Initial clinical experience with the VentrAssist left ventricular assist device: the pilot trial

Numerical assessment of hemodynamic perspectives of a left ventricular assist device and subsequent proposal for improvisation

Due to the unavailability of donors, the use of left ventricular assist devices has emerged to be a reliable line of alternative treatment for heart failure. However, ventricular assist devices (VAD) have been associated with several postoperative complications such as thrombosis, hemolysis, etc. Despite considerable improvements in technology, blood trauma due to high shear stress generation has been a major concern that is largely related to the geometrical feature of the VAD. This study aims to establish the design process of a centrifugal pump by considering several variations in the geometrical feature of a base design using the commercial solver ANSYS-CFX. To capture the uncertain behavior of blood as fluid, Newtonian, as well as non-Newtonian (Bird-Carreau model), models are used for flow field prediction. To assess the possibility of blood damage maximum wall shear stress and hemolysis index have been estimated for each operating point. The results of the simulations yield an optimized design of the pump based on parameters like pressure head generation, maximum shear stress, hydraulic efficiency, and hemolysis index. Further, the design methodology and the steps of development discussed in the paper can serve as a guideline for developing small centrifugal pumps handling blood.

Contemporary outcomes of continuous-flow left ventricular assist devices-a systematic review

Background

End stage heart failure is a major cause of morbidity and mortality, and its prevalence is expected to rise with the ageing population. For suitable patients, orthotopic heart transplantation remains the gold standard therapy, however, a paucity of donor organs has led to the development of left ventricular assist devices (LVAD). These devices can be utilized as either a bridge-to-transplant (BTT) or as an alternative to heart transplantation. While these devices can prolong life and improve quality of life, they are associated with a significant number of adverse events. We aim to systematically review the literature to quantify survival and the incidence of adverse events following implantation of continuous-flow LVADs (cf-LVAD).

Methods

A systematic review was performed to determine outcomes following implantation of a cf-LVAD. Primary outcomes were survival and frequency of adverse events (such as bleeding, infection, thrombosis, stroke and right ventricular failure). Secondary outcomes included quality of life and assessment of functional status.

Results

Sixty-three studies reported clinical outcomes of 9,280 patients. Survival after cf-LVAD varied between studies. Industry-funded trials generally reported better overall survival than the single- and multi-center case series, which showed significant variation. The largest registry report documented twelve, twenty-four and forty-eight-month survival rates of 82%, 72% and 57% respectively. The most commonly reported adverse events were gastrointestinal bleeding (GIB), device-related infection, neurological events and right heart failure (RHF). Bleeding, RHF and infection were the most frequent complications experienced by those supported with cf-LVAD, occurring in up to 35%, 40% and 55% of patients, respectively. Quality of life as measured using the Kansas City Cardiomyopathy Questionnaire (KCCQ) and functional status as measured with the 6-minute walk test (6MWT) improved after cf-LVAD implantation with no decline evident two years after implantation.

Conclusions

The paucity of donor hearts has led to the development of left-ventricular assist devices as a BTT or as a destination therapy (DT). Outcomes after cf-LVAD implantation are excellent, with short-term survival comparable to heart transplantation, but long-term survival remains limited due to the incidence of post-implantation adverse events. Despite these complications, quality of life and functional status improve significantly post-implantation and remain improved over the long-term. This study demonstrates the potential benefits of cf-LVAD therapy whilst also identifying adverse events as an area of increased morbidity and mortality.

Preload-based starling-like control for rotary blood pumps: numerical comparison with pulsatility control and constant speed operation

In this study, we evaluate a preload-based Starling-like controller for implantable rotary blood pumps (IRBPs) using left ventricular end-diastolic pressure (PLVED) as the feedback variable. Simulations are conducted using a validated mathematical model. The controller emulates the response of the natural left ventricle (LV) to changes in PLVED. We report the performance of the preload-based Starling-like controller in comparison with our recently designed pulsatility controller and constant speed operation. In handling the transition from a baseline state to test states, which include vigorous exercise, blood loss and a major reduction in the LV contractility (LVC), the preload controller outperformed pulsatility control and constant speed operation in all three test scenarios. In exercise, preload-control achieved an increase of 54% in mean pump flow ([Formula: see text]) with minimum loading on the LV, while pulsatility control achieved only a 5% increase in flow and a decrease in mean pump speed. In a hemorrhage scenario, the preload control maintained the greatest safety margin against LV suction. PLVED for the preload controller was 4.9 mmHg, compared with 0.4 mmHg for the pulsatility controller and 0.2 mmHg for the constant speed mode. This was associated with an adequate mean arterial pressure (MAP) of 84 mmHg. In transition to low LVC, [Formula: see text] for preload control remained constant at 5.22 L/min with a PLVED of 8.0 mmHg. With regards to pulsatility control, [Formula: see text] fell to the nonviable level of 2.4 L/min with an associated PLVED of 16 mmHg and a MAP of 55 mmHg. Consequently, pulsatility control was deemed inferior to constant speed mode with a PLVED of 11 mmHg and a [Formula: see text] of 5.13 L/min in low LVC scenario. We conclude that pulsatility control imposes a danger to the patient in the severely reduced LVC scenario, which can be overcome by using a preload-based Starling-like control approach.

Our experience with implantation of VentrAssist left ventricular assist device

Perioperative anaesthetic management of the VentrAssist™ left ventricular assist device (LVAD) is a challenge for anaesthesiologists because patients presenting for this operation have long-standing cardiac failure and often have associated hepatic and renal impairment, which may significantly alter the pharmacokinetics of administered drugs and render the patients coagulopathic. The VentrAssist is implanted by midline sternotomy. A brief period of cardiopulmonary bypass (CPB) for apical cannulation of left ventricle is needed. The centrifugal pump, which produces non-pulsatile, continuous flow, is positioned in the left sub-diaphragmatic pocket. This LVAD is preload dependent and afterload sensitive. Transoesophageal echocardiography is an essential tool to rule out contraindications and to ensure proper inflow cannula position, and following the implantation of LVAD, to ensure right ventricular (RV) function. The anaesthesiologist should be prepared to manage cardiac decompensation and acute desaturation before initiation of CPB, as well as RV failure and severe coagulopathic bleeding after CPB. Three patients had undergone implantation of VentrAssist in our hospital. This pump provides flow of 5 l/min depending on preload, afterload and pump speed. All the patients were discharged after an average of 30 days. There was no perioperative mortality.

Left ventricular assist devices: from the bench to the clinic

The development of ventricular assist devices (VADs) over the past 5 decades as therapy for advanced heart failure (HF) has been extraordinary. Since the original VAD design by Michael DeBakey in the early 1960s, numerous devices for mechanical circulatory support have been engineered, assessed in preclinical studies, applied to human patients in large multicenter clinical trials, and now, select devices are Food and Drug Administration-approved therapy for advanced HF patients. This review highlights select examples of durable VADs from the engineering aspect of design and conception to experimental studies and clinical application underscoring the remarkable progression of such technology to now becoming the standard of care for many advanced HF patients.

Third-generation continuous flow left ventricular assist devices

Tremendous advances have been made in the treatment of end-stage heart failure patients with left ventricular assist devices (LVADs). An important factor playing a role in the improved clinical outcomes is the development of continuous flow, rotary LVADs. New technology using magnetic levitation and hydrodynamic suspension to eliminate contact bearings offers the potential of more durable and efficacious mechanical circulatory blood pumps. Clinical trials evaluating these novel "third-generation" LVADs are in progress.

Extra corporeal membrane oxygenation as right heart support following left ventricular assist device placement: a new cannulation technique

Extracorporeal membrane oxygenation is an established treatment for acute respiratory failure, or low cardiac output syndrome. This can be veno-venous, in which de-oxygenated blood is drained from the venous system and oxygenated before being returned to the venous system, and veno-arterial where the re-oxygenated venous blood is returned to the arterial system. Haemorrhage, sepsis and thrombo-embolism are common and potentially lethal complications. Left ventricular assist devices are a continually evolving technology, that may be used as a bridge to transplantation or destination therapy in end-stage cardiac failure. The VentrAssist™ left ventricular assist device is a small implantable, continuous flow centrifugal pump, that is controlled and powered by a percutaneous lead. However, in these patients, right heart failure may present as an acute event following weaning from cardiopulmonary bypass (CPB), or post-operatively in the intensive care unit. Patients who do not respond to inotropes and pulmonary vasodilators may need a right ventricular assist device (RVAD). We report a successful case of right heart assist extra corporeal membrane oxygenation used as temporary right heart support in combination with a VentrAssist™ left ventricular assist device. The use of right heart assist extra corporeal membrane oxygenation to help a failing right heart during left ventricular assist device placement is not new, however, our technique describes a novel method of cannulation of the femoral vein and pulmonary trunk via a tunnelled vascular tube graft, which allows the chest to be closed whilst on right heart support, and decannulation to proceed without resternotomy. This technique has also been used successfully subsequent to this.

Right heart failure and "failure to thrive" after left ventricular assist device: clinical predictors and outcomes

BACKGROUND

This study determined predictors of early post-operative right heart failure (RHF) and its consequences, as well as predictors of those who clinically thrive longer term after insertion of a continuous-flow left ventricular assist device (LVAD).

METHODS

Pre-operative and latest follow-up data were analyzed for 40 consecutive patients who received third-generation centrifugal-flow LVADs. RHF was defined using previously described criteria, including post-operative inotropes, pulmonary vasodilator use, or right-sided mechanical support. Patients were also categorized according to clinical outcomes after LVAD insertion.

RESULTS

LVADs were implanted as a bridge to transplantation (BTT) in 33 patients and as destination therapy in 7. Before LVAD implant, 22 patients were Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) level 1, and 17 were at level 2. Temporary mechanical assistance was present in 50% of the cohort at LVAD implantation. The 6-month survival/progression to transplant was 92.5%. Average LVAD support time was 385 days (range, 21-1,011 days). RHF developed postoperatively in 13 of 40 patients (32.5%). RHF patients had more severe pre-operative tricuspid incompetence than non-RHF patients. The BTT patients with evidence of RHF had poorer survival to transplant (6 of 11 [54.5%]) than those without RHF (20 of 22 [90.9%]), p = 0.027). There were no other hemodynamic or echocardiographic predictors of short-term RHF. After LVAD, 22 of the 40 patients (55%) thrived clinically. For BTT patients, 20 of 21 (95%) of those who thrived progressed to transplant or were alive at latest follow-up vs 6 of 12 (50%) of those who failed to thrive (FTT; p < 0.005). The thrivers had lower New York Heart Association class (1.5 vs 2.9, p < 0.001), spent less time in the hospital, and had less ventricular tachycardia than the FTT patients. However, no differences were noted in pre-operative INTERMACS level, echocardiographic, hemodynamic, and biochemical indices, or in early post-operative RHF. Age was the only significant predictor: the thrivers were significantly younger (43.7 ± 15.9 vs 60.3 ± 12.6 years; p < 0.001). This age difference was unchanged after exclusion of destination strategy patients. RV function deteriorated in the FTT patients and remained stable in those who thrived.

CONCLUSIONS

Early post-operative RHF results in poorer survival/progression to transplantation for BTT patients and is predicted by greater pre-operative tricuspid incompetence. The most important predictor for those who will clinically thrive longer-term after LVAD insertion is younger age.

Surgical treatment of functional mitral regurgitation in dilated cardiomyopathy

Functional mitral regurgitation is a significant complication of end-stage cardiomyopathy. Dysfunction of one or more components of the mitral valve apparatus occurs in 39-74% and affects almost all heart failure patients. Survival is decreased in subjects with more than mild mitral regurgitation irrespective of the aetiology of heart failure. The goal of treating functional mitral regurgitation is to slow or reverse ventricular remodelling, improve symptoms and functional class, decrease the frequency of hospitalization for congestive heart failure, slow progression to advanced heart failure (time to transplant) and improve survival. This article reviews the role of mitral valve surgery in patients with heart failure and dilated cardiomyopathy.

[Assisted circulation: an overview from a clinical perspective]

A higher grade cardiac failure is associated with poor prognosis. In addition to medical conservative treatment and traditional cardiac surgery, in the past years different forms of an assisted circulation evolved. Short-term devices serve to bridge an acute life-threatening situation. The chosen system is dependent on the anticipated clinical course. It is possible to fall back on slightly assisting techniques up to a complete takeover of the cardiac pump function. In the case of severe cardiac failure, the question for transplantation has to be addressed because transplantation is the treatment of choice to date. For an assisted circulation in cases of chronic congestive failure, devices of different generations are available. First generation pulsatile systems are used for assistance of the left ventricle and results have been shown to be superior to medical therapy (REMATCH). With second generation continuous-flow systems, results regarding infections, thromboembolism and also quality of life appear to be further improved. Contact-free centrifugal pumps as third generation systems are in clinical evaluation. So-called "total artificial hearts" are successfully used for bridge-to-transplantation. Taken together, a graded safe treatment of cardiac failure is available today. In the near future, it could be possible to reach results similar to those of cardiac transplantation.

Development of data communication system with ultra high frequency radio wave for implantable artificial hearts

In order to minimize infection risks of patients with artificial hearts, wireless data transmission methods with electromagnetic induction or light have been developed. However, these methods tend to become difficult to transmit data if the external data transmission unit moves from its proper position. To resolve this serious problem, the purpose of this study is to develop a prototype wireless data communication system with ultra high frequency radio wave and confirm its performance. Due to its high-speed communication rate, low power consumption, high tolerance to electromagnetic disturbances, and secure wireless communication, we adopted Bluetooth radio wave technology for our system. The system consists of an internal data transmission unit and an external data transmission unit (53 by 64 by 16 mm, each), and each has a Bluetooth module (radio field intensity: 4 dBm, receiver sensitivity: -80 dBm). The internal unit also has a micro controller with an 8-channel 10-bit A/D converter, and the external unit also has a RS-232C converter. We experimented with the internal unit implanted into pig meat, and carried out data transmission tests to evaluate the performance of this system in tissue thickness of up to 3 mm. As a result, data transfer speeds of about 20 kbps were achieved within the communication distance of 10 m. In conclusion, we confirmed that the system can wirelessly transmit the data from the inside of the body to the outside, and it promises to resolve unstable data transmission due to accidental movements of an external data transmission unit.