Elsevier

Journal of Biomechanics

Volume 79, 5 October 2018, Pages 135-146
Journal of Biomechanics

Prediction of stenting related adverse events through patient-specific finite element modelling

https://doi.org/10.1016/j.jbiomech.2018.08.006Get rights and content

Abstract

Right ventricular outflow tract (RVOT) calcific obstruction is frequent after homograft conduit implantation to treat congenital heart disease. Stenting and percutaneous pulmonary valve implantation (PPVI) can relieve the obstruction and prolong the conduit lifespan, but require accurate pre-procedural evaluation to minimize the risk of coronary artery (CA) compression, stent fracture, conduit injury or arterial distortion.

Herein, we test patient-specific finite element (FE) modeling as a tool to assess stenting feasibility and investigate clinically relevant risks associated to the percutaneous intervention.

Three patients undergoing attempted PPVI due to calcific RVOT conduit failure were enrolled; the calcific RVOT, the aortic root and the proximal CA were segmented on CT scans for each patient. We numerically reproduced RVOT balloon angioplasty to test procedure feasibility and the subsequent RVOT pre-stenting expanding the stent through a balloon-in-balloon delivery system.

Our FE framework predicted the occurrence of CA compression in the patient excluded from the real procedure. In the two patients undergoing RVOT stenting, numerical results were consistent with intraprocedural in-vivo fluoroscopic evidences. Furthermore, it quantified the stresses on the stent and on the relevant native structures, highlighting their marked dependence on the extent, shape and location of the calcific deposits. Stent deployment induced displacement and mechanical loading of the calcific deposits, also impacting on the adjacent anatomical structures.

This novel workflow has the potential to tackle the analysis of complex RVOT clinical scenarios, pinpointing the procedure impact on the dysfunctional anatomy and elucidating potential periprocedural complications.

Introduction

The surgical palliation of many complex congenital heart diseases, e.g., the Ross surgery for aortic valve disease, involves the implantation of homograft conduits in the right ventricular outflow tract (RVOT) (Frigiola et al., 2008, Hasan et al., 2014). Long-term post-operative RVOT dysfunctions are frequent, with progressive conduit calcification next to the pulmonary valve (PV) leading to PV stenosis (Lurz et al., 2009). Currently, the lifespan of surgically-treated pulmonary RVOT conduits can be extended by treating these complications through the combination of metal “pre-stenting” of the conduit and percutaneous pulmonary valve implantation (PPVI). Pre-stenting relieves the conduit obstruction (Aggarwal et al., 2007, Lurz et al., 2009) and provides anchoring support for the stented prosthetic valve, while preventing from valve malfunctions potentially caused by the direct interaction between the prosthetic valve and the adjacent calcific deposits (Momenah et al., 2009, Nordmeyer et al., 2011).

Stent fractures remain the dominant complication in as high as 25% of treated patients (McElhinney et al., 2011, Nordmeyer et al., 2007). Less frequently, the effect of the stent on the surrounding structures leads to life-threatening complications (Malone et al., 2017): conduit injury is reported in about 10% of cases (Boudjemline et al., 2016); coronary artery (CA) compression affects 5% of PPVI patients, although the risk for it is assessed through RVOT balloon angioplasty prior to pre-stenting (Fraisse et al., 2014, Morray et al., 2013); some degree of aortic root (AR) insufficiency has been reported and may constitute an important contraindication for PPVI (Torres et al., 2016). The risk for these adverse events is highly influenced by the morphology of the RVOT conduit and of the surrounding native structures (i.e. AR and CAs), and by their mechanical interplay with the implanted metal stent. Hence, finite element (FE) modeling could be an appropriate tool to investigate and predict them.

FE modeling has been used mostly to analyze stent fracture phenomena (Cosentino et al., 2014, Schievano et al., 2010). (Schievano et al., 2010) simulated the stent deployment within a patient-specific but rigid RVOT anatomy by pre-defined pressure loads directly applied on the stent, and showed that geometrical asymmetries lead to high stresses at the typical sites of stent fracture. Cosentino et al. (2014) retrospectively assessed stent deformations from intraprocedural biplane fluoroscopy images and identified that asymmetries in stent section geometry and cells shape were associated with higher risk of stent fracture. Bosi et al. (2015) recently tried to account for the impact of the stenting procedure on a compliant patient-specific RVOT site by inflating the stent through a purposely designed balloon model and to assess the mechanical interplay between the device and the RVOT wall only.

All the mentioned studies represent fundamental steps to investigate the patient-specific response to RVOT stenting; nonetheless, they do not still allow for an exhaustive assessment of all the mentioned procedural stenting complications and their clinical implications.

In this paper, for the first time, we propose a FE model comprising patient-specific RVOT, calcifications, CAs and AR, all represented as deformable tissues. Furthermore, we simulate the actual steps of the RVOT pre-stenting procedure, accounting for the standard armamentarium, i.e. the CP-stent® (Numed, Hopkinton, NY USA) and its balloon-in-balloon delivery system (BiB®, Numed, Hopkinton, NY USA).

We tested our numerical strategy on the anatomies of three patients with previous RVOT homograft surgery referred at a single hospital as candidates for PPVI due to moderate or severe RVOT conduit obstruction (Table 1). FE analyses were performed blinded to the clinical outcomes from the catheterization laboratory (CathLab). Our goal was twofold: on the one hand, testing the feasibility of our modeling pipeline and its effectiveness in predicting actual in vivo evidences from the CathLab; on the other hand, quantifying the biomechanical impact of the implanted stent on the site of implantation and on the surrounding anatomies.

Section snippets

Materials and methods

FE analyses were run using ABAQUS/Explicit© 6.10 (SIMULIA, Dessault Systèmes). Patient-specific models were defined accordingly, through a dedicated working pipeline (Fig. S1), as described in the next sub-sections.

Risk of coronary compression

The risk of coronary compression (Fig. 4) is typically associated to dCA-PA values lower than 0.8 mm (Malone et al., 2017). In patients 1 and 2, dCA-PA decreased from 7.1 mm to 4.1 mm and from 15.3 mm to 8.9 mm, respectively. In patient 3, dCA-PA decreased from 2.1 mm to 0.2 mm (Fig. 4b). These results were consistent with the evidences from the real balloon angioplasty procedures: following complete balloon expansion, a lack of coronary inflow was detected only in patient 3, who did not

Discussion

Stenting is an effective treatment to relieve RVOT conduit obstruction and prolong the lifespan of RVOT conduits, also providing a valid anchoring support for a subsequent PPVI (Aggarwal et al., 2007, Peng et al., 2006). Nonetheless, life-threatening periprocedural complications, related to device damage or to undesired effects of the device on the native structures, are not rare and can require urgent surgical repair (Boudjemline et al., 2016, Kostolny et al., 2008). In the present work, we

Limitations

Four main limitations of our FE modeling approach should be taken into consideration when interpreting results.

First, anatomies were complete and patient-specific, but tissue mechanical properties were not; instead, averaged mechanical properties extracted from fresh autografts (Azadani et al., 2012) (Carr-White et al., 2000) or homografts (Jia et al., 2017) can be prescribed, taking the type of procedure into account. This simplifying assumption affected computed stresses, but not the

Conflict of interest

None.

Acknowledgements

This work has been supported by the IRCCS Policlinico San Donato, a Clinical Research Hospital partially funded by the Italian Ministry of Health.

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