Three-dimensional echocardiography-derived myocardial mechanistic insights into obstructive hypertrophic cardiomyopathy with moderate septal hypertrophy

BACKGROUND: In hypertrophic cardiomyopathy (HCM) patients with moderate septal hypertrophy (≤ 18 mm), left ventricular outflow tract obstruction (LVOTO) cannot be fully explained by septal thickness alone, thereby complicating therapeutic decision-making. This study aimed to investigate the association between three-dimensional speckle-tracking echocardiography (3D-STE)-derived myocardial mechanics and LVOTO in patients with moderate hypertrophic HCM. METHODS: We retrospectively analyzed 216 HCM patients with moderate septal hypertrophy, stratified into nonobstructive (n = 38), provokable LVOTO (n = 63), and resting LVOTO (n = 115) groups. LV geometry, LVOT diameter, and anterior mitral leaflet length were assessed using transthoracic echocardiography, and mitral subvalvular papillary muscle abnormalities were evaluated and composited into a SubMV score. 3D-STE quantified strain parameters, including global longitudinal, circumferential, radial, and area (GAS) strain, twist, and torsion. Measurement differences were analyzed among the LVOTO subgroups, and associations with LVOTO were evaluated using multivariate regression, restricted cubic spline (RCS) modeling, and receiver operating characteristic (ROC) curve analysis. RESULTS: Both LVOTO subgroups showed significantly augmented strain mechanics versus nonobstructive patients, most pronounced in resting LVOTO (p < 0.05). Twist and torsion were the strongest discriminators (p < 0.001). Multivariate regression showed that, beyond LVOT diameter and SubMV score, torsion (B = 9.47), twist (B = 1.92), and GAS (B = 1.29) were independently associated with provoked LVOT gradients (all p < 0.05). RCS revealed nonlinear twist/torsion–LVOTO relationships, with the obstruction risk rising above twist = 15° and torsion = 3°/cm, especially under provocation. Torsion achieved 81% specificity for identifying provokable LVOTO (cutoff 2.4°/cm, AUC = 0.72), outperforming all single structural parameters. Integrating 3D-STE mechanics with structural metrics improved discrimination (AUC 0.84 vs. 0.76, DeLong p = 0.003). CONCLUSIONS: In moderately hypertrophic HCM, 3D-STE–derived strain mechanics, particularly LV torsional mechanics, are independently associated with LVOTO beyond established structural parameters including anatomical narrowing and cumulative papillary muscle abnormalities. These findings provide mechanics insights into LVOTO and support refined risk stratification and longitudinal monitoring in this heterogeneous population.