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EDITORIAL |
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Department of Cardiovascular Surgery Damascus University Medical School Damascus, Syria |
In countries that boast optimal education and health facilities, thromboembolic complications of valve replacement are reported within the range of 1 to 3 per 100 patient-years.1 However, once we move to regions with less fortunate economic and health standards, we encounter a totally different picture. Patients are often too poor to afford the medications and laboratory tests that are a prerequisite to anticoagulation. They frequently lack the health awareness necessary for an altered demanding lifestyle. Nor is the uncertain quality of medications and laboratory facilities in these regions, or the fact that the valve in question is often the mitral, the more notorious for thromboembolic complications, of any help in this regard.
In a study of patients followed up after mitral valve replacement with the St. Jude Medical valve in an Indian community hospital, the risk of thromboembolism was 12.5 per 100 patient-years. This rose to 22.2 per 100 patient-years in double valve replacement. Subtherapeutic anticoagulation was considered the key factor for this potentially fatal complication.2 Women of childbearing age are particularly prone to thromboembolic and bleeding sequelae of mechanical valve replacement, not to mention the risk of anticoagulant embryopathy.3,4 Young rheumatic patients with mechanical valves are also subject to the bleeding and thromboembolic complications associated with accidents and incidental operations.5 All of these must reflect on survival rates which are rendered extremely poor after mechanical (especially mitral) valve replace-ment in developing countries, and which must be much worse than the already low rates reported in the West.6 Replacing an irreparable rheumatic mitral valve with a mechanical prosthesis may be a straightforward expeditious operation for the surgeon, but it undoubtedly puts the patient in constant jeopardy. What can be done to ameliorate this problem, so common in Third World countries?
One theoretical possibility is to improve the way we conduct our anticoagulation, but this has been notoriously unsuccessful over the years. It is now evident that antiplatelet drugs cannot replace warfarin, and combining them with oral anticoagulants (in the hope of reducing the dosage of the latter) can increase hemorrhagic complications.7 The new expensive low- molecular-weight heparin is not foolproof, and anticoagulation self-management, although claiming some advantages in the West, is not practical nor affordable in emergent societies.8,9 The optimal level of anticoagulation for an individual patient remains as elusive as ever.10 Another theoretical possibility is to make the durable mechanical valve nonthrombogenic, but this has never yet been achieved, despite all the efforts of physicians, biochemists, and bioengineers. Every time a new valve hits the market, claims of low thrombogenicity are made, only to be refuted by the sobering postoperative data. The more practical solution is to change the offending valve substitute, the mechanical prosthesis, which implies the alternative use of tissue valves.
The stented bioprostheses are obviously not an acceptable tissue option in the mostly young rheumatic patients, because of their early degeneration and calcification, especially in the mitral position.11 Furthermore, the rigid contours and bulky rings cause obstruction in the smaller sizes, and impair cardiac function, just as they do in mechanical prostheses. This leaves us with the alternative of stentless tissue valves. Several attractive tissue options are now established substitutes for the aortic valve, such as the pulmonary autograft (Ross procedure), the aortic homograft, and the stentless aortic heterograft. However, the same cannot be claimed for the mitral valve, disorders of which continue to make up the most common indication for open heart surgery in the developing world where rheumatic fever is still rampant.12 Nevertheless, there are 3 suitable options for mitral replacement that the Third World cardiac surgeon ought to recognize (Table 1
). One is to replace the mitral valve with a homograft.13 While this excellent substitute is flexible, nonthrombogenic, and nonobstructive, its use is hampered by problems of availability, valve-size mismatch, and difficulty in obtaining a secure papillary muscle attachment. The durability of the mitral homograft is still in question and will only be determined when we have sufficient follow-up data, but it is doubtful that it is going to match that of the aortic homograft. The second option is the inverted pulmonary autograft supported by Dacron tubing and implanted within the left atrium.14 This operation is more difficult than the previous one and harbors a "learning curve" but has the main advantage of utilizing autogenous potentially permanent tissue, in addition to providing a flexible, nonobstructive, and nonthrombogenic mitral substitute. Sizing does not seem to be a problem, and the Dacron tubing acts as a stabilizing mechanism against progressive annular dilatation. As with the classic Ross operation, the late outcome will be dictated by the fate of the pulmonary graft, but survivals of up to 14 years were reported from the early series.15 The last option is to use the quadrileaflet bovine heterograft, the "Quattro" valve of St. Jude Medical, which is not yet commercially available.16 Although the operation here is somewhat more difficult than the standard replacement with a mechanical prosthesis because the valve is "chordally supported", it can be mastered relatively quickly. It is hoped that the stentless design of the valve and the anti-calcification treatment of pericardium will translate into a lower incidence of calcification and tissue wear. Again, this will have to be substantiated by sufficient follow-up information.
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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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 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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 A T. Pezzella Is It Time to Look for an Alternative? Asian Cardiovasc Thorac Ann, December 1, 2001; 9(4): 356 - 356. [Full Text] [PDF]
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