Author + information
- John W. Moore, MD, MPH⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. John W. Moore, Division of Cardiology, Rady Children's Hospital/University of California San Diego, 3020 Children's Way, MC 5004, San Diego, California 92123
Rarely in one's professional lifetime does one experience the introduction of a game-changing technology. The transcatheter heart valve is a game changer. Only a few years ago, transcatheter valve replacement was thought to be impossible. Today, however, this new technology heralds a revolution in valve replacement therapies that promises to extend the lives of the “inoperable” and to offer less-invasive alternatives to other patients.
Available evidence already supports the use of transcatheter valve technology in patients with severe senile calcific aortic stenosis and in patients with pulmonary conduit valve dysfunction. With respect to aortic stenosis, the PARTNER (Placement of AoRTic TraNscathetER Valve) trial results are available for the cohort of patients deemed not suitable for surgery (cohort B). In this cohort, patients having transcatheter aortic valve implantation with the Edwards Sapien heart-valve system (Edwards Lifesciences, Irvine, California) experienced improved 1-year survival and reduced repeat hospitalizations as compared with patients receiving medical therapy (including balloon valvuloplasty) (1). Among patients with congenital heart disease, it has not been feasible to conduct adequately powered randomized controlled studies such as the PARTNER trial. However, patients with pulmonary conduit valve dysfunction have been evaluated with a rigorous, single-arm, multicenter controlled study, using performance criteria derived from historical data. Patients having implantation of the Melody transcutaneous pulmonary valve (Medtronic, Minneapolis, Minnesota) were found to have 1-year safety and efficacy outcomes similar to those expected from surgical valve/conduit replacement (2). Although both the Sapien and the Melody devices are early generation technologies, the current valve designs have been granted regulatory approvals in the Eurozone. In the United States, approval of the Sapien valve for aortic stenosis seems likely, given the PARTNER trial results, and the Melody valve has already been granted approval for pulmonary conduit valve dysfunction.
In this issue of the Journal, Roberts et al. (3) report an “off-label” application for the Melody transcutaneous pulmonary valve: replacement of the tricuspid valve. In their report, Roberts et al. (3) have combined anecdotal experiences from 8 active “Melody centers,” each of which obtained institutional review board approval of Melody valves for use in the tricuspid valve position. Fifteen patients who had dysfunctional, surgically placed tricuspid bioprostheses and subsequent percutaneous implantation of a Melody valve were identified and combined into a small case series. Using percutaneous approaches, the authors successfully implanted Melody valves in stenotic and/or regurgitant tricuspid tissue valves either in the orthotopic position or in right atrium to right ventricle conduits. Patients undergoing these procedures were uniformly symptomatic and high risk. Among those treated primarily for valve stenosis, there was an impressive drop in the mean valve gradient to only 3.9 mm Hg. Furthermore, no patient had more than mild regurgitation after implantation, and most patients had no detectable regurgitation. One critically ill patient died 20 days later from complications unrelated to valve implantation. Another patient required pacemaker implantation for heart block, and a third patient developed endocarditis in the Melody valve requiring device explant. At last follow-up (median 4 months), 13 patients retained the Melody valve in the tricuspid position, and 12 patients have experienced improvement in New York Heart Association functional class.
This is a limited report. It demonstrates that implantation of Melody valves to replace dysfunctional tissue valves in the tricuspid position is feasible, usually functional, and probably relatively safe. However, no definitive statements about the durability of this valve in the tricuspid position, about efficacy, or about safety can be made; nor does this report add testimony to the controversy about whether bioprosthetic or mechanical valves should be used to replace dysfunctional tricuspid valves.
This report is significant because it chronicles a measured step toward a new application for transcatheter valve technology. In doing so, it also opens the door for another measured step in the same direction: use of the larger diameter Sapien valve in similar clinical circumstances. As compared with the Melody valve, the Sapien valve has the potential advantage of extending the range of applicable valve annuli or conduit diameters, and thereby expanding the number of patients with tricuspid valve disease who may be eligible for percutaneous valve therapy.
Through many such measured steps, transcatheter valve technology will likely evolve and progress. For example, transcatheter aortic valves will likely be implanted in lower-risk patients. Recently presented results of the PARTNER trial's cohort A (patients with high surgical risk) suggest that transcatheter aortic valve replacement is not inferior to surgical valve replacement in preventing mortality at 1 year. However, because the rates of neurological complications favored surgical aortic valve replacement, the cohort A results are not definitively in favor of the transcatheter valve (4). Yet, this is not the final word on the subject. After all, the CoreValve (Medtronic) has a completely different design, and Medtronic is just now embarking on a major randomized clinical trial structured much like the PARTNER trial. The Medtronic study will provide another rigorous dataset comparing high-risk patients randomized between surgery and percutaneous CoreValve implantation. Furthermore, transcatheter valve technology will also be applied to a wider spectrum of patient pathologies including bicuspid aortic valves (5), failed stentless bioprostheses (6), and possibly also to younger patients with aortic valve disease.
Other steps are also being taken in completely different arenas. For example, 3-dimensional models generated from magnetic resonance images of dilated pulmonary trunks found in patients with severe pulmonary insufficiency are being used to design valved stent grafts suitable for percutaneous implantation (7,8). This work raises the possibility that percutaneous valves may become available as the first valve implant in patients with valve-less repair of tetralogy of Fallot and other right heart maladies. Alternative ideas, such as dual-valve implantation in the pulmonary artery branches or surgical implant of a “valve landing zone” consisting of an expandable ring during initial repair, may have similar potential implications.
The mitral valve is also worthy of mention as it is a major challenge for transcatheter valve technology. It should be feasible to re-valve dysfunctional mitral tissue valves with Sapien or Melody valves. Although individual cases may have been attempted, none have been reported as of this writing. On the other hand, it is noteworthy that an unrelated technology, percutaneous mitral valve repair, is showing considerable promise. The MitraClip System (Abbott Laboratories, Abbott Park, Illinois), which employs edge-to-edge technology, is the most developed. This technology is being compared with surgical valve repair in the EVEREST II (Endovascular Valve Edge-to-Edge Repair Study) trial (9). The results will undoubtedly be interesting.
Finally, valve and implant system designs are also evolving by numerous small steps. A variety of valves and valve materials are being used, including intact bovine venous valves, valves constructed from bovine or porcine pericardium, and valves constructed of nitinol foil. A large number of valve designs and technologies are being explored, including at least 17 different aortic valves. Improved valve designs and technologies have facilitated reduction of percutaneous implant systems to diameters as small as 16-F (10). In addition, a variety of percutaneous and hybrid techniques are being evaluated for valve implant. Taken all together, these activities are facilitating development of more functional and more durable valves, and permitting valve implantation in smaller patients.
Today, the future role of transcatheter valve technology in the “big picture” of valve repair and replacement therapies is clear. It is fair to say that transcatheter valve technology will continue to advance, and it will become a significant alternative to traditional valve surgery. This technology is challenging our assumptions and changing our practice. The Roberts et al. (3) report is a harbinger of things to come. (9)
Dr. Moore has reported that he has no relationships to disclose.
↵⁎ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
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