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EDITORIAL |
Créteil, France
Daniel Loisance, MD Email: Daniel.loisance{at}wanadoo.fr
Selection of the optimal valve substitute is one of the most difficult issues in the young adult. The recent recommendations of the American Heart Association have solved the problem in patients above 65 years of age: tissue valves are preferable. However, the guidelines are not very precise for patients aged less than 65 years. They point out the recent extension of longevity of the tissue valve and recommend discussing lifestyle issues and risks of anticoagulation and reoperation with the patient. In real life, this recommendation leaves the surgeon with a very difficult predicament, especially in adults aged from 20 to 50 years.
The alternatives are many when valve replacement becomes necessary in the young adult population, i.e., when valve repair appears not to be indicated or has failed. The choice is between a mechanical valve and a tissue valve. Among tissue valves, there is the natural tissue valve: the autograft (Ross operation); the homograft; and the bioprosthesis, porcine or bovine, stented or stentless. All large longitudinal follow-up studies comparing mechanical valves with tissue valves have yielded interesting data at odds with the general perception: patient longevity and rate of reoperation do not differ between tissue and mechanical valves. The only differences are the nature of the valve-related events and the causes of reoperation; mechanical valves are more likely to give hemorrhagic complications, while tissue valves fail because of structural dysfunction and more frequently need repeat replacement. The limitations of these large studies are nevertheless obvious: they did not consider the different age groups in the young adult population; and they involved only the first generation of tissue valves, which obviously are not used anymore. This therefore leaves the cardiologist and the surgeon with a problem. This editorial is intended to help in this difficult decision-making process.
THE PATIENT
Valve selection depends on the patient’s characteristics and general condition, and will differ between a quite healthy athletic young adult and one with comorbidities such as renal insufficiency. For the former, quality of life is probably the main issue, outweighing even length of life, and this type of patient will usually not accept any limitation, unlike the latter who is used to living with restrictions. It is also necessary to consider the underlying valve disease. Despite the high prevalence of rheumatic heart disease in Asia, a frequent indication for aortic valve surgery in the young adult is some variety of congenital disease. It might be a bicuspid valve, either asymptomatic or with aortic stenosis or regurgitation. In this case, the associated pathology of the aortic sinus will eventually lead to the selection of a root replacement with or without valve replacement, radical excision of the abnormal tissue being advisable in view of the risk of progression of aortic wall pathology after valve replacement. In a patient with a small aortic orifice requiring an additional annulus enlargement technique, the surgeon will prefer a mechanical valve, to minimize the risk of reoperation. The condition of the left ventricle is another important parameter because, in a patient with a low ejection fraction, selection of the best valve in terms of hemodynamic performance is important to optimize left ventricular mass regression.
Evaluation of the patient’s lifestyle remains a difficult issue. Considerations will differ between a patient who lives far from any possibility of coagulation monitoring and one resident in a developed city, between a patient who leads an active life, travels, and engages in risky activities and one who lives quietly at home. A well-educated individual will have a better understanding of post-replacement healthcare issues, including prevention of infection, than someone who has difficulty grasping the basics of artificial valves. The noise of a mechanical valve is another issue and may be a problem in psychologically fragile patients. To keep the issue simple, one may contrast the comfort of a tissue valve with daily evidence of the presence of a mechanical valve. Psychological behavior is also important because the risk of reoperation will be accepted more readily by a patient at ease with the idea of repeat surgery than by one terrified by the first operation. Affordability must also be considered: tissue valves tend to be more expensive, and the greater durability of a mechanical valve gives the impression that it is the best option in terms of cost. However, there is nothing more economically catastrophic than a patient with a mechanical valve dying prematurely because of intracranial bleeding.
ANTICOAGULATION
If the patient’s condition and associated problems mandate an anticoagulation regimen, then a mechanical valve is the right decision. However, quite often, anticoagulation is required because of atrial fibrillation, which nowadays may be treated efficiently by ablative techniques. Yet there are no studies showing that tissue valve replacement associated with some efficient technique of ablation for atrial fibrillation is a better option in terms of comfort and longevity than mechanical valve replacement. Also, improvements in the management of anticoagulation should minimize the risk of bleeding, and so a mechanical valve would be preferable to a tissue valve. Home monitoring of the international normalized ratio is effective, but is not used in many countries. Finally, the introduction of oral antithrombin agents should be a turning point in the management of anticoagulation, but is not likely in the near future.
HOMOGRAFT AVAILABILITY
It is widely accepted that the Ross operation is superb and gives outstanding results in the hands of experienced practitioners. However, it cannot be performed routinely because of the scarcity of good homografts, which are necessary for the pulmonary reconstruction. In Europe, this scarcity is the consequence of problems of organ harvesting and of the development of cardiac transplantation: the good hearts are used for organ transplantation. Homografts are obtained from recipient hearts, usually old, or from donor hearts rejected for transplantation purposes. Suboptimal homografts will create a new problem: pulmonary stenosis. The situation looks no better in most Asian countries. Recent developments in percutaneous techniques, such as dilation of the pulmonary valve and transcatheter valve technology, may eventually improve the situation.
VALVE PERFORMANCE
Valve performance is adjudged in various ways, starting with ease of implantation. Mechanical valves present no specific problem; most are extremely low-profile valves, with comfortable sewing rings. However, primary valve dysfunction may result from an inadequate technique; suture entrapment in the orifice, leading to a leaflet or disk blockage, is a serious and very often underestimated risk. Tissue valves are no different with regards to ease of implantation. The height of the stent post, for example, which often raises the fear of rupture of the left ventricular wall, is actually not a problem even in a small left ventricle associated with tight mitral valve stenosis. There are almost no reports of this kind of complication. The risk of a suture loop at the tip of the stent post is more real, and is never addressed. Stented valves look very much like mechanical valves, despite a higher profile. Stentless valves may appear more difficult to implant, the technique being closer to that of the autograft than that of the mechanical valve. This technical limitation can, however, be overcome by adequate training of the surgeon and standardization of the technique.
Hemodynamic performance will depend on transvalvular gradients and the effective orifice area, and also on parameters rarely considered or even known by surgeons: the duration and mode of leaflet opening, regurgitant flow during closure, and closure time. These parameters determine energy loss that defines the extent of left ventricular remodeling, expressed by loss of left ventricular mass, which is a key parameter for survival of the patient.
The durability of the valve and the mode of failure (acute or progressive) are important in the selection of the optimal valve for an individual patient; the extent of freedom from valve structural dysfunction is the parameter most often considered. Nevertheless, few studies are available on freedom from structural valve dysfunction in the very young age ranges only. Structural valve dysfunction being very closely related to the actual age, major differences can be expected between the very young patient and one close to the 65-year limit.
The mode of failure, acute or slow, is probably as important in real life as the actual duration of good function; the chances of the patient getting back to a specialized hospital are minimal in the case of acute failure. In addition, the operative risk per se may be expected to be higher in an emergency operation for acute failure than in an elective operation for semi-acute dysfunction. Mechanical valves are more likely to show acute dysfunction than tissue valves. The nature of the valve-related complication is another key parameter. The severity of bleeding events, especially intracranial bleeding in patients on anticoagulation regimens, which is difficult to treat, must be weighed against progressive calcification of the tissue valve which can be replaced with minimal risk.
ADVANCES IN TECHNOLOGY
Technological developments are rapidly changing the outlook, and transcatheter valve technology may have the most significant impact on younger patients in terms of optimal valve selection. So far, the transcatheter valve has been used in inoperable patients only. However, considering the rapidity of the learning curve and the pace of technological progress, transcatheter valves may in the very near future be used in operable patients, and offer an alternative to conventional techniques. Transcatheter placement of a valve affords rapid functional improvement without the need for general anesthesia, surgical closure of the femoral artery access, circulatory support, or rapid pacing during the implantation. These benefits are appealing and meet the expectations of many patients who are ready to try any treatment that avoids the need for major surgery.
Uncertainties about the medium- and long-term results of transcatheter valve insertion might not be a problem; the long-term benefit of a surgical intervention has less impact on the patient’s decision than the invasiveness of the procedure. The preference for stenting techniques over surgery in triple coronary artery disease clearly shows the lack of impact of scientific data on the patient’s decision (surgery gives better long-term results than the percutaneous techniques of revascularization), inasmuch as the noninvasive technique may be repeated without discomfort as many times as necessary. Nevertheless, the cardiologist should inform the patient about the issue of the durability of the repair. Actually, one may be skeptical about transcatheter valve durability, which may be seriously affected by abrasion of the leaflets by calcified excrescences crossing the stent frame. This may alter the integrity of the cusp, cause minimal cusp dysfunction due to suboptimal placement of the valve, or changes in the mechanical properties of the material after implantation (the stent itself and the tissue of the cusp), possibly precipitating structural valve dysfunction and the evolution of perivalvular leaks, which are quite frequent in the post-deployment period.
Despite these words of caution, interventional cardiologists are already promoting a new strategy: the valve-in-valve concept. The first valve is implanted surgically. The next valve, following structural valve dysfunction, is implanted using a percutaneous technique. Cardiologists even claim that it should be easier to implant a transcatheter valve in a stented or stentless valve than in a native calcified orifice. This new strategy might be very attractive for the young patient afraid of the risks of repeat conventional surgical replacement. Solid data are nevertheless necessary to put this new approach on a solid footing.
We can conclude from this analysis that there is a trend towards more frequent use of tissue valves in younger patients, mainly because they offer a better quality of life. Nevertheless, there is clearly still a need for prospective randomized trials to compare the best available mechanical and tissue valves in younger patients.
Asian Cardiovasc Thorac Ann 2010;
18:10-12
© 2010 by SAGE Publications
DOI: 10.1177/0218492309355724
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