Transcatheter Aortic Valve Replacement: Here and Now, But Lots to Learn

From the Department of Cardiology, Emory University Hospital, Atlanta, Georgia. The author reports no conflicts of interest regarding the content herein. Address for correspondence: Peter C. Block, MD, Department of Cardiology, Emory University Hospital, 1364 Clifton Rd. NE, F606, Atlanta, GA 30322-1059. E-mail: peter.block@emoryhealthcare.org

J INVASIVE CARDIOL 2009;21:99–100

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In this issue of the Journal of Invasive Cardiology, Tamburino and colleagues from Catania, Italy, report on their single-center registry experience with the third-generation CoreValve percutaneous aortic valve replacement device (CoreValve, Inc., Irvine, California). Only acute and short-term outcomes are described, reflecting experience from January, 2007 through July, 2008. Thirty patients met the eligibility criteria and were enrolled. Their acute procedural success was good, with 1 patient having pericardial tamponade requiring pericardiocentesis and 1 patient having too high an initial placement of the prosthesis, with a second valve-in-valve placement solving the problem. The expected reductions in valve gradient and increase in valve area were achieved. What is learned from this report? Unfortunately, it is a report of a registry comprised of only 30 patients. Thus, it suffers from the fact that it is only a registry, and a small one at that. But there are a number of positive issues that deserve mentioning. First, all implantations were done truly percutaneous, using the CoreValve system which can be introduced through an 18 French (Fr) sheath; second, more than 90% of the patients had procedural success; and third, follow up showed improvement in NYHA functional class. Nevertheless, the report, though it includes only a small number of patients, still shows us that we have a long way to go in refining percutaneous valve replacement. Implantation itself is not perfect. Misplacement can occur even in experienced hands, and as highlighted in this study, can be pseudo-rectified percutaneously by valve-in-valve placement urgently while the patient is still in the operating room or catheterization laboratory, wherever the procedure is performed. Paravalvular leakage is still an important potential drawback. In short-term reports, paravalvular leakage has been well tolerated after percutaneous valve replacement, but despite the clinical sense that mild (1+) or moderate (2+) aortic paravalvular regurgitation is well tolerated by the left ventricle that has been “used to” aortic stenosis, the long-term outcome of such volume loading in a hypertrophied, relatively noncompliant ventricle has not yet been clarified. As with most reports of transcatheter aortic valve replacement, local vascular complications head the list of major problems. Vascular access complications occurred in 17% of patients in this report. One might expect that with a device that passes through an 18 Fr introducer, vascular complications might be significantly reduced over those of larger percutaneous devices. This is not uniformly the case. There were 4 cases of femoral artery pseudoaneurysm, 1 case of total occlusion of the femoral artery treated with thromboendarterectomy, and 1 patient had major bleeding. Perhaps we are all a bit seduced by the concept of an “18 French device”. In truth, all percutaneous transcatheter valve devices are labeled similarly — whether they are called “18 French”, “23 French” or “26 French”, do not be misled by the label. The devices pass through the sheath that is similarly labeled, but the outer diameter of an “18 French” sheath is not 18 French — it is larger by the width of the sheath tubing — usually at least 1 to 2 French sizes greater. Femoral arteries used for insertion of even an “18 French” device must be at least 6 mm in diameter, and ideally 7 mm or more to allow safe passage of the sheaths and device. For a “23 French” device, the femoral artery must be at least 8 mm in diameter. The good news is that many arteries in the pelvis will stretch slightly; the bad news is that not all, especially those with atherosclerotic disease with calcification, do. Finally, the incidence of new-onset complete heart block required for permanent pacemaker implantation was 20%. This apparently high incidence of heart block may be somewhat unique to the CoreValve device, which exerts a continuing expansile force against the upper interventricular septum for a variable time after implantation depending on how much compression the outflow tract exerts on implantation and how much counterforce the expanding nitinol supporting cage exerts. Theoretically, such complete heart block might occur hours or days after implantation as the nitinol slowly expands and compresses the upper septum. The problems associated with all percutaneous transcatheter valve devices are not insurmountable. We as interventional cardiologists can help minimize complications by careful selection of patients, and by not allowing enthusiasm to trump judgment. But in reality, the gauntlet must be thrown to the engineers and designers of any transcatheter therapy. Smaller is almost always better, and we (they) have a long way to go. At 30-day follow up, 2 patients (7%) had died. The report points out that the deaths were not related to the procedure, which is probably correct, but to state that the deaths were not related to percutaneous valve implantation is a reach. One patient died of a hemorrhagic stroke. The authors point out that this was likely due to double antiplatelet therapy with clopidogrel and aspirin, but without a percutaneous valve implantation having been performed, it is unlikely that the patient would have been exposed to that hemorrhagic risk. The second patient died of an “ischemic stroke”. We are not told more, but if the patient was not in atrial fibrillation and possibly had a thromboembolic stroke, certainly the valve struts in the ascending aorta could have been the culprit. On the positive side, no other major adverse events occurred at a mean follow up of 4.9 ± 4.0 months (range 1–13 months). All of these issues are not unique to one or another percutaneous transcatheter valve system, but the list of potential problems using such novel (and exciting) devices is not short, and demands careful attention. Until we know a good deal more about how to minimize complications and problems, such devices should be used in carefully selected patients who have little or no other therapeutic options. I would agree with the authors’ conclusion that their initial short-term experience of percutaneous aortic valve replacement using the CoreValve device in a cohort of older and high-risk surgical patients is encouraging. Clearly, many such patients are high-risk or possibly prohibitive-risk candidates for conventional aortic valve replacement surgery. Successful percutaneous aortic valve replacement for patients who are symptomatic from aortic stenosis will hopefully produce improvement in quality of life, NYHA classification, and most importantly, reduce mortality compared to so-called “conventional” medical therapy. All of these statements are conjectural. Only one randomized trial is under way to evaluate such outcomes — the Edwards Lifesciences PARTNER Trial currently under way in the United States. That trial will attempt to answer a number of questions concerning the safety and efficacy of patients randomized to medical therapy versus percutaneous valve implantation, surgical aortic valve replacement versus transapical (transcatheter) aortic valve implantation, and finally, transcatheter, transfemoral aortic valve implantation versus standard surgical aortic valve replacement. “Softer” endpoints such as 6-minute walking results and NYHA class are also being measured in PARTNER and will likely shed more light on the quality-of-life improvement that percutaneous and surgical aortic valve replacement can produce. Ultimately, it is trials such as PARTNER that will scientifically answer the important questions surrounding the best use of percutaneous valve therapy.