Dysfunction of the systemic right ventricle after atrial switch: physiological implications of altered septal geometry and load

Abstract

Atrial switch operation in patients with transposition of the great arteries (TGA) leads to leftward shift and changes the geometry of the interventricular septum. By including the implications of regional work and septal curvature, this study investigates if changes in septal function and geometry contribute to reduced function of the systemic right ventricle (RV) in adult TGA patients. Regional myocardial work estimation has been possible by applying a recently developed method for noninvasive work calculation based on echocardiography. In 14 TGA patients (32 ± 6 yr, means ± SD) and 14 healthy controls, systemic ventricular systolic strains were measured by speckle tracking echocardiography and regional work was calculated by pressure-strain analysis. In TGA patients, septal longitudinal strain was reduced to −14 ± 2 vs. −20 ± 2% in controls ( P < 0.01) and septal work was reduced from 2,046 ± 318 to 1,146 ± 260 mmHg·% ( P < 0.01). Septal circumferential strain measured in a subgroup of patients was reduced to −11 ± 3 vs. −27 ± 3% in controls ( P < 0.01), and a reduction of septal work (540 ± 273 vs. 2,663 ± 459 mmHg·%) was seen ( P < 0.01). These reductions were in part attributed to elevated afterload due to increased radius of curvature of the leftward shifted septum. To conclude, in this mechanistic study we demonstrate that septal dysfunction contributes to failure of the systemic RV after atrial switch in TGA patients. This is potentially a long-term response to increased afterload due to a flatter septum and suggests that medical therapy that counteracts septal flattening may improve function of the systemic RV. NEW & NOTEWORTHY We have demonstrated that transposition of the great arteries patients with systemic right ventricles (RVs) have reduced function of the interventricular septum (IVS). Since the IVS is constructed to eject into the systemic circulation, it may seem unexpected that it does not maintain function when being part of the systemic RV. By applying the principles of regional work, wall tension, and geometry, we have identified unfavorable working conditions for the IVS when the RV adapts to systemic pressures.