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Ann Thorac Surg 2000;69:1651-1652
© 2000 The Society of Thoracic Surgeons
a Division of Cardiovascular Surgery, Damascus University Medical School, Damascus, Syria
Address reprint requests to Dr Kabbani, PO Box 2837, Damascus, Syria
e-mail: kabanism{at}cyberia.net.lb
The problem of securing an optimal, near-ideal substitute for the aortic valve in a particular clinical setting seems now to have been largely solved. Given a reasonable level of surgical experience, a favorable anatomy and an acceptable myocardial function, the pulmonary autograft (Ross procedure) probably provides the best alternative for the young patient. For the middle-aged patient the aortic homograft (when available) or stentless bioprosthesis is probably the most suitable option, although long-term results for use of the latter are still forthcoming. All three substitutes obviate the need for anticoagulation and allow free flow of blood without producing a gradient (ie, for improved ventricular function), with viability an added bonus in the case of the autograft. As for the elderly patient, the stented heterograft is probably the valve of choice, barring the presence of a small annulus, which may again invite the use of a stentless bioprosthesis. The mechanical valve is thus relegated to those situations in which the surgeon is not comfortable with the first three options, in which homografts and stentless heterografts are not available, or in which the patient’s clinical condition demands a fast, expedient operation.
This salutary state of affairs enjoyed by the aortic valve, however, does not apply to the mitral valve, disorders of which continue to make up the most common indication for open heart surgery in developing countries still suffering from the ravages of rheumatic fever [1, 2].
Although, contrary to the aortic valve, the mitral valve frequently lends itself to repair, reconstruction of the rheumatic mitral in particular is fraught with many difficulties. It is associated with a high early and late failure rate and is plagued with a high reoperative rate, especially in young patients who suffer from repeated rheumatic exacerbations [3]. Sooner or later, almost all of these valves require replacement, at which time the surgeon has to face the quandary of what to replace them with.
The customarily employed mechanical prosthesis harbors an incidence of thromboembolism in most of Asia, Africa, and South America that in all probability far exceeds the traditionally quoted 2 to 3 per 100 patient-years. Many of the rheumatic patients come from remote areas with no laboratory facilities. When available, these laboratories do not produce standardized, dependable results. Anticoagulants in many of these regions are not uniform, are sometimes outdated, and are in many instances too expensive for the poorer patients. Inadequate health education and noncompliance of the affected children and young adults add their deleterious effects to all of the above, making long-term survival rates after mitral replacement in developing countries extremely poor, and lower than the already low survival rates reported in the West. The polished, polymerized new mechanical models are manufactured to last the duration of the patient’s life—only the patient’s life, at least in the developing world, is usually rendered too short to benefit from their superior qualities.
The argument that atrial fibrillation, from which about half of the adults with mitral disease suffer, legitimizes the use of mechanical valves (as these patients need to be anticoagulated anyway) misses the point that the risk of thromboembolism from mechanical prostheses far outweighs the risk of thromboembolism from atrial fibrillation alone. Furthermore, many patients revert to sinus rhythm after their mitral operation, and ways and means for dealing with atrial fibrillation secondary to mitral disease are continuously developing [4, 5].
Although the issue of thromboembolism is largely avoided with stented bioprostheses, these heterografts are not a valid option for the mostly young rheumatic patients in Third World countries. They calcify in the young, and do so faster in the mitral than in the aortic position. Use of these substitutes should probably be confined to the few elderly mitral patients. Both mechanical prostheses and stented heterografts, furthermore, have rigid contours that do not comply with the flexible native annulus, thus probably impairing cardiac function, and both produce significant gradients in the smaller sizes.
The recent revival of the idea of mitral replacement with mitral homograft has been cause for enthusiasm and excitement [6]. Application of this technique, however has been sporadic and not outstandingly successful. Like all homografts this substitute is not freely available. Other problems include those of choosing the best method of graft handling and preservation; of assessing graft size and avoiding homograft/patient valve mismatch; of establishing the proper length, tension, and appropriate alignment of the subvalvular apparatus; and of obtaining a secure papillary muscle attachment. Of course, durability of this potentially excellent, nonthrombogenic, nonobstructive valve substitute cannot be judged until we have sufficient follow-up data on the few reported series. (We may recall that the aortic homograft in the mitral position, antibiotic-sterilized and implanted within a Dacron tube support, started to degenerate about 7 years after implantation [7]). Nonetheless, one can surmise that the mitral homograft is still a long way from attaining the stature that the aortic homograft enjoys at present.
Two new alternative substitutes have recently been advertised. A stentless heterograft, chordally supported and made of four tanned bovine pericardium leaflets, has had a multicenter trial with encouraging early results [8, 9]. The designers hope that anticalcification treatment of the pericardium and the stentless design will decrease the incidence of valve failure from calcification and tissue wear. This is the closest corollary to the stentless aortic heterografts yet tried in the mitral position in humans. Along the same line, a stentless mitral xenograft is presently being tested in the animal laboratory [10]. Again, only time will tell how durable these attractive heterografts are going to be.
The second recent development is the revitalization of the original Ross principle applied to the mitral valve [11]. The inverted pulmonary autograft is supported by a Dacron tubing and its distal end sutured to the annulus of the excised mitral valve. The patient’s pericardium is used as a collar proximally to anchor the conduit to the adjacent atrial wall and to cover prosthetic material. Although this operation is rather difficult and harbors a "learning curve," it promises to do for the mitral valve what the classical Ross procedure has offered the aortic.
The pulmonary autograft conduit is fully flexible and accommodates to the natural annulus, is nonthrombogenic and nonobstructive, and results in minor or no residual insufficiency, qualities it shares with the homograft and quadricusp heterograft. Sizing does not seem to be an important issue, and the Dacron tubing acts as a stabilizing mechanism against progressive annular dilatation. The advantage of maintaining valve–left ventricular continuity enjoyed by the mitral homograft and heterograft can be kept in the case of the pulmonary autograft by any one of the mitral valve preservation techniques, or by leaving the mitral leaflets intact if they are not causing any obstruction to blood flow. Of course, the chief merit of the pulmonary autograft is in its being living autogenous, potentially permanent tissue, which makes it especially suitable for young patients. As with the classic Ross operation, however, the late outcome will be tempered by the fate of the right ventricular outflow graft.
Rheumatic heart disease, although rapidly disappearing in the industrial nation-states, is still rampant in the developing countries, which make up more than two-thirds of the world population. Rather than showing evidence of decline, its incidence may even be increasing in some of these countries because of the effects of declining economic standards, malnutrition, overcrowding, and urbanization [12].
Although great stress should be laid on proplylaxis and control of rheumatic fever, more efficient methods should also be developed to treat the tens of millions of young people who are presently disabled by rheumatic heart disease, the great majority of whom suffer from disorders of the mitral valve, whether alone or in combination with other heart valves. To say that this problem does not deserve much of our attention because rheumatic fever is sooner or later going to disappear from the world health scene is, to my mind, akin to saying that we should not pursue improved ways of managing coronary artery disease because it is going to dwindle with the progress being made in the proplylaxis of arteriosclerosis.
There are candidates for operations on the mitral valve in the world today that out-number candidates for coronary artery surgery many-fold; yet the thrust of medical research and technical development in our specialty has been mainly directed at improving the management of coronary artery disease and its off-shoot, heart failure. I believe it is time that we rearrange our priorities and concentrate our endeavor on solving this vexing international problem, which is seriously affecting the very elements on whom world development depends: the young people. Finding an affordable, readily available, optimal substitute for the mitral valve is one great step in that direction.
References
This article has been cited by other articles:
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  S. Kabbani, H. Jamil, F. Nabhani, A. Hamoud, K. Katan, N. Sabbagh, A. Koudsi, L. Kabbani, and G. Hamed Analysis of 92 mitral pulmonary autograft replacement (Ross II) operations. J. Thorac. Cardiovasc. Surg., October 1, 2007; 134(4): 902 - 908.e7. [Abstract] [Full Text] [PDF]
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 T. Athanasiou, A. Cherian, and D. Ross The Ross II Procedure: Pulmonary Autograft in the Mitral Position Ann. Thorac. Surg., October 1, 2004; 78(4): 1489 - 1495. [Abstract] [Full Text] [PDF]
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S. S. Kabbani, H. Jamil, A. Hammoud, J. A. Hatab, F. Nabhani, R. Hariri, N. Sabbagh, and D. Ross The mitral pulmonary autograft: assessment at midterm Ann. Thorac. Surg., July 1, 2004; 78(1): 60 - 65. [Abstract] [Full Text] [PDF]
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S. S. Kabbani, H. Jamil, and A. Hammoud Technique for replacing the mitral valve with a pulmonary autograft: the Ross-Kabbani operation Ann. Thorac. Surg., September 1, 2001; 72(3): 947 - 950. [Abstract] [Full Text] [PDF]
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 S. S. Kabbani, H. Jamil, A. Hammoud, F. Nabhani, R. Hariri, N. Sabbagh, and D. N. Ross Use of the pulmonary autograft for mitral replacement: short- and medium-term experience Eur. J. Cardiothorac. Surg., August 1, 2001; 20(2): 257 - 261. [Abstract] [Full Text] [PDF]
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 S. S Kabbani Is it Time to Look for an Alternative? Asian Cardiovasc Thorac Ann, June 1, 2001; 9(2): 79 - 81. [Full Text] [PDF]
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