Abstract 19155: Quantification of Progressive Pulmonary Valvular Insufficiency Using 4-Dimensional Flow Magnetic Resonance Imaging in an Ovine Model

Abstract

Introduction: Chronic postoperative pulmonary insufficiency (PPI) is the major cause of long-term morbidity and mortality in patients (pts) with tetralogy of Fallot (TOF). Pulmonary valve replacement (PVR) can mitigate the risk, but optimal timing for PVR remains controversial. Time-resolved 3D phase-contrast MRI (4DF) provides insight into complex intracardiac flow patterns. 4DF may help inform management decisions regarding timing of PVR. We describe the first quantitative serial 4DF analysis in an ovine model of PPI. Methods: A baseline cardiac MRI (CMRI) was performed on four Dorsett sheep (36-39kg) on a 3-Tesla Siemens scanner. Following baseline MRI, animals underwent pulmonary valvectomy and transannular patch (TAP) placement yielding PPI. Follow-up CMRI were obtained at 5mo and 7mo post-valvectomy (PoVa). Pathlines were emitted from a circular region of interest (ROI) representing the pulmonary valve annulus. Velocities, flow rate, and stresses were obtained throughout a complete cardiac cycle and compared across time. Results: Systolic max velocity, average velocity, and flow rate normal to the ROI plane decreased over time. Diastolic velocities increased at 5mo before decreasing at 7mo PoVa. Regurgitant flow was observed in diastole PoVa , and regurgitant flow rate increased with time. The max and average component of shear stress (viscosity = 3 cP) along the pulmonary artery wall decreased over time in systole. In diastole, shear stress increased at 5mo and decreased at 7mo. Parameters plotted in Figure 1. Conclusion: 4DF provides a new method for visualization and quantification of alterations in blood flow patterns in the right side of the heart in an ovine model of PPI. Alterations in above parameters may indicate myocardial and pulmonary vascular deterioration precedent to morphological changes. Characterization of altered flow patterns in human pts with TOF may help to ultimately inform decisions regarding timing of PVR.