Subaortic Right Ventricular Characteristics and Relationship to Exercise Capacity in Congenitally Corrected Transposition of the Great Arteries

Abstract

In congenitally corrected transposition of the great arteries (cc-TGA), the morphologic right ventricle acts as the subaortic (systemic) ventricle, and deterioration of the ventricle over time is a well-known complication. The objective of this study was to characterize the right ventricle and explore factors that may be contributing to ventricular dilation and dysfunction and the relationship with exercise capacity. This was a prospective study of adults with cc-TGA. All patients underwent cardiopulmonary stress testing, ventricular volume and fibrosis assessment by cardiac magnetic resonance imaging, and Velocity Vector Imaging strain echocardiography. Twenty-six patients were included (mean age, 38 ± 16 years; 54% women). Exercise capacity wassignificantly reduced in patients with cc-TGA compared with normal subjects (20.9 ± 6.0 vs 30.8 ± 9.2mL/kg/min, P= .001). The majority of patients (61%) had right ventricular (RV) ejection fractions ≤ 40%. There was no evidence of fibrosis on cardiac magnetic resonance imaging. There was a significant difference in diastolic volumes among those with RV ejection fractions > 40% versus ≤ 40% (173 ± 29mL vs 233 ± 65 mL, P=.02) and moderate or severe versus no or mild tricuspid regurgitation (240 ± 80mL vs 190 ± 38mL, P=.04). RV apical longitudinal and mid free wall circumferential strain was decreased compared with these values in controls. In this relatively "well" cc-TGA population, subaortic RV dilation, dysfunction, and exercise intolerance are a common problem. Significant systemic tricuspid atrioventricular valvular regurgitation is an important contributor to the problem. In this study, subaortic RV myocardial deformation parameters were found to be abnormal, suggesting that there is a failure of the ventricle to adapt to systemic pressures, and therapies to reduce afterload should be explored. Recurrent ischemia resulting in fibrosis likely does not contribute to RV dilation or dysfunction as demonstrated by the magnetic resonance imaging findings in this study.