Flow Hemodynamics in Children with Tetralogy of Fallot: A Comparison Study of Cardiac Catheterization and Phase-Contrast MRI.

Pulmonary hemodynamics are necessary to measure for lifelong surveillance of cardiovascular function in children with tetralogy of Fallot (TOF). To measure cardiac index, invasive cardiac catheterization using the Fick principle or phase-contrast MRI (PC-MRI) can be used. However, estimates of oxygen consumption and other assumptions used in the Fick method may lead to significant inaccuracy, which are further exacerbated by disease characteristics such as pulmonary regurgitation. By comparison, PC-MRI can directly measure blood flow and regurgitant fraction. To investigate the potential complications of using the Fick principle, flow hemodynamics in 33 repaired TOF patients (7.6 ± 3.9 years) were investigated in patients who underwent cardiac catheterization and cardiac MRI. Pulmonary blood flow (Qp) measured by catheterization and PC-MRI showed poor agreement with an absolute bias of 0.80 ± 0.910 L/min/m2. Qp by Fick was significantly higher than PC-MRI (3.15 ± 0.60 L/min/m2 vs. 2.35 ± 0.95 L/min/m2 [p < 0.001]). Patients were also stratified by the presence of severe pulmonary regurgitant fraction (RF > 40%). A mean difference of 1.18L/min/m2 in Qp was found in patients with RF over 40% (n = 18), while patients with RF under 40% (n = 15) had a mean Qp difference of 0.34 L/min/m2 (p = 0.013). PC-MRI may address errors associated with oxygen consumption as well as assumptions affecting Fick in all patient populations. Additional advantages may exist when assessing children with repaired TOF, especially given the common presence of regurgitant pulmonary flow in this population.