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Department of Cardiovascular Surgery, University of Kiel School of Medicine, Arnold-Heller-Str 7, Kiel, D-24105 Germany
(Email: lutter{at}kielheart.uni-kiel.de; jcremer{at}kielheart.uni-kiel.de).
The article by Meng and coworkers [1] presents the results of a long-term animal feasibility study using a newly designed, self-expanding nitinol stent supporting a bovine jugular vein valve for transventricular pulmonary valve replacement. In this experiment, 6 sheep received a valved stent during a beating heart procedure. The implantation was successful in all animals, and the valve performed well in all but in one in which an increased transvalvular gradient was measured after 2 months. In another, mild regurgitation was present after 2 months.
Although the pulmonary artery valved stent implantation using a transventricular or percutaneous approach is already clinically applied, this study is pioneering work: The authors constructed a new nitinol stent made of 3 rings of a nitinol Z-structure. The distal part of the stent bends outward like a bell and is 20% larger than the proximal tubular part. Thus, the 2-month evaluation revealed good structural and functional outcome, without perforation or migration of the new stents (25% oversizing) in virginal pulmonary arteries.
This new stent shape was designed because tubular valved stents tend to migrate [2]. Permanent movement and the complex anatomy of the right ventricular outflow tract (RVOT) in animals and also in patients cause this migration. Morphology varies greatly between patients, and tortuous pulmonary anatomy is not infrequently seen in patients who undergo operations in infancy for tetralogy of Fallot after long-standing pulmonary regurgitation. Patients who have already undergone transannular patch repair of tetralogy of Fallot during infancy can also have pulmonary trunks that often exceed 24 mm in diameter, making percutaneous implantation technically impossible with the current clinical approach [3].
First, various solutions, such as oversizing of the flexible nitinol stent [1, 2], to resolve this problem have been proposed. Second, it is possible to implant 2 valved stents, 1 in each pulmonary artery. However, this solution will not eliminate blood regurgitation from the pulmonary trunk. Third, more interestingly, cooperation between surgeons and cardiac interventionists would permit a stepwise implantation without requiring extracorporeal circulation. Through a thoracotomy, the pulmonary artery could be banded, allowing for subsequent percutaneous implantation of a pulmonary valve. Fourth, implantation of a downsizing stent would permit reduction of the pulmonary trunk to the desired diameter and enable the consecutive implantation of a valved stent [3].
None of these solutions is fully satisfactory; therefore, investigations, such as by Meng and colleagues [1] have the potential to aid in the design of future devices in this field.
Several research groups, such as ours, recommend individually constructed, fully aligned valved stents that completely represent the 3-dimensional, anatomic nature of the RVOT for this patient cohort. This type of valved stent will come.
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