Progress versus precision: challenges in clinical trial design for left ventricular assist devices

Considerations and Recommendations for the Introduction of Objective Performance Criteria for Transcatheter Aortic Heart Valve Device Approval

In the United States, new surgical heart valves can be approved on the basis of objective performance criteria (OPC). In contrast, the US Food and Drug Administration traditionally requires stricter criteria for transcatheter heart valve (THV) approval, including randomized, clinical trials. Recent US Food and Drug Administration approval of new-generation THVs based on single-arm studies has generated interest in alternative study approaches for THV device approval. This review evaluates whether THV device approval could follow a pathway analogous to that of surgical heart valves by incorporating OPC and provides several considerations and recommendations. Factors to be taken into account in the construction of OPC include the maturity of THV technology, variability in transcatheter aortic valve replacement practice, end points included as OPC, follow-up terms for specific OPC, patient populations to which these OPC apply, and (statistical) methods for OPC development. We recommend that approval of THV devices in the United States for low- and intermediate-risk patients or for new indications should provisionally rely on data from randomized, clinical trials. However, it is recommended that formal OPC be applied for approval of new-generation THVs for use in high- and extreme-risk patient populations.

Dynamics of device innovation: implications for assessing value

BACKGROUND

In recent years, there has been growing interest in evaluating the health and economic impact of medical devices. Payers increasingly rely on cost-effectiveness analyses in making their coverage decisions, and are adopting value-based purchasing initiatives. These analytic approaches, however, have been shaped heavily by their use in the pharmaceutical realm, and are ill-adapted to the medical device context.

METHODS

This study focuses on the development and evaluation of left ventricular assist devices (LVADs) to highlight the unique challenges involved in the design and conduct of device trials compared with pharmaceuticals.

RESULTS

Devices are moving targets characterized by a much higher degree of post-introduction innovation and "learning by using" than pharmaceuticals. The cost effectiveness ratio of left ventricular assist devices for destination therapy, for example, decreased from around $600,000 per life year saved based on results from the pivotal trial to around $100,000 within a relatively short time period.

CONCLUSIONS

These dynamics pose fundamental challenges to the evaluation enterprise as well as the policy-making world, which this paper addresses.

Current challenges for clinical trials of cardiovascular medical devices

Several features of cardiovascular devices raise considerations for clinical trial conduct. Prospective, randomized, controlled trials remain the highest quality evidence for safety and effectiveness assessments, but, for instance, blinding may be challenging. In order to avoid bias and not confound data interpretation, the use of objective endpoints and blinding patients, study staff, core labs, and clinical endpoint committees to treatment assignment are helpful approaches. Anticipation of potential bias should be considered and planned for prospectively in a cardiovascular device trial. Prospective, single-arm studies (often referred to as registry studies) can provide additional data in some cases. They are subject to selection bias even when carefully designed; thus, they are generally not acceptable as the sole basis for pre-market approval of high risk cardiovascular devices. However, they complement the evidence base and fill the gaps unanswered by randomized trials. Registry studies present device safety and effectiveness in day-to-day clinical practice settings and detect rare adverse events in the post-market period. No single research design will be appropriate for every cardiovascular device or target patient population. The type of trial, appropriate control group, and optimal length of follow-up will depend on the specific device, its potential clinical benefits, the target patient population and the existence (or lack) of effective therapies, and its anticipated risks. Continued efforts on the part of investigators, the device industry, and government regulators are needed to reach the optimal approach for evaluating the safety and performance of innovative devices for the treatment of cardiovascular disease.

Statement regarding the pre and post market assessment of durable, implantable ventricular assist devices in the United States: executive summary

The incorporation of complex medical device technologies into clinical practice is governed by critical oversight of the US Food and Drug Administration. This regulatory process requires a judicious balance between assuring safety and efficacy, while providing efficient review to facilitate access to innovative therapies. Recent contrasting views of the regulatory process have emphasized the difficulties in obtaining an optimal balance. Mechanical circulatory support has evolved to become an important therapy for patients with advanced heart failure with the advent of more durable, implantable ventricular assist devices. The regulatory oversight of these new technologies has been difficult owing to the complexities of these devices, associated adverse event profile, and severity of illness of the intended patient population. Maintaining a regulatory environment to foster efficient introduction of safe and effective technologies is critical to the success of ventricular assist device therapy and the health of patients with advanced heart failure. Physicians representing key surgical and cardiology societies, and representatives from the Food and Drug Administration, National Heart, Lung, and Blood Institute, Centers for Medicare and Medicaid Services, Interagency Registry of Mechanically Assisted Circulatory Support, and industry partners gathered to discuss relevant issues regarding the current regulatory environment assessing ventricular assist devices. The goal of the meeting was to explore innovative ways to foster the introduction of technologically advanced, safe, and effective ventricular assist devices. The following summary reflects opinions and conclusions endorsed by The Society of Thoracic Surgeons, American Association for Thoracic Surgery, American Heart Association, Heart Failure Society of America, International Society for Heart and Lung Transplantation, and the Interagency Registry of Mechanically Assisted Circulatory Support.

Randomised clinical trials in surgery: a look at the ethical and practical issues

An ethically conducted randomised controlled trial (RCT) is the backbone of evidence based medicine. In surgical practice however, RCTs have taken a backseat, drawing much adverse comment. There are several reasons to explain surgeons' disinclination to conduct RCTs. These include many practical difficulties such as the problem of blinding surgical procedures, design and funding issues. There are also many ethical issues which need to be considered including the concept of equipoise as well as the ethical issues associated with sham surgery as a control. While there is no doubt that RCTs are essential and in fact have helped to weed out several unnecessary surgical procedures, it is important not to lose sight of the fact that they may not be always necessary in order to obtain evidence in favour of a procedure. Possible solutions could be to follow guidelines that have been issued by learned bodies and a strict adherence to all ethical norms that have been recommended in the conduct of trials.

INTERMACS: interval analysis of registry data

BACKGROUND

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) is an NIH-sponsored registry of US FDA-approved mechanical circulatory support devices (MCSDs) used for destination therapy, bridge to transplantation (BTT), or recovery of the heart. INTERMACS data were analyzed through the most recent quarter ending March 31, 2008.

STUDY DESIGN

INTERMACS variables include demographics, patient outcomes (survival and adverse events), hemodynamic data, and laboratory values. Data were analyzed with competing outcomes methods. Risk factors were identified for death and transplantation.

RESULTS

Ninety-four sites have prospectively enrolled 483 patients in INTERMACS (BTT, 80%; destination therapy, 15%; bridge to recovery, 5%). Forty-two percent of patients had critical cardiogenic shock before implantation, 38% had progressive circulatory decline despite inotropic agents, and 8% were stable but inotropic agent-dependent. The remaining 12% had recurrent advanced heart failure, severe exercise intolerance, or advanced class III heart failure. At 6 months postimplantation, the competing outcomes for the 483 patients included ongoing support (42%), cardiac transplantation (33%), cardiac recovery with pump removal (3%), or death (22%). The most common causes of death were central nervous system events (11%), cardiovascular failure (8%), or respiratory failure (8%). Less common causes were infection (4%), device malfunction (4%), and liver failure (3%). Survival for BTT and destination therapy were similar (p = 0.53). Patient profile at the time of implantation (critical cardiogenic shock versus others) influenced survival (p = 0.007), as did device configuration (left ventricular assist device versus biventricular ventricular assist device; p < 0.0001).

CONCLUSIONS

INTERMACS has increasing participation among domestic MCSD centers. The influence of preimplantation patient condition on survival underscores the importance of timely referral before critical cardiogenic shock occurs. As more devices achieve US FDA approval, INTERMACS will become useful for comparing MCSDs.

Destination therapy: does progress depend on left ventricular assist device development?

The role of therapy using mechanical circulatory support devices has evolved rapidly over the last two decades. New developments in the field achieved smaller adverse events, but, currently, only minor improvements in survival were observed in published observational data. The authors discuss the development of mechanical circulatory support devices as a "destination therapy" option for patients who have end-stage heart failure and are ineligible for heart transplantation as it relates to left ventricular assist device development.

Designs for Mechanical Circulatory Support Device Studies

BACKGROUND

There is increased interest in mechanical circulatory support devices (MCSDs), such as implantable left ventricular assist devices (LVADs), as "destination" therapy for patients with advanced heart failure. Because patient availability to evaluate these devices is limited and randomized trials have been slow in enrolling patients, a workshop was convened to consider designs for MCSD development including alternatives to randomized trials.

METHODS AND RESULTS

A workshop was jointly planned by the Heart Failure Society of America and the US Food and Drug Administration and was convened in March 2006. One of the panels was asked to review different designs for evaluating new MCSDs. Randomized trials have many advantages over studies with no controls or with nonrandomized concurrent or historical controls. These advantages include the elimination of bias in the assignment of treatments and the balancing, on average, of known and unknown baseline covariates that influence response. These advantages of randomization are particularly important for studies in which the treatments may not differ from one another by a large amount (eg, a head-to-head study of an approved LVAD with a new LVAD). However, researchers have found it difficult to recruit patients to randomized studies because the number of clinical sites that can carry out the studies is not large. Also, there is a reluctance to randomize patients when the control device is considered technologically inferior. Thus ways of improving the design of randomized trials were discussed, and the advantages and disadvantages of alternative designs were considered.

CONCLUSIONS

The panel concluded that designs should include a randomized component. Randomized designs might be improved by allowing the control device to be chosen before randomization, by first conducting smaller vanguard studies, and by allowing crossovers in trials with optimal medical management controls. With use of data from completed trials, other databases, and registries, alternative designs that include both a randomized component (eg, 2:1 allocation for new device versus control) and a nonrandomized component (eg, concurrent nonrandomized control, historical control, or a comprehensive cohort design) should be evaluated. This will require partnerships among academic, government, and industry scientists.