Altered 4-D magnetic resonance imaging flow characteristics in complex congenital aortic arch repair

Four-Dimensional flow Magnetic Resonance Imaging for Assessment of Pediatric Coarctation of the Aorta

BACKGROUND

Coarctation of the aorta (CoA) typically requires repair, but re-interventions and vascular complications occur, particularly with associated defects like bicuspid aortic valve (BAV). Magnetic resonance imaging (MRI) may identify anatomic and hemodynamic factors contributing to clinical complications.

PURPOSE

To investigate 4D flow MRI characteristics in pediatric CoA to determine parameters for long-term clinical surveillance.

STUDY TYPE

Retrospective.

POPULATION

CoA (n = 21), CoA with BAV (n = 24), BAV alone (n = 29), and healthy control (n = 25).

FIELD STRENGTH/SEQUENCE

A 1.5 T, 3D CE IR FLASH MRA, 4D flow MRI using 3D time resolved PC-MRI with velocity encoding.

ASSESSMENT

Thoracic aorta diameters were measured from 3D CE-MRA. Peak systolic velocities and wall shear stress were calculated and flow patterns were visualized throughout the thoracic aorta using 4D flow. Repair characteristics, re-interventions, and need for anti-hypertensive medications were recorded.

STATISTICS

Descriptive statistics, ANOVA with post hoc t-testing and Bonferroni correction, Kruskal-Wallis H, intraclass correlation coefficient, Fleiss' kappa.

RESULTS

Patients with CoA with or without repair had smaller transverse arch diameters compared to BAV alone and control cohorts (P < 0.05), higher peak systolic flow velocities and wall shear stress compared to controls in the transverse arch and descending aorta (P < 0.05), and flow derangements in the descending aorta. The most common CoA repairs were extended end-to-end anastomosis (n = 22/45, 48.9%, age at repair 1 ± 2 years, seven re-interventions) and stent/interposition graft placement (n = 10/45, 22.2%, age at repair 12 ± 3 years, one re-intervention). Anti-hypertensive medications were prescribed to 33.3% (n = 15/45) of CoA and 34.4% of BAV alone patients (n = 10/29).

DATA CONCLUSIONS

Despite repair, CoA alters hemodynamics and flow patterns in the transverse arch and descending aorta. These findings may contribute to vascular remodeling and secondary complications. 4D flow MRI may be valuable in risk stratification, treatment selection and postintervention assessment. Long-term, prospective studies are warranted to correlate patient and MRI factors with clinical outcomes.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 3.

4D flow MRI applications in congenital heart disease

Advances in the diagnosis and management of congenital heart disease (CHD) have resulted in a growing population of patients surviving well into adulthood and requiring lifelong follow-up. Flow quantification is a central component in the assessment of patients with CHD. 4D flow magnetic resonance imaging (MRI) has emerged as a tool that enables comprehensive study of flow. It involves the acquisition of a three-dimensional time-resolved volume with velocity encoding in all three spatial directions along the cardiac cycle. This allows flow quantification and visualization of blood flow patterns as well as the study of advanced hemodynamic parameters as kinetic energy and wall shear stress. 4D flow MRI-based study of flow has given insight into the altered hemodynamics in CHD particularly in bicuspid aortic valve disease and Fontan circulation. The aim of this review is to discuss the expanding clinical and research applications of 4D flow MRI in CHD as well its limitations.Key Points• Three-dimensional velocity encoding allows not only flow quantification but also the visualization of multidirectional flow patterns and the study of advanced hemodynamic parameters.• 4D flow MRI has added insight into the abnormal hemodynamics involved in congenital heart disease in particular in bicuspid aortic valve and Fontan circulation.• The main limitation of 4D flow MRI in congenital heart disease is the relatively long scan duration required for the complete coverage of the heart and great vessels with adequate spatiotemporal resolution.