# Whole-Heart Assessment of Turbulent Kinetic Energy in the Repaired Tetralogy of Fallot
###### Abstract  
Approximately 10% of congenital heart diseases (CHDs) include Tetralogy of Fallot (TOF). Fortunately, due to advanced surgical techniques, most patients survive until adulthood. However, these patients require frequent monitoring for postoperative complications leading to heart hemodynamic alterations. Turbulent kinetic energy (TKE), as derived from 4D-flow magnetic resonance imaging (4D-flow MRI), has been used to characterize abnormal heart hemodynamics in CHD. Hence, this study aimed to assess the difference in TKE between patients with repaired TOF (rTOF) and healthy volunteers. A total of 35 subjects, 17 rTOF patients and 18 controls, underwent standard-of-care cardiac MRI and research 4D-flow MRI using a clinical 3T scanner. Heart chambers and great vessels were segmented using 3D angiograms derived from 4D-flow MRI. The TKE was quantified within segmented volumes. TKE was compared to standard cardiac MRI metrics. Controls demonstrated higher TKE in the left atria and left ventricle. However, patients demonstrated higher TKE in the right atria, right ventricle (\(p<0.05\)), and pulmonary artery. Lastly, no correlation was observed between TKE and standard clinical measurements. TKE can be a key indicator of the abnormal hemodynamics present in patients with rTOF and can assist future interventions and help monitor long-term outcomes. repaired tetralogy of fallot; magnetic resonance imaging; 4D-flow MRI; heart hemodynamics; turbulent kinetic energy +
Footnote †: journal: Medical Imaging Centre, University of Calgary, Calgary, AB T2N 1N4, Canada
patients now surviving into adulthood, these patients still require frequent and long-term monitoring for many postoperative complications that still arise over time, including right ventricle (RV) dilation and hypertrophy, left or right ventricular dysfunction, RV outflow tract obstruction, and pulmonary regurgitation (PR) [4]. These complications are due to the adverse effects faced within the hemodynamics of the cardiovascular system, contributing to poor long-term outcomes including sudden cardiac death, progressive exercise intolerance, and ventricular arrhythmia [5; 6; 7]. Surgical and percutaneous pulmonary valve replacements could prevent some of these long-term complications. Unfortunately, guideline indications are not well-supported for these procedures since a better understanding of heart (dys)function and hemodynamics in rTOF is needed. Transthoracic echocardiography is the first line imaging modality for assessing cardiovascular diseases given its easy accessibility, low cost, and safety [8; 9]. However, it may be limited by poor acoustic windows, beam alignments, operator dependence, and inaccuracy for quantifying regurgitan lesions [10; 11; 12]. Currently, standard cardiac magnetic resonance (CMR) is the gold standard for monitoring heart functions and remodeling in patients with rTOF [13]. CMR is able to identify rTOF complications based on morphological and simplified functional parameters including ejection fraction, ventricular volume, etc. [14]. However, these measurements provide a late expression of the physiological changes that occur, resulting in an inaccurate prediction of the true outcome [15; 16]. Flow is usually evaluated using 2D phase contrast, which can provide unidirectional velocity measurements perpendicular to the acquisition plane in the vessel of interest. In addition, these measurements do not provide us with an accurate representation of the 3D complexity of the blood flow due to its 2D nature, hence limiting access to flow information in all directions [17]. Furthermore, due to this restriction, it does not provide detailed information or a complete picture regarding alterations in the hemodynamic patterns within the entire heart. In addition, noninvasive Doppler methods allow us to measure adverse velocity fluctuations, but they are also limited in one direction due to the restriction of the ultrasound beam and have an elevated user variability [18; 19].