Is Bridge to Recovery More Likely With Pulsatile Left Ventricular Assist Devices Than With Nonpulsatile-Flow Systems?

Current status and future directions in pediatric ventricular assist device

A ventricular assist device (VAD) is a form of mechanical circulatory support that uses a mechanical pump to partially or fully take over the function of a failed heart. In recent decades, the VAD has become a crucial option in the treatment of end-stage heart failure in adult patients. However, due to the lack of suitable devices and more complicated patient profiles, this therapeutic approach is still not widely used for pediatric populations. This article reviews the clinically available devices, adverse events, and future directions of design and implementation in pediatric VADs.

Durable left ventricular assist device explantation following recovery in paediatric patients: Determinants and outcome after explantation

OBJECTIVES

Myocardial recovery in children supported by a durable left ventricular assist device is a rare, but highly desirable outcome because it could potentially eliminate the need for a cardiac transplant and the lifelong need for immunosuppressant therapy and the risk of complications. However, experience with this specific outcome is extremely limited.

METHODS

All patients < 19 years old supported by a durable left ventricular assist device from the European Registry for Patients with Mechanical Circulatory Support database were included. Participating centres were approached for additional follow-up data after explantation. Associated factors for explantation due to myocardial recovery were explored using Cox proportional hazard models.

RESULTS

The incidence of recovery in children supported by a durable left ventricular assist device was 11.7% (52/445; median duration of support, 122.0 days). Multivariable analyses showed body surface area (hazard ratio 0.229; confidence interval 0.093-0.565; P = 0.001) and a primary diagnosis of myocarditis (hazard ratio 4.597; confidence interval 2.545-8.303; P < 0.001) to be associated with recovery. Left ventricular end-diastolic diameter in children with myocarditis was not associated with recovery. Follow-up after recovery was obtained for 46 patients (88.5%). Sustained myocardial recovery was reported in 33/46 (71.7%) at the end of the follow-up period (28/33; >2 year). Transplants were performed in 6/46 (11.4%) (in 5 after a ventricular assist device was reimplanted). Death occurred in 7/46 (15.2%).

CONCLUSIONS

Myocardial recovery occurs in a substantial portion of paediatric patients supported with durable left ventricular assist devices, and sustainable recovery is seen in around three-quarters of them. Even children with severely dilated ventricles due to myocarditis can show recovery. Clinicians should be attentive to (developing) myocardial recovery. These results can be used to develop internationally approved paediatric weaning guidelines.

Longitudinal analysis left ventricular chamber responses under durable LVAD support

BACKGROUND

Left ventricular assist device (LVAD) support offers remodeling potential in some patients. Our goal was to use noninvasively derived pressure-volume (PV) loops to understand the effect of demographic and device variables on serial changes in cardiac function under pump support.

METHODS

Thirty-two consecutive Medtronic HeartWare Ventricular Assist Device (HVAD) patients (mean 55.9 ± 12.3 years, 81.3% male) were prospectively recruited. Single-cycle ventricular pressure and volume were estimated using a validated algorithm. PV loops (n = 77) and corresponding cardiac chamber dynamics were derived at predefined postimplant timepoints (1, 3, 6 months). Changes in PV loop parameters sustained across the 6-month period were characterized using mixed-effects modeling. The influence of demographic and device variables on the observed changes was assessed.

RESULTS

Across a 6-month period, the mean ventricular function parameters remained stable. Significant predictors of monthly improvement of stroke work include: lower pump speeds (2400 rpm vs 2500-2800 rpm) [0.0.051 mm Hg/liter/month (p = 0.001)], high pulsatility index (>1.0 vs <1.0) [0.052 mm Hg/liter/month (p = 0.012)], and ischemic cardiomyopathy indication for LVAD implantation (vs nonischemic) [0.0387 mm Hg/liter/month (p = 0.007)]. Various other cardiac chamber function parameters including cardiac power, peak systolic pressure, and LV elastance also showed improvements in these cohorts.

CONCLUSIONS

Factors associated with improvement in ventricular energetics and hemodynamics under LVAD support can be determined with noninvasive PV loops. Understanding the basis of increasing ventricular load to optimize myocardial remodeling may prove valuable in selecting eligible recovery candidates.

Hemodynamic Evaluation of Asynchronous Speed Modulation of a Continuous-Flow Left Ventricular Assist Device in an Acute-Myocardial Injury Sheep Model

Asynchronous rotational-speed modulation of a continuous-flow left ventricular assist device (LVAD) can increase pulsatility; however, the feasibility of hemodynamic modification by asynchronous modulation of an LVAD has not been sufficiently verified. We evaluated the acute effect of an asynchronous-modulation mode under LVAD support and the accumulated effect of 6 consecutive hours of driving by the asynchronous-modulation mode on hemodynamics, including both ventricles, in a coronary microembolization-induced acute-myocardial injury sheep model. We evaluated 5-min LVAD-support hemodynamics, including biventricular parameters, by switching modes from constant-speed to asynchronous-modulation in the same animals ("acute-effect evaluation under LVAD support"). To determine the accumulated effect of a certain driving period, we evaluated hemodynamics including biventricular parameters after weaning from 6-hour (6 h) LVAD support by constant-speed or asynchronous-modulation mode ("6h-effect evaluation"). The acute-effect evaluation under LVAD support revealed that, compared to the constant-speed mode, the asynchronous-modulation mode increased vascular pulsatility but did not have significantly different effects on hemodynamics, including both ventricles. The 6 h-effect evaluation revealed that the hemodynamics did not differ significantly between the two groups except for some biventricular parameters which did not indicate negative effects of the asynchronous-modulation mode on both ventricles. The asynchronous-modulation mode could be feasible to increase vascular pulsatility without causing negative effects on hemodynamics including both ventricles. Compared to the constant-speed mode, the asynchronous-modulation mode increased pulsatility during LVAD support without negative effects on hemodynamics including both ventricles in the acute phase. Six hours of LVAD support with the asynchronous-modulation mode exerted no negative effects on hemodynamics, including both ventricles, after weaning from the LVAD.

Developments and Challenges in Durable Ventricular Assist Device Technology: A Comprehensive Review with a Focus on Advancements in China

Heart transplantation is currently the most effective treatment for end-stage heart failure; however, the shortage in donor hearts constrains the undertaking of transplantation. Mechanical circulatory support (MCS) technology has made rapid progress in recent years, providing diverse therapeutic options and alleviating the dilemma of donor heart shortage. The ventricular assist device (VAD), as an important category of MCS, demonstrates promising applications in bridging heart transplantation, destination therapy, and bridge-to-decision. VADs can be categorized as durable VADs (dVADs) and temporary VADs (tVADs), according to the duration of assistance. With the technological advancement and clinical application experience accumulated, VADs have been developed in biocompatible, lightweight, bionic, and intelligent ways. In this review, we summarize the development history of VADs, focusing on the mechanism and application status of dVADs in detail, and further discuss the research progress and use of VADs in China.

Myocardial recovery in children supported with a durable ventricular assist device-a systematic review

OBJECTIVES

A small percentage of paediatric patients supported with a ventricular assist device (VAD) can have their device explanted following myocardial recovery. The goal of this systematic review is to summarize the current literature on the clinical course in these children after weaning.

METHODS

A systematic literature search was performed on 27 May 2022 using Embase, Medline ALL, Web of Science Core Collection, Cochrane Central Register of Controlled Trials and Google Scholar to include all literature on paediatric patients supported by a durable VAD during the last decade. Overlapping study cohorts and registry-based studies were filtered out.

RESULTS

Thirty-seven articles were included. Eighteen of them reported on the incidence of recovery in cohort studies, with an overall incidence rate of 8.7% (81/928). Twenty-two of the included articles reported on clinical outcomes after VAD explantation (83 patients). The aetiologies varied widely and were not limited to diseases with a natural transient course like myocarditis. Most of the patients in the included studies (70; 84.3%) were supported by a Berlin Heart EXCOR, and in 66.3% (55/83), only the left ventricle had to be supported. The longest follow-up period was 19.1 years, and multiple studies reported on long-term myocardial recovery. Fewer than half of the reported deaths had a cardiac cause.

CONCLUSIONS

Myocardial recovery during VAD support is dependent on various contributing components. The interactions among patient-, device-, time- and hospital-related factors are complex and not yet fully understood. Long-term recovery after VAD support is achievable, even after a long duration of VAD support, and even in patients with aetiologies different from myocarditis or post-cardiotomy heart failure. More research is needed on this favourable outcome after VAD support.

Myocardial recovery in a patient with dilated cardiomyopathy after short-term biventricular assist device support

Management of patients with end-stage heart failure is still challenging. We report a case of idiopathic dilated cardiomyopathy who went through a challenging course. The case was presented as acute heart failure syndrome, which rapidly declined into cardiogenic shock and cardiac arrest that required an extracorporeal membrane oxygenator, then biventricular assist device implantation for circulatory support. The course was complicated with severe gastrointestinal bleeding and multiorgan failure until achieving full cardiac and organ recovery. The left ventricle ejection fraction improved from 10% to 50% at discharge.

The hemodynamics and blood trauma in axial blood pump under different operating model

Speed modulation of blood pump has been proved to help restore vascular pulsatility and implemented clinically during treatment for cardiac failure. However, its effect on blood trauma has not been studied thoroughly. In this paper, we study the flow field of an axial pump FW-X under the modes of co-pulse, counter pulse and constant speed to evaluate the blood trauma. Based on the coupling model of cardiovascular system and axial blood pump, aortic pressure and the pump flow were obtained and applied as the boundary conditions at the pump outlet and inlet. The level of shear stress and hemolysis index were derived from computational fluid dynamics (CFD) simulation. Results showed the constant speed mode had the lowest shear stress level and hemolytic index at the expense of diminished pulsatility. Compared with the constant speed mode, the hemolysis index of co-pulse and counter pulse mode was higher, but it was helpful to restore vascular pulsatility. This method can be easily incorporated in the in vitro testing phase to analyze and decrease a pump's trauma before animal experimentation, thereby reducing the cost of blood pump development.

LVAD as a Bridge to Remission from Advanced Heart Failure: Current Data and Opportunities for Improvement

Left ventricular assist devices (LVADs) are an established treatment modality for advanced heart failure (HF). It has been shown that through volume and pressure unloading they can lead to significant functional and structural cardiac improvement, allowing LVAD support withdrawal in a subset of patients. In the first part of this review, we discuss the historical background, current evidence on the incidence and assessment of LVAD-mediated cardiac recovery, and out-comes including quality of life after LVAD support withdrawal. In the second part, we discuss current and future opportunities to promote LVAD-mediated reverse remodeling and improve our pathophysiological understanding of HF and recovery for the benefit of the greater HF population.

Weaning from ventricular assist device support after recovery from left ventricular failure with or without secondary right ventricular failure

Although complete myocardial recovery after ventricular assist device (VAD) implantation is rather seldom, systematic search for recovery is worthwhile because for recovered patients weaning from VADs is feasible and can provide survival benefits with long-term freedom from heart failure (HF) recurrence, even if a chronic cardiomyopathy was the primary cause for the drug-refractory HF necessitating left ventricular (LVAD) or biventricular support (as bridge-to-transplantation or definitive therapy) and even if recovery remains incomplete. LVAD patients explanted for myoacardial recovery compared to those transplanted from LVAD support showed similar survival rates and a significant proportion of explanted patients can achieve cardiac and physical functional capacities that are within the normal range of healthy controls. In apparently sufficiently recovered patients, a major challenge remains still the pre-explant prediction of the weaning success which is meanwhile reliably possible for experienced clinicians. In weaning candidates, the combined use of certain echocardiography and right heart catheterization parameters recorded before VAD explantation can predict post-weaning cardiac stability with good accuracy. However, in the absence of standardization or binding recommendations, the protocols for assessment of native cardiac improvement and also the weaning criteria differ widely among centers. Currently there are still only few larger studies on myocardial recovery assessment after VAD implantation. Therefore, the weaning practice relies mostly on small case series, local practice patterns, and case reports, and the existing knowledge, as well as the partially differing recommendations which are based mainly on expert opinions, need to be periodically systematised. Addressing these shortcomings, our review aims to summarize the evidence and expert opinion on the evaluation of cardiac recovery during mechanical ventricular support by paying special attention to the reliability of the methods and parameters used for assessment of myocardial recovery and the challenges met in both evaluation of recovery and weaning decision making.

Left ventricular assist device recovery: does duration of mechanical support matter?

Heart failure is a widespread condition in the United States that is predicted to significantly increase in prevalence in the next decade. Many heart failure patients are given a left ventricular assist device (LVAD) while they wait for a heart transplant, while those that are not able to undergo a heart transplant may be given an LVAD permanently. However, past studies have observed a small subset of heart failure patients that recovered cardiac function of their native heart after being placed on an LVAD. As a result, some patients have been able to have their LVAD explanted and no longer needed a heart transplant. In this review, we analyzed the data of 15 studies that observed recovery of cardiac function in LVAD patients in order to investigate the effects that duration of LVAD support has on patient outcomes. From our review, we identified that there may be negative consequences of prolonged duration of mechanical support such as myocardial atrophy and abnormal calcium cycling as well as circumstances that may allow for a longer duration of LVAD support such as in patients using a continuous-flow LVAD, non-ischemic cardiomyopathy patients, and the specific pharmacological therapy.

Comparative analysis of cardiac mechano-energetics in isolated hearts supported by pulsatile or rotary blood pumps

The previously more frequently implanted pulsatile blood pumps (PBPs) showed higher recovery rates than the currently preferred rotary blood pumps (RBPs), with unclear causality. The aim of this study was to comparatively assess the capability of PBPs and RPBs to unload the left ventricle and maintain cardiac energetics as a possible implication for recovery. An RBP and a heartbeat synchronized PBP were alternately connected to isolated porcine hearts. Rotational speed of RBPs was set to different support levels. For PBP support, the start of ejection was phased to different points during the cardiac cycle, prescribed as percentage delays from 0% to 90%. Cardiac efficiency, quantified by the ratio of external work over myocardial oxygen consumption, was determined. For RBP support, higher degrees of RBP support correlated with lower left atrial pressures (LAP) and lower cardiac efficiency (r = 0.91 ± 0.12). In contrast, depending on the phase delay of a PBP, LAP and cardiac efficiency exhibited a sinusoidal relationship with the LAP minimum at 90% and efficiency maximum at 60%. Phasing of a PBP offers the possibility to maintain a high cardiac efficiency and simultaneously unload the ventricle. These results warrant future studies investigating whether optimized cardiac energetics promotes functional recovery with LVAD therapy.

Haemodynamic evaluation of the new pulsatile-flow generation method in vitro

Continuous-flow ventricular-assist devices are widely used to support patients with advanced heart failure, because continuous-flow ventricular-assist devices are more durable, have smaller sizes and have better survival rates for patients compared to the pulsatile-flow ventricular-assist devices. Nevertheless, continuous-flow ventricular-assist devices often cause complications such as gastrointestinal bleeding, haemorrhagic stroke, and aortic insufficiency and have a negative impact on the microcirculation for both long-time implantable and short-time extracorporeal systems. The aim of this study is the evaluation of the pulsatile-flow generation method in continuous-flow ventricular-assist device without pump speed changes. The method may be used for short-time extracorporeal continuous-flow mechanical circulatory support and long-time implantable mechanical circulatory support. A shunt with a controlled adjustable valve, that clamps periodically, is connected in parallel to the continuous-flow ventricular-assist device. We compared the continuous-flow ventricular-assist device operating with and without the shunt on the mock circulation loop. The continuous-flow ventricular-assist device-shunt system was connected according to the left ventricle-aorta circuit and worked in phase with the ventricle. Heart failure was simulated on the mock circulation circuit. Rotaflow (Maquet Inc.) was used as the continuous-flow pump. Haemolysis studies of the system for generating a pulse flow were carried out at a flow rate of 5 L/min and a pressure drop of 100 mm Hg. To compare the haemodynamic efficiency, we used the aortic pulsation index I_p, the equivalent energy pressure and the surplus haemodynamic energy. These indexes were higher in the pulsatile mode (I_p - 4 times, equivalent energy pressure by 7.36% and surplus haemodynamic energy - 10 times), while haemolysis was the same. The normalised index of haemolysis was 0.0015 ± 0.001. The results demonstrate the efficiency of the pulsatile-flow generation method for continuous-flow ventricular-assist devices without impeller rotation rate changes.

High-frequency operation of pulsatile ventricular assist devices: A computational study on circular and elliptically shaped pumps

Pulsatile positive displacement pumps as ventricular assist devices were gradually replaced by rotary devices due to their large volume and high adverse event rates. Nevertheless, pulsatile ventricular assist devices might be beneficial with regard to gastrointestinal bleeding and cardiac recovery. Therefore, aim of this study was to investigate the flow field in new pulsatile ventricular assist devices concepts with an increased pump frequency, which would allow lower stroke volumes to reduce the pump size. We developed a novel elliptically shaped pulsatile ventricular assist devices, which we compared to a design based on a circular shape. The pump size was adjusted to deliver similar flow rates at pump frequencies of 80, 160, and 240 bpm. Through a computational fluid dynamics study, we investigated flow patterns, residence times, and wall shear stresses for different frequencies and pump sizes. A pump size reduction by almost 50% is possible when using a threefold pump frequency. We show that flow patterns inside the circular pump are frequency dependent, while they remain similar for the elliptic pump. With slightly increased wall shear stresses for higher frequencies, maximum wall shear stresses on the pump housing are higher for the circular design (42.2 Pa vs 18.4 Pa). The calculated blood residence times within the pump decrease significantly with increasing pump rates. A smaller pump size leads to a slight increase of wall shear stresses and a significant improvement of residence times. Hence, high-frequency operation of pulsatile ventricular assist devices, especially in combination with an elliptical shape, might be a feasible mean to reduce the size, without any expectable disadvantages in terms of hemocompatibility.

Competing Flow Between Partial Circulatory Support and Native Cardiac Output: A Clinical Computational Fluid Dynamics Study

Partial circulatory support is a promising concept for the treatment of heart failure patients. A better understanding of induced hemodynamic changes is essential for optimizing treatment efficacy. Computational fluid dynamics (CFD) is an alternative method to gain insight into flow phenomena difficult to obtain in vivo. In 10 patients implanted with a Circulite Synergy Micro-pump (HeartWare, Framingham, Massachusetts) (a continuous flow partial circulatory assist device connecting the left atrium to the right subclavian artery), transient CFD simulations were performed. Patients were divided into two groups depending on their cardiac output (CO; high CO group: 5.5 ± 1.1 L/min, low CO group: 1.7 ± 0.7 L/min). The partial assist device provided a supporting flow of 1.5 ± 0.8 L/min. Support was highest at diastole and decreased during systole because of a collision of the blood flows from the partial assist device and the CO. Reversed flow counteracting the flow of the device was significantly higher for the high CO group (mean flow in peak systole: -2.18 ± 1.08 vs. 0.23 ± 0.59 L/min; p = 0.002) showing an inverse correlation between CO and amount of reversed flow during peak systole (R = -0.7; p < 0.02). The flow collision lead to higher total pressures at the point of collision and consequently in the Circulite outflow graft. The CFD simulations allow quantifying hemodynamic alterations in patients with partial support consisting of a flow collision, thereby reducing effectiveness of the circulatory support. Partial support in heart failure patients alternates their hemodynamics not only in providing support for the circulation but also inducing unfavorable changes in flow patterns.

In Vitro Endothelialization of Surface-Integrated Nanofiber Networks for Stretchable Blood Interfaces

Despite major technological advances within the field of cardiovascular engineering, the risk of thromboembolic events on artificial surfaces in contact with blood remains a major challenge and limits the functionality of ventricular assist devices (VADs) during mid- or long-term therapy. Here, a biomimetic blood-material interface is created via a nanofiber-based approach that promotes the endothelialization capability of elastic silicone surfaces for next-generation VADs under elevated hemodynamic loads. A blend fiber membrane made of elastic polyurethane and low-thrombogenic poly(vinylidene fluoride- co-hexafluoropropylene) was partially embedded into the surface of silicone films. These blend membranes resist fundamental irreversible deformation of the internal structure and are stably attached to the surface, while also exhibiting enhanced antithrombotic properties when compared to bare silicone. The composite material supports the formation of a stable monolayer of endothelial cells within a pulsatile flow bioreactor, resembling the physiological in vivo situation in a VAD. The nanofiber surface modification concept thus presents a promising approach for the future design of advanced elastic composite materials that are particularly interesting for applications in contact with blood.

Recovery of failing hearts by mechanical unloading: Pathophysiologic insights and clinical relevance

By reduction of ventricular wall-tension and improving the blood supply to vital organs, ventricular assist devices (VADs) can eliminate the major pathophysiological stimuli for cardiac remodeling and even induce reverse remodeling occasionally accompanied by clinically relevant reversal of cardiac structural and functional alterations allowing VAD explantation, even if the underlying cause for the heart failure (HF) was dilated cardiomyopathy. Accordingly, a tempting potential indication for VADs in the future might be their elective implantation as a therapeutic strategy to promote cardiac recovery in earlier stages of HF, when the reversibility of morphological and functional alterations is higher. However, the low probability of clinically relevant cardiac improvement after VAD implantation and the lack of criteria which can predict recovery already before VAD implantation do not allow so far VAD implantations primarily designed as a bridge to cardiac recovery. The few investigations regarding myocardial reverse remodeling at cellular and sub-cellular level in recovered patients who underwent VAD explantation, the differences in HF etiology and pre-implant duration of HF in recovered patients and also the differences in medical therapy used by different institutions during VAD support make it currently impossible to understand sufficiently all the biological processes and mechanisms involved in cardiac improvement which allows even VAD explantation in some patients. This article aims to provide an overview of the existing knowledge about VAD-promoted cardiac improvement focusing on the importance of bench-to-bedside research which is mandatory for attaining the future goal to use long-term VADs also as therapy-devices for reversal of chronic HF.

In-Vitro Evaluation of Cardiac Energetics and Coronary Flow with Volume Displacement and Rotary Blood Pumps

Bridge to recovery with left ventricular assist device (LVAD) support has been more prominent with volume displacement pumps (VDPs) than with rotary blood pumps (RBPs), which may be due to VDPs providing greater ventricular unloading and coronary artery flow. To compare ventricular unloading and coronary flow of VDPs and RBPs in a repeatable environment, a physiologic coronary circulation was added to a pre-existing mock circulatory loop. In this study, a physiologic coronary circulation, mimicking a healthy or diseased auto-regulatory response was implemented in a mock circulatory loop. Using the mock circulation loop, a VDP with original (Björk-Shiley) and then replacement (jellyfish) valves was operated in clinically recommended modes and compared to full and partial assist RBP operating at constant speed and rapid speed modulated modes. The Björk-Shiley VDP resulted in increased pressure-volume area, which resulted in greater coronary artery flow when compared to the improved jellyfish valves. Full assist RBP support reduced left ventricular stroke work, pressure-volume area and coronary flow compared to partial assist, whilst the effect of speed modulation modes was not as significant. Of all LVAD operating modes, the counter-pulsed VDP with jellyfish valves demonstrated the greatest reduction in pressure-volume area and improved coronary flow. This study provides a basis for further investigation into RBP speed modulation profiles to match the improved haemodynamic performance of VDPs.

Shear stress and blood trauma under constant and pulse-modulated speed CF-VAD operations: CFD analysis of the HVAD

Modulation of pump speed has been proposed and implemented clinically to improve vascular pulsatility in continuous flow ventricular assist device patient. The flow dynamics of the HVAD with a promising asynchronous pump speed modulation and its potential risk for device-induced blood trauma was investigated numerically. The boundary conditions at the pump inlet and outlet were defined using the pressure waveforms adapted from the experimentally recorded ventricular and arterial pressure waveforms in a large animal ischemic heart failure (IHF) model supported by the HVAD operated at constant and modulated pump speeds. Shear stress fields and hemolysis indices were derived from the simulated flow fields. The overall features of the computationally generated flow waveforms at simulated constant and pulse-modulated speed operations matched with those of the experimentally recorded flow waveforms. The simulations showed that the shear stress field and hemolysis index vary throughout the cardiac cycle under the constant speed operation, and also as a function of modulation profile under modulated speed operation. The computational model did not demonstrate any differences in the time average hemolysis index between constant and modulated pump speed operations, thereby predicting pulse-modulated speed operation may help to restore vascular pulsatility without any further increased risk of blood trauma. Graphical abstract The streamline inside the HVAD pump and the wall shear stress distribution on the impeller surface at six discrete time instants over one cardiac cycle under constant speed operation (3000 rpm) (a) and under pulse-modulated speed operation (b). c Computationally predicted flow rate waveform under pulse-modulated speed operation. d Computationally predicted time-varying HI generated by the HVAD pump under the two operation modes constant speed (dash line) and pulse-modulated speed (solid line). These figures indicate that the pulse-modulated speed operation may help to restore vascular pulsatility without any further increased risk of blood trauma.

Living Without a Pulse: The Vascular Implications of Continuous-Flow Left Ventricular Assist Devices

Pulsatility seems to have a teleological role because evolutionary hierarchy favors higher ordered animals with more complex, multichamber circulatory systems that generate higher pulse pressure compared with lower ordered animals. Yet despite years of such natural selection, the modern generation of continuous-flow left ventricular assist devices (CF-LVADs) that have been increasingly used for the last decade have created a unique physiology characterized by a nonpulsatile, nonlaminar blood flow profile with the absence of the usual large elastic artery Windkessel effect during diastole. Although outcomes and durability have improved with CF-LVADs, patients supported with CF-LVADs have a high rate of complications that were not as frequently observed with older pulsatile devices, including gastrointestinal bleeding from arteriovenous malformations, pump thrombosis, and stroke. Given the apparent fundamental biological role of the pulse, the purpose of this review is to describe the normal physiology of ventricular-arterial coupling from pulsatile flow, the effects of heart failure on this physiology and the vasculature, and to examine the effects of nonpulsatile blood flow on the vascular system and potential role in complications seen with CF-LVAD therapy. Understanding these concomitant vascular changes with CF-LVADs may be a key step in improving patient outcomes as modulation of pulsatility and flow characteristics may serve as a novel, yet simple, therapy for reducing complications.

High-frequency operation of a pulsatile VAD - a simulation study

Ventricular assist devices (VADs) are mechanical blood pumps that are clinically used to treat severe heart failure. Pulsatile VADs (pVADs) were initially used, but are today in most cases replaced by turbodynamic VADs (tVADs). The major concern with the pVADs is their size, which prohibits full pump body implantation for a majority of patients. A reduction of the necessary stroke volume can be achieved by increasing the stroke frequency, while maintaining the same level of support capability. This reduction in stroke volume in turn offers the possibility to reduce the pump's overall dimensions. We simulated a human cardiovascular system (CVS) supported by a pVAD with three different stroke rates that were equal, two- or threefold the heart rate (HR). The pVAD was additionally synchronized to the HR for better control over the hemodynamics and the ventricular unloading. The simulation results with a HR of 90 bpm showed that a pVAD stroke volume can be reduced by 71%, while maintaining an aortic pulse pressure (PP) of 30 mm Hg, avoiding suction events, reducing the ventricular stroke work (SW) and allowing the aortic valve to open. A reduction by 67% offers the additional possibility to tune the interaction between the pVAD and the CVS. These findings allow a major reduction of the pVAD's body size, while allowing the physician to tune the pVAD according to the patient's needs.

Myocardial Recovery in Patients Receiving Contemporary Left Ventricular Assist Devices: Results From the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS)

BACKGROUND

Time course and predictors of myocardial recovery on contemporary left ventricular assist device support are poorly defined because of limited number of recovery patients at any implanting center. This study sought to investigate myocardial recovery using multicenter data from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS).

METHODS AND RESULTS

Thirteen thousand four hundred fifty-four adult patients were studied. Device explant rates for myocardial recovery were 0.9% at 1-year, 1.9% at 2-year, and 3.1% at 3-year follow-up. Independent predictors of device explantation for recovery were age <50 years (odds ratio [OR] 2.5), nonischemic etiology (OR 5.4), time since initial diagnosis <2 years (OR 3.4), suboptimal heart failure therapy before implant (OR 2.2), left ventricular end-diastolic diameter <6.5 cm (OR 1.7), pulmonary systolic artery pressure <50 mm Hg (OR 2.0), blood urea nitrogen <30 mg/dL (OR 3.3), and axial-flow device (OR 7.6). Patients with myocarditis (7.7%), postpartum cardiomyopathy (4.4%), and adriamycin-induced cardiomyopathy (4.1%) had highest rates of device explantation for recovery. Use of neurohormonal blockers on left ventricular assist device support was significantly higher in patients who were explanted for recovery. Importantly, 9% of all left ventricular assist device patients who were not explanted for recovery have demonstrated substantial improvement in left ventricular ejection fraction (partial recovery) and had remarkable overlap in clinical characteristic profile compared with patients who were explanted for recovery (complete recovery). Complete and partial recovery rates have declined in parallel with recent changes observed in device indications and technology.

CONCLUSIONS

Myocardial recovery is a spectrum of improvement rather than a binary clinical end point. One in every 10 left ventricular assist device patients demonstrates partial or complete myocardial recovery and should be targeted for functional assessment and optimization.

Papillary muscle rupture after myocardial infarction during left ventricular assist device support

We report a rare case of papillary muscle rupture due to myocardial infarction during left ventricular assist device support. A 69-year-old woman with cardiogenic shock due to acute myocardial infarction requiring venoarterial extracorporeal membrane oxygenation support was transferred for further surgical intervention. Six days after the event, extracorporeal membrane oxygenation was decannulated, and an extracorporeal left ventricular assist device was implanted. On postoperative day 11, she suffered from sudden onset hypoxia due to pulmonary edema. Transesophageal echocardiography showed new onset severe mitral regurgitation. No further surgical intervention was performed according to the family's wishes, and she passed away on the 22nd postoperative day. Autopsy findings revealed papillary muscle rupture. Although the left ventricle is unloaded by the left ventricular assist device, papillary muscle rupture should be recognized as a possible complication after myocardial infarction.

Left ventricular assist device-induced reverse remodeling: it's not just about myocardial recovery

INTRODUCTION

The abnormal structure, function and molecular makeup of dilated cardiomyopathic hearts can be partially normalized in patients supported by a left ventricular assist device (LVAD), a process called reverse remodeling. This leads to recovery of function in many patients, though the rate of full recovery is low and in many cases is temporary, leading to the concept of heart failure remission, rather than recovery. Areas covered: We summarize data indicative of ventricular reverse remodeling, recovery and remission during LVAD support. These terms were used in searches performed in Pubmed. Duplication of topics covered in depth in prior review articles were avoided. Expert commentary: Although most patients undergoing mechanical circulatory support (MCS) show a significant degree of reverse remodeling, very few exhibit sufficiently improved function to justify device explantation, and many from whom LVADs have been explanted have relapsed back to the original heart failure phenotype. Future research has the potential to clarify the ideal combination of pharmacological, cell, gene, and mechanical therapies that would maximize recovery of function which has the potential to improve exercise tolerance of patients while on support, and to achieve a higher degree of myocardial recovery that is more likely to persist after device removal.

Mechanical Circulatory Support for Advanced Heart Failure: Are We about to Witness a New "Gold Standard"?

The impact of left ventricular assist devices (LVADs) for the treatment of advanced heart failure has played a significant role as a bridge to transplant and more recently as a long-term solution for non-eligible candidates. Continuous flow left ventricular assist devices (CF-LVADs), based on axial and centrifugal design, are currently the most popular devices in view of their smaller size, increased reliability and higher durability compared to pulsatile flow left ventricular assist devices (PF-LVADs). The trend towards their use is increasing. Therefore, it has become mandatory to understand the physics and the mathematics behind their mode of operation for appropriate device selection and simulation set up. For this purpose, this review covers some of these aspects. Although very successful and technologically advanced, they have been associated with complications such as pump thrombosis, haemolysis, aortic regurgitation, gastro-intestinal bleeding and arterio-venous malformations. There is perception that the reduced arterial pulsatility may be responsible for these complications. A flow modulation control approach is currently being investigated in order to generate pulsatility in rotary blood pumps. Thrombus formation remains the most feared complication that can affect clinical outcome. The development of a preoperative strategy aimed at the reduction of complications and patient-device suitability may be appropriate. Patient-specific modelling based on 3D reconstruction from CT-scan combined with computational fluid dynamic studies is an attractive solution in order to identify potential areas of stagnation or challenging anatomy that could be addressed to achieve the desired outcome. The HeartMate II (axial) and the HeartWare HVAD (centrifugal) rotary blood pumps have been now used worldwide with proven outcome. The HeartMate III (centrifugal) is now emerging as the new promising device with encouraging preliminary results. There are now enough pumps on the market: it is time to focus on the complications in order to achieve the full potential and selling-point of this type of technology for the treatment of the increasing heart failure patient population.

Current status of the implantable LVAD

With the ongoing shortage of available organs for heart transplantation, mechanical circulatory support devices have been increasingly utilized for managing acute and chronic heart failure that is refractory to medical therapy. In particular, the introduction of the left ventricular assist devices (LVAD) has revolutionized the field. In this review, we will discuss a brief history of the LVAD, available devices, current indications, patient selection, complications, and outcomes. In addition, we will discuss recent outcomes and advancements in the field of noncardiac surgery in the LVAD patient. Finally, we will discuss several topics for surgical consideration during LVAD implantation.

Physiologic effects of continuous-flow left ventricular assist devices

BACKGROUND

Within the past 10 years, continuous-flow left ventricular assist devices (LVADs) have replaced pulsatile-flow LVADs as the standard of care for both destination therapy and bridging patients to heart transplantation. Despite the rapid clinical adoption of continuous-flow LVADs, an understanding of the effects of continuous-flow physiology, as opposed to more natural pulsatile-flow physiology, is still evolving.

MATERIALS AND METHODS

A thorough review of the relevant scientific literature regarding the physiological and clinical effects of continuous-flow physiology was performed. These effects were analyzed on an organ system basis and include an evaluation of the cardiovascular, respiratory, hematologic, gastrointestinal, renal, hepatic, neurologic, immunologic, and endocrine systems.

RESULTS

Continuous-flow physiology is, generally speaking, well tolerated over the long term. However, several changes are manifest at the organ system level. Although many of these changes are without appreciable clinical significance, other changes, such as an increased rate of gastrointestinal bleeding, appear to be associated with continuous-flow physiology.

CONCLUSIONS

Continuous-flow LVADs confer a significant advantage over their pulsatile-flow counterparts with regard to size and durability. From a physiological standpoint, continuous-flow physiology has limited clinical effects at the organ system level. Although improved over previous generations, challenges with this technology remain. Approaching these problems with a combination of clinical and engineering solutions may be needed to achieve continued progression in the field of durable mechanical circulatory support.

MicroRNA Expression in Myocardial Tissue and Plasma of Patients with End-Stage Heart Failure during LVAD Support: Comparison of Continuous and Pulsatile Devices

Aim

Pulsatile flow left ventricular assist devices (pf-LVADs) are being replaced by continuous flow LVADs (cf-LVADs) in patients with end-stage heart failure (HF). MicroRNAs (miRs) play an important role in the onset and progression of HF. Our aim was to analyze cardiac miR expression patterns associated with each type of device, to analyze differences in the regulation of the induced cardiac changes.

Methods and Results

Twenty-six miRs were selected (based on micro-array data and literature studies) and validated in myocardial tissue before and after pf- (n = 17) and cf-LVAD (n = 17) support. Of these, 5 miRs displayed a similar expression pattern among the devices (miR-129*, miR-146a, miR-155, miR-221, miR-222), whereas others only changed significantly during pf-LVAD (miR-let-7i, miR-21, miR-378, miR-378*) or cf-LVAD support (miR-137). In addition, 4 miRs were investigated in plasma of cf-LVAD supported patients (n = 18) and healthy controls (n = 10). Circulating miR-21 decreased at 1, 3, and 6 months after LVAD implantation. MiR-146a, miR-221 and miR-222 showed a fluctuating time pattern post-LVAD.

Conclusion

Our data show a different miR expression pattern after LVAD support, suggesting that differentially expressed miRs are partially responsible for the cardiac morphological and functional changes observed after support. However, the miR expression patterns do not seem to significantly differ between pf- and cf-LVAD implying that most cardiac changes or clinical outcomes specific to each device do not relate to differences in miR expression levels.

Review of recent results using computational fluid dynamics simulations in patients receiving mechanical assist devices for end-stage heart failure

Many end-stage heart failure patients are not eligible to undergo heart transplantation due to organ shortage, and even those under consideration for transplantation might suffer long waiting periods. A better understanding of the hemodynamic impact of left ventricular assist devices (LVAD) on the cardiovascular system is therefore of great interest. Computational fluid dynamics (CFD) simulations give the opportunity to study the hemodynamics in this patient population using clinical imaging data such as computed tomographic angiography. This article reviews a recent study series involving patients with pulsatile and constant-flow LVAD devices in which CFD simulations were used to qualitatively and quantitatively assess blood flow dynamics in the thoracic aorta, demonstrating its potential to enhance the information available from medical imaging.