An in vitro phantom study on the influence of tear size and configuration on the hemodynamics of the lumina in chronic type B aortic dissections

ObjectiveManagement and follow-up of chronic aortic dissections continue to be a clinical challenge due to progressive dilatation and subsequent rupture. To predict complications, guidelines suggest follow-up of aortic diameter. However, dilatation is triggered by hemodynamic parameters (pressures/wall shear stresses) and geometry of false (FL) and true lumen (TL), information not captured by diameter alone. Therefore, we aimed at better understanding the influence of dissection anatomy on TL and FL hemodynamics.MethodsIn vitro studies were performed using pulsatile flow in realistic dissected latex/silicone geometries with varying tear number, size, and location. We assessed three different conformations: (1) proximal tear only; (2) distal tear only; (3) both proximal and distal tears. All possible combinations (n = 8) of small (10% of aortic diameter) and large (25% of aortic diameter) tears were considered. Pressure, velocity, and flow patterns were analyzed within the lumina (at proximal and distal sections) and at the tears. We also computed the FL mean pressure index (FPImean%) as a percentage of the TL mean pressure, to compare pressures among models.ResultsThe presence of large tears equalized FL/TL pressures compared with models with only small tears (proximal FPImean% 99.85 ± 0.45 vs 92.73 ± 3.63; distal FPImean% 99.51 ± 0.80 vs 96.35 ± 1.96; P < .001). Thus, large tears resulted in slower velocities through the tears (systolic velocity <180 cm/s) and complex flows within the FL, whereas small tears resulted in lower FL pressures, higher tear velocities (systolic velocity >290 cm/s), and a well-defined flow. Additionally, both proximal and distal tears act as entry and exit. During systole, flow enters the FL through all tears simultaneously, while during diastole, flow leaves through all communications. Flow through the FL, from proximal to distal tears or vice versa, is minimal.ConclusionsOur results suggest that FL hemodynamics heavily depends on cumulative tear size, and thus, it is an important parameter to take into account when clinically assessing chronic aortic dissections.Clinical RelevanceTherapeutic decision making in chronic aortic dissection is mainly based on maximum total aortic diameter, while it was shown that diameter alone is not a reliable determinant of rupture and progression. Recent findings in patients have demonstrated the influence of tear size on the chronic evolution. Our approach complements these findings and makes it possible to understand the hemodynamic changes that are involved in tears of different sizes, both with regard to pressures and flows. Helping to understand these changes will provide more insight into determining what the exact clinical factors are that should be looked at during the follow-up of patients