Anatomic Correlates of Mitral Systolic Anterior Motion in Transposition of the Great Arteries Following Atrial Switch Operation

Introduction: We sought to investigate whether the development of sub-pulmonic systolic anterior motion (SAM) may be inherent to the anatomy of the the mitral valve (MV) or affected by external factors, such as a dilated right ventricle or chest abnormalities in d-looped transposition of the great arteries post atrial switch operation (d-TGA/AtS). Methods: Analysis was performed of clinical and cardiac imaging studies acquired on 19 adult patients with d-TGA/AtS (age 42 +/- 6 years old, 56% male) between 2015-2019. Echocardiography data included mitral apparatus anatomy, and CT/MRI data included biventricular dimensions, function, and Haller index (HI) for pectus deformity. Results: Patients with leaflet SAM (n = 6) compared to patients without SAM (n = 13) had higher MV protrusion height (2.3 +/- 0.5 vs. 1.5 +/- 0.4 cm, p <= 0.01) and longer anterior MV leaflet length (3.1 +/- 0.4 cm vs. 2.6 +/- 0.3 cm p <= 0.05), when compared to those without. CT/MRI showed higher sub-pulmonic left ventricular ejection fraction (LVEF) in the SAM group (71% +/- 8% vs. 54% +/- 7%, respectively). RV size and function, significant chest deformity (HI > 3.5), presence of a ventricular lead pacemaker, and septal thickness did not play a role in development of SAM. Conclusions: An elongated mitral apparatus is associated with the development of SAM, and the development of left ventricular outflow tract obstruction (LVOTO), in d-TGA/AtS. LV hyperkinesia is associated with SAM. Systemic RV dimensions, septal thickness, and degree of chest deformity did not differ significantly between subjects with SAM and those without.