Abnormal aortic flow conduction is associated with increased viscous energy loss in patients with repaired tetralogy of Fallot

OBJECTIVES: Aortopathy in tetralogy of Fallot (TOF) is characterized by increased aortic stiffness, dilation and reduced left ventricular (LV) function. Repair in infancy normalizes aortic dimensions in early childhood. Our prior work demonstrated that early TOF repair does not normalize aortic compliance and that abnormal ascending aortic flow patterns are prevalent. The objectives of this study were to: (i) determine whether proximal aortic flow-mediated viscous energy loss (EL') is elevated in patients with early TOF repair compared with healthy controls, and (ii) determine whether the degree of EL' is associated with LV function. METHODS: Forty-one patients post TOF repair with normalized aortic size and 15 healthy controls underwent 4-dimenisonal-flow magnetic resonance imaging flow analysis and EL' assessment. Correlations between EL', aortic size, and LV function were assessed. RESULTS: The TOF group had increased peak systolic thoracic aorta EL' (3.8 vs 1.5 mW, P = 0.004) and increased averaged EL' throughout the cardiac cycle (1.2 vs 0.5 mW, P = 0.003). Peak and mean systolic EL' in the ascending aorta was increased 2-fold in the TOF group compared with control (peak: 2.0 vs 0.9 mW, P = 0.007). Peak EL' measured along the entire thoracic aortic length correlated with LV ejection fraction (R = -0.45, P = 0.009), indexed LV end-systolic volume (R = -0.40, P = 0.010), and right ventricular end-systolic volume (R = -0.37, P = 0.034). CONCLUSIONS: Patients with repaired TOF exhibit abnormal aortic flow associated with increased EL' in the thoracic aorta. The magnitude of EL' is associated with LV function and volumes. Increased aortic EL' in TOF is likely due to inherently abnormal LV outflow geometry and or right ventricular interaction. Reduced aortic flow efficiency in TOF increases cardiac work and may be an important factor in long-term cardiac performance.