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a Universität Leipzig, Herzzentum, Klinik für Herzchirurgie, Strümpellstr. 39, Leipzig, 04289 Germany
b Edwards Lifesciences Inc, Irvine, California
(Email: walt{at}medizin.uni-leipzig.de).
Zegdi and colleagues [1] brought up some important comments regarding valve in a valve implantation, and we would like to thank them for their contribution. They are absolutely right in their statement that valve in a valve (VinV) implantation is a relatively new field requiring further careful investigation. However, several important achievements have been made in the past years leading to initial successful clinical applications of this promising therapeutic option. We have to keep in mind that VinV implantation is believed to be a suitable procedure in elderly and higher risk patients suffering from structural valve degeneration of previously implanted conventional xenografts. Because of previous surgery and advanced patient age, such patients would be at elevated risk for conventional surgery. In such high-risk elderly patients, the primary therapeutic goals are adequate hemodynamic valvular function allowing for relief of symptoms without the need for repeat valve intervention. The evolving field of transcatheter valve implantation, be it through a transfemoral or a transapical approach, offers new therapeutic options for such patients. Especially with the direct, antegrade, relatively straightforward, and safe method of transapical valve implantation [2], high-risk patients with degenerated xenografts may be particularly suitable for an off-pump minimally invasive redo procedure.
Zegdi and colleagues [1] raise several concerns. Hemodynamic function may theoretically be impaired when implanting a stent-based prosthesis inside a conventional xenograft. However, the steel stent of the Edwards Sapien prosthesis (Edwards Lifesciences, Irvine, CA) has a very low profile that is much thinner than the stents and sewing rings of conventional valves. The hemodynamic function should therefore be minimally compromised, if at all. Indeed, the experience from our center and others has demonstrated that these valves exhibit very low transvalvular gradients, especially in view of their limited external diameter [2]. Thus, comparable hemodynamic function as with the initially implanted conventional xenograft can be anticipated after VinV implantation. Clinically, we have seen excellent function in that initial patient [3] at discharge, and now we have seen excellent function at 1-year follow-up. It should also be pointed out that the internal diameter of a 21-mm Carpentier Edwards aortic valve (Edwards Lifesciences) is 20 mm [4] and not 17 mm as stated by Zegdi and colleagues [1]. Our oversizing was therefore only 3 mm and not 6 mm as stated in their letter.
The potential durability of VinV implantation has also been questioned. The durability of VinV implantation has been extensively tested pre-clinically at Edwards Laboratories. This includes specific pulse duplicator evaluation on the longer term function of a 23-mm transcatheter-delivered Sapien prosthesis inside a 21-mm Perimount prosthesis (Edwards Lifesciences). Thus VinV implantation after specific preoperative pulse-duplicator testing should be considered relatively durable. We also need to keep in mind that only elderly, higher-risk patients, in which valve durability is not as much of an issue as in younger patients, are presently deemed suitable candidates for these procedures.
In addition to bench testing, our group has performed several preclinical experimental studies proving VinV function in the aortic and mitral positions [5, 6]. Based on this overall experience, we believe such procedures will be applicable in a fair number of patients and we are optimistic that such patients will benefit from this new minimally invasive approach.
Spatial orientation was another issue brought up by Zegdi and colleagues [1]. Spatial orientation of the commissures prior to valve implantation would be nice to achieve when performing all types of transcatheter aortic valve implantation. We are aware of the potentially positive impact of an anatomical orientation. With currently available devices, however, be it the CoreValve (CoreValve, Irvine, CA) or the Edwards Sapien prostheses, anatomical orientation of the commissures is impossible to achieve. It may be that in the future there will be other devices allowing for correct alignment of the commissures prior to valve deployment.
We believe VinV implantation has several clinical benefits, based on experimental studies as well as the initial clinical cases that have been performed. Repeat valve failure as argued by Zegdi and colleagues [1] may be a problem leading to insufficient functional outcome during longer-term follow-up. However, the presently performed preclinical tests allow us to predict sufficient longevity. In the unlikely event that structural valve dysfunction develops in these elderly patients, it may even be possible to perform a repeat VinV implantation.
At present, VinV implantation using the Edwards Sapien prosthesis has been performed inside degenerated Edwards valves only after preoperative bench testing. VinV implantation in other types of bioprosthetic valves should also be feasible. However, specific preoperative bench testing is not yet available for these other valves. When looking at the stent design of the Edwards Sapien prosthesis, we believe it will function well inside almost any degenerated xenograft. Obviously, patients who received a previous mechanical valve would not be candidate for a VinV procedure.
In summary, VinV implantation has undergone extensive experimental testing, but clinical experience is still limited. However, VinV implantation is such an intriguingly simple and straightforward concept that we believe it will withstand the test of time and hopefully lead to good outcomes in multiple patients in the future.
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