Computational Fluid Dynamics Simulations to Predict False Lumen Enlargement After Surgical Repair of Type-A Aortic Dissection

Abstract

We aim to use computational fluid dynamics to investigate the hemodynamic conditions that may predispose to false lumen enlargement in this patient population. Nine patients who received surgical repairs of their type-A aortic dissections between 2017-2018 were retrospectively identified. Multiple contrast-enhanced post-operative CT scans were used to construct 3D models of aortic geometries. Computational fluid dynamics simulations of the models were run on a high-performance computing cluster using SimVascular - an open-source simulation package. Physiological pulsatile flow conditions (4.9 L/min) were used at the aortic true lumen inlet, and physiological vascular resistances were applied at the distal vascular ends. Exploratory analyses showed no correlation between rate of false lumen growth and blood pressure, immediate post-op aortic diameter, or the number of fenestrations (p = 0.2). 1-year post-operative CT scans showed a median false lumen growth rate of 4.31 (3.66, 14.67) mm/year Median (Interquartile range) peak systolic, mid-diastolic, and late diastolic velocity magnitudes were 0.90 (1.40); 0.10 (0.16); and 0.06 (0.06) cm/s respectively. Spearman's ranked correlations between fenestration velocity and 1-year false lumen growth rates were found to be statistically significant: Velocity magnitude at peak systolic (p = 0.025; rho = 0.75), mid diastolic (p = 0.025; rho = 0.75) and late diastolic phases of the cardiac cycle (p = 0.006; rho = 0.85). We have shown that false lumen growth is strongly correlated to fenestration flow velocity, which has potential implications for post-operative surveillance and risk stratification.

Keywords: Aortic dissection; Chronic type-B; Computational fluid dynamics; Fluid dynamics; Stanford type-A.

Figure 1.

Patient specific model generation pipeline with SimVascular (from left to right) detailing the steps undertaken to create 3D models from a Reference CT scan (left most): First pathline generation, vessel boundary segmentation, 3D-model lofting, high resolution mesh generation.

Figure 2.

(Left) Render of blood flow velocity streamlines with proximal and distal fenestrations marked (A) and (B). (Right) Velocity magnitude waveform during a cardiac cycle at fenestrations marked A and B respectively.

Figure 3.

Correlation plots between 1-year false lumen growth rates and fenestration velocity at peak systolic, mid-diastolic, and late diastolic phases of the cardiac cycle. At peak systolic velocities greater than 2 cm/s the false lumen growth rates are 5 mm/year or more

Figure 4.

Oscillatory Shear Index (OSI) and Time Averaged Wall Shear Stress (TAWSS) seen from two different views for one of the simulated cases. The false lumen shows regional high OSI and low TAWSS proximal to the entry tear. The TAWSS increases locally opposite the entry tear eventually plateauing distally.