2.2 Preoperative evaluation
Preoperative transthoracic echocardiography (TTE) examination was performed to define (1) the location and magnitude of any left ventricular pressure gradient, both at rest and with provocation; (2) the distribution and severity of myocardial hypertrophy; (3) MV anatomy and function; (4) the presence of mitral subvalvular anomalies including abnormal chordae tendineae attached to the ventricular septum or free wall (false cords), fibrotic and retracted secondary chordae inserted on the anterior mitral leaflet body, and papillary muscle (PM) abnormalities (hypertrophy, and direct insertion into the anterior mitral valve leaflet); and (5) the presence of intrinsic MV disease including lesions of mitral leaflets and mitral annulus. Resting LVOT velocity was measured by continuous-wave Doppler of the outflow tract from an apical window, and the resting LVOT pressure gradient was estimated by using the modified Bernoulli equation (i.e., gradient = 4v2, where v = peak LVOT velocity). In patients with resting LVOT gradients < 30 mmHg, maneuvers such as the Valsalva maneuver and stand-to-squat were frequently used. In addition, cardiac magnetic resonance was frequently used to measure basal septal thickness and for characterization of PM morphology and location within the left ventricular cavity, PM thickness, and PM mobility.