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Eur J Cardiothorac Surg 2005;28:198-199
© 2005 Elsevier Science NL
Original articles |
Department of Cardiovascular Surgery, University of Kiel, School of Medicine, 24105 Kiel, Germany
* Corresponding author. Tel.: +49 431 597 4401; fax: +49 431 597 4402 (Email: lutter{at}kielheart.uni-kiel.de).
The pioneering introduction of the Starr–Edwards valve allowed complete replacement of the diseased mitral valve. With improved cardiopulmonary bypass, myocardial protection, and surgical techniques the mortality rate associated with mitral valve replacement decreased. Augmented use of mitral valve repair techniques has resulted in a substantial decrease in long-term morbidity and mortality when treating patients with mitral regurgitation. Some believed that this resulted from maintaining continuity of the mitral annular papillary muscle continuity during mitral valve repair. Additional studies have validated the positive long-term effects of maintaining the integrity of the mitral valve subvalvular apparatus [1]. Although surgical approaches to reduce mitral regurgitation associated with congestive heart failure have been reported, the high mortality rate that accompanies surgery in patients with severe heart failure and the short-term hemodynamic effect of alleviating mitral regurgitation in the setting of a failing ventricle are still of significant concern [2,3].
The maintenance of integrity of the subvalvular apparatus has also been performed in a new off-pump mitral valve study providing a very attractive treatment option: in this month's edition of the journal, the von Segesser group report the acute results of a new double-crowned valved stent implantation technique (pages 194–199) in their experimental study [4]. The goal was to assess the feasibility of a mitral valved stent deployment and verify the hemodynamic stability during this procedure. Both endpoints were successfully reached. All implanted valves worked properly and no significant changes in the hemodynamic parameters were observed during deployment.
The present study demonstrates that mitral valve replacement using an atrial approach can be successfully performed on the beating heart in an animal model without cardiopulmonary bypass [4]. The porcine model provides a challenging model for demonstrating functionality of the off-pump technique for several reasons. The pig mitral valve leaflets are thinner than human leaflets, being more sensitive to trauma from the application device and the procedure. Furthermore, the porcine left atrium provides limited space to manipulate the application catheter, especially in comparison to the dilated left atrium associated with human mitral insufficiency.
This study is limited to the short-term evaluation of the off-pump valve repair technique. Long-term animal data are mandatory to assess long-term device performance, which should include issues of thrombogenicity, neointimalization, calcification, stability of position, histomorphologic examination, and function during long-term follow-up.
The simplicity and proven efficacy of off-pump mitral valved stent implantation make it attractive as an endovascular method of replacing the structurally or functionally deficient mitral valve. The prospect of percutaneous valve replacement is immensely promising for the management of patients. Endovascular valve implantation entails: the development of a foldable biologic or synthetic valve, mounting it on a balloon- or self-expandable stent, percutaneously delivering it through standard catheter-based techniques and implanting it within a diseased valve annulus [5].
Recent reports of percutaneous implantation of pulmonary valves in pediatric patients, as well as aortic valves in adults, indicate that percutaneous valve implantation may become an effective and versatile procedure for special indications. The biological valves presently used have a collapsible valved stent that can be crimped onto a carrier catheter and inserted through the vascular access. However, the current designs require large vascular access and delivery systems for deployment. This could potentially limit the application of this system especially in the pediatric population in which a large vascular access is difficult to obtain [5].
Furthermore, the amount of biologic valve material which has to be transported by the application device when performing valved stent implantation is largest for the mitral valve compared to pulmonary or aortic valves. Therefore, it will take more time to design and evaluate a mitral valved stent implantation technique for percutaneous access which will be flexible enough to perform an easy deployment of the valved stent. This will be even more demanding when the mitral valved stent is placed antegrade by means of a transseptal catheterization. In addition, an ideal valved stent may be achieved for long-term use by individually lining the entire mitral annulus and small part of the left atrium to avoid any shift caused by shear stress [6].
This study introduces the first technology for off-pump mitral valve replacement [4]. The safety and efficacy of the system in humans experiencing mitral valve dysfunction remain to be proven; however, the success of this method in a short-term animal model encourages supporting subsequent human clinical trials. Moreover, as an off-pump intervention, this method, would offer the opportunity for substantial reduction in the morbidity and mortality associated with on-pump mitral valve surgery. The technology could especially provide a therapeutic alternative for patients with significant mitral valve disease and advanced left ventricular dysfunction or with significant comorbidities who are not amenable to surgical intervention. Patients after previous heart surgery could also be candidates for this new technique.
Although the gold standard of mitral valve treatment, the reconstruction, has reached a high surgical plateau with low morbidity and mortality, off-pump valved stent implantation through a transatrial approach could help us, as surgeons, to perform complex mitral operations for specific patients. In consent with recent developments in other fields, training of heart surgeons in endovascular techniques represents a most reasonable change in daily practice. Finally, it has to be presumably expected that this technique would not be a competitive procedure to the well-elaborated repair techniques.
References
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