent developments in the utilization of mechanical circulatory support (MCS) devices as bridge-to-transplant strategies and to discuss trends in MCS use following the changes to the United Network for Organ Sharing (UNOS) heart allocation system.

Background

MCS devices have played an increasingly important role in the treatment of heart failure patients. Over the past several years, technological advancements have led to new developments in MCS devices and expanding indications for MCS use. In October of 2018, the UNOS heart allocation policy was revised to prioritize higher-urgency patients, including those supported with temporary MCS devices. Since then, changes in trends of MCS utilization have been observed.

Methods

Articles from the PubMed database regarding the use of MCS devices as bridge-to-transplant strategies were reviewed.

Conclusions

Over the past decade, utilization of temporary MCS devices, which include the intra-aortic balloon pump (IABP), percutaneous ventricular assist devices (pVADs), and extracorporeal membrane oxygenation (ECMO), has become increasingly common. Recent advancements in MCS include the development of pVADs that can fully unload the left ventricle (LV) as well as devices designed to provide right-sided support. Technological advancements in durable left ventricular assist devices (LVADs) have also led to improved outcomes both on the device and following heart transplantation. Following the 2018 UNOS heart allocation policy revision, the utilization of temporary MCS in advanced heart failure patients has further increased and the proportion of patients bridged directly from a temporary MCS device has exponentially risen. However, following the start of the COVID-19 pandemic, the trends have reversed, with a decrease in the percentage of patients bridged from a temporary MCS device. As long-term data following the allocation policy revision becomes available, future studies should investigate how trends in MCS use for patients with advanced heart failure continue to evolve.

In vitro Hemocompatibility Evaluation of the HeartWare Ventricular Assist Device Under Systemic, Pediatric and Pulmonary Support Conditions

The development of adult use right ventricular assist devices (RVADs) and pediatric left ventricular assist devices (pediatric LVADs) have significantly lagged behind compared to adult use left ventricular assist devices (LVADs). The HeartWare ventricular assist device (HVAD) intended to be used for adult's systemic support, is increasingly used off-label for adult pulmonary and pediatric systemic support. Due to different hemodynamics and physiology, however, the HVAD's hemocompatibility profiles can be drastically different when used in adult pulmonary circulation or in children, compared to its intended usage state, which could have a direct clinical and developmental relevance. Taking these considerations in mind, we sought to conduct in vitro hemocompatibility testing of HVAD in adult systemic, pediatric systemic and adult pulmonary support conditions. Two HVADs coupled to custom-built blood circulation loops were tested for 6 hours using bovine blood at 37°C under adult systemic, pediatric systemic, and adult pulmonary flow conditions (flow rate = 5.0, 2.5, and 4.5 L/min; differential pressure = 100, 69, and 20 mm Hg, respectively). Normalized index of hemolysis for adult systemic, pediatric systemic, and adult pulmonary conditions were 0.0083, 0.0039, and 0.0017 g/100 L, respectively. No significant difference was seen in platelet activation for these given conditions. High molecular weight von Willebrand factor multimer degradation was evident in all conditions (p < 0.05). In conclusion, alterations in the usage mode produce substantial differences in hemocompatibility of the HVAD. These findings would not only have clinical relevance but will also facilitate future adult use RVAD and pediatric LVAD development.

Contemporary outcomes of continuous-flow biventricular assist devices

Background

Significant right ventricular failure (RVF) complicating left ventricular assist device (LVAD) placement has been reported at 10-30%. Although primarily indicated for left ventricular failure, ventricular assist devices (VADs) have become utilized in a biventricular setup to combat right ventricular failure (RVF) following LVAD implantation. With the advent of continuous-flow LVADs (CF-LVADs) superseding their pulsatile predecessors, the shift towards CF-biventricular assist devices (CF-BiVADs) come with the prospect of improved outcomes over previous pulsatile BiVADs. We aim to review the literature and determine the outcomes of CF-BiVAD recipients.

Methods

A systematic review was performed to determine the outcomes of CF-BiVADs. Pre-operative demographics and device configuration data was collected. Primary outcomes evaluated were short-term survival, long-term survival, duration of support, and survival to transplant. Secondary outcomes evaluated included intensive care unit (ICU) and hospital length of stay (ICU-LOS and HLOS, respectively), pump thrombosis, pump exchange. Median and interquartile range was reported where appropriate. A major limitation was the likely overlap of cohorts across publications, which may have contributed to some selection bias.

Results

Of 1,282 screened, 12 publications were evaluated. Sample size ranged from 4 to 93 CF-BiVAD recipients, and follow-up ranged from 6 to 24 months. Mean age ranged from 34 to 52 years old. Forty-five percent of CF-BiVADs had right atrial (RA-) inflow cannulation, with the remaining being right ventricular (RV). Thirty-day survival was a median of 90% (IQR 82-97.8%) and 12-month survival was a median of 58.5% (IQR 47.5-62%). Where reported, rate of pump thrombosis (predominantly the right VAD) was a median of 31% (IQR 14-36%), although pump exchange was only 9% (IQR 1.5-12.5%).

Conclusions

RVF post-LVAD implantation is a high morbidity and mortality complication. There is no on-label continuous-flow RVAD currently available. Thus, the modifications of LVADs for right ventricular support to combat pump thrombosis has resulted in various techniques. BiVAD recipients are predominantly transplant candidates, and complications of pump thrombosis and driveline infection whilst on wait-list are of great consequence. This study demonstrates the need for an on-label CF-BiVAD.