Left Ventricular Assist Devices Design Research Articles

Left Ventricular Assist Device in Advanced Refractory Heart Failure: A Comprehensive Review of Patient Selection, Surgical Approaches, Complications and Future Perspectives.

The management of advanced heart failure (HF) has long posed significant challenges due to its complex and chronic nature. Heart transplantation, while effective, is not always feasible due to the limited availability of donor organs. In this context, long term mechanical circulatory support and mainly left ventricular assist devices (LVADs) have emerged as a vital intervention to fill this gap. LVAD superiority compared to medical therapy for some patients in advanced heart failure has been demonstrated either as a bridge to transplantation or as destination therapy. This literature review provides a comprehensive overview of the effectiveness, challenges, and advancements in the use of LVADs for treating advanced heart failure. It evaluates clinical outcomes associated with LVAD therapy, focusing on survival rates and quality of life improvements. The review synthesizes findings from recent studies, highlighting both the benefits and complications of LVAD implantation, such as infectious risk, thromboembolic events, hemorrhage and device malfunction. Additionally, it explores the latest technological and biomedical advancements in LVAD design, including innovations in biocompatibility, miniaturization, and power management. By examining current research, this review aims to elucidate how LVADs are transforming heart failure treatment and to offer insights into future directions for clinical practice and research.

Cellular and Molecular Mechanisms Activated by a Left Ventricular Assist Device.

Left ventricular assist devices (LVADs) represent the final treatment for patients with end-stage heart failure (HF) not eligible for transplantation. Although LVAD design has been further improved in the last decade, their use is associated with different complications. Specifically, inflammation, fibrosis, bleeding events, right ventricular failure, and aortic valve regurgitation may occur. In addition, reverse remodeling is associated with substantial cellular and molecular changes of the failing myocardium during LVAD support with positive effects on patients' health. All these processes also lead to the identification of biomarkers identifying LVAD patients as having an augmented risk of developing associated adverse events, thus highlighting the possibility of identifying new therapeutic targets. Additionally, it has been reported that LVAD complications could cause or exacerbate a state of malnutrition, suggesting that, with an adjustment in nutrition, the general health of these patients could be improved.

CARC6: Longitudinal Cardiac Dimensions in Patients Undergoing Left Ventricular Assist Device Implantation

Background: In conventional left ventricular assist devices (LVADs) a separate outflow graft is sutured to the aorta. Novel device designs may include intracardiac outflow grafts crossing the aortic valve. While transversal ventricular dimensions are well investigated in patients undergoing LVAD implantation, little is known about the longitudinal cardiac dimensions. These dimensions are, however, particularly critical for the design of LVADs with transaortic outflow graft. We characterized the longitudinal dimensions in patients with dilated cardiomyopathy prior to LVAD implantation. Methods: In an explorative retrospective cohort study at the University Medical Center Freiburg, Germany, the longitudinal cardiac dimensions in patients undergoing computed tomography angiography (CTA) between 06/2002 and 06/2021 prior to LVAD implantation were analyzed. In 14 patients, a postoperative CTA was performed. Figure A and B show the measured dimensions: (a) apex to aortic valve (AV), (b) apex to mitral valve, (c) aortic valve to sinotubular junction (STJ), (d) apex to sinotubular junction, (e) apex to brachiocephalic artery (BCA) and (f) aortic valve to brachiocephalic artery. Correlation between these dimensions and body height was calculated (R, Austria). Results: In total, 44 patients (36 male, age 55.8 years, height 1.75 m) were included. The longitudinal cardiac dimensions measured were (a) 114.5 ± 11.9 mm, (b) 108.0 ± 12.3 mm, (c) 20.9 ± 2.8, (d) 135.4 ± 13.2 mm, (e) 206.0 ± 18.1 and (f) 91.5 ± 9.7 mm. Among LVAD patients these dimensions varied by 12 mm (c) to 72 mm (e). As shown in Figure C, a moderate correlation was found between the selected dimensions and body height. Postoperatively, the distances (a) and (b) decreased by 31.5 and 39.5 %, respectively (n = 14). Conclusions: The analysis presents data about the preoperative longitudinal cardiac dimensions in patients with dilated cardiomyopathy undergoing LVAD implantation, and provides an estimate about changes after LVAD support. A better knowledge of these dimensions and their postoperative alterations may improve surgical planning of patients undergoing LVAD implantation, and helps to design assist devices with transaortic outflow graft.

Dynamic pressure-flow curve analysis of the native heart and left ventricular assist device for full and partial bypass conditions.

During left ventricular assist device (LVAD) support, the external work performed by the native heart combines with the work performed by the rotary LVAD to provide cyclic flow through the LVAD and, in some conditions, through the aortic valve. In this study, a balance of external work was developed and validated for both full and partial bypass conditions that includes valve opening and aortic compliance. The theory assumes a steady-state contribution of external work from the rotary LVAD and a dynamic portion from the heart. Cyclic flow may be ejected through either the LVAD or ascending aorta, and an energy absorption term accounts for aortic compliance. Mock loop studies were performed for LV ejection fractions of 10%-28% combined with HeartMate II LVAD support at 8 and 11krpm to produce a range of full and partial bypass conditions. The external work of the LVAD and native heart was computed from the experimental pressure-flow (H-Q) relations and compared to the theory. Native heart contraction produces a counterclockwise loop in the pressure-flow relation of the LVAD which increased with ejection fraction, and during full bypass conditions the external work was preserved in the total systemic flow. During partial bypass conditions, forward flow through the ascending aorta was accompanied by a reversal during aortic valve closure resulting in a reduction in energy in the downstream flow. The study presents a balance of external work during full and partial bypass LVAD support. Experimental data validated the additional terms corresponding to forward flow and aortic compliance that contribute to the system balance. This expanded theory can be applied to LVAD design and control to improve pulsatility and aortic valve biomechanics.

Less Invasive Left Ventricular Assist Device Implantation: One Right Step Toward the Future

Less Invasive Left Ventricular Assist Device Implantation: One Right Step Toward the Future

Invited Commentary

Left ventricular assist devices (LVADs) continue to be an important therapy for patients with end-stage heart failure. While survival with a LVAD is superior to medical therapy alone, device-related complications are unfortunately common. Nonsurgical bleeding is a particularly serious challenge, as it negatively affects a large percentage of patients receiving LVAD therapy. This phenomenon is thought, in part, to result from the mechanical interface of the device with patient blood. Supraphysiologic shear stress is notable in the newer generation of nonpulsatile LVADs and can induce degradation of important clotting factors, including von Willebrand Factor (vWF). In this article, the authors [1Bartoli C.R. Kang J. Zhang D. et al.Left ventricular assist device design reduces von Willebrand factor degradation: a comparative study between the HeartMate II and the EVAHEART left ventricular assist system.Ann Thorac Surg. 2017; 103: 1239-1245Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar] use a mock circulatory loop to compare two devices: the axial flow HeartMate II and the centrifugal pump EVAHEART LVAS. Whole blood was run through each of the mock loops, and levels of vWF and its degradation products were measured at 6-hour intervals. This study found a significant increase in the breakdown of vWF with the axial flow device compared with the centrifugal pump. While they acknowledge that other design features might affect their results, the authors attribute less breakdown of vWF with the centrifugal pump to the relatively larger blood gaps and lower revolutions per minute associated with the device. This study is an important demonstration of how pump mechanics can dramatically affect the components of circulating blood. The bench model does not account for endothelial function or other physiologic parameters found in vivo. However, the purity of design enables researchers to examine directly how a change in pump properties can help to minimize blood trauma. Ultimately, more patients are now living longer with mechanical circulatory support. To minimize device-related complications, such as nonsurgical bleeding, it is important to understand the effects of design features. Studies such as these will help to inform the next generation of devices. Left Ventricular Assist Device Design Reduces von Willebrand Factor Degradation: A Comparative Study Between the HeartMate II and the EVAHEART Left Ventricular Assist SystemThe Annals of Thoracic SurgeryVol. 103Issue 4PreviewSupraphysiologic shear stress from continuous-flow left ventricular assist devices (LVADs) accelerates von Willebrand factor (vWF) degradation and predisposes patients to nonsurgical bleeding. It is unknown whether unique design characteristics of LVADs differentially affect vWF degradation. We tested the hypothesis that the centrifugal-flow EVAHEART (Evaheart, Houston, TX) left ventricular assist system (LVAS), which was designed to minimize shear stress (low operational revolutions per minute [rpm], larger flow gaps, low shear stress, flat H-Q curve), reduced vWF degradation versus the axial-flow HeartMate II (Thoratec, Pleasanton, CA) LVAD. Full-Text PDF

Intrapericardial Left Ventricular Assist Device for Advanced Heart Failure

BackgroundMechanical circulatory support with a left ventricular assist device (LVAD) is an established treatment for patients with advanced heart failure. We compared a newer LVAD design (a small intrapericardial centrifugal-flow device) against existing technology (a commercially available axial-flow device) in patients with advanced heart failure who were ineligible for heart transplantation.MethodsWe conducted a multicenter randomized trial involving 446 patients who were assigned, in a 2:1 ratio, to the study (centrifugal-flow) device or the control (axial-flow) device. Adults who met contemporary criteria for LVAD implantation for permanent use were eligible to participate in the trial. The primary end point was survival at 2 years free from disabling stroke or device removal for malfunction or failure. The trial was powered to show noninferiority with a margin of 15 percentage points.ResultsThe intention-to treat-population included 297 participants assigned to the study device and 148 participants assigned to the control device. The primary end point was achieved in 164 patients in the study group and 85 patients in the control group. The analysis of the primary end point showed noninferiority of the study device relative to the control device (estimated success rates, 55.4% and 59.1%, respectively, calculated by the Weibull model; absolute difference, 3.7 percentage points; 95% upper confidence limit, 12.56 percentage points; P=0.01 for noninferiority). More patients in the control group than in the study group had device malfunction or device failure requiring replacement (16.2% vs. 8.8%), and more patients in the study group had strokes (29.7% vs. 12.1%). Quality of life and functional capacity improved to a similar degree in the two groups.ConclusionsIn this trial involving patients with advanced heart failure who were ineligible for heart transplantation, a small, intrapericardial, centrifugal-flow LVAD was found to be noninferior to an axial-flow LVAD with respect to survival free from disabling stroke or device removal for malfunction or failure. (Funded by HeartWare; ENDURANCE ClinicalTrials.gov number, NCT01166347.)

Left Ventricular Assist Device Design Reduces von Willebrand Factor Degradation: A Comparative Study Between the HeartMate II and the EVAHEART Left Ventricular Assist System

Supraphysiologic shear stress from continuous-flow left ventricular assist devices (LVADs) accelerates von Willebrand factor (vWF) degradation and predisposes patients to nonsurgical bleeding. It is unknown whether unique design characteristics of LVADs differentially affect vWF degradation. We tested the hypothesis that the centrifugal-flow EVAHEART (Evaheart, Houston, TX) left ventricular assist system (LVAS), which was designed to minimize shear stress (low operational revolutions per minute [rpm], larger flow gaps, low shear stress, flat H-Q curve), reduced vWF degradation versus the axial-flow HeartMate II (Thoratec, Pleasanton, CA) LVAD. Whole human blood was obtained from volunteer donors (n= 22). Blood was circulated for 12 hours in mock circulatory loops through a HeartMate II (n= 10; 11,400 rpm, 6.3 ± 0.8 L/min, 76 ± 2 mm Hg) or an EVAHEART LVAS (n= 12; 2,300 rpm, 5.7 ± 0.1 L/min, 80± 1 mm Hg). vWF degradation was characterized with electrophoresis and immunoblotting for large vWF multimers and 11 vWF degradation fragments. The HeartMate II eliminated large vWF multimers and significantly (p < 0.05) increased 10 of 11 vWF degradation fragments at 6 and 12 hours. The increase was approximately 2.0-fold at 6 hours and 2.2-fold at 12 hours. In contrast, the EVAHEART LVAS modestly reduced large vWF multimers and significantly increased 5 of 11 and 8 of 11 vWF degradation fragments at 6 and 12 hours, respectively. The increase was approximately 1.5-fold at 6 hours and 1.7-fold at 12 hours. The EVAHEART LVAS caused significantly less degradation (p < 0.01) than the HeartMate II of the 140 kDa vWF fragment (cleavage product of ADAMTS-13, the vWF protease). The EVAHEART LVAS caused significantly less vWF degradation than the HeartMate II in a mock circulatory loop with whole human blood. LVAD design features may minimize vWF degradation. These data may inform the design and operation of next-generation LVADs to minimize blood trauma.

From bench to bedside: Can the improvements in left ventricular assist device design mitigate adverse events and increase survival?

ObjectiveIn vitro tests demonstrated that the new cone-bearing configuration of the Jarvik 2000 (Jarvik Heart Inc, New York, NY) left ventricular assist device exhibits better hydraulic efficiency than the previous pin-bearing design. We investigated the long-term outcomes of patients who received the Jarvik 2000 left ventricular assist device, depending on bearing design. MethodsA retrospective review of prospectively collected data from 18 centers included in the Italian Registry was performed. From May 2008 to September 2013, 99 patients with end-stage heart failure were enrolled. Patients were divided into 2 groups according to their Jarvik 2000 suspending mechanism: Group pin included patients with pin bearings (May 2008 to June 2010), and group cone included patients with newer cone bearings (July 2010 to September 2013). The 2 groups did not differ significantly in terms of baseline characteristics. ResultsA total of 30 of 39 patients (group pin) and 46 of 60 patients (group cone) were discharged. During follow-up, 6 patients underwent transplantation, and in 1 patient the left ventricular assist device was explanted. The cumulative incidence competing risk of the entire cohort for noncardiovascular-related death was 28% (20%-40%); the cumulative incidence competing risk for cardiovascular-related death was 56% (42%-73%): 71% in group pin versus 26% in group cone (P = .034). The multivariate analyses confirmed that the pin-bearing design was a risk factor for cardiovascular death, along with Interagency Registry for Mechanically Assisted Circulatory Support class. Right ventricular failures and ischemic and hemorrhagic strokes were significantly higher in group pin. ConclusionsPatients with the new pump configuration showed a better freedom from cardiovascular death and lower incidence of fatal stroke and right ventricular failure. Further studies are needed to prove the favorable impact of pump-enhanced fluid dynamics on long-term results.

A novel design of ventricular assist device: An in vitro feasibility study

Left ventricular assist devices (LVADs) work as a bypass between the left ventricular apex and the ascending aorta. The surgical procedure for their insertion requires the opening of the cardiac cavities and the dissection of the great vessels, the blood is constrained to flow through the device components and the risk can be run of thrombogenesis, haemolysis and infections. A possible strategy to overcome this limitation consists in utilizing external systems that assist the heart in its contraction from the outside without directly transporting the blood. In this study we conduct the feasibility analysis of a novel external LVAD design that does not require the opening of the cardiac cavities and the dissection of the great vessels and that allows the removal procedure to be easily achieved. The device, including a stepper motor, three metallic wires and three elastic elements, works alternatively between a contraction condition where it induces an elastic compulsion on the heart and a release condition where it elastically releases the organ. The values of force acting on the wires and the values of current supplied to the motor were measured and utilized for a preliminary study design. The experimental measurements demonstrated the feasibility of the system.

Computational fluid dynamics analysis of surgical adjustment of left ventricular assist device implantation to minimise stroke risk

Background. Currently, mechanical support is the most promising alternative to cardiac transplantation. Ventricular assist devices (VADs) were originally used to provide mechanical circulatory support in patients awaiting planned heart transplantation (‘bridge-to-transplantation’ therapy). The success of short-term bridge devices led to clinical trials evaluating the clinical suitability of long-term support (‘destination’ therapy) with left ventricular assist devices (LVADs). The first larger scale, randomised trial that tested long-term support with an LVAD reported a 44% reduction in the risk of stroke or death in patients with an LVAD. In spite of the success of LVADs as bridge-to-transplantation and long-term support, patients managed by these devices are still at risk of several adverse events. The most devastating complication is caused by embolisation of thrombi formed within the LVAD or inside the heart into the brain. Prevention of thrombi formation is attempted through anticoagulation management and by improving LVADs design; however, there is still significant occurrence of thromboembolic events in patients. Investigators have reported that the incidence of thromboembolic cerebral events ranges from 14% to 47% over a period of 6–12 months.Methods and approach. An alternative method to reduce the incidence of cerebral embolisation is proposed by the co-authors, and the hypothesis is that it is possible to minimise the number of thrombi flowing into the carotid and vertebral arteries by an optimal placement of the LVAD outflow conduit, with or without the addition of aortic bypass connecting the ascending aorta and the innominate artery (IA), or left carotid artery. This paper presents the computational fluid dynamics (CFD) analysis of the aortic arch haemodynamics using a representative geometry of the human aortic arch with or without an alternative aortic bypass. In order to study the trajectory of the thrombi within the aortic arch bed, the CFD code, Fluent 6.3, is utilised to resolve the flow field and to solve the Lagrangian particle tracking of thrombi released randomly at the inlet of the LVAD cannula.Results. Results are presented for simulations of thrombi in the range of 2–5 mm. The percentage of individual diameter as well as aggregate diameter thrombi flowing to the carotid and vertebral arteries as a function of LVAD conduit placement and aortic bypass implantation is reported. The influence of the LVAD conduit implantation and bypass reveals a nearly 50% variation in predicted cerebral embolism rates.Conclusions. The adjustment of the location of the anastomosis of the LVAD outflow cannula as well as its angle of incidence plays a significant role in the level of thromboembolisms. By proper adjustment in this CFD study of a synthetic model of an aortic arch bed, we found that nearly a 50% reduction in cerebral embolism could be achieved for a configuration consisting of a shallow angle of implantation over a baseline normal incidence of the LVAD cannula. Within the limitations of our model, we have established that the LVAD implantation geometry is an important factor and should be taken into consideration when implanting an LVAD. It is possible that other parameters such as distance of the LVAD outflow cannula to the root of the IA could affect the thrombi embolisation probabilities. However, the results of this study suggest that the risk of stroke may be significantly reduced by as much as 50% by tailoring the VAD implantation by a simple surgical manoeuvre. The results of this line of research may ultimately lead to techniques that can be used to estimate the optimal LVAD configuration in a patient-specific manner by pre-operative imaging.

Performance Characterization of a Rotary Centrifugal Left Ventricular Assist Device With Magnetic Suspension

The MiTiHeart (MiTiHeart Corporation, Gaithersburg, MD, USA) left ventricular assist device (LVAD), a third-generation blood pump, is being developed for destination therapy for adult heart failure patients of small to medium frame that are not being served by present pulsatile devices. The pump design is based on a novel, patented, hybrid passive/active magnetic bearing system with backup hydrodynamic thrust bearing and exhibits low power loss, low vibration, and low hemolysis. Performance of the titanium alloy prototype was evaluated in a series of in vitro tests with blood analogue to map out the performance envelop of the pump. The LVAD prototype was implanted in a calf animal model, and the in vivo pump performance was evaluated. The animal's native heart imparted a strong pulsatility to the flow rate. These tests confirmed the efficacy of the MiTiHeart LVAD design and confirmed that the pulsatility does not adversely affect the pump performance.

Evaluation of Left Ventricular Assist Device Performance and Hydraulic Force in a Complete Mock Circulation Loop

Centrifugal pump performance characteristics are vital in determining the ability of a prototype left ventricular assist device (LVAD) to meet the physiological circulation requirements of the cardiovascular system. These characteristics influence the static hydraulic forces encountered by the pump impeller, which determine the required load stiffness of suspension type bearings to minimize impeller touchdown. Performance investigations were conducted on an LVAD design while characterizing the impeller static hydraulic forces of various impeller/volute configurations. The pumps were inserted into a complete systemic and pulmonary mock circulation rig configured to provide suitable nonpulsatile or simulated pulsatile left heart failure environments. The single volute and closed shroud impeller configuration exhibited lowest radial (0.01 N) and axial (3 N) force at nonpulsatile design flow conditions, respectively. Normal hemodynamic conditions of 5.1 L/min at 94 mm Hg were re-established upon inserting the device into the left heart failure environment, where the pump operated along the nonpulsatile characteristic curve for 2200 rpm. The operational limits on this curve were dictated by the required pressure differential across the pump during systolic and diastolic periods. The reduction of left atrial pressure (25 to 8 mm Hg) indicated the alleviation of pulmonary congestion. The ability for the LVAD to support circulation in a left heart failure environment was successfully demonstrated in the mock circulation loop. The impeller hydraulic force characteristics attained will aid the bearing designer to select the best volute and impeller configuration to minimize impeller touchdown in magnetic, hydrodynamic or mechanical type bearing applications.