Patient-Specific Analysis of Ascending Thoracic Aortic Aneurysm with the Living Heart Human Model

Salvatore Cutugno,Michele Pilato,Salvatore Pasta,Giovanni Gentile,Julius M. Guccione,Giuseppe M. Raffa,Valentina Agnese,Andrew D. Wisneski

doi:10.3390/bioengineering8110175

Abstract

In ascending thoracic aortic aneurysms (ATAAs), aneurysm kinematics are driven by ventricular traction occurring every heartbeat, increasing the stress level of dilated aortic wall. Aortic elongation due to heart motion and aortic length are emerging as potential indicators of adverse events in ATAAs; however, simulation of ATAA that takes into account the cardiac mechanics is technically challenging. The objective of this study was to adapt the realistic Living Heart Human Model (LHHM) to the anatomy and physiology of a patient with ATAA to assess the role of cardiac motion on aortic wall stress distribution. Patient-specific segmentation and material parameter estimation were done using preoperative computed tomography angiography (CTA) and ex vivo biaxial testing of the harvested tissue collected during surgery. The lumped-parameter model of systemic circulation implemented in the LHHM was refined using clinical and echocardiographic data. The results showed that the longitudinal stress was highest in the major curvature of the aneurysm, with specific aortic quadrants having stress levels change from tensile to compressive in a transmural direction. This study revealed the key role of heart motion that stretches the aortic root and increases ATAA wall tension. The ATAA LHHM is a realistic cardiovascular platform where patient-specific information can be easily integrated to assess the aneurysm biomechanics and potentially support the clinical management of patients with ATAAs.

Highlights

An ascending thoracic aortic aneurysm (ATAA) is diagnosed in approximately 10 out of 100,000 persons per year in developed countries [1]
Material descriptors can be considered effective upon an engineering strain of 0.18, and this span is likely caused by the premature failure of the tissue specimen at hooks
Material descriptors were a = 0.24 MPa, b = 6.6, a f = 0.05 MPa, b f = 5.0, as = 0.02 MPa, bs = 2.0. These values were found to be higher than the material parameters adopted for the healthy aorta in the unmodified Living Heart Human Model (LHHM) (e.g., 60% increase for a and 230% for b), suggesting increased stiffness of the ATAA tissue compared to normal aorta

Summary

Introduction

An ascending thoracic aortic aneurysm (ATAA) is diagnosed in approximately 10 out of 100,000 persons per year in developed countries [1]. The condition is lethal with an estimated 5 year mortality rate of 39% for aortic diameters ≤6 cm and 62%. Elective surgical repair of ATAA is a major operation that carries high morbidity and mortality; if the dilated ascending aorta is left untreated, spontaneous aortic rupture or dissection may occur. Current clinical guidelines suggest that the threshold governing the timing for optimal intervention of surgical repair is a diameter of 5.5 cm [3]. Type A dissections have an aneurysm size below the surgical threshold [4]. The prognostic capability of the maximum diameter criterion may be poor because it considers the high risk of spontaneous dissections in patients with genetic predisposition, population statistics, and inconsistent use of imaging methods for diagnosis [5]

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