Evaluation of a non-invasive right ventriculo-arterial coupling parameter in repaired tetralogy of Fallot by cardiovascular magnetic resonance imaging and correlation with exercise testing
Authors: Mets G , Bitterman Y , Wald R , Friedberg M K 
Published: January 2025

Abstract

Background and purpose
Invasively measured right ventricle (RV) to pulmonary arterial coupling (RVPAc) quantifies RV performance within the context of its afterload but requires cardiac catheterization thereby limiting widespread use. We sought to compare a volumetric non-invasive RVPAc parameter in a contemporary cohort of children and adults with repaired tetralogy of Fallot (rToF), to investigate the impact of pulmonary regurgitation (PR) and RV outflow tract obstruction (RVOTO), and to correlate RVPAc with exercise capacity.

Methods
We retrospectively compared 99 pediatric and 117 adult patients with rToF who had performed cardiovascular magnetic resonance imaging (CMR) and exercise testing (CPET) within 1 year. Sanz’s method was used to non-invasively calculate RV-PA coupling as the ratio of RV end-systolic volume over stroke volume (ESV/SV); where a ratio &gt;1 is considered ‘uncoupled’ [1]. Right-ventricular outflow tract gradient was obtained by echocardiography; PR fraction and Nakata-index [2], to quantify PA size, were calculated by CMR. We also calculated ‘effective SV’ by subtracting regurgitant volume from RV SV; which allowed for calculation of ‘effective’ RVPAc. Exercise capacity was measured as percentage of predicted peak oxygen consumption (%VO2) during cardio-pulmonary exercise testing. Subgroups were established depending on PR-RVOTO combination (cut-off defined as PR &gt;30% and RVOTO &gt; 25mmHg).

Results
RVPAc was significantly higher in the adult group [1.24 (1.03-1.49) vs. 1.00 (0.88-1.15); p&lt;0.001]. According to PR-RVOTO, RVPAc was overall comparable between pediatric and adult cohorts (respectively p=0.379 and 0.053). RVPAc highly correlated with RV ejection fraction (RVEF) (r=-0.991, p&lt;0.001), moderately correlated with indexed RV ESV (r= 0.696, p&lt;0.001) and QRS duration (0.598, p&lt;0.001), and weakly correlated with indexed RV end-diastolic volume (RVEDVi) (r=0.351, p&lt;0.001), indexed RV SV (r= -0.241, p&lt;0.001), LV ejection fraction (LVEF)(r= -0.382, p&lt;0.001) and Nakata-index (r=0.264, p=0.002). There was no significant association between RVPAc and RV outflow tract gradient (p=0.109) or pulmonary regurgitant fraction (p=0.411). RVPAc was not significantly correlated with %VO2 (p=0.294). This remained true for subgroup analysis in the pediatric and adult cohorts separately. Regression models, which included age, BSA and either RVEF, RVPAc or ‘effective RVPAc’ to predict exercise capacity (%VO2) demonstrated an overall poor fit (adjusted R2 0.170; 0.176 and 0.181 respectively).

Conclusion
Adults with rToF have higher RVPAc ratio than pediatric patients which could signify progressive RV-PA ‘uncoupling’ with age or era-related pathological effects. Non-invasive RVPAc correlates with RVEF, RV volumes, PA size, LVEF and QRS duration, which could be used to track progressive RV dysfunction. Nonetheless, its clinical use appears limited as it does not predict exercise capacity better than RVEF.