Less frequent opening of the aortic valve and a continuous flow pump are risk factors for postoperative onset of aortic insufficiency in patients with a left ventricular assist device

Management of aortic valve insufficiency in patients with continuous-flow left ventricular assist device: a republication of the review published in Japanese Journal of Artificial Organs

Since 2011, implantable ventricular assist devices have been a standard treatment for severe heart failure alongside heart transplantation in Japan. However, the limited availability of donors has led to a prolonged wait for transplants, now averaging 1719 days, intensifying the issue of aortic insufficiency in patients with continuous flow ventricular assist devices. These devices limit the opening of the aortic valve, leading to sustained closure and increased shear stress, which accelerates valve degradation. Risk factors for aortic insufficiency include having a smaller body surface area, being of advanced age, and the presence of mild aortic insufficiency prior to device implantation. In patients presenting with mild or moderate aortic regurgitation at the time of ventricular assist device implantation, interventions such as aortic valve repair or bioprosthetic valve replacement are performed with the aim of halting its progression. The choice of surgical procedure should be tailored to each patient's individual condition. The management of de novo aortic insufficiency in patients with continuous flow ventricular assist devices remains challenging, with no clear consensus on when to intervene. Interventions for significant aortic insufficiency typically consider the patient's symptoms and aortic insufficiency severity. De novo aortic insufficiency progression in continuous flow ventricular assist devices patients necessitates careful monitoring and intervention based on individual patient assessments and valve condition. This review was created based on a translation of the Japanese review written in the Japanese Journal of Artificial Organs in 2023 (Vol. 52, No. 1, pp. 77-80), with some modifications.

The Impact of Left Ventricular Assist Device Outflow Graft Positioning on Aortic Hemodynamics: Improving Flow Dynamics to Mitigate Aortic Insufficiency

Heart failure is a global health concern with significant implications for healthcare systems. Left ventricular assist devices (LVADs) provide mechanical support for patients with severe heart failure. However, the placement of the LVAD outflow graft within the aorta has substantial implications for hemodynamics and can lead to aortic insufficiency during long-term support. This study employs computational fluid dynamics (CFD) simulations to investigate the impact of different LVAD outflow graft locations on aortic hemodynamics. The introduction of valve morphology within the aorta geometry allows for a more detailed analysis of hemodynamics at the aortic root. The results demonstrate that the formation of vortex rings and subsequent vortices during the high-velocity jet flow from the graft interacted with the aortic wall. Time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) indicate that modification of the outflow graft location changes mechanical states within the aortic wall and aortic valve. Among the studied geometric factors, both the height and inclination angle of the LVAD outflow graft are important in controlling retrograde flow to the aortic root, while the azimuthal angle primarily determines the rotational direction of blood flow in the aortic arch. Thus, precise positioning of the LVAD outflow graft emerges as a critical factor in optimizing patient outcomes by improving the hemodynamic environment.

Mechanical circulatory support for adults in Japan: A 10-year perspective

Globalization in Asia and consequent strengthening of healthcare economic factors in tandem with an increasing heart failure (HF) population have enhanced potential for development and progress in the fields of HF medicine and mechanical circulatory support (MCS). In Japan, there are unique opportunities to investigate the outcome of acute and chronic MCS and a national registry for percutaneous and implantable left ventricular assist device (LVAD) including Impella pumps has been established. A Peripheral extracorporeal membrane oxygenation (ECMO) for acute MCS has been used in more than 7000 patients annually and Impella usage in more than 4000 patients over the past 4 years was noted. Recently, a novel centrifugal pump with hydrodynamically levitated impeller was developed and approved for mid-term extracorporeal circulatory support. In terms of chronic MCS more than 1200 continuous flow LVADs have been implanted during the past decade, and 2-year survival rate after primary LVAD implantation is 91%. Because of donor organ shortage, more than 70% of heart transplant recipients required LVAD support for more than 3 years and prevention and treatment of complications during long-term LVAD support have become important. Five important topics including hemocompatibility-related complications, LVAD infections, aortic valve insufficiency, right ventricular failure and cardiac recovery during LVAD support are discussed in this review for improving clinical outcomes. Findings from Japan will continue to provide useful information regarding MCS for the Asia-Pacific region and beyond.

Reciprocal interferences of the left ventricular assist device and the aortic valve competence

Patients suffering from end-stage heart failure tend to have high mortality rates. With growing numbers of patients progressing into severe heart failure, the shortage of available donors is a growing concern, with less than 10% of patients undergoing cardiac transplantation (CTx). Fortunately, the use of left ventricular assist devices (LVADs), a variant of mechanical circulatory support has been on the rise in recent years. The expansion of LVADs has led them to be incorporated into a variety of clinical settings, based on the goals of therapy for patients ailing from heart failure. However, with an increase in the use of LVADs, there are a host of complications that arise with it. One such complication is the development and progression of aortic regurgitation (AR) which is noted to adversely influence patient outcomes and compromise pump benefits leading to increased morbidity and mortality. The underlying mechanisms are likely multifactorial and involve the aortic root-aortic valve (AV) complex, as well as the LVAD device, patient, and other factors, all of them alter the physiological mechanics of the heart resulting in AV dysfunction. Thus, it is imperative to screen patients before LVAD implantation for AR, as moderate or greater AR requires a concurrent intervention at the time of LVADs implantation. No current strict guidelines were identified in the literature search on how to actively manage and limit the development and/or progression of AR, due to the limited information. However, some recommendations include medical management by targeting fluid overload and arterial blood pressure, along with adjusting the settings of the LVADs device itself. Surgical interventions are to be considered depending on patient factors, goals of care, and the underlying pathology. These interventions include the closure of the AV, replacement of the valve, and percutaneous approach via percutaneous occluding device or transcatheter aortic valve implantation. In the present review, we describe the interaction between AV and LVAD placement, in terms of patient management and prognosis. Also it is provided a comprehensive echocardiographic strategy for the precise assessment of AV regurgitation severity.

Hemodynamic Effect of Pulsatile on Blood Flow Distribution with VA ECMO: A Numerical Study

The pulsatile properties of arterial flow and pressure have been thought to be important. Nevertheless, a gap still exists in the hemodynamic effect of pulsatile flow in improving blood flow distribution of veno-arterial extracorporeal membrane oxygenation (VA ECMO) supported by the circulatory system. The finite-element models, consisting of the aorta, VA ECMO, and intra-aortic balloon pump (IABP) are proposed for fluid-structure interaction calculation of the mechanical response. Group A is cardiogenic shock with 1.5 L/min of cardiac output. Group B is cardiogenic shock with VA ECMO. Group C is added to IABP based on Group B. The sum of the blood flow of cardiac output and VA ECMO remains constant at 4.5 L/min in Group B and Group C. With the recovery of the left ventricular, the flow of VA ECMO declines, and the effective blood of IABP increases. IABP plays the function of balancing blood flow between left arteria femoralis and right arteria femoralis compared with VA ECMO only. The difference of the equivalent energy pressure (dEEP) is crossed at 2.0 L/min to 1.5 L/min of VA ECMO. PPI’ (the revised pulse pressure index) with IABP is twice as much as without IABP. The intersection with two opposing blood generates the region of the aortic arch for the VA ECMO (Group B). In contrast to the VA ECMO, the blood intersection appears from the descending aorta to the renal artery with VA ECMO and IABP. The maximum time-averaged wall shear stress (TAWSS) of the renal artery is a significant difference with or not IABP (VA ECMO: 2.02 vs. 1.98 vs. 2.37 vs. 2.61 vs. 2.86 Pa; VA ECMO and IABP: 8.02 vs. 6.99 vs. 6.62 vs. 6.30 vs. 5.83 Pa). In conclusion, with the recovery of the left ventricle, the flow of VA ECMO declines and the effective blood of IABP increases. The difference between the equivalent energy pressure (EEP) and the surplus hemodynamic energy (SHE) indicates the loss of pulsation from the left ventricular to VA ECMO. 2.0 L/min to 1.5 L/min of VA ECMO showing a similar hemodynamic energy loss with the weak influence of IABP.

Predictors and Long-Term Impact of De Novo Aortic Regurgitation in Continuous Flow Left Ventricular Assist Devices Using Vena Contracta

The aim of this study was to identify the optimal echocardiographic measurement of aortic regurgitation (AR) in continuous flow left ventricular assist devices (LVAD) and determine risk factors and clinical implications of de novo AR. Echocardiographic images from consecutive patients who underwent LVAD implantation from February 2007 to March 2017 were reviewed. Severity of de novo AR was determined by vena contracta (VC). Preimplant clinical characteristics, LVAD settings at discharge, and outcomes including heart failure hospitalizations, all-cause mortality, and ventricular arrhythmias of patients with greater than or equal to moderate de novo AR were compared with those with mild or no AR. Among 219 patients, greater than or equal to moderate de novo AR occurred in 65 (29.7%). Left ventricular assist devices support duration was longer with greater than or equal to moderate AR than no or mild AR. In multivariable analysis, preimplant trivial AR and persistent aortic valve (AV) closure were independently associated with de novo AR. By time-varying covariate analysis, survival and freedom from cardiovascular events in greater than or equal to moderate AR were significantly worse (hazard ratio [HR] = 3.947, p < 0.001 and HR = 4.666, p < 0.001). In conclusion, de novo greater than or equal to moderate AR measured by VC increases risk of adverse events. Longer LVAD support duration, preimplant trivial AR, and a closed AV are associated with occurrence of greater than or equal to moderate de novo AR.

Can the intermittent low-speed function of left ventricular assist device prevent aortic insufficiency?

Aortic insufficiency (AI) is known to associate with a persistently closed aortic valve during continuous-flow ventricular assist device support. Some devices carry an intermittent low-speed (ILS) function, which facilitates aortic valve opening, but whether this function prevents AI is unknown. In this study, the Jarvik 2000 device, which is programmed to reduce the pump speed each minute for 8 s, was chosen to examine this potential effect. Prospectively collected data of 85 heart transplant-eligible Jarvik 2000 recipients who met the study criteria (no pre-existing AI and aortic valve surgery) were retrospectively analyzed for the incidence, correlating factors, and clinical outcomes of de novo AI. All data were provided by the Japanese Registry for Mechanically Assisted Circulatory Support. De novo AI occurred in 58 patients, 23 of whom developed at least moderate AI during a median support duration of 23.5 months. Freedom from moderate or greater AI was 84.4%, 66.1% and 60.2% at 1, 2 and 3 years, respectively. Multivariate analyses revealed that progressive AI was correlated with decreased pulse pressure after implantation (hazard ratio 1.060, 95% confidence interval 1.001–1.127, p = 0.045). No correlation was found for mortality or other adverse events, including stroke, bleeding, infection, pump failure, hemolysis, and readmission. The benefit of the Jarvik 2000′s current ILS mode against AI appears to be minimal. However, in this limited cohort where all recipients underwent implantation as a bridge to transplantation, the impact of de novo progressive AI on other clinical adversities was also minimal.

Biomechanical effects of the novel series LVAD on the aortic valve

BACKGROUND AND OBJECTIVE

The series type of LVAD (i.e., BJUT-II VAD) is a novel left ventricular assist device, whose effects on the aortic valve remain unclear.

METHODS

The biomechanical effects of BJUT-II VAD on the aortic valve were investigated by using a fluid-structure interaction method. The geometric model of BJUT-II VAD was virtually implanted into the ascending aorta to generate the realistic flow pattern for the aortic valve (i.e., support). In addition, the biomechanical states of the aortic valve without BJUT-II VAD support was computed as control (i.e., control case).

RESULTS

Results demonstrated that the biomechanical effects of BJUT-II VAD were quite different from that resulting from traditional "bypass LVAD." Compared with those in the control case, BJUT-II VAD support could significantly reduce the stress load of the leaflet (maximum stress, 0.5 MPa in the control case vs. 0.12 MPa in the support case). Similarly, the rapid valve opening time (100 ms in the control case vs. 175 ms in the support case) and rapid valve closing time (50 ms in the control case vs. 150 ms in the support case) in the support case were obviously longer than those in the control case. Moreover, BJUT-II VAD support reduced retrograde blood flow during the diastolic phase and significantly changed the distribution of WSS of the leaflets.

CONCLUSIONS

In summary, while unloading the left ventricle, BJUT-II VAD could provide beneficial biomechanical states for the aortic leaflets, thereby reducing the risk of aortic valve disease.

Biomechanical effects of the working modes of LVADs on the aortic valve: A primary numerical study

Aortic valve diseases caused by the support from left ventricular assist devices (LVADs) have attracted increasing attention due to the wide application of the LVADs. However, the biomechanical effects of the working modes of LVADs on the aortic valve are still poorly understood. Hence, in this study, these biomechanical effects are investigated using a novel fluid-structure interaction method, which combines the lattice Boltzmann and the finite element methods. On the basis of the clinical practice, three working modes of LVADs, namely, the constant flow, co-pulse, and counter pulse modes, are chosen. Results demonstrate that the working mode of LVADs is an important factor as it can change the biomechanical states of the aortic valve and the hemodynamic environment in the aortic root directly. Compared with the constant flow mode, the two other working modes can provide better biomechanical effects on the aortic valve. However, the advantages of the co-pulse and the counter pulse modes on the aortic valve are not the same. The LVADs in the co-pulse mode can remarkable reduce the pressure load of the leaflets during the diastolic phase (maximum stress: co-pulse mode, 0.85 MPa; constant flow mode, 1.23 MPa; counter pulse mode, 1.50 MPa). By contrast, the LVADs in the counter pulse mode can achieve the highest effective orifice area of the aortic valve (co-pulse mode: 0.12 cm², constant flow mode: 0.17 cm², counter pulse mode: 0.25 cm²). In sum, the co-pulse mode is suitable for patients with certain cardiac function, because this mode keeps the valve open intermittently and reduces the pressure load on the aortic leaflets during the diastolic phase to prevent valve remodeling. By contrast, the counter pulse mode is suitable for patients with severely impaired cardiac function, because this mode keeps the valve open as much as possible and provides high blood perfusion.

Ultrasound-based estimation of remaining cardiac function in LVAD-supported ex vivo hearts

Left ventricular assist devices (LVAD) provide cardiac support to patients with advanced heart failure. Methods that can directly measure remaining LV function following device implantation do not currently exist. Previous studies have shown that a combination of loading (LV pressure) and deformation (strain) measurements enables quantitation of myocardial work. We investigated the use of ultrasound (US) strain imaging and pressure–strain loop analysis in LVAD‐supported hearts under different hemodynamic and pump unloading conditions, with the aim of determining LV function with and without LVAD support. Ex vivo porcine hearts (n = 4) were implanted with LVADs and attached to a mock circulatory loop. Measurements were performed at hemodynamically defined “heart conditions” as the hearts deteriorated from baseline. Hemodynamic (including LV pressure) and radio‐frequency US data were acquired during a pump‐ramp protocol at speeds from 0 (with no pump outflow) to 10 000 revolutions per minute (rpm). Regional circumferential (ε_circ) and radial (ε_rad) strains were estimated over each heart cycle. Regional ventricular dyssynchrony was quantitated through time‐to‐peak strain. Mean change in LV pulse pressure and ε_circ between 0 and 10 krpm were −21.8 mm Hg and −7.24% in the first condition; in the final condition −46.8 mm Hg and −19.2%, respectively. ε_rad was not indicative of changes in pump speed or heart condition. Pressure–strain loops showed a degradation in the LV function and an increased influence of LV unloading: loop area reduced by 90% between 0 krpm in the first heart condition and 10 krpm in the last condition. High pump speeds and degraded condition led to increased dyssynchrony between the septal and lateral LV walls. Functional measurement of the LV while undergoing LVAD support is possible by using US strain imaging and pressure–strain loops. This can provide important information about remaining pump function. Use of novel LV pressure estimation or measurement techniques would be required for any future use in LVAD patients.

Hemodynamic effects of support modes of LVADs on the aortic valve

As the alternative treatment for heart failure, left ventricular assist devices (LVADs) have been widely applied to clinical practice. However, the effects of the support modes of LVADs on the biomechanical states of the aortic valve are still poorly understood. Hence, the present study investigates such effects and proposes a novel fluid-structure interaction (FSI) approach that combines the lattice Boltzmann method (LBM) and finite element (FE) method. Two support modes of LVADs, namely constant speed mode and constant flow mode, which have been widely applied to clinical practice, are also designed. Results demonstrate that the support modes of LVADs could significantly affect the biomechanical states of the aortic valve and the blood flow pattern of the ascending aorta. Compared with those in the constant flow mode, the leaflets in the constant speed mode could achieve better dynamic performance and lower stress during the systolic phase. The max radial displacement of the leaflets in the constant speed mode is at 8 mm, whereas that in the constant flow mode is at 0.8 mm. Furthermore, the outflow of LVADs directly impacts the aortic surfaces of the leaflets during the diastolic phase by increasing the level of wall shear stress of the leaflets. The leaflets in the constant speed mode receive less impact than those in the constant flow mode. The condition with such minimal impact is conducive to maintaining the normal structure of leaflets and benefits the reduction of the risk of valvular diseases. In sum, the support modes of LVADs exert a crucial effect on the biomechanical environment of the aortic valve. The constant speed mode is better than the constant flow mode in terms of providing a good hemodynamic environment for the aortic valve.

Left ventricular assist devices and their complications: A review for emergency clinicians

INTRODUCTION

End stage heart failure is associated with high mortality. However, recent developments such as the ventricular assist device (VAD) have improved patient outcomes, with left ventricular assist devices (LVAD) most commonly implanted.

OBJECTIVE

This narrative review evaluates LVAD epidemiology, indications, normal function and components, and the assessment and management of complications in the emergency department (ED).

DISCUSSION

The LVAD is a life-saving device in patients with severe heart failure. While first generation devices provided pulsatile flow, current LVAD devices produce continuous flow. Normal components include the pump, inflow and outflow cannulas, driveline, and external controller. Complications related to the LVAD can be divided into those that are LVAD-specific and LVAD-associated, and many of these complications can result in severe patient morbidity and mortality. LVAD-specific complications include device malfunction/failure, pump thrombosis, and suction event, while LVAD-associated complications include bleeding, cerebrovascular event, infection, right ventricular failure, dysrhythmia, and aortic regurgitation. Assessment of LVAD function, patient perfusion, and mean arterial pressure is needed upon presentation. Electrocardiogram and bedside ultrasound are key evaluations in the ED. LVAD evaluation and management require a team-based approach, and consultation with the LVAD specialist is recommended.

CONCLUSION

Emergency clinician knowledge of LVAD function, components, and complications is integral in optimizing care of these patients.

In Vitro Hemodynamic Evaluation of ECG-Synchronized Pulsatile Flow Using i-Cor Pump as Short-Term Cardiac Assist Device for Neonatal and Pediatric Population

The objective of this study was to assess the hemodynamic properties of the i-cor ECG-synchronized cardiac assist system for off-label use as a short-term cardiac assist device for neonatal and pediatric patients and compare nonpulsatile to pulsatile flow with different amplitudes. The circuit consisted of the i-cor diagonal pump with 3 feet of ¼ inch arterial and venous tubing and a soft-shell reservoir, primed with lactated Ringer's solution and human packed red blood cells (hematocrit 42%). Trials were conducted with three different sets of cannulas (8-Fr arterial 10-Fr venous, 10-Fr arterial 12 Fr-venous, and 12-Fr arterial 14-Fr venous) with increasing flow rates at varying pseudo-patient pressures (40, 60, 80, and 100 mm Hg) and under nonpulsatile mode and pulsatile mode with pulsatile amplitudes 2000, 2500, and 3000 rpm at 36°C. Pressure and flow waveforms were recorded using a custom-made data acquisition device for each trial. Energy equivalent pressure (EEP) was higher than mean pressure under pulsatile mode, and increased with increasing pseudo-patient's pressure and flow rate while EEP was the same as the mean pressure under nonpulsatile mode. Total hemodynamic energy (THE) levels increased with pressure and pulsatile amplitude and slightly decreased with increasing flow rate. The percent THE lost throughout the circuit increased with flow rate and pulsatile amplitude and decreased with pseudo-patient's pressure. SHE levels also increased with pseudo-patient pressure and pulsatile amplitude and decreased with increasing flow rate. The i-cor diagonal pump can be used as a short term cardiac assist device for neonatal and pediatric patients and is able to provide nonpulsatile as well as pulsatile flow. Compared with nonpulsatile flow, pulsatile flow can generate and deliver more hemodynamic energy to the patients.

In Vitro Evaluation of ECG-Synchronized Pulsatile Flow Using the i-cor Diagonal Pump in Neonatal and Pediatric ECLS Systems

The objective was to assess the i-cor electrocardiogram-synchronized diagonal pump in terms of hemodynamic energy properties for off-label use in neonatal and pediatric extracorporeal life support (ECLS) circuits. The neonatal circuit consisted of an i-cor pump and console, a Medos Hilite 800 LT oxygenator, an 8Fr arterial cannula, a 10Fr venous cannula, 91 cm of 0.6-cm ID arterial tubing, and 91 cm of 0.6-cm ID venous tubing. The pediatric circuit was identical except it included a 12Fr arterial cannula, a 14Fr venous cannula, and a Medos Hilite 2400 LT oxygenator. Neonatal trials were conducted at 36°C with hematocrit 40% using varying flow rates (200-600 mL/min, 200 mL increments) and postarterial cannula pressures (40-100 mm Hg, 20 mm Hg increments) under nonpulsatile mode and pulsatile mode with various pulsatile amplitudes (1000-4000 rpm, 1000 rpm increments). Pediatric trials were conducted at different flow rates (800-1600 mL/min, 400 mL/min increments). Mean pressure and energy equivalent pressure increased with increasing postarterial cannula pressure, flow rate, and pulsatile amplitude. Physiologic-like pulsatility was achieved between pulsatile amplitudes of 2000-3000 rpm. Pressure drops were greatest across the arterial cannula. Pulsatile flow generated significantly higher total hemodynamic energy (THE) levels than nonpulsatile flow. THE levels at postarterial cannula site increased with increasing postarterial cannula pressure, pulsatile amplitude, and flow rate. No surplus hemodynamic energy (SHE) was generated under nonpulsatile mode. Under pulsatile mode, preoxygenator SHE increased with increasing postarterial cannula pressure and pulsatile amplitude, but decreased with increasing flow rate. The i-cor system can provide nonpulsatile and pulsatile flow for neonatal and pediatric ECLS. Pulsatile amplitudes of 2000-3000 rpm are recommended for use in neonatal and pediatric patients.

Outflow graft anastomosis site design could be correlated to aortic valve regurgitation under left ventricular assist device support

Aortic valve regurgitation (AR) is a critical complication during circulatory support with a left ventricular assist device (LVAD). The time-course of AR and related factors, including outflow graft anastomosis site design, were investigated. Twenty-three patients who had continuous-flow LVAD implantation and were supported for more than 6 months were investigated. AR grade (none, 0; trivial, 0.5; mild, 1; mild-moderate, 1.5; moderate, 2; moderate-severe, 2.5; severe, 3) and aortic valve opening were evaluated with echocardiography. Computed tomography was performed to all the patients postoperatively. The angle of the outflow graft to the aorta (O-A angle, parallel 0; tangent 90°, 0-180°), aortic diameter at the anastomosis site, sino-tubular junction (STJ) diameter, distance between the STJ and the anastomosis site, and distance between the anastomosis site and the brachiocephalic artery were measured. The patients' age was 38 ± 11 years. Support duration was 686 ± 354 days. Mean AR grade after continuous-flow LVAD implantation was increased to around mild and was maintained thereafter. No patient needed any intervention to the aortic valve. The aortic valves of 82.6% of patients were closed continuously. The O-A angle (83 ± 14) was positively correlated with maximum AR grade (p = 0.0095). The O-A angle was significantly smaller in patients with maximum AR grade of 1 or less (77 ± 9°) than in those with 1.5 or greater (94 ± 15°, p = 0.021). The other CT measurements had no correlation with AR grade. In conclusion, the O-A angle was correlated with AR grade progression. The O-A angle appears to be one of the important factors related to AR under continuous-flow LVAD support.

Physical Capacity in LVAD Patients: Hemodynamic Principles, Diagnostic Tools and Training Control

Over time left ventricular assist devices (LVAD) have become an alternative to heart transplantation because of enormous technical development and miniaturization. Most patients present a significant improvement in clinical conditions and exercise capacity. Nevertheless, exercise tolerance remains markedly limited even after LVAD implantation compared to a control group. The complex physiological and hemodynamic changes in LVAD patients, both at rest and during exercise, are not yet understood, or at least not completely.

It is the aim of the present paper to describe the current state of scientific knowledge. Furthermore, the spectrum of diagnostic tools, including the noninvasive inert gas rebreathing method for measurement of cardiac output and associate parameters, are discussed. Options for training control in this special patient group are presented.

Ventricular Assist Devices in Pediatric Cardiac Intensive Care

OBJECTIVES

The objectives of this review are to discuss the process of patient and mechanical device selection, operative management, and postoperative care with a focus on the management of right ventricular failure, anticoagulation strategies, device-related infections and neurologic sequelae.

DATA SOURCES

MEDLINE, PubMed.

CONCLUSION

The number of patients with advanced heart failure due to either acquired or congenital heart disease continues to increase, necessitating in some mechanical circulatory support and in others cardiac transplantation. With a limited cardiac donor pool, mechanical circulatory support is playing a greater role in the management of this population. The perioperative morbidity associated with mechanical circulatory support has lessened with improved postoperative management strategies.

Challenges faced in long term ventricular assist device support

INTRODUCTION

The development of ventricular assist device (VAD) has been one of the revolutionary advancements in end-stage heart failure management. Although the device has developed and improved significantly over the last few decades, we still face multiple challenges.

AREAS COVERED

This review will discuss quality of life, survival, and clinically encountered complications in patients with VAD support. The literature was extensively reviewed for studies describing the above topic area. We describe the impact of major challenges faced in VAD support and discuss their future and expectations. Expert commentary: The technological advancement of VADs has contributed to major improvement of overall survival, enhancement of quality of life and decrease of incidence of complications. It is expected that technologies will continue to evolve. At the same time, the indications for and timing of device implantation, and selection of device type are continuously important in clinical practice setting.

Aortic Valve Pathology in Patients Supported by Continuous-Flow Left Ventricular Assist Device

BACKGROUND

Continuous-flow left ventricular assist devices (CF-LVAD) may induce pathological changes to the aortic wall and aortic valve. We assessed histological changes in the relevant anatomic structures exposed to continuous flow over time and compared the histological results with clinical features in patients supported with CF-LVAD.

METHODS AND RESULTS

A retrospective histological analysis was performed of 38 explanted hearts supported with CF-LVAD from patients who received heart transplantation between July 2003 and February 2014. Sections of formalin-fixed paraffin-embedded tissue showing the continuity of aortic wall and left-sided valves were examined histologically. Thickness of aorta, aortic root and aortic valve as well as 3 layers of the aortic cusps were measured individually on Elastica van Gieson-stained slides using specific software. Clinical parameters concerning aortic valve dysfunction were evaluated and validated against the histology. The aortic valve spongiosa and fibrosa layers showed no significant differences in thickness with regard to support duration or occurrence of aortic insufficiency. Longer CF-LVAD support duration correlated with a thinner aortic valve ventricularis layer (rS=-0.496).

CONCLUSIONS

Long-term CF-LVAD support appears to cause involution of the ventricularis layer of the aortic valve cusp, consistent with more pronounced degenerative change with longer LVAD exposure, which may be explained by continuous coaptation of the cusps. (Circ J 2016; 80: 1371-1377).

[Rehabilitation standards for follow-up treatment and rehabilitation of patients with ventricular assist device (VAD)]

The increasing use of ventricular assist devices (VADs) in terminal heart failure patients provides new challenges to cardiac rehabilitation physicians. Structured cardiac rehabilitation strategies are still poorly implemented for this special patient group. Clear guidance and more evidence for optimal modalities are needed. Thereby, attention has to be paid to specific aspects, such as psychological and social support and education (e.g., device management, INR self-management, drive-line care, and medication).In Germany, the post-implant treatment and rehabilitation of VAD Patients working group was founded in 2012. This working group has developed clear recommendations for the rehabilitation of VAD patients according to the available literature. All facets of VAD patients' rehabilitation are covered. The present paper is unique in Europe and represents a milestone to overcome the heterogeneity of VAD patient rehabilitation.

Preservation of native aortic valve flow and full hemodynamic support with the TORVAD using a computational model of the cardiovascular system

This article describes the stroke volume selection and operational design for the toroidal ventricular assist device (TORVAD), a synchronous, positive-displacement ventricular assist device (VAD). A lumped parameter model was used to simulate hemodynamics with the TORVAD compared with those under continuous-flow VAD support. Results from the simulation demonstrated that a TORVAD with a 30 ml stroke volume ejecting with an early diastolic counterpulse provides comparable systemic support to the HeartMate II (HMII) (cardiac output 5.7 L/min up from 3.1 L/min in simulated heart failure). By taking the advantage of synchronous pulsatility, the TORVAD delivers full hemodynamic support with nearly half the VAD flow rate (2.7 L/min compared with 5.3 L/min for the HMII) by allowing the left ventricle to eject during systole and thus preserving native aortic valve flow (3.0 L/min compared with 0.4 L/min for the HMII, down from 3.1 L/min at baseline). The TORVAD also preserves pulse pressure (26.7 mm Hg compared with 12.8 mm Hg for the HMII, down from 29.1 mm Hg at baseline). Preservation of aortic valve flow with synchronous pulsatile support could reduce the high incidence of aortic insufficiency and valve cusp fusion reported in patients supported with continuous-flow VADs.

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.

Why pulsatility still matters: a review of current knowledge

Continuous-flow left ventricular assist devices (LVAD) have become standard therapy option for patients with advanced heart failure. They offer several advantages over previously used pulsatile-flow LVADs, including improved durability, less surgical trauma, higher energy efficiency, and lower thrombogenicity. These benefits translate into better survival, lower frequency of adverse events, improved quality of life, and higher functional capacity of patients. However, mounting evidence shows unanticipated consequences of continuous-flow support, such as acquired aortic valve insufficiency and acquired von Willebrand syndrome. In this review article we discuss current evidence on differences between continuous and pulsatile mechanical circulatory support, with a focus on clinical implications and potential benefits of pulsatile flow.

Investigation of hemodynamics in an in vitro system simulating left ventricular support through the right subclavian artery using 4-dimensional flow magnetic resonance imaging

OBJECTIVES

Left ventricular assist devices are an important treatment option for patients with heart failure alter the hemodynamics in the heart and great vessels. Because in vivo magnetic resonance studies of patients with ventricular assist devices are not possible, in vitro models represent an important tool to investigate flow alterations caused by these systems. By using an in vitro magnetic resonance-compatible model that mimics physiologic conditions as close as possible, this work investigated the flow characteristics using 4-dimensional flow-sensitive magnetic resonance imaging of a left ventricular assist device with outflow via the right subclavian artery as commonly used in cardiothoracic surgery in the recent past.

METHODS

An in vitro model was developed consisting of an aorta with its supra-aortic branches connected to a left ventricular assist device simulating the pulsatile flow of the native failing heart. A second left ventricular assist device supplied the aorta with continuous flow via the right subclavian artery. Four-dimensional flow-sensitive magnetic resonance imaging was performed for different flow rates of the left ventricular assist device simulating the native heart and the left ventricular assist device providing the continuous flow. Flow characteristics were qualitatively and quantitatively evaluated in the entire vessel system.

RESULTS

Flow characteristics inside the aorta and its upper branching vessels revealed that the right subclavian artery and the right carotid artery were solely supported by the continuous-flow left ventricular assist device for all flow rates. The flow rates in the brain-supplying arteries are only marginally affected by different operating conditions. The qualitative analysis revealed only minor effects on the flow characteristics, such as weakly pronounced vortex flow caused by the retrograde flow via the brachiocephalic artery.

CONCLUSIONS

The results indicate that, despite the massive alterations in natural hemodynamics due to the retrograde flow via the right subclavian and brachiocephalic arteries, there are no drastic consequences on the flow in the brain-feeding arteries and the flow characteristics in the ascending and descending aortas. It may be beneficial to adjust the operating condition of the left ventricular assist device to the residual function of the failing heart.

A novel passive left heart platform for device testing and research

Integration of biological samples into in vitro mock loops is fundamental to simulate real device's operating conditions. We developed an in vitro platform capable of simulating the pumping function of the heart through the external pressurization of the ventricle. The system consists of a fluid-filled chamber, in which the ventricles are housed and sealed to exclude the atria from external loads. The chamber is connected to a pump that drives the motion of the ventricular walls. The aorta is connected to a systemic impedance simulator, and the left atrium to an adjustable preload. The platform reproduced physiologic hemodynamics, i.e. aortic pressures of 120/80 mmHg with 5 L/min of cardiac output, and allowed for intracardiac endoscopy. A pilot study with a left ventricular assist device (LVAD) was also performed. The LVAD was connected to the heart to investigate aortic valve functioning at different levels of support. Results were consistent with the literature, and high speed video recordings of the aortic valve allowed for the visualization of the transition between a fully opening valve and a permanently closed configuration. In conclusion, the system showed to be an effective tool for the hemodynamic assessment of devices, the simulation of surgical or transcatheter procedures and for visualization studies.

Comparison of continuous-flow and pulsatile-flow left ventricular assist devices: is there an advantage to pulsatility?

BACKGROUND

Continuous-flow left ventricular assist devices (CFVAD) are currently the most widely used type of mechanical circulatory support as bridge-to-transplant and destination therapy for end-stage congestive heart failure (HF). Compared to the first generation pulsatile-flow left ventricular assist devices (PFVADs), CFVADs have demonstrated improved reliability and durability. However, CFVADs have also been associated with certain complications thought to be linked with decreased arterial pulsatility. Previous studies comparing CFVADs and PFVADs have presented conflicting results. It is important to understand the outcome differences between CFVAD and PFVAD in order to further advance the current VAD technology.

METHODS

In this review, we compared the outcomes of CFVADs and PFVADs and examined the need for arterial pulsatility for the future generation of mechanical circulatory support.

RESULTS

CVADs offer advantages of smaller size, increased reliability and durability, and subsequent improvements in survival. However, with the increasing duration of long-term support, it appears that CFVADs may have specific complications and a lower rate of left ventricular recovery associated with diminished pulsatility, increased pressure gradients on the aortic valve and decreased compliance in smaller arterial vessels. PFVAD support or pulsatility control algorithms in CFVADs could be beneficial and potentially necessary for long term support.

CONCLUSIONS

Given the relative advantages and disadvantages of CFVADs and PFVADs, the ultimate solution may lie in incorporating pulsatility into current and emerging CFVADs whilst retaining their existing benefits. Future studies examining physiologic responses, end-organ function and LV remodeling at varying degrees of pulsatility and device support levels are needed.

Concomitant aortic valve procedures in patients undergoing implantation of continuous-flow left ventricular assist devices: An INTERMACS database analysis

BACKGROUND

Management of existing aortic insufficiency (AI) and mechanical aortic valves in patients undergoing left ventricular assist device (LVAD) implantation remains controversial. Surgical options to address these issues include closure, repair or replacement of the valve.

METHODS

Continuous-flow LVAD/biventricular VAD patients entered into the INTERMACS database between June 2006 and December 2012 were included (n = 5,344) in this analysis. Outcomes were compared between patients who underwent aortic valve (AV) closure (n = 125), repair (n = 95) and replacement (n = 85).

RESULTS

Among patients who underwent an AV procedure, actuarial survival was significantly reduced for AV closures (63.2%) compared with AV repairs (76.8%) and replacements (71.8%) (p = 0.0003). Differences were greater between groups when only INTERMACS Level 1 or 2 patients were analyzed (p = 0.003). After multivariate adjustment, AV closure remained a significant risk factor for mortality (hazard ratio = 1.87, 95% confidence interval 1.39 to 2.53, p < 0.0001). At 6 to 12 months post-operatively, moderate to severe AI developed in 19%, 5%, 9% and 10% of patients with available echocardiography who underwent repair, closure, replacement and no intervention, respectively (p < 0.0001). Competing outcomes demonstrate that, at 1-year, fewer patients with AV closures were transplanted compared with patients with repairs/replacements (14% vs 19%). No differences were observed between groups with respect to cause of death, re-hospitalization, right heart failure or stroke.

CONCLUSIONS

AV closure was associated with increased mortality when compared with repair or replacement in patients with AI who underwent LVAD insertion. The reasons for this association require further investigation. This is the largest study to date to examine concomitant AV procedures in patients undergoing LVAD insertion.