Presenting Author:

Maria Joh

Principal Investigator:

Joshua Robinson, M.D.

Department:

Pediatrics

Keywords:

4D flow MRI, kinetic energy, repaired tetralogy of Fallot, hemodynamic inefficiency

Location:

Ryan Family Atrium, Robert H. Lurie Medical Research Center

C95 - Clinical

4D flow MRI derived energetic biomarkers are abnormal in repaired tetralogy of Fallot patients and may predict deteriorating hemodynamics

Background: Conventional MRI assessment with repaired tetralogy of Fallot (TOF) relies heavily on morphologic and simplified global functional parameters (e.g. ventricular volumes and ejection fraction) which reflect late disease expression. Our aim was to assess whether 4D flow MRI derived right ventricular (RV) and pulmonary artery (PA) kinetic energy (KE) measures: 1) differentiate pediatric patients with repaired TOF from controls and 2) are associated with disease progression. Methods: In this retrospective case-control cohort study, pediatric patients status-post TOF repair (n=21) and controls (n=24) underwent 4D flow MRI for assessment of in-vivo 3D blood flow. Informed consent was obtained for performing 4D flow per a prospective IRB-approved, HIPAA-compliant protocol. 4D flow data analysis included phase offset error correction (velocity aliasing, Maxwell terms, eddy currents) and calculation of 3D PC-MR angiograms. Systolic and diastolic 3D RV and PA segmentation was performed (Figure 1A). For each voxel inside a segmentation volume, kinetic energy (KE) was calculated (KE = 1/2 mv^2 ; m = mass, or voxel volume multiplied by blood density 1.05 g/mL; v = absolute velocity). Total KERV and KEPA were determined as the sum of the KE of all voxels within the respective segmentation, and calculated for peak systole and diastole. KE maps were generated for each time point by projecting mean KE on a 2D plane transecting the RV and PA, respectively (Figure 1B). To normalize for patient size, total KERV and KEPA were indexed to body surface area (BSA). Results: Across the cardiac cycle, KEPA was increased in TOF vs. controls (median 12.5 [IQR 8-18.4] vs. 8.2 [6.1-10.4] mJ/m^^2 , p < 0.01 during peak systole; 2.3 [1.3-4] vs. 1.4 [1-1.9] mJ/m2 , p < 0.01 during peak diastole; see Table 1 and example KE maps in Figure 2). Elevated diastolic KERV and KEPA correlated with increased RV end-diastolic volume (EDV) (R2 =0.33, p < 0.001; R2 =0.50, p < 0.001; Figure 3A&B). Diastolic KEPA exhibited a non-linear relationship with RVEDV, with an inflection point near 120 ml/m^2 . Higher systolic KERV and KEPA strongly correlated with increased RV stroke volume (R2 =0.58, p < 0.001; R2 =0.60, p < 0.001; Figure 3B&C), denoting elevated KE at higher cardiac outputs. Similarly, KERV and KEPA correlated with systolic KERV and KEPA (Figure 3E&F). Conclusions: 4D flow MRI energetic measures, such as KE, were abnormal in repaired TOF compared to controls and have a direct relationship with traditional measures of disease progression. As a non-invasive and comprehensive method for measuring RV myocardial demand and TOF disease progression, KE biomarkers may help to refine criteria for reintervention in TOF.