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Letters to the Editor |
Nanyang Technological University, School of Mechanical and Aerospace Engineering, Division of Thermal and Fluids Engineering, 50 Nanyang Avenue, Singapore 639798, Singapore
Received 21 August 2008; accepted 23 August 2008.
* Corresponding author. Tel.: +65 67905500.
Key Words: Autologous • Valve • Pericardium
We appreciate the interest of Siondalski et al. [1] and his group beside numerous other international groups in working on autologous aortic valve prosthesis. We experienced tremendous interest, especially in countries where patients need a priceless and reliable bioprosthesis without the need for anticoagulation and with advantageous hemodynamics especially in the smaller sizes.
Siondalski et al. developed a prosthesis with flat leaflets. Since 1960 flat pericardium was used in aortic valve repair [2]. Our group studied the concept of a pericardial bioprosthesis with flat leaflets and performed long-term animal studies already in 2001 with a temporarily stented, autologous pericardial aortic valve prosthesis. We could demonstrate functionality of the flat pericardial prosthesis. But previous experiences in human [2] and our in-vitro experiences showed bending of the free leaflet edge in flat leaflets which can occlude the coronary ostia.
Further studies showed that coaptation area in the flat leaflet shape is reduced in comparison with a curved shape [3]. Independent of the leaflet shape, one characteristic common to this type of prosthesis is the wide opening with low transvalvular gradient. Finite element studies [3] carried out by our group could demonstrate that the forces at the commissures are reduced in curved cusps in comparison with a flat design and we studied the forces acting at such structures extensively [4].
Our objectives were: to design the prosthesis closer to the native valve which has a curved shape in closed position, to avoid free leaflet edge bending by reducing the prosthesis height, to increase leaflet coaptation area, to decrease forces acting at the commissures by forming a cusp shape, and to simplify and expedite the construction and implantation process of the prosthesis by using single point attached commissures (SPAC).
We developed the concept SPAC in autologous pericardial aortic prosthesis with a curved shape and low profile resembling the native valve shape.
The design went through rigorous engineering investigations, including computational finite element analyses and in-vitro testings, comparing it with various valve mold geometries. Long-term animal studies [5] demonstrated safety and efficacy of the final design of a molded SPAC valve prosthesis with reliable competence, exceptionally low transvalvular gradient and no free leaflet edge bending.
We shared the concerns about the connection between the leaflet-commissure and the aortic wall. In our studies we found the aortic wall to be the weakest structure that needs to be supported [4]. Changing the prosthesis design does not help the condition of the aorta; also adding T-shaped laps at the leaflet commissures does not prevent the sutures from cutting through the aortic wall but makes implantation more difficult. We found that simply reinforcing the commissural sutures with a pericardial pledget outside of the aortic wall will provide a safe anchor for the commissures. In our long-term animal studies we used only one suture at each commissure to prove the safety of the SPAC [5]. Concerns about using only a single suture can be overcome by simply placing more than one suture in a line down from the commissural point.
References
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