Fast Approximate Quantification of Endovascular Stent Graft Displacement Forces in the Bovine Aortic Arch Variant

Sturla F, Caimi A, Romarowski RM, Nano G, Glauber M, Redaelli A, Votta E, Marrocco-Trischitta MM. Fast Approximate Quantification of Endovascular Stent Graft Displacement Forces in the Bovine Aortic Arch Variant. J Endovasc Ther. 2022 May 19:15266028221095403. doi: 10.1177/15266028221095403. Epub ahead of print. PMID: 35588222. Abstract <strong>Purpose: </strong>Displacement forces (<strong><em>DF</em></strong>s) identify hostile landing zones for stent graft deployment in thoracic endovascular aortic repair (TEVAR). However, their use in TEVAR planning is hampered by the need for time-expensive computational fluid dynamics (CFD). We propose a novel fast-approximate computation of <strong><em>DF</em></strong>s merely exploiting aortic arch anatomy, as derived from the computed tomography (CT) and a measure of central aortic pressure. <strong>Materials and methods: </strong>We tested the fast-approximate approach against CFD gold-standard in 34 subjects with the "bovine" aortic arch variant. For each dataset, a 3-dimensional (3D) model of the aortic arch lumen was reconstructed from computed tomography angiography and CFD then employed to compute <strong><em>DF</em></strong>s within the aortic proximal landing zones. To quantify fast-approximate <strong><em>DF</em></strong>s, the wall shear stress contribution to the <strong><em>DF</em></strong> was neglected and blood pressure space-distribution was averaged on the entire aortic wall to reliably approximate the patient-specific central blood pressure. Also, <strong><em>DF</em></strong> values were normalized on the corresponding proximal landing zone area to obtain the equivalent surface traction (<strong><em>EST</em></strong>). <strong>Results: </strong>Fast-approximate approach consistently reflected (r²=0.99, p&lt;0.0001) the <strong><em>DF</em></strong> pattern obtained by CFD, with a -1.1% and 0.7° bias in <strong><em>DF</em></strong>s magnitude and orientation, respectively. The normalized <strong><em>EST</em></strong> progressively increased (p&lt;0.0001) from zone 0 to zone 3 regardless of the type of arch, with proximal landing zone 3 showing significantly greater forces than zone 2 (p&lt;0.0001). Upon DF normalization to the corresponding aortic surface, fast-approximate <strong><em>EST</em></strong> was decoupled in blood pressure and a dimensionless shape vector (S) reflecting aortic arch morphology. <strong><em>S</em></strong> showed a zone-specific pattern of orientation and proved a valid biomechanical blueprint of <strong><em>DF</em></strong> impact on the thoracic aortic wall. <strong>Conclusion: </strong>Requiring only a few seconds and quantifying clinically relevant biomechanical parameters of proximal landing zones for arch TEVAR, our method suits the real preoperative decision-making process. It paves the way toward analyzing large population of patients and hence to define threshold values for a future patient-specific preoperative TEVAR planning.