Flow volume asymmetry in the right aortic arch in children with magnetic resonance phase encoded velocity mapping.

Background: The right aortic arch is not uncommon in pediatrics. Flow dynamics in this type of aortic arch, which is important for cardiac energetics, organ perfusion, and Doppler flow calculations, have not been defined. Although there are complex secondary flow patterns, bulk axial flow makes up most of the energy use.

Methods: We examined 14 children with a right aortic arch by using through-plane phase-encoded magnetic resonance velocity mapping in the ascending and descending aorta to determine flow volume symmetry and velocity. The aortic cross section was divided into 4 quadrants aligned along the long axis of the aorta. Significance was defined as a P value <.05.

Results: In the ascending aorta, the posterior right quadrant demonstrated significantly greater blood flow than the other quadrants across the entire cardiac cycle (28% vs 23%-25%) and at the point of maximum flow (29% vs 22%-25%). Flow asymmetry was also present in the descending aorta; there was significantly more flow in the posterior quadrants than the anterior quadrants in total flow across the cardiac cycle (28% vs 21%-23%) and at the point of maximum flow (27%-28% vs 20%-24%). The time to maximum flow was significantly shorter in the ascending than the descending aorta (18% vs 24% of the cardiac cycle). In 10 of 14 patients, maximum velocity occurred in the right half of both the ascending and descending aorta. Flow reversal at end-systole was haphazard, occurring in all quadrants.

Conclusion: Flow volume asymmetry exists in the ascending and descending portions of the right aortic arch, which has implications for cardiac energetics, organ perfusion, and Doppler scanning flow calculations. This information may be useful in designing improved aortic surgical reconstructions in cases of congenital heart disease.