The Western Thoracic Surgical Association

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Reduced Proximal Aortic Compliance And Elevated Wall Stress Are Present In Preadolescent And Adolescent Patients With Tetralogy Of Fallot Despite Early Repair And Normalized Aortic Dimensions
Michal Schafer, Lorna P Browne, Gareth J Morgan, Alex J Barker, Brian Fonseca, Dunbar Ivy, *Max B Mitchell
Children's Hospital Colorado, Denver, CO

OBJECTIVES:
Tetralogy of Fallot (TOF) is associated with proximal aortic enlargement at birth and in patients repaired beyond infancy. Early complete repair eliminates volume overload and normalizes proximal aortic size by age 7 years. Degenerative aortic changes have been found in dilated ascending aortas of infants studied at the time of early TOF repair suggesting that intrinsic aortic wall abnormalities are causative factors in TOF-associated aortopathy. It is not known if early repair (and normalized aortic dimensions) ameliorates pathologic aortic histology or if normalized dimensions are maintained in later life. Magnetic resonance imaging (MRI) assessments in other aortopathies indicate that abnormal flow-mediated shear forces and altered flow patterns contribute to increased aortic wall stiffness and dilation associated with life-threatening complications. MRI assessments of aortic flow and wall characteristics have not been reported in TOF. The purpose of this study was to assess 4D-Flow MRI derived aortic flow patterns and wall shear stress (WSS) in pediatric patients who underwent early TOF repair and compare them to normal controls.
METHODS:
Comprehensive aortic geometry and flow dynamics were analyzed with 4D-Flow MRI in 12 TOF patients at mean age 13.2 4.1 years and compared to 12 age/size matched controls. All repairs were performed in infancy (mean age 7.7 3.2 months). Relative area change (RAC), peak systolic WSSmax and time-averaged WSSTA were determined in 8 standardized planes, Figure 1A. Qualitative grade scale flow analysis using interactive pathline visualization assessed the presence of pathologic aortic flow patterns during systole.
RESULTS:
Gross aortic dimensions and z-scores at all levels, cardiac index, stroke volume index, and aortic regurgitation fraction were not different from controls. Ascending aortic RAC was reduced in TOF (23% vs. 35%, P = 0.002). TOF WSSmax and WSSTA were increased in the ascending aorta, arch and mid-descending aorta (planes S1-S5, S8 all P < 0.05) but not different in proximal descending aorta (S6-7), Figure 1B. Supra-physiologic ascending aortic systolic helical formations were observed in 10 TOF patients (83%), Figure 1C. Cohesive laminar flow was present in all controls throughout systole.
CONCLUSIONS: This study provides the first detailed assessment of aortic flow dynamics and wall characteristics in TOF patients at any age using 4D-Flow MRI. Reduced compliance, elevated WSS, and unfavorable flow formations were found in preadolescent and adolescent TOF patients despite early repair and normalization of aortic size. These findings suggest that early TOF repair does not prevent pathologic aortic degeneration and may not prevent late complications. Comprehensive longitudinal monitoring of aortic flow and wall characteristics in TOF patients could guide strategies to avoid late aortic complications.


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