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.