Abstract Body (Do not enter title and authors here): INTRODUCTION: In the Single Ventricle Reconstruction Trial, long-term follow up (SVRIII), morbidity and mortality compounded with age regardless of shunt type at Norwood procedure.
AIMS: We aimed to describe SVRIII MRI findings by shunt type and determine associations between cardiac MRI and exercise performance.
METHODS: Cardiac magnetic resonance imaging (CMR) and cardiopulmonary exercise testing (CPET) were performed at ages 10-14 years. Demographics and CMR parameters were compared by shunt type. An estimate of aortopulmonary collaterals (APC) and fenestration (Fen) flow was calculated by subtracting total vena cava flow from aorta flow. All SVR III, CMR, and demographics data were used to determine univariate and multivariable predictors of right ventricular function (RVEF %). CMR parameters were used to determine predictors of ventilatory efficiency (VE/VCO₂) and peak VO₂ (ml/min/kg).
RESULTS: Among 237 participants enrolled in SVR III, 168 participants had complete CMR exams (79 mBTTS, 89 RVPAS, 33% female). RV volumes (BTTS 91.9 ml/m2 vs RVPAS 93.4 ml/m2, cardiac output (BTTS 42ml/beat vs RVPAS 46ml/beat), and APC+Fen flow were similar between shunt types, while the RVPAS group tended to have higher SVC flow (BTTS 16.1ml/beat vs RVPAS 18.3 ml/beat P=0.04). The mBTTS group had a slightly larger isthmus (13.8mm vs 12.8mm), but similar ascending aorta (AAO mm), and branch PA sizes. Table 1 shows CMR univariate predictors of RVEF, VE/VCO₂ and peak VO₂. Both RVESVi (ml/m²) and RVEDVi (ml/m²) were negatively associated with RVEF. Despite a negative association between higher RPA:LPA flow balance and RVEF, there was also a weakly negative association between LPA size and RVEF. Higher total vena cava flow (ml/beat) and pulmonary blood flow were associated with improved VE/VCO₂. Right ventricular volumes and mass were negatively associated with Peak VO₂, while AAO and RVEF were positively associated with peak VO₂. By multivariable analysis RV mass and AAO size explain approximately 11% of the variability in peak VO₂ (Table 2).
CONCLUSION: Chronic volume loading of the single right ventricle in the setting of low systemic blood flow and pulmonary flow imbalance are associated with RV dysfunction. CMR measures of RV size and systemic blood flow have a modest association with ventilatory efficiency and peak exercise performance. Higher Qs is associated with improved ventilatory efficiency, while larger AAO and lower RV mass are associated with improved peak VO₂.