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Eur J Cardiothorac Surg 2007;31:1-3. doi:10.1016/j.ejcts.2006.10.001
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved
Editorials |
Cardiothoracic Surgery, University Hospital, 3000 Coimbra Codex, Coimbra, Portugal
* Corresponding author. Tel.: +351 39 400418; fax: +351 39 829674. (Email: antunes.cct.huc{at}sapo.pt).
Since the introduction of the first valve prosthesis in the early 60's, aortic valve replacement (AVR) has contributed to better, and in many cases to save, the lives of hundreds of thousands of patients. From the early Starr ball-valve (not to mention the precocious Hufnagel valve), several types of prostheses, both mechanical and biological, were developed and recent models have reached high-level performances, which succeed in returning patients to good quality of life and to survivals that match those of the normal population. Today, aortic valve replacement is the most common valve operation and one of the most common open heart procedures, after CABG, performed throughout the world. In most cases, the procedure is performed to treat aortic stenosis, which affects between 2% and 5% of elderly individuals in most developed countries.
Currently, on-pump aortic valve replacement is carried out with very low mortality and acceptable morbidity in the vast majority of patients and only exceptionally it is denied to patients considered to be too high-risk because of the presence of significant co-morbidity. Hence, this procedure remains as the golden standard for the treatment of aortic valve stenosis and/or regurgitation. Nonetheless, it may be conceded that there are a few patients who may constitute unacceptably high risk for open heart procedures. Hence, efforts to treat aortic stenosis by less invasive, lower risk methods have been made in the last decade. Following a relatively successful utilization in neonatal aortic stenosis, balloon commissurotomy was attempted in patients with calcific aortic stenosis (AS), especially in the elderly, mostly with deceptive results and the procedure was almost abandoned. Results from several individual centres and the multicentre NHLBI registry showed only a modest early clinical improvement, a substantial incidence of peripheral vascular complications, a 30-day mortality of up to 10%, and a high incidence of re-stenosis at 6 months. Its use is currently limited to desperate situations.
Hence, the concept of non-surgical valve replacement has evolved. It was first applied to the pulmonary valve, because this valve is more easily reached and tolerates less than perfect results better than the aortic valve. After a short period of animal experimentation, the first implantation of a valved stent in the pulmonary position was reported in 2002 by Bonhoeffer et al. [1,2] in patients with ventricle to pulmonary artery prosthetic or allograft conduit dysfunction. To date, more than 100 patients have been treated by the abovementioned authors, with only one procedure-related death and good results in paediatric patients with congenital heart disease who otherwise would face repeated open heart procedures. Clearly, percutaneous pulmonary valve replacement has been remarkably successful, but the experience is limited to a small number of teams and only short-term results are available [3–5].
Extension to the aortic valve was inevitable and was most probably behind the initial interest in the pulmonary valve, since percutaneous valve therapy developed initially with aortic valve replacement, described in 1992 in a swine model [6]. Early experimental work in animals by Bonhoeffer and Boudjemline and others [7–9] paved the way for use in man, but Cribier et al. [10] is credited with the first human percutaneous transcatheter implantation of an aortic valve prosthesis for calcific aortic stenosis. Since then, many operators and teams, both cardiological and surgical, throughout the world have enthusiastically embarked on programs of non-invasive or minimally invasive, off-pump, aortic valve replacement. Several models of stent-fixed valve have been developed and newer modifications are introduced almost on a daily basis [11]. Currently, more than 20 companies work in the development of these valve substitutes and the Cribier–Edwards stent-fixed aortic valve prosthesis is already being utilised regularly in the clinical setting, using a percutaneous approach. From past experience with other novelties, the magnitude of the funds currently being invested by major medical companies and startup companies will clearly drive this technology forward rapidly.
In the initial procedures, the catheter-mounted valved stents were delivered into the aortic annulus by an antegrade transeptal approach, but this method was technically difficult to master, especially with regard to the ability to accurate intraannular positioning and was soon abandoned in favour of a retrograde arterial method. The ability of patients to tolerate the retrograde approach is clearly better than for the antegrade technique, but large-calibre arterial access remains a major limitation of this method, which requires femoral arterial anatomy that permits the introduction of a 24F sheath to deliver a 26 mm prosthesis. The smaller valve used in the early experience was linked to a high incidence of periprosthetic leakage and the larger 26 mm valve is now preferentially used.
Peripheral vascular access in patients with diseased or small iliac-femoral vessels will be a stumbling block in many of these elderly patients. Additionally, these transcatheter-based methods have some other limitations which include risk of embolization due to pre-dilatation and detachment or fragmentation of atherosclerotic plaques, migration of the valved stent, paravalvular leakage and, probably, limited durability of the prosthesis. Finally, for someone who has seen more than a thousand of extremely ‘rocky’ valves, it is unimaginable that some of these valves can be pre-dilated. Nonetheless, several papers published in the last 2 years are testimony of the interest triggered by these procedures, and the technique was recently extended to the mitral valve [12,13].
To offset some of the limitations of transarterial approaches, an alternative method was developed which consists of a transapical transcatheter delivery of the valved stent, which may be performed endoscopically or through a small thoracotomy. Direct access through the left ventricular apex has some advantages but presents additional technical challenges [14,15]. Easier and more accurate deployment without the many complications of intravascular manipulation, especially those related to atherosclerotic plaques which are present in the majority of these cases, are the recognized advantages of this method. In most cases, surgeons, alone or in association with cardiologists, were in the forefront of this development and it is clear that it was undertaken as their response to the cardiologists’ endeavours and an effort to ‘stay in business’. The papers by Tozzi et al. [16] and Ye et al. [17], which appear in this issue of the Journal, are indicative of the current status and initial results of this method. Other groups have also reported encouraging early results [18].
Percutaneous stent-mounted bioprosthetic implants for valve replacement may have a special role in repeat valve replacements. Besides replacement of degenerated homograft conduits in the right ventricular outflow tract which constituted the original pulmonary valve experience, this may be important, for example, in Fontan patients with bioprosthetic valve conduits. Bonhoeffer [19] have already reported re-replacement of percutaneous stent-mounted valves and a few patients have already undergone re-replacement with a third valve.
Naturally, perhaps because of the very fast development of these techniques, a great deal of controversy and confusion is installed. In an attempt to clarify the subject, the Society of Thoracic Surgeons (STS) and the American Association for Thoracic Surgery (AATS), in conjunction with the Society for Cardiovascular Angiography and Interventions (SCAI), have recently issued a position statement on the clinical development of percutaneous heart valve technology, which cautions against unjustified wide use of these procedures: ‘Many critical questions remain unanswered, including the durability of these devices and the potential adverse effects they may have on subsequent heart valve surgery. Therefore, one cannot justify the use of these experimental technologies in patients for whom published guideline indications do not exist or in situations of prophylactic therapy until data on safety and effectiveness are gathered from well-designed clinical trials’ [20].
Up to now, percutaneous aortic valve insertion has allegedly been carried out on a compassionate basis in patients considered to be ‘extremely high-risk’ for surgical AVR. However, significant para-valvular regurgitation and early mortality characterize the experience thus far and this raises many questions about the indications and may have important ethical implications. Yet, as stated by Loisance [21], ‘the concept of a less than perfect, temporary repair, is now surprisingly widely accepted, a concept surgeons are nevertheless not intellectually ready to accept!’.
Although the concept of percutaneous replacement of heart valves appear promising, it is clear that this technology is in its infancy with a manifest inability to achieve consistent results, which have, up to now, failed to meet the expectations. As stated by Feldman [22] in a recent editorial, ‘at the stage of concept and early design development, all new devices appear to offer novel, definitive solutions to important clinical problems. The first stages of animal testing typically amplify the excitement of the design phase. It is only when initial human experience begins that the real limitations of new approaches become apparent. It is unavoidable that unanticipated challenges will arise in the first patients treated with a new device. It is only at this stage that problems can be solved. It is the solution of these problems that ultimately leads to successful therapies’.
I have little difficulty in accepting that percutaneous valve replacement may eventually offer substantial advantages to some patients. It constitutes a less invasive procedure, which may help reduce surgical risks and lower complication rates and shorten rehabilitation times. From an economic standpoint, shorter hospital stays result in overall cost reduction [23], but these desiderates are still far from being fully achieved. Above all, they cannot be pursued at the expense of patients’ safety. Immediate results are important but medium and long-term outcome is also under scrutiny. The durability of the stent-mounted tissue valve is yet unknown. Most models are constructed of equine pericardium, a tissue that was not adequately tested in classical valve prostheses. Haemolysis from the perivalvar leaks may be more of an issue than the haemodynamic burden of the regurgitation [24]. All these concerns need to be addressed if these techniques are to achieve widespread application, not just in high-risk cases.
On the other hand, the term ‘high-risk’ surgical patient is very broad and can accommodate virtually any situation. Patient selection in these first experiences may be questioned. Experienced cardiac surgical teams performing valve surgery have consistently reported excellent results, even in elderly high-risk populations. As correctly stated by our Chief-editor, ‘it behoves the cardiac valve surgeon to support and explore surgical innovations based on developments in direct access and percutaneous valve replacement, advancing the art and science of minimally invasive cardiac techniques’ [14], but we must perform the science rigorously to ensure patient safety and learn how to advise patients about the variety of options that will ultimately be available. The model of ‘bail-out’ cardiac surgery after failed percutaneous coronary intervention for coronary artery disease will not be easily transferred to percutaneous approaches to valve replacement [24]. These procedures require skilled operators who still need specific training before engaging in percutaneous valve procedures, which should be confined to only experienced intervention cardiologists and surgeons. On the other hand, this is a field where collaboration between the surgeon and cardiologist, functioning as a team, will become essential. Together they can develop the techniques that ensure appropriate patient selection and guarantee patient safety.
In conclusion, however enthusiastic the current mood may be, in my opinion, which may not be read as a condemnation, this technology is still far from the stage of mass application and it probably will never replace conventional valve replacement surgery. Obviously, after this initial enthusiasm, which is not necessarily unhealthy, and auto-proclaimed good results [25], the time has been reached to implement well planned and appropriately conducted comparative studies to determine the potential advantages of these technologies. Study candidates should consist of symptomatic patients in whom medium and long-term survival is anticipated to be severely compromised and the results of conventional surgical valve replacement rigorously calculated to be well above acceptable values. These studies would allow the collection of mid-term device durability data while providing much needed clinically relevant safety and effectiveness data. But this may be hampered by the continuous evolution of the devices.
The road to progress must be walked but, as stated in the abovementioned joint position statement, ‘our collective enthusiasm for new, less-invasive cardiovascular approaches should not divert us from the importance of evaluating these devices in the context of a controlled clinical trial environment’.
Only then may we be in a position to predict the future.
References
This article has been cited by other articles:
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  R. H. Bombien, M. Appel, T. Attmann, G.-R. Klaws, M. Schunke, C. Hass, J. Cremer, and G. Lutter Percutaneous aortic valve replacement: gross anatomy and histological findings after transapical and endoluminal resection of human aortic valves in situ Eur. J. Cardiothorac. Surg., July 1, 2009; 36(1): 112 - 117. [Abstract] [Full Text] [PDF]
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 M. E. McRae, M. Rodger, and B. A. Bailey Transcatheter and Transapical Aortic Valve Replacement Crit. Care Nurse, February 1, 2009; 29(1): 22 - 36. [Full Text] [PDF]
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N. Khaladj, M. Shrestha, S. Peterss, I. Kutschka, M. Strueber, L. Hoy, A. Haverich, and C. Hagl Isolated surgical aortic valve replacement after previous coronary artery bypass grafting with patent grafts: is this old-fashioned technique obsolete? Eur. J. Cardiothorac. Surg., February 1, 2009; 35(2): 260 - 264. [Abstract] [Full Text] [PDF]
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 M. J. Antunes Percutaneous aortic valve implantation. The demise of classical aortic valve replacement? Eur. Heart J., June 1, 2008; 29(11): 1339 - 1341. [Full Text] [PDF]
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 R. Quaden, T. Attmann, M. Schunke, D. Theisen-Kunde, J. Cremer, and G. Lutter Percutaneous aortic valve replacement: Endovascular resection of human aortic valves in situ. J. Thorac. Cardiovasc. Surg., May 1, 2008; 135(5): 1081 - 1086. [Abstract] [Full Text] [PDF]
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