Post-valvular energy exchange in bicuspid aortic valve with regurgitation and stenosis and its association with left ventricular workload: a 4D flow magnetic resonance imaging cross-sectional study

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BACKGROUND: Bicuspid aortic valve (BAV) regurgitation and stenosis considerably alter post-valvular flow dynamics and impose additional energetic load on the left ventricle (LV). We therefore sought to determine whether 4D Flow MRI-derived ascending-aortic kinetic energy (KE) and viscous energy loss (EL), can differentiate BAV subtypes and healthy controls, and are associated with LV remodeling markers. METHODS: Seventy-one participants (19 BAV without valve dysfunction, 17 with isolated aortic regurgitation (BAV-AR), 15 with isolated aortic stenosis (BAV-AS), and 20 healthy controls) underwent 3.0 T magnetic resonance imaging (MRI), including cine balanced SSFP and 4D-Flow. Post valvular KE, viscous EL, and the dimensionless EL index were computed from the 4D Flow velocity fields. Global 3D LV strain metrics were derived via cine SSFP feature-tracking technique. Between-group differences were assessed with one-way ANOVA or Kruskal-Wallis tests, and associations were evaluated using Spearman's rank correlation. RESULTS: Average ascending aortic KE rose progressively from controls (3.3[2.3-4.3]) to uncomplicated BAV (6.7[5.3-9.1]), to BAV-AS (15.4[12.2-29.5]) and peaked in the BAV-AR (19.4[14.9-21.3], p < 0.001). Peak-systolic viscous EL was significantly elevated in both the stenotic (16.2 [9.1-24.4] mW) and regurgitant (11.4 [9.5-17.6] mW) groups compared to controls (4.1 [3.4-5.7] mW), but not in the uncomplicated BAV (6.4 [5.1-8.0] mW). Over the entire systole, viscous EL in the uncomplicated BAV (3.3 [2.5-4.1] mW) was also statistically increased compared to controls (1.7 [1.3-2.3] mW). KE correlated more strongly with regurgitation severity (rho = 0.50, p < 0.001), and EL with stenosis severity (rho = 0.48, p < 0.001). Aortic surgery referral was more closely associated with elevated KE (rho = 0.65, p < 0.001) and viscous EL (rho = 0.64, p < 0.001) than with aortic diameter (rho = 0.50, p < 0.001). Left ventricular Mass index and peak diastolic strain rate circumferential were correlated but more strongly with KE than viscous EL. CONCLUSIONS: 4D Flow MRI-derived post-valvular KE and viscous EL may serve as sensitive early biomarkers of LV dysfunction, and might outperform aortic diameter in risk stratification, and guide optimal intervention timing in BAV diseases while they need to be validated in broader populations.

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