Performance of the 'forgotten ventricle' in patients with repaired congenital heart disease and pulmonary arterial hypertension

Abstract

Once regarded as the ‘forgotten ventricle’, the importance of the right ventricle has been increasingly recognised in the recent half-century. Prognostic significance of right ventricular (RV) function had been evidenced in a multitude of heart conditions, including congenital heart disease post-repair and pulmonary hypertension. The right ventricle is notorious for its difficulty to examine non-invasively owing to its unfavourable position. With the advancement of cardiac imaging techniques, however, such limitation post minimal hurdle on RV functional assessment. High compliance of the RV free wall and adaptive interactions between the right ventricle and its outflow tract renders RV impairment to present late. Often, patients present with severe RV dysfunction when interventions are deemed ineffective. Strategies to detect early RV dysfunction are therefore highly demanded. These include assessment of RV-pulmonary arterial (PA) coupling and RV functional reserve. The central objective of this thesis is to evaluate RV-PA coupling in repaired tetralogy of Fallot (TOF), and RV systolic and diastolic reserve in impaired in repaired TOF, transposition great arteries (TGA) and pulmonary arterial hypertension (PAH). In the first study, 60 adults with repaired TOF and 60 controls were studied using echocardiography. Right ventricular-PA coupling, as reflected by the ratios of RV area change to end-systolic area (ESA) and peak tricuspid annular systolic myocardial (s) velocity to RV ESA indexed to body surface area, was measured in both populations. This study revealed impaired RV-PA coupling in patients with repaired TOF compared to the healthy population. Non-invasively-derived ratios of RV-PA coupling positively associated with tricuspid annular myocardial velocities, left ventricular and RV deformation and negatively associated with severity of pulmonary regurgitation (PR) and tricuspid regurgitation (TR). Right ventricular systolic strain rate, PR and TR were independent predictors of both ratios of RV-PA coupling, while age, gender and LV systolic strain additionally predicted RV peak tricuspid s velocity/indexed RV ESA ratio. The second study reviewed existing studies that assessed RV functional reserve during pharmacological and exercise stress. Systolic and diastolic functional reserve were measured in patients with repaired TOF, complete TGA post-atrial repair, congenitally corrected TGA and PAH. Right ventricular systolic functional reserve was impaired in all three patient groups, while diastolic reserve is reduced in repaired congenital heart disease. Impaired systolic and diastolic functional reserves associated with worse baseline functional parameters, and RV systolic functional reserve positively associated with exercise capacity and overall survival in all three patient groups. In conclusion, impaired RV-PA coupling and RV functional reserve were demonstrated in patients with a diseased subpulmonary or systemic right ventricle. These findings support the inclusion of the RV outflow tract assessment and stress cardiac imaging in serial follow up of patients with repaired congenital heart disease and PAH.