Computational predictions of damage propagation preceding dissection of ascending thoracic aortic aneurysms

Summary

Dissections of ascending thoracic aortic aneurysms (ATAA) cause significant morbidity and mortality worldwide. They occur when a tear in the intima-media of the aorta permits the penetration of the blood and the subsequent delamination and separation of the wall in two layers, forming a false channel. In order to predict computationally the risk of tear formation, stress analyses should be performed layer-specifically and they should consider internal or residual stresses which exist in the tissue. In the present paper, we propose a novel layer–specific damage model based on the constrained mixture theory (CMT) which intrinsically takes into account these internal stresses and which can predict appropriately the tear formation. The model is implemented in finite-element commercial software Abaqus coupled with user material subroutine (UMAT). Its capability is tested by applying it to the simulation of different exemplary situations, going from in vitro bulge-inflation experiments on aortic samples to in vivo over-pressurizing of patient-specific ATAAs. The simulations reveal that damage correctly starts from the intimal layer (luminal side) and propagates across the media as a tear, but never hits the adventitia. This scenario is typically the first stage of development of an acute dissection, which is predicted for pressures of about 2.5 times the diastolic pressure by the model after calibrating the parameters against experimental data carried out on collected ATAA samples. Further validations on a larger cohort of patients should hopefully confirm the potential of the model in predicting patient-specific damage evolution and possible risk of dissection during aneurysm growth for clinical applications.

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