PHVT Disruptive Technology Could Revolutionize Heart Failure Treatment
The early clinical promise of percutaneous heart valve technology (PHVT)—a group of minimally invasive devices designed to treat cardiac valve dysfunction without the need for cardiopulmonary bypass—could one day play a prominent role in curbing the steep costs associated with treating heart failure (HF), which is the number-one driver of hospitalization among Medicare patients. Although still in the very early stages of development and currently implanted in a catheterization lab only in patients who are contraindicated for surgical heart valve repair or replacement, PHVT is rapidly gaining traction as an alternative to surgically implanted valves among end-stage HF patients. The technology also has the potential to provide a “life-saving or quality of life-enhancing” option for early stage HF patients. Several obstacles to adoption have yet to be overcome, but industry observers say the technology’s eventual proliferation is likely to blur the lines between interventional cardiology and cardiac surgery if surgeons decide to learn percutaneous techniques to avoid losing HF market share to their interventionalist colleagues (Advisory Board research, 2005; Gilad and Somogyi, University of Toronto Medical Journal, May 2005; Medtech Insight, August 2005).
PHVT aims to expand treatment options for elderly, young valve recipients
Traditionally, heart valve repair is performed during the course of open-heart surgery, which requires surgeons to open the patient’s chest, stop the heart, and place the patient on a cardiopulmonary bypass machine for at least one hour while inserting the valve replacement. However, two patient groups are contraindicated for surgery: 1) elderly patients with multiple comorbidities who require either aortic valve repair because of aortic stenosis and calcification or mitral valve repair to correct mitral regurgitation, and 2) children and young adults who need heart valve replacement to treat congenital heart disease (UTMJ, May 2005). While the former group may be too ill or weak to withstand the stress of open-heart surgery, the latter group often experiences treatment delays because of the difficulty associated with locating heart valves that are suitably small to be implanted in children; in addition, valve repair performed at a young age can necessitate multiple, highly invasive follow-up procedures to replace the valve as the patient grows. PHVT seeks to provide an alternative treatment option for these patient groups.
Percutaneous valve design features flexibility
Unlike a surgically implanted heart valve, which is mounted on a rigid stent, a percutaneous heart valve (PHV) is attached to a collapsible stent, which is initially compressed to a small enough diameter and inserted into the vein or artery and then expands to its final diameter postinsertion. Once expanded, the PHV holds position by keeping the valve inside it open and by “exert[ing] sufficient radial force” to keep the valve from moving out of place (UTMJ, May 2005). In 2002, researchers performed the first human PHV procedure in the aortic position using a valve composed of equine pericardium leaflets mounted on a steel stent. Today, some PHVs in development feature bovine and porcine pericardia; stents with a “non-uniform diameter” that allows for more effective anchoring; and materials such as Nitinol, which enables the stent to expand on its own, thereby eliminating the need for balloon expansion and facilitating more secure valve deployment (UTMJ, May 2005; Medtech Insight, August 2005). In clinical trials, PHVs have been shown to reduce the transvalvular gradient and to curb pulmonary insufficiency; on a practical level, patients receiving PHVs in clinical trials conducted across the past five years have shown improvement in metabolic exercise test results.
Aortic valve repair suitable for aortic stenosis patients ineligible for surgery
With the rapidly aging Medicare population and the frequency of aortic stenosis in elderly patients who are contraindicated for surgical treatment, PHVT is a particularly attractive alternative to surgical repair for aortic valves (Medtech Insight, August 2005). Currently under debate is whether percutaneous aortic valve repair (PAVR) can be used to treat end-stage HF patients with lethal lesions or whether such patients should undergo medical management or balloon valvuloplasty; the development of new and highly compressible materials may help answer this question.
In addition to demonstrating valve durability, which is of particular importance given that percutaneously implanted valves need to be compressed without causing tissue damage, PAVR has yet to prove its mettle in facilitating vascular access, ensuring accuracy in valve retrieval and repositioning; avoiding mitral valve trauma, paravalvular leakage, and valve embolization; and eradicating unevenly distributed calcification. Despite these lingering uncertainties, 52% of conference attendees at the April 2005 Transcatheter Valve Symposium predicted that PAVR would likely have the greatest impact on the field 10 years from now, while 8% to 11% of attendees selected percutaneous mitral valve repair (PMVR) instead.
Mitral valve repair appropriate for early-stage HF patients
While last year’s TVS attendees concluded that advanced HF patients may best benefit from PAVR, some researchers believe that PMVR may be more beneficial for patients in the earlier stages of HF (Medtech Insight, August 2005). To that end, PMVR device makers are aiming to develop devices capable of treating HF earlier and more aggressively, particularly given that HF patients with significant mitral regurgitation (MR) are 50% more likely than those without significant MR to die within five years of diagnosis.
Myriad unresolved clinical questions may hinder PHVT adoption
Widespread adoption of PHVT currently faces multiple barriers, such as concerns about valve longevity and durability (UTMJ, May 2005). In addition, the fact that PHVs must be implanted in a peripheral vein or artery limits the technology’s utility in treating patients with outflow tracts that are either too large or too small to accommodate the device; manufacturers are addressing this shortcoming by developing more flexible stents made of thinner materials. Other questions up for debate include: What metrics should be used to compare PHVT with traditional surgery? What constitutes appropriate patient eligibility criteria? Can PHVT improve upon surgical outcomes overall or only in small patient subgroups?
To address some of these issues, several professional societies, including the Society of Thoracic Surgeons, the American Association for Thoracic Surgery, and the Society for Cardiovascular Angiography and Interventions, last year published a joint position statement on trial designs, control groups, assessment end points, technological development rate, institutional and investigator obligations, and safety issues for PHVT (Vassiliades et al., Journal of the American College of Cardiology, 5/3/05). The position statement notes that the success of clinical trials of PHVT devices “ultimately depends upon a sincere commitment to collaboration between cardiology and cardiac surgery.” Given the steep learning curve associated with PHVT, cardiac surgeons initially may be more intimately involved with the technology’s deployment because they have a greater understanding of valve anatomy than interventionalists (JACC, 5/3/05; Medtech Insight, August 2005). In fact, industry observers note PHVT “appears to be heralding an unusually close collaboration between interventionalists and surgeons” and in the longer term “could help initiate a paradigm shift for cardiology in general, marked by a blurring of specialties.”
Future prospects: From market expansion to surgical threat?
According to some researchers, the future success of PHVT is contingent on the development of “collapsible and compressible valves and stents for delivery and deployment, advances in biomaterials, anticalcification treatment, and innovative valve to stent bonding technologies” (UTMJ, May 2005). Given that PHVT is currently in the very early stages of human development, the Advisory Board expects that the technology will not substantially impact clinical practice until after 2008 (Advisory Board analysis, 2005). Recently, individual human case studies have appeared in prominent journals, and reported procedural results appear promising. However, PHVT is still a long way from demonstrating clinical benefit using methodologies required for FDA approval. As a first step, PHVT is likely to be used to treat severely symptomatic HF patients with no other options. Should the percutaneous implantations prove successful, however, substantial procedural volumes could result post-2008 given a sense among clinicians that the candidate pool—defined by aortic stenosis or MR, presence of severe symptoms despite optimal medical therapy, and inability to receive surgery—is large. Importantly, in its current form, PMVR does not appear to provide a therapy of the caliber required to pose a serious threat to surgical mitral valve repair in patients who can tolerate surgery. Thus, as noted, percutaneous device utilization would represent an expansion of mitral valve therapy in a wholly new population. In contrast, however, stent-based PAVR appears to represent a more credible substitute for surgery, and more specifically, for the 60% of aortic valve surgeries not involving coronary artery bypass graft.
While not representing an immediate threat to valve surgery volumes, it appears inevitable that PHVT will play a larger, if primarily palliative, role in the future of HF treatment. Notably, this technology may be the development that drives cardiac surgeons to learn catheterization-based techniques.
“Technology Watch” from Advisory.com
