Designs for Mechanical Circulatory Support Device Studies

Cost-effectiveness of the implantable HeartMate II left ventricular assist device for patients awaiting heart transplantation

BACKGROUND

Left ventricular assist devices (LVADs) are being proposed as a life-saving therapeutic alternative to conventional medical management for people with end-stage heart failure awaiting transplantation. However, cost-effectiveness assessments of first-generation LVADs have not been encouraging. The cost-effectiveness of the enhanced second-generation LVAD HeartMate II (Thoratec, Pleasanton, CA) is estimated here.

METHODS

A probabilistic Markov model was developed to extrapolate survival, utility, and resource use over the total lifetime of a hypothetic cohort of patients with end-stage heart failure under the 2 competing therapeutic strategies, using the most robust and recently published evidence about their performance. Cost data are based on UK activity to consider reimbursement in the UK National Health Service setting.

RESULTS

HeartMate II had a mean cost per quality-adjusted life-year (QALY) of £258,922 ($414,275). The sensitivity analysis showed that 2 factors mainly explain why HeartMate II is not a cost-effectiveness strategy as a bridge-to-transplant: (1) the survival of heart transplant candidates treated conventionally while on the waiting list has significantly improved in recent years, and (2) the high acquisition cost of the device, £94,200 ($150,720).

CONCLUSIONS

Although HeartMate II LVAD implantation significantly increases survival compared with conventional medical management, it does not provide good value for the money spent according to established thresholds of cost-effectiveness in the UK. HeartMate II is unlikely to become cost-effective unless the additional survival gained by its use raises and/or the device is given free of charge. Therefore, its implantation to transplant candidates lacks justification in terms of cost-effectiveness.

Contemporary use of ventricular assist devices

The introduction of the heart lung machine more than 50 years ago proved in principle that heart function can be replaced, albeit for short periods. This was followed by attempts to produce total or partial artificial hearts that could function for prolonged periods of time. Progress in this field has been intermittent but has accelerated considerably in the past 10 years, with ventricular assist devices (VADs) reaching an impressive degree of sophistication and complexity owing to the contributions from clinicians, engineers, scientists, industrialists, and others. This review describes the currently available types of VADs, their current clinical use, the patient selection process, the trend toward use of VADs in patients with less severe heart failure, and the use of VADs for myocardial recovery in combination with novel pharmacological strategies, gene therapy, and cell therapy.

Numerical Study of Blood Flow at the End-to-Side Anastomosis of a Left Ventricular Assist Device for Adult Patients

We use an implicit large eddy simulation (ILES) method based on a finite volume approach to capture the turbulence in the anastomoses of a left ventricular assist device (LVAD) to the aorta. The order-of-accuracy of the numerical schemes is computed using a two-dimensional decaying Taylor–Green vortex. The ILES method is carefully validated by comparing to documented results for a fully developed turbulent channel flow at Reτ=395. Two different anastomotic flows (proximal and distal) are simulated for 50% and 100% LVAD supports and the results are compared with a healthy aortic flow. All the analyses are based on a planar aortic model under steady inflow conditions for simplification. Our results reveal that the outflow cannulae induce high exit jet flows in the aorta, resulting in turbulent flow. The distal configuration causes more turbulence in the aorta than the proximal configuration. The turbulence, however, may not cause any hemolysis due to low Reynolds stresses and relatively large Kolmogorov length scales compared with red blood cells. The LVAD support causes an acute increase in flow splitting in the major branch vessels for both anastomotic configurations, although its long-term effect on the flow splitting remains unknown. A large increase in wall shear stress is found near the cannulation sites during the LVAD support. This work builds a foundation for more physiologically realistic simulations under pulsatile flow conditions.

Practical Bayesian design and analysis for drug and device clinical trials

Perhaps the most valuable contribution of Bayesian methods to health care evaluation involves study design. Drug and medical device clinical trialists are increasingly confronted with data that feature complex correlation structures, and are costly and difficult to obtain. In such settings, Bayesian trial designs are attractive since they can incorporate historical data or information from published literature, thus saving time and expense and minimizing the number of subjects exposed to an inferior treatment. Bayesian designs can also adapt to unexpected changes in the protocol, and allow the investigator to explore the plausibility of various outcome scenarios before any patients are enrolled in the trial. Recently, the FDA Center for Devices has encouraged hierarchical Bayesian statistical approaches which allow for the incorporation of such valuable historical data into the design and analysis of new device trials. The practical application of these methods has only become feasible in the last decade due to advances in computing via Markov chain Monte Carlo (MCMC) methods, especially as implemented in the popular BUGS software package. In this paper we illustrate Bayesian analysis and sample size calculations using BRugs, a function for calling BUGS from R. We provide illustrations in two applied settings where incorporation of available historical information is crucial, one concerning an AIDS drug trial and the other a comparison of left ventricular assist devices (LVADs).