Flow quantification within the aortic ejection tract using 4D flow cardiac MRI in patients with bicuspid aortic valve: Implications for the assessment of aortic regurgitation.

PURPOSE The purpose of this study was to evaluate the performance of four-dimensional (4D) flow cardiac MRI in quantifying aortic flow in patients with bicuspid aortic valve (BAV). MATERIALS AND METHODS Patients with BAV who underwent transthoracic echocardiography (TTE) and 4D flow cardiac MRI were prospectively included. Aortic flow was quantified using two-dimensional phase contrast velocimetry at the sinotubular junction and in the ascending aorta and using 4D flow in the regurgitant jet, in the left ventricular outflow tract, at the aortic annulus, the sinotubular junction, and the ascending aorta, with or without anatomical tracking. Flow quantification was compared with ventricular volumes, pulmonary flow using Pearson correlation test, bias and limits of agreement (LOA) using Bland Altman method, and with multiparametric transthoracic echocardiography quantification using weighted kappa test. RESULTS Eighty-eight patients (63 men, 25 women) with a mean age of 50.5 ± 14.8 (standard deviation) years (age range: 20.8-78.3) were included. Changes in flow with or without tracking were modest (< 5 mL). The best correlation was obtained at the aortic annulus for forward volume (r = 0.84; LOA [-28.4; 25.3] mL) and at the regurgitant jet and sinotubular junction for regurgitant volume (r = 0.68; LOA [-27.8; 33.8] and r = 0.69; LOA [-28.6; 24.2] mL). A combined approach for regurgitant fraction and net volume calculations using forward volume measured at ANN and regurgitant volume at sinotubular junction performed better than each level taken separately (r = 0.90; LOA [-20.7; 10.0] mL and r = 0.48, LOA [-33.8; 33.4] %). The agreement between transthoracic echocardiography and 4D flow cardiac MRI for aortic regurgitation grading was poor (kappa, 0.13 to 0.42). CONCLUSION In patients with BAV, aortic flow quantification by 4D flow cardiac MRI is the most accurate at the annulus for the forward volume, and at the sinotubular junction or directly in the jet for the regurgitant volume.