Predicting Aneurysmal Degeneration in Uncomplicated Residual Type B Aortic Dissection

Abstract

The formation of an aneurysm in the false lumen (FL) is a long-term complication in a significant percentage of type B aortic dissection (AD) patients. The ability to predict which patients are likely to progress to aneurysm formation is key to justifying the risks of interventional therapy. The investigation of patient-specific hemodynamics has the potential to enable a patient-tailored approach to improve prognosis by guiding disease management for type B dissection. CFD-derived hemodynamic descriptors and geometric features were used to retrospectively assess individual aortas for a population of residual type B AD patients and analyze correlations with known outcomes (i.e., rapid aortic growth, death). The results highlight great variability in flow patterns and hemodynamic descriptors. A rapid aortic expansion was found to be associated with a larger FL. Time-averaged wall shear stress at the tear region emerged as a possible indicator of the dynamics of flow exchange between lumens and its effect on the evolution of individual aortas. High FL flow rate and tortuosity were associated with adverse outcomes suggesting a role as indicators of risk. AD induces complex changes in vessel geometry and hemodynamics. The reported findings emphasize the need for a patient-tailored approach when evaluating uncomplicated type B AD patients and show the potential of CFD-derived hemodynamics to complement anatomical assessment and help disease management.

Keywords: CFD; aneurysmal degeneration; aortic dissection; hemodynamics.

Figure 1

(Left): three-dimensional reconstruction of the aortic lumen for two example geometries; patient A with rapidly growing aorta and patient B with stable aortic size. (Right): flow rate extracted from PC-MRI images on a plane including the ascending and descending aorta.

Figure 2

Sensitivity analysis for a case example. (Top): mean WSS as a function of the number of elements in the mesh (Left) and mean WSS relative percentage difference for each mesh with respect to the finer mesh (Right). (Bottom): maximum WSS as a function of the number of elements in the mesh (Left) and the maximum WSS relative percentage difference for each mesh with respect to the finer mesh (Right).

Figure 3

Flow features in the dissected aorta. Streamlines for the example cases at three instances of the cardiac cycle. Patients 1 and 3 belong to the rapid-growth group, patient 12 to the stable-size group/favorable outcome subgroup, and patient 19 to the stable-size group/adverse-outcome subgroup.

Figure 4

Luminal distribution of TAWSS, OSI, and RRT: example cases. Patients 1 and 3 belong to the rapid-growth group, patient 12 to the stable-size group/favorable outcome subgroup, and patient 19 to the stable-size group/adverse-outcome subgroup.

Figure 5

Luminal distribution of TAWSS for all the AD anatomies in the study population: patients 1–11 belong to the rapid-growth group, patients 12–22 to the stable-size group with patients 12–18 belonging to the favorable outcome subgroup, and patients 19–22 to the adverse-outcome subgroup.

Figure 6

Pressure difference between the false and true lumens: differences were obtained as average FL pressure minus average TL pressure on cross-sectional planes perpendicular to the vessel’s centerline along the length of the descending aorta. The difference is reported at systolic peak, systolic deceleration, and diastole for the four representative examples. TOP row from the left: patients 1 and 3 belong to the rapid-growth group; BOTTOM row from the left: patient 12 belongs to the stable-size group/favorable outcome subgroup and patient 19 to the stable-size group/adverse-outcome subgroup.