Right ventricular regional wall curvedness and area strain in patients with repaired tetralogy of Fallot

Abstract

A quantitative understanding of right ventricular (RV) remodeling in repaired tetralogy of Fallot (rTOF) is crucial for patient management. The objective of this study is to quantify the regional curvatures and area strain based on three-dimensional (3-D) reconstructions of the RV using cardiac magnetic resonance imaging (MRI). Fourteen (14) rTOF patients and nine (9) normal subjects underwent cardiac MRI scan. 3-D RV endocardial surface models were reconstructed from manually delineated contours and correspondence between end-diastole (ED) and end systole (ES) was determined. Regional curvedness (C) and surface area at ED and ES were calculated as well as the area strain. The RV shape and deformation in rTOF patients differed from normal subjects in several respects. Firstly, the curvedness at ED (mean for 13 segments, 0.030 ± 0.0076 vs. 0.029 ± 0.0065 mm(-1); P < 0.05) and ES (mean for 13 segments, 0.040 ± 0.012 vs. 0.034 ± 0.0072 mm(-1); P < 0.001) was decreased by chronic pulmonary regurgitation. Secondly, the surface area increased significantly at ED (mean for 13 segments, 982 ± 192 vs. 1,397 ± 387 mm(2); P < 0.001) and ES (mean for 13 segments, 576 ± 130 vs. 1,012 ± 302 mm(2); P < 0.001). In particular, rTOF patients had significantly larger surface area than that in normal subjects in the free wall but not for the septal wall. Thirdly, area strain was significantly decreased (mean for 13 segments, 56 ± 6 vs. 34 ± 7%; P < 0.0001) in rTOF patients. Fourthly, there were increases in surface area at ED (5,726 ± 969 vs. 6,605 ± 1,122 mm(2); P < 0.05) and ES (4,280 ± 758 vs. 5,569 ± 1,112 mm(2); P < 0.01) and decrease in area strain (29 ± 8 vs. 18 ± 8%; P < 0.001) for RV outflow tract. These findings suggest significant geometric and strain differences between rTOF and normal subjects that may help guide therapeutic treatment.

Fig. 1.

Sample segmented trueFISP two-dimensional cine MR images of short-axis (A) slices acquired at the base, middle, and apex (from top to bottom, respectively) and long axis (B) of the heart. End-diastolic (ED) and end-systolic (ES) phases are at left and right, respectively.

Fig. 2.

Plots represent principal curvature analysis done on the endocardial wall of the right ventricle. Arrowheads on the endocardial surface represent directions of maximum principal curvature (left) and minimum principal curvature (right) of the endocardial surface repaired tetralogy of Fallot (rTOF; A) and normal subjects (B).

Fig. 3.

Standardized myocardial segmentation and nomenclature of right ventricle (RV). LV, left ventricle.

Fig. 4.

Variation of curvedness (C_ED and C_ES) of the RV in normal subjects and in rTOF patients. A and B: C_ED and C_ES assessment in 13 segments. C and D: C_ED and C_ES assessment in 3 levels. E and F: C_ED and C_ES assessment in free wall and septal wall. G and H: C_ED and C_ES assessment in RV outflow tract (RVOT) and RV inflow tract (RVIT). Values are means ± SD. *Significant difference between rTOF vs. normal subjects.

Fig. 5.

Variation of surface area (SA_ED and SA_ES) of the right ventricle in normal subjects and in rTOF patients. A and B: SA_ED and SA_ES assessment in 13 segments. C and D: SA_ED and SA_ES assessment in 3 levels. E and F: SA_ED and SA_ES assessment in free wall and septal wall. G and H: SA_ED and SA_ES assessment in RV outflow tract RVOT and RVIT. Values are means ± SD. *Significant difference between rTOF vs. normal subjects.

Fig. 6.

Variation of area strain (AS) of the RV in normal subjects and in rTOF patients in 13 segments (A), 3 levels (B), between free wall and septal wall (C) and between RVOT and RVIT (D). Values are means ± SD. *Significant difference between rTOF vs. normal subjects.

Fig. A1.

Voronoi areas subtended by a vertex p.

Fig. A2.

Area strain mapping in 15 segments of RV in a rTOF and a normal heart. Color coding of the magnitude of area deformation is more uniform in the normal than that in rTOF. Value of area strain is lower in rTOF.

Fig. B1.

Schematic drawing of RV segmentation. Two sets of intersecting contours were traced to mark the anterior and inferior intersection points at each RV contour. These intersection points line up to form two boundaries on the RV mesh separating 2 walls: the septal wall and the free wall.

Fig. B2.

Segments of the RV. The 3 longitudinal levels were termed basal, mid, and apical. In the basal and mid levels, the horizontal regions were termed anterior, lateral, and inferior for free wall, and inferior and anterior for septal wall based on the 2:3 ratio of circumference. In the apical level, the horizontal regions were termed anterior and inferior for the free wall and septal (for the septal wall based on 1:2 ratio of circumference). RV outlet (segment 14) component was deemed to extend from the distal border of basal section to the attachments of the leaflets of the pulmonary valve. RV inlet (segment 15) was deemed to extend from the atrioventricular junction to the distal border of basal section.

Fig. B3.

P_14,15 is a midpoint separating RV inlet and RV outlet when it starts branching up, while P_1,2 and P_4,5 are the points that mark the boundary between segments 1 and 2 and the boundary between segments 4 and 5, respectively. The 2 boundary lines between RV Inlet and RV outlet (segments 14 and 15) are formed nearby the lines P_1,2P_14,15 and P_4,5P_14,15. Each of these lines is determined by nearest points on the mesh at each level of RV inlet and RV outlet contours.