1 INTRODUCTION
Percutaneous transseptal transcatheter mitral valve implantation (TMVI) using balloon-expandable valve systems is developing as an alternative to open heart mitral valve (MV) surgery for high-risk surgical patients with degenerated bioprosthetic valves, failed repairs with annuloplasty ring, and native MV insufficiency or stenosis.1-3Although safety and feasibility of this new approach and acceptable one-year outcome after procedure have been reported,4-6 there are still several challenges to overcome: stent malposition, embolization, and left ventricular outflow tract (LVOT) obstruction. Therefore, a comprehensive approach or planning to prevent these complications is required.7,8
LVOT obstruction following transseptal TMVI in bioprosthetic valves [valve-in-valve (ViV)], surgical MV annuloplasty rings [valve-in-ring (ViR)], and native MV [valve-in-native valve (ViN)] has been recognized early in the development of this technique and increases mortality in these patients.3,9The TMVI device elongates the pre-existing native outflow tract toward the LV apex and creates a new LVOT (neo-LVOT) surrounded by surgical valve leaflet or native mitral anterior leaflet and interventricular septum. Accordingly, the geometry and function of the left ventricle, aortic valve, and mitral valve may lead to narrow LVOT area after TMVI. Yoon et al. reported that estimated neo-LVOT area from pre-procedural multidetector low computed tomography (MDCT) could help identify the patients at high risk for LVOT obstruction assessed by peak LVOT gradient.10 However, there were limited studies directly assessing the LVOT cross sectional area after TMVI and identifying its association with anatomical/functional factors such as septal hypertrophy, left ventricular (LV) cavity size, LV wall motion, and angulation between the aortic annulus and the mitral annulus (aorto-mitral angle). Notably, the degree of aorto-mitral (AM) angle as an obtuse angle may be closely related to the LVOT narrowing. If the angle would be small, valve stent implanted at the mitral position would project into the LVOT, resulting in the narrowing of the LVOT space. While, if the angle is enough large, valve stent would project to the LV cavity and thus did not alter the LVOT geometry. Three-dimensional transesophageal echocardiography (3D TEE) can contribute to our understanding of the relationships between MV and basal LV wall with the unique morphology of the neo-LVOT space.11 Furthermore, this technology is well established in the assessment of dynamic LVOT size in hypertrophic obstructive cardiomyopathy.12Accordingly, we tested the hypothesize that intraprocedural real-time 3D TEE can quantify the LVOT area and that pre-procedural AM angle can be associated with LVOT narrowing in patients undergoing transcatheter mitral ViV, ViR, and ViN implantation.