Improved quantification of aortic regurgitation with direct regurgitant jet measurement by 4D flow CMR in complex congenital heart disease

Background
Due to the presence of complex flow states and significant jet eccentricity in patients with congenital heart disease (CHD), accurate quantification of aortic regurgitation (AR) using standard echocardiographic or conventional cardiovascular magnetic resonance (CMR) imaging measures remains challenging. Four-dimensional flow (4DF) CMR permits transvalvular flow quantification under non-laminar flow states, although it has not been well validated for AR quantification in CHD.

Methods
In 186 patients with moderate or complex CHD, we evaluated the agreement between different methods of AR quantification by 4DF CMR when compared to volumetry. Regurgitant flow volumes were measured (1) conventionally on time-resolved, velocity-encoded 4DF sequences at the aortic annulus, sinotubular junction (STJ), and ascending aorta (AAo), and via (2) direct regurgitant jet quantification 5 mm proximal to the vena contracta.

Results
Moderate overall agreement in AR quantification was observed between study methods (ρ=0.58-0.73). Compared with conventional flow quantification at the annulus, STJ, and AAo, direct regurgitant jet measurements showed improved correlation with volumetry (ρ=0.76), especially in patients with significant aortic dilation (r=0.95-0.97). In this latter group, regurgitant flow quantification at all other aortic levels resulted in AR severity classifications that were nearly a full grade lower (mean aortic regurgitant fraction difference: 7-12% ± 10-12%; p<0.001).

Conclusion
4DF CMR permits AR quantification in complex CHD with comparable accuracy to volumetry. Under non-laminar or complex flow states, as observed with significant aortic dilation, direct regurgitant jet measurements may be preferable to regurgitant flow quantification at all other aortic levels.