The Effect of Aortic Regurgitation on Left Ventricular Flow Dynamics Assessed by 4D-Flow MRI
Aortic regurgitation (AR) alters normal blood flow patterns in the left ventricle (LV), affecting diastolic filling dynamics, and is commonly quantified by the regurgitant fraction (RF). However, conventional diagnostic methods have notable limitations, prompting growing interest in four-dimensional flow magnetic resonance imaging (4D-flow MRI) as a tool for quantitatively assessing AR severity. In parallel, viscous energy dissipation (VED), which captures the energy loss caused by viscous forces within blood flow, provides additional important insight into the hemodynamic burden imposed on the LV by valvular dysfunction. This study aims to investigate the potential correlation between RF and VED in patients with AR, hypothesizing that higher RF values are associated with increased VED, thereby reflecting greater hemodynamic compromise. This pilot study included 10 patients with diagnosed AR and 9 healthy controls, all of whom underwent standardized cardiac MRI, including 4D-flow MRI. Volumetric blood flow and VED were assessed using validated post-processing techniques. Statistical analyses were conducted to evaluate group differences and explore the correlation between RF and VED. In healthy controls, LV flow exhibited a typical pattern during diastole and systole, forming a vortex during filling. Severe AR patients displayed disrupted LV flow, with regurgitant jets altering the flow dynamics. Quantitatively, integrated kinetic energy (iKE), vorticity (iVRT), and VED (iVED) were significantly elevated in AR patients compared to controls: iKE (0.003 ± 0.002 J vs. 0.001 ± 0.0004 J, p = 0.019), iVRT (0.304 ± 0.0738 s−1 vs 0.251 ± 0.0466 s−1, p = 0.077), and iVED (0.434 ± 0.307 mW vs. 0.166 ± 0.055 mW, p = 0.020). An increase was observed in patients with severe AR compared to controls, iKE rose to (0.005 J vs. 0.001 J), iVRT (0.335 s−1 vs. 0.233 s−1), and iVED (0.792 mW vs. 0.174 mW). All three parameters positively correlated with RF: iVRT (R2 = 0.175, p = 0.1263; Spearman R = 0.486), iVED (R2 = 0.628, p = 0.0038; Spearman R = 0.597), and iKE (R2 = 0.601, p = 0.0051; Spearman R = 0.616), indicating that increasing regurgitation severity is associated with greater intraventricular energy and flow disruption. This study quantifies the impact of AR on LV flow dynamics and demonstrates elevated VED in patients with AR. The observed correlation underscores the potential of VED as a complementary metric to RF in evaluating the hemodynamic impact of valvular regurgitation. Further studies with larger cohorts are needed to validate these findings and explore their clinical implications.
