Biomechanical evaluation of a personalized external aortic root support applied in the Ross procedure

Abstract

A commonly heard concern in the Ross procedure, where a diseased aortic valve is replaced by the patient's own pulmonary valve, is the possibility of pulmonary autograft dilatation. We performed a biomechanical investigation of the use of a personalized external aortic root support or exostent as a possibility for supporting the autograft. In ten sheep a short length of pulmonary artery was interposed in the descending aorta, serving as a simplified version of the Ross procedure. In seven of these cases, the autograft was supported by an external mesh or so-called exostent. Three sheep served as control, of which one was excluded from the mechanical testing. The sheep were sacrificed six months after the procedure. Samples of the relevant tissues were obtained for subsequent mechanical testing: normal aorta, normal pulmonary artery, aorta with exostent, pulmonary artery with exostent, and pulmonary artery in aortic position for six months. After mechanical testing, the material parameters of the Gasser-Ogden-Holzapfel model were determined for the different tissue types. Stress-strain curves of the different tissue types show significantly different mechanical behavior. At baseline, stress-strain curves of the pulmonary artery are lower than aortic stress-strain curves, but at the strain levels at which the collagen fibers are recruited, the pulmonary artery behaves stiffer than the aorta. After being in aortic position for six months, the pulmonary artery tends towards aorta-like behavior, indicating that growth and remodeling processes have taken place. When adding an exostent around the pulmonary autograft, the mechanical behavior of the composite artery (exostent + artery) differs from the artery alone, the non-linearity being more evident in the former.

Numerical simulation of arterial remodeling in pulmonary autografts

“…Histological parameters Remodeling parameters 10 In the current implementation, and as discussed in Section 4, we do not explicitly account for volumetric growth. Instead, to account for the influence of extra constituent deposition, we modify Equation 2, by changing ( ) to (0).…”

“…As a test case for the algorithm described in the previous section, we use the results obtained by [10] and [31]. In this experimental study, a section of the pulmonary autograft was placed in the descending aorta in two sheep.…”

“…Six months after the procedure, the sheep were sacrificed and planar biaxial tests were carried out on the following tissues: healthy pulmonary artery, healthy aorta, and pulmonary artery (autograft) that remained in the aortic position for six months. A more detailed description of the experimental protocol can be found in [10].…”

“…As described in [10], we preliminarily characterized the adaptive biomechanical responses in vascular wall explants of mature sheep in which, six months before the characterization, a valveless pulmonary autograft had been implanted in the aorta. Our results show that a valveless pulmonary autograft placed in aortic position will remodel such that its macroscopic behavior leans more towards aorta-like behavior, as measured through planar biaxial tensile tests.…”

“…After presenting in detail this algorithm, we show its very good ability to predict the biomechanical adaptation of pulmonary autografts by comparing the predictions to our experimental results in the sheep experiments. [10] 2 MATERIALS AND METHODS…”