Three-Dimensional Shape Analysis of Right Ventricular Remodeling in Repaired Tetralogy of Fallot

Abstract

Understanding of right ventricular (RV) remodeling is needed to elucidate the mechanism of RV dysfunction in the overloaded right ventricle, but is hampered by the chamber's complex shape. We imaged 15 patients with repaired tetralogy of Fallot (TOF) and 8 normal subjects by magnetic resonance imaging in long- and short-axis views. We reconstructed the right ventricles in 3 dimensions using the piecewise smooth subdivision surface method. Shape was analyzed from cross-sectional contours generated by intersecting the right ventricle with 20 planes evenly spaced from apex to tricuspid annulus. Patients with TOF had dilated right ventricles compared with normal (end-diastolic volume index 216 ± 99 vs 81 ± 16 ml/m², p <0.001) but near-normal function (ejection fraction 40 ± 9% vs 48 ± 12%, respectively, p=NS). RV shape in patients with TOF differed from normal subjects in several ways. First, the right ventricle had a larger normalized cross-sectional area in patients with TOF (p <0.01 in apical planes). Second, the cross-sectional shape was rounder in patients with TOF (p <0.05 in apical planes). Also, the interventricular septum underwent relatively less enlargement so that it comprised only 27 ± 4% of total RV surface area in patients with TOF, compared with 33 ± 2% in normal subjects (p = 0.0001). In addition, the right ventricle in patients with TOF exhibited bulging basal to the tricuspid valve (4 ± 4% of total RV length), unlike normals (1 ± 2%, p <0.001). This basal bulging was amplified by tilting of the tricuspid annulus (29 ± 11° vs 15 ± 7°, respectively, p <0.005). In conclusion, the right ventricle remodels in several directions rather than following a shape continuum. Characterization of RV remodeling from 3-dimensional reconstructions provides novel insights.