Postoperative analysis of the mechanical interaction between stent and host tissue in patients after transcatheter aortic valve implantation

The analysis is based on a finite element procedure to extract the contact forces between an implanted Nitinol stent and the surrounding host tissue using postoperative CT images. The methodology was applied for patients (N=46) which have undergone a TAVI procedure with the Medtronic CoreValve Revalving System (MCRS) to obtain corresponding deformation and force maps. The postoperative CT data were recorded for each patient in both systolic and diastolic phase of the heart cycle. Scalar parameters were defined, which map deformed geometry and contact force field to mechanically relevant quantities: radial dilatation, radial shape distortion, non-convex points, mean force, a force deviation measure and a pressure equivalent. The latter demonstrates that in the area of the aortic root, the added circumferential loading is of the same order as the baseline average blood pressure, thus leading to a doubling of the local mechanical load. Generally the force distribution along the stent is non-homogeneous. A comparison of systolic and diastolic data revealed slightly higher contact forces during the diastole, indicating that the stent has to carry more load in this phase. The geometrical and mechanical parameters were compared for two types of clinical complication: para-valvular leakage (PVL) and permanent pacemaker requirement (PPM). It was found that an increase in mean force can be associated with both complications; significantly for PVL and as a trend for PPM.