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Mitral Valved Stent Implantation: Transesophageal Echocardiographic Guidance for Asymmetrically Shaped Stent Designs
Katharina Huenges, Saskia Pokorny, Telse Bähr, Matthias Gegenwart, Justus Gross, Jochen Cremer, Georg Lutter.
University Hospital Schleswig-Holstein, Campus Kiel, Department of Cardiovascular Surgery, Kiel, Germany.

OBJECTIVE: Different valved stent designs have been presented for off-pump implantation into the mitral valve. In this study our experiences with 2D and real-time 3D transesophageal echocardiographic (TEE) guidance and evaluation of symmetrical and irregularly shaped stents are presented.
METHODS: Two mitral valved stent prototypes were developed, comprised of a circular atrial element, a ventricular body accommodating a bioprosthetic heart valve and an apical fixation system. The first design AP (n=10) was symmetrically shaped. In the second design SUB (n=10), asymmetrically distributed fixation elements were included at sub-annular level.
The stents were implanted into the native mitral annulus of pigs (50±2kg) via transapical approach in the beating heart under sole TEE guidance. Echocardiographic and hemodynamic parameters were assessed following a standardized protocol before (n=20) and 1h after implantation (n=18).
RESULTS: Two animals were excluded from the study due to ventricular fibrillation prior to stent deployment. 3D TEE provided dependable spatial visualization of the left heart, mitral apparatus, delivery system and valved stent. It was an adequate method for correct positioning of the stent with symmetrical design. Disadvantage of this technique were the strong artefacts caused by the metal frame, shadowing the structures beyond the stent. This showed to be particularly challenging during positioning of the asymmetrically shaped stents. Rotational orientation was correct in seven of eight cases. However, visibility of the asymmetrically distributed fixation elements was small and the judgement of the stent orientation therefore time consuming.
CONCLUSIONS: 3D TEE provides accurate views and allowed assessment of regurgitations and 3D imaging of the stent. Drawback is the sound cancellation beyond the valved stent. This particularly limits the evaluation of the correct stent orientation of assymmetrically shaped stents. If the landmarks are small, it might be beneficial to perform additional fluoroscopy for judgment of the stent orientation. Choosing the optimal imaging technique or combination optimizes the results, not solely in experimental developments. Each prototype may require different imaging techniques as the challenges depend on individual design features.

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