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