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Aims Post-procedure conduction abnormalities (CA) remain a common complication of transcatheter aortic valve implantation (TAVI), highlighting the need for personalized prediction models. We used machine learning (ML), integrating statistical and mechanistic modelling to provide a patient-specific estimation of the probability of developing CA after TAVI. Methods and results The cohort consisted of 151 patients with normal conduction and no pacemaker at baseline who underwent TAVI in nine European centres. Devices included CoreValve, Evolut R, Evolut PRO, and Lotus. Preoperative multi-slice computed tomography was performed. Virtual valve implantation with patient-specific computer modelling and simulation (CM&S) allowed calculation of valve-induced contact pressure on the anatomy. The primary composite outcome was new onset left or right bundle branch block or permanent pacemaker implantation (PPI) before discharge. A supervised ML approach was applied with eight models predicting CA based on anatomical, procedural and mechanistic data. CA occurred in 59% of patients (n = 89), more often after mechanical than first or second generation self-expanding valves (68% vs. 60% vs. 41%). CM&S revealed significantly higher contact pressure and contact pressure index in patients with CA. The best model achieved 83% accuracy (area under the curve 0.84) and sensitivity, specificity, positive predictive value, negative predictive value, and F1-score of 100%, 62%, 76%, 100%, and 82%. Conclusion ML, integrating statistical and mechanistic modelling, achieved an accurate prediction of CA after TAVI. This study demonstrates the potential of a synergetic approach for personalizing procedure planning, allowing selection of the optimal device and implantation strategy, avoiding new CA and/or PPI.

Valve size selection for transcatheter aortic valve replacement (TAVR) is currently based on cardiac CT-scan. At variance with patient-specific computer simulation, this does not allow the assessment of the valve-host interaction. We aimed to compare clinical valve size selection and valve size selection by an independent expert for computer simulation. A multicenter retrospective analysis of valve size selection by the physician and the independent expert in 141 patients who underwent TAVR with the self-expanding CoreValve or Evolut R. Baseline CT-scan was used for clinical valve size selection and for patient-specific computer simulation. Simulation results were not available for clinical use. Overall true concordance between clinical and simulated valve size selection was observed in 47 patients (33%), true discordance in 15 (11%) and ambiguity in 79 (56%). In 62 (44%, cohort A) one valve size was simulated whereas two valve sizes were simulated in 79 (56%, cohort B). In cohort A, concordance was 76% and discordance was 24%; a smaller valve size was selected for simulation in 10 patients and a larger in 5. In cohort B, a different valve size was selected for simulation in all patients in addition to the valve size that was used for TAVR. The different valve size concerned a smaller valve in 45 patients (57%) and a larger in 34 (43%). Selection of the valve size differs between the physician and the independent computer simulation expert who used the same source of information. These findings indicate that valve sizing in TAVR is still more intricate than generally assumed.

This study proposes a new framework to optimize the design of a transcatheter aortic valve through patient-specific finite element and fluid dynamics simulation. Two geometrical parameters of the frame, the diameter at ventricular inflow and the height of the first row of cells, were examined using the central composite design. The effect of those parameters on postoperative complications was investigated by response surface methodology, and a Nonlinear Programming by Quadratic Lagrangian algorithm was used in the optimization. Optimal and initial devices were then compared in 12 patients. The comparison was made in terms of device performance [i.e., reduced contact pressure on the atrioventricular conduction system and paravalvular aortic regurgitation (AR)]. Results suggest that large diameters and high cells favor higher anchoring of the device within the aortic root reducing the contact pressure and favor a better apposition of the device to the aortic root preventing AR. Compared to the initial device, the optimal device resulted in almost threefold lower predicted contact pressure and limited AR in all patients. In conclusion, patient-specific modelling and simulation could help to evaluate device performance prior to the actual first-in-human clinical study and, combined with device optimization, could help to develop better devices in a shorter period.

Transcatheter aortic valve implantation has become an established procedure to treat severe aortic stenosis. Correct device sizing/positioning is crucial for optimal outcome. Lotus valve sizing is based upon multiple aortic root dimensions. Hence, it often occurs that two valve sizes can be selected. In this study, patient-specific computer simulation is adopted to evaluate the influence of Lotus size/position on paravalvular aortic regurgitation (AR) and conduction abnormalities, in patients with equivocal aortic root dimensions. First, simulation was performed in 62 patients to validate the model in terms of predicted AR and conduction abnormalities using postoperative echocardiographic, angiographic and ECG-based data. Then, two Lotus sizes were simulated at two positions in patients with equivocal aortic root dimensions. Large valve size and deep position were associated with higher contact pressure, while only large size, not position, significantly reduced the predicted AR. Despite general trends, simulations revealed that optimal device size/position is patient-specific.

Providing therapies tailored to each patient is the vision of precision medicine, enabled by the increasing ability to capture extensive data about individual patients. In this position paper, we argue that the second enabling pillar towards this vision is the increasing power of computers and algorithms to learn, reason, and build the 'digital twin' of a patient. Computational models are boosting the capacity to draw diagnosis and prognosis, and future treatments will be tailored not only to current health status and data, but also to an accurate projection of the pathways to restore health by model predictions. The early steps of the digital twin in the area of cardiovascular medicine are reviewed in this article, together with a discussion of the challenges and opportunities ahead. We emphasize the synergies between mechanistic and statistical models in accelerating cardiovascular research and enabling the vision of precision medicine. ispartof: EUROPEAN HEART JOURNAL vol:41 issue:48 pages:4556-+ ispartof: location:England status: published

The number of transcatheter aortic valve implantation (TAVI) procedures is expected to increase significantly in the coming years. Improving efficiency will become essential for experienced operators performing large TAVI volumes, while new operators will require training and may benefit from accurate support. In this work, we present a fast deep learning method that can predict aortic annulus perimeter and area automatically from aortic annular plane images. We propose a method combining two deep convolutional neural networks followed by a postprocessing step. The models were trained with 355 patients using modern deep learning techniques, and the method was evaluated on another 118 patients. The method was validated against an interoperator variability study of the same 118 patients. The differences between the manually obtained aortic annulus measurements and the automatic predictions were similar to the differences between two independent observers (paired diff. of 3.3 ± 16.8 mm2 vs. 1.3 ± 21.1 mm2 for the area and a paired diff. of 0.6 ± 1.7 mm vs. 0.2 ± 2.5 mm for the perimeter). The area and perimeter were used to retrieve the suggested prosthesis sizes for the Edwards Sapien 3 and the Medtronic Evolut device retrospectively. The automatically obtained device size selections accorded well with the device sizes selected by operator 1. The total analysis time from aortic annular plane to prosthesis size was below one second. This study showed that automated TAVI device size selection using the proposed method is fast, accurate, and reproducible. Comparison with the interobserver variability has shown the reliability of the strategy, and embedding this tool based on deep learning in the preoperative planning routine has the potential to increase the efficiency while ensuring accuracy.

Background and aim Post-procedure conduction abnormalities (CA) and paravalvular aortic regurgitation (PAR) continue to strain TAVI outcomes. Computer simulations, based on patient-specific anatomy, valve properties, and implantation position, have been validated for prediction of these complications. The new-generation CoreValve Evolut PRO has been shown to have lower levels of PAR and CA than previous generations. The aim was to compare clinical outcomes after Evolut Pro implantation in real-life with outcomes of virtual deployment of the same size, implantation depth adjusted CoreValve Evolut R. Methods Patients undergoing Evolut Pro implantation at a single centre were included into the study. Postoperative Doppler echocardiography was assessed to define PAR, the pre- and postoperative 12-lead ECGs for CA, and the postoperative angiograms to measure implantation depth based on annular plane distance from the non-coronary and left coronary aortic valve cusps. Preoperative multislice computed tomography was used to generate patient-specific models of the native aortic root. Implantation of the Evolut R valve and corresponding aortic root deformation was simulated using computational mechanics, whereas blood flow and level of PAR were predicted using computational fluid dynamics. Prediction of CA – new onset left bundle branch block or atrioventricular block type II or III -was based on calculations of contact pressure in a patient-specific region of the aortic root containing the AV conduction system (ROI). Outcomes were predicted in three implantation depth positions - high, medium, low – where the position closest to the real-life implantation depth was chosen for outcome comparisons. Results Study diagram is shown in Figure 1. Thirty-three patients (57% female, mean age 82±6 years old) underwent a TAVI intervention with an Evolut PRO valve. Evolut PRO implantation depths were, in general, closest to the lowest modeled Evolut R depth. Comparison demonstrated similar overall incidence of moderate-to-severe PAR. The Evolut R simulation predicted 18 patients without PAR and 2 with PAR. With the Evolute PRO, 1 of the 18 not predicted developed significant PAR, and 1 of the 2 predicted did not develop PAR. CA were notably higher with the Evolut R simulation, where CA were present in 9 out of 12 patients, as compared to the observed 5 out of 12 with the Evolut PRO. Figure 1 Conclusion Single-centre outcomes after Evolut Pro implantation in real-life showed a similar overall incidence of moderate-to-severe PAR and a lower incidence of conduction abnormalities as compared to the same size, implantation depth adjusted, patient-specific Evolut R modeled outcomes. As inferred from the results, computer simulations may have high clinical utility in supporting clinical decisions regarding valve choice in TAVI procedures. Acknowledgement/Funding Horizon 2020 European Commission Project H2020-MSCA-ITN-2016 (764738)

Summary Objective of the study Transcatheter mitral valve interventions are emerging as a viable alternative for patients at high risk. Two key aspects are crucial during the preoperative planning: left ventricular outflow tract assessment and anatomical analysis. Given that the manual anatomical analysis is time-consuming, an automated approach may introduce efficiency during preoperative planning. In this study, we present an automatic method to detect the mitral valve annulus and discuss possible implementation of this method in clinical practice. Patients This retrospective study used the data of 71 patients collected from multiple centra. The mean age of this cohort was 74.2 ± 13.1 years, and 56.1% of the patients were female and 43.9% male. Materials and methods We trained three deep learning models to segment the area around the mitral valve annulus. In a post-processing step, we extracted the mitral valve annulus from this segmentation. As a final step, clinically relevant measurements such as 2D perimeter, trigone-to-trigone (TT) distance, septal-to-lateral (SL) distance and commissure-to-commissure (IC) distance were derived from the predicted mitral valve annulus. The method was cross-validated with k-folding. Results The predicted measurements showed excellent correlation with the manually obtained clinical measurements: 2D perimeter: R2 = 0.93, TT-distance: R2 = 0.86, SL-distance: R2 = 0.86 and IC-distance: R2 = 0.90. The total analysis time per patient of the automatic method was less than 1 second, which is an enormous speed-up as compared to the manual process (25 minutes). Conclusion The efficiency and accuracy of the proposed method give the confidence to move towards implementation of this technology in clinical practice. We propose a possible implementation of this method in clinical practice, which, in our opinion, will facilitate safe and efficient preoperative planning of transcatheter mitral valve interventions.

Background: A patient-specific computer simulation of transcatheter aortic valve replacement (TAVR) in tricuspid aortic valve has been developed, which can predict paravalvular regurgitation and conduction disturbance. We wished to validate a patient-specific computer simulation of TAVR in bicuspid aortic valve and to determine whether patient-specific transcatheter heart valve (THV) sizing and positioning might improve clinical outcomes. Methods: A retrospective study was performed on TAVR in bicuspid aortic valve patients that had both pre- and postprocedural computed tomography imaging. Preprocedural computed tomography imaging was used to create finite element models of the aortic root. Finite element analysis and computational fluid dynamics was performed. The simulation output was compared with postprocedural computed tomography imaging, cineangiography, echocardiography, and electrocardiograms. For each patient, multiple simulations were performed, to identify an optimal THV size and position for the patient’s specific anatomic characteristics. Results: A total of 37 patients were included in the study. The simulations accurately predicted the THV frame deformation (minimum-diameter intraclass correlation coefficient, 0.84; maximum-diameter intraclass correlation coefficient, 0.88; perimeter intraclass correlation coefficient, 0.91; area intraclass correlation coefficient, 0.91), more than mild paravalvular regurgitation (area under the receiver operating characteristic curve, 0.86) and major conduction abnormalities (new left bundle branch block or high-degree atrioventricular block; area under the receiver operating characteristic curve, 0.88). When compared with the implanted THV size and implant depth, optimal patient-specific THV sizing and positioning reduced simulation-predicted paravalvular regurgitation and markers of conduction disturbance. Conclusions: Patient-specific computer simulation of TAVR in bicuspid aortic valve may predict the development of important clinical outcomes, such as paravalvular regurgitation and conduction abnormalities. Patient-specific THV sizing and positioning may improve clinical outcomes of TAVR in bicuspid aortic valve.

Treatment of coronary bifurcation lesions remains an ongoing challenge for interventional cardiologists. Stenting of coronary bifurcations carries higher risk for in-stent restenosis, stent thrombosis, and recurrent clinical events. This review summarizes the current evidence regarding application and use of biomechanical modeling in the study of stent properties, local flow dynamics, and outcomes after percutaneous coronary interventions in bifurcation lesions. Biomechanical modeling of bifurcation stenting involves computational simulations and in vitro bench testing using subject-specific arterial geometries obtained from in vivo imaging. Biomechanical modeling has the potential to optimize stenting strategies and stent design, thereby reducing adverse outcomes. Large-scale clinical studies are needed to establish the translation of pre-clinical findings to the clinical arena.

Background— The extent to which pressure generated by the valve on the aortic root plays a role in the genesis of conduction abnormalities after transcatheter aortic valve replacement (TAVR) is unknown. This study elucidates the role of contact pressure and contact pressure area in the development of conduction abnormalities after TAVR using patient-specific computer simulations. Methods and Results— Finite-element computer simulations were performed to simulate TAVR of 112 patients who had undergone TAVR with the self-expanding CoreValve/Evolut R valve. On the basis of preoperative multi-slice computed tomography, a patient-specific region of the aortic root containing the atrioventricular conduction system was determined by identifying the membranous septum. Contact pressure and contact pressure index (percentage of area subjected to pressure) were quantified and compared in patients with and without new conduction abnormalities. Sixty-two patients (55%) developed a new left bundle branch block or a high-degree atrioventricular block after TAVR. Maximum contact pressure and contact pressure index (median [interquartile range]) were significantly higher in patients with compared with those without new conduction abnormalities (0.51 MPa [0.43–0.70 MPa] and 33% [22%–44%], respectively, versus 0.29 MPa [0.06–0.50 MPa] and 12% [1%–28%]). By multivariable regression analysis, only maximum contact pressure (odds ratio, 1.35; confidence interval, 1.1–1.7; P =0.01) and contact pressure index (odds ratio, 1.52; confidence interval, 1.1–2.1; P =0.01) were identified as independent predictors for conduction abnormalities, but not implantation depth. Conclusions— Patient-specific computer simulations revealed that maximum contact pressure and contact pressure index are both associated with new conduction abnormalities after CoreValve/Evolut R implantation and can predict which patient will have conduction abnormalities.

Objectives This study sought to better understand and optimize provisional main vessel stenting with final kissing balloon dilation (FKBD). Background Main vessel stenting with FKBD is widely used, but many technical variations are possible that may affect the final result. Furthermore, most contemporary stent designs have a large cell size, making the impact of stent platform selection for this procedure unclear. Methods Finite element simulations were used to virtually deploy and post-dilate 3 stent platforms in 3 bifurcation models. Two FKBD strategies were evaluated: simultaneous FKBD (n = 27) and modified FKBD (n = 27). In the simultaneous FKDB technique, both balloons were simultaneously inflated and deflated. In the modified FKBD technique, the side branch balloon was inflated first, then partially deflated, followed by main branch balloon inflation. Results Modified FKBD results in less ostial stenosis compared with simultaneous FKBD (15 ± 9% vs. 20 ± 11%; p Conclusions The modified FKBD procedure reduces elliptical stent deformation and optimizes side branch access.

The aim of this study is to analyze the shape and flow changes of a patient-specific carotid artery after carotid artery stenting (CAS) performed using an open-cell (stent-O) or a closed-cell (stent-C) stent design. First, a stent reconstructed from micro-computed tomography (microCT) is virtually implanted in a left carotid artery reconstructed from CT angiography. Second, an objective analysis of the stent-to-vessel apposition is used to quantify the lumen cross-sectional area and the incomplete stent apposition (ISA). Third, the carotid artery lumen is virtually perfused in order to quantify its resistance to flow and its exposure to atherogenic or thrombogenic hemodynamic conditions. After CAS, the minimum cross-sectional area of the internal carotid artery (ICA) (external carotid artery [ECA]) changes by +54% (-12%) with stent-O and +78% (-17%) with stent-C; the resistance to flow of the ICA (ECA) changes by -21% (+13%) with stent-O and -26% (+18%) with stent-C. Both stent designs suffer from ISA but the malapposed stent area is larger with stent-O than stent-C (29.5 vs. 14.8 mm(2)). The untreated vessel is not exposed to atherogenic flow conditions whereas an area of 67.6 mm(2) (104.9) occurs with stent-O (stent-C). The area of the stent surface exposed to thrombogenic risk is 5.42 mm(2) (7.7) with stent-O (stent-C). The computer simulations of stenting in a patient's carotid artery reveal a trade-off between cross-sectional size and flow resistance of the ICA (enlarged and circularized) and the ECA (narrowed and ovalized). Such a trade-off, together with malapposition, atherogenic risk, and thrombogenic risk is stent-design dependent.

AIMS: Mechanisms of lumen compromise after provisional side branch (SB) stenting are poorly understood. In this study we aimed to investigate the impact of bifurcation angle, plaque composition, and procedural strategy on SB compromise. METHODS AND RESULTS: Computer simulations of stent implantation were performed in Medina (1,1,1) bifurcation models. Provisional SB stenting was replicated including post-dilation after main branch stenting. Two bifurcation angles (45°, 70°) and four plaque types (fully lipid, fully fibrous, lipid with half and fully calcified ring distal to the carina) were tested. Two post-dilation balloons of different lengths (15 mm and 9 mm) were also investigated. Provisional stenting caused an ovalisation of the SB ostium (i.e., increase of ellipticity from 0.27 to 0.58±0.21, p

There is a growing interest in virtual tools to assist clinicians in evaluating different procedures and devices for endovascular treatment. In the present study we use finite element analysis to investigate the influence of stent design and vessel geometry for stent assisted coiling of intracranial aneurysms. Nine virtual stenting procedures were performed: three nitinol stent designs ((i) an open cell stent resembling the Neuroform, (ii) a generic stiff and (iii) a more flexible closed cell design), were deployed in three patient-specific cerebral aneurysmatic vessels. We investigated the percentage of strut area covering the aneurysm neck, the straightening induced on the cerebrovasculature by the stent placement (quantified by the reduction in tortuosity), and stent apposition to the wall (quantified as the percentage of struts within 0.2mm of the vessel). The results suggest that the open cell design better covers the aneurysm neck (11.0±1.1%) compared to both the stiff (7.8±1.6%) and flexible (8.7±1.6%) closed cell stents, and induces less straightening of the vessel (-5.1±1.6% vs. -42.9±9.8% and -26.9±11.9% ). The open cell design has, however, less struts apposing well to the vessel wall (56.0±6.4%) compared to the flexible (73.4±4.6%) and stiff (70.4±5.1%) closed cell design. With the presented study, we hope to contribute to and improve aneurysm treatment, using a novel patient specific environment as a possible pre-operative tool to evaluate mechanical stent behavior in different vascular geometries.

Objectives This study sought to evaluate post-dilation strategies in bifurcation stenting. Background In bifurcation stenting practice, it is still controversial how post-dilation should be performed and whether the kissing balloon (KB) technique is mandatory when only the main vessel (MV) receives a stent. Methods A series of drug-eluting stents (DES) (n = 26) were deployed in a coronary bifurcation model following a provisional approach. After the deployment of the stent in the MV, post-dilation with the KB technique was compared with a 2-step, sequential post-dilation of the side branch (SB) and MV without kissing. Results The percentage of the SB lumen area free of stent struts was similar after KB (79.1 ± 8.7%) and after the 2-step sequence (74.4 ± 11.6%, p = 0.25), a considerable improvement compared with MV stenting only without dilation of the stent at the SB ostium (30.8 ± 7.8%, p Conclusions Sequential 2-step post-dilation of the SB and MV may offer a simpler and more efficient alternative to final KB technique for provisional stenting of bifurcations.

Aims: The aim of this study was to compare the stent strut apposition and stent induced vessel wall stresses of currently used coronary stent designs. This may help to better understand their clinical performance and provide the insights necessary for further optimisation. Methods and results: We compared the stent strut apposition of six different stent designs when deployed (at 12 atm) in an idealised stenosed vessel using a novel approach based on finite element simulations. Additional insights into the mechanical behaviour of the investigated stents were obtained by virtually quantifying the stent induced vessel wall stresses. For the investigated stenosed vessel model, the percentage of malapposed struts (distance to wall > 10 mu m) ranged between 9% (Integrity stent) and 43% (Promus Element stent). The largest strut-artery distances were observed at the plaque shoulders. The 95 percentile of the axial stress within the intima ranges from 32 (Promus Element stent) to 83 kPa (Liberte stent). Stress peaks were mainly located at the inner curvatures of the vessel model and at the stent ends. Conclusions: For the investigated case, considerable differences were observed between the studied stent platforms in terms of stent strut apposition and stent induced vessel wall stresses. These differences in mechanical behaviour may help to explain clinical observations.

Patient-specific computer simulation of transcatheter aortic valve replacement (TAVR) in bicuspid aortic valve morphology has previously been demonstrated to reliably predict the development of both paravalvular regurgitation (PVR) and conduction disturbance. We hypothesised that patient-specific

The introduction of drug-eluting stents (DES) has reduced the occurrence of restenosis in coronary arteries. However, restenosis remains a problem in stented coronary bifurcations. This study investigates and compares three different second generation DESs when being implanted in the curved main branch of a coronary bifurcation with the aim of providing better insights into the related changes of the mechanical environment. The 3D bifurcation model is based on patient-specific angiographic data that accurately reproduce the in vivo curvatures of the vessel segments. The layered structure of the arterial wall and its anisotropic mechanical behavior are taken into account by applying a novel algorithm to define the fiber orientations. An innovative simulation strategy considering the insertion of a folded balloon catheter over a guide wire is proposed in order to position the stents within the curved vessel. Straightening occurs after implantation of all stents investigated. The resulting distributions of the wall stresses are strongly dependent on the stent design. Using a parametric modeling approach, two design modifications, which reduce the predicted maximum values of the wall stress, are proposed and analyzed.

The widespread acceptance of carotid artery stenting (CAS) to treat carotid artery stenosis and its effectiveness compared with surgical counterpart, carotid endarterectomy (CEA), is still a matter of debate. Transient or permanent neurological deficits may develop in patients undergoing CAS due to distal embolization or hemodynamic changes. Design, development, and usage of embolic protection devices (EPDs), such as embolic protection filters, appear to have a significant impact on the success of CAS. Unfortunately, some drawbacks, such as filtering failure, inability to cross tortuous high-grade stenoses, malpositioning and vessel injury, still remain and require design improvement. Currently, many different designs of such devices are available on the rapidly growing dedicated market. In spite of such a growing commercial interest, there is a significant need for design tools as well as for careful engineering investigations and design analyses of such nitinol devices. The present study aims to investigate the embolic protection filter design by finite element analysis. We first developed a parametrical computer-aided design model of an embolic filter based on micro-CT scans of the Angioguard™ XP (Cordis Endovascular, FL) EPD by means of the open source pyFormex software. Subsequently, we used the finite element method to simulate the deployment of the nitinol filter as it exits the delivery sheath. Comparison of the simulations with micro-CT images of the real device exiting the catheter showed excellent correspondence with our simulations. Finally, we evaluated circumferential basket-vessel wall apposition of a 4 mm size filter in a straight vessel of different sizes and shape. We conclude that the proposed methodology offers a useful tool to evaluate and to compare current or new designs of EPDs. Further simulations will investigate vessel wall apposition in a realistic tortuous anatomy.

Stent implantation has become a widely accepted endovascular intervention for the treatment of stenosed arteries. This minimally invasive technique has shown excellent results in unbranched arteries. However, stenting bifurcation lesions remains a challenge in coronary intervention as it is associated with a lower success rate. Many different techniques have been proposed in medical practice but all the suggested methodologies have specific limitations. Numerical simulations may help to understand and eliminate the shortcomings of current clinical techniques and devices. In this study, one of the currently applied techniques is analysed which involves the implantation of a stent in the main branch, followed by subsequent inflation of a balloon through the side of the stent. This improves the side branch patency and provides access to the side branch for later stent implantations. The impact of using different balloon sizes and stent designs was investigated. The stent cell through which the balloon is inflated increases considerably and as intuitively expected, using a larger balloon results in a larger opening. Furthermore, it was observed that this procedure may compromise the downstream main branch lumen. These observations correspond well with previously reported results, which were based on in vitro studies. The added value of the proposed numerical model is the ability to study many different techniques/stents, without the need for various expensive stent samples.

At present, the deployment of self-expandable braided stents has become a common and widely used minimally invasive treatment for stenotic lesions in the cardiovascular, gastrointestinal and respiratory system. To improve these revascularization procedures (e.g. increase the positioning accuracy) the optimal strategy lies in the further development of the stent design. In the context of optimizing braided stent designs, computational models can provide an excellent research tool complementary to analytical models. In this study, a finite element based modelling strategy is proposed to investigate and optimize the mechanics of braided stents. First a geometrical and finite element model of a braided Urolume endoprosthesis was built with the open source pyFormex design tool. The results of the reference simulation of the Urolume stent are in close agreement with both analytical and experimental data. Subsequently, a simplex-based design optimization algorithm automatically adjusts the reference Urolume geometry to facilitate precise positioning by reducing the foreshortening with 20% while maintaining the radial stiffness. Therefore, the proposed modelling strategy appears to be a promising optimization methodology in braided stent design.

Aims: The size of stent cells is an important design parameter influencing the resulting wall coverage and strut positioning of several bifurcation stenting techniques. Therefore, we report accurate geometrical information on stent cell size of five different stents with the key purpose to assist with stent selection for bifurcation lesions. Methods and results: We developed an innovative technique to assess cell size with high accuracy based on micro-CT images. In addition, the size of the ostium was calculated for several idealised bifurcations with a cylindrical main and side branch. The cell circumferences of the investigated stents vary substantially, with values between 9.5 and 19.8 mm (or an equivalent maximal cell diameter between 3.0 and 6.3 mm). Comparison of these cell circumferences with the calculated ostium circumferences shows which stents should preferably be used for which bifurcations, as these stents have cells that can be sufficiently enlarged by dilating through the side. Conclusions: The cell sizes of the investigated stents differ considerably. This should be taken into account when applying a particular bifurcation stenting technique. The risk on limited main or side branch patency due to obstructing stent struts can be minimised by using the reported data for stent selection.

Aims: Our aim was to validate patient-specific software integrating baseline anatomy and biomechanical properties of both the aortic root and valve for the prediction of valve morphology and aortic leaflet calcium displacement after TAVI. Methods and results: Finite element computer modelling was performed in 39 patients treated with a Medtronic CoreValve System (MCS; n=33) or an Edwards SAPIEN XT (ESV; n=6). Quantitative axial frame morphology at inflow (MCS, ESV) and nadir, coaptation and commissures (MCS) was compared between multislice computed tomography (MSCT) post TAVI and a computer model as well as displacement of the aortic leaflet calcifications, quantified by the distance between the coronary ostium and the closest calcium nodule. Bland-Altman analysis revealed a strong correlation between the observed (MSCT) and predicted frame dimensions, although small differences were detected for, e.g., Dmin at the inflow (mean +/- SD MSCT vs. model: 21.6 +/- 2.4 mm vs. 22.0 +/- 2.4 mm; difference +/- SD: -0.4 +/- 1.3 mm, p

Outcome of transcatheter aortic valve replacement (TAVR) depends on a combination of patient-, procedure-, and operator-related variables. Specific device–host-related interactions may also be involved and may result in, for instance, incomplete and/or nonuniform frame expansion that in turn may

In Western countries, cardiovascular disease is the most common cause of death, often related to atherosclerosis which can lead to a narrowing of the arteries. To restore perfusion of downstream tissues, an intravascular stent (i.e. a small tube-like structure) can be deployed in the obstructed vessel. The vast majority of stents are balloon expandable and crimped on a folded balloon to obtain a low profile for deliverability and lesion access. Several studies have exploited the finite element method to gain insight in their mechanical behaviour or to study the vascular reaction to stent deployment. However, to date – to the best of our knowledge – none of them include the balloon itself in its actual folded shape. Furthermore, literature on the effect of the crimping process on the expansion behaviour of the stent is even scarcer. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with data provided by the manufacturer and consequently our approach could be the basis for new realistic computational models of angioplasty procedures. The plastic deformation, prior to the stent expansion and induced by the crimping procedure, has a minor influence on the overall expansion behaviour of the stent but nevertheless influences the maximum von Mises stress and nominal strain. The maximum von Mises stress drops from 440 N/mm² to 426 N/mm² and the maximum nominal strain value lowers from 0.23 to 0.22 at the end of the expansion phase when neglecting the presence of the residual stresses. Depending on the context in which to use the developed mathematical models, the crimping phase can be discarded from the simulations in order to speed up the analyses.

A common treatment to restore normal blood flow in an obstructed artery is the deployment of a stent (i.e. small tube-like structure). The vast majority of stents are crimped on a folded balloon and laser cut from 316L stainless steel tubes. Although, several numerical studies (exploiting the Finite Element Method) are dedicated to the mechanical behaviour of balloon expandable stents, there seems to be no consensus regarding the mechanical properties to describe the inelastic material behaviour of SS316L. Moreover, as the typical dimensions of stent struts (e.g. 100 μm for coronary stents) are of a similar order of magnitude as the average grain size in stainless steel (i.e. 25 μm), continuum approaches relying on macroscopic material properties may be questionable. In addition, an experimental study on stainless steel stent strut specimens showed a size-dependency of the failure strain. In this study the impact of the magnitude of the yield stress on the stent expansion behavior is examined. An increase in the yield stress (from 205 N/mm² to 375 N/mm²) results in an increase of the pressure (from about 0.3 N/mm² to approximately 0.4 N/mm²) which the clinician needs to exert for the balloon to unfold and to reach its cylindrical expanded shape. Furthermore, the effect of the size dependency behavior of the material is studied by monitoring the nominal strain during stent expansion. The maximum value of the nominal strain in the expanded stent (e.g. εn = 23 %) does not exceed the critical value of the failure strain, (i.e. εn = 33 %), moreover the critical values are nowhere exceeded in the whole stent during the expansion. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with pressure/diameter data supplied by the manufacturer. Consequently, this study shows that the free expansion of new generation balloon-expandable stents can be studied accurately with computational analysis based on the Finite Element Method (FEM) and relying on macroscopic material properties. In this context, there is no need to implement a size-based constitutive material model, but before accepting the results of the study, one should check in any case the maximum strain against the limit as shown above.

Provisional side branch (SB) stenting is the recommended treatment strategy in the vast majority of bifurcation lesions. Over the past 10 years, advances in fundamental knowledge have led to a better understanding and to improvements of this technical approach. This strategy has reached maturity, and long-term clinical results are now comparable to those of non-bifurcation lesions. This paper describes in detail simple rules and tips and tricks which may help physicians in daily practice to use provisional side branch (SB) stenting as the gold standard treatment for the majority of bifurcation lesions.

John Doe, an 81-year-old patient with a significant distal left main (LM) stenosis, was treated using a provisional stenting approach. As part of an European Bifurcation Club (EBC) project, the complete stenting procedure was repeated using computational modelling. First, a tailored three-dimensional (3D) reconstruction of the bifurcation anatomy was created by fusion of multislice computed tomography (CT) imaging and intravascular ultrasound. Second, finite element analysis was employed to deploy and post-dilate the stent virtually within the generated patient-specific anatomical bifurcation model. Finally, blood flow was modelled using computational fluid dynamics. This proof-of-concept study demonstrated the feasibility of such patient-specific simulations for bifurcation stenting and has provided unique insights into the bifurcation anatomy, the technical aspects of LM bifurcation stenting, and the positive impact of adequate post-dilatation on blood flow patterns. Potential clinical applications such as virtual trials and preoperative planning seem feasible but require a thorough clinical validation of the predictive power of these computer simulations.

© Europa Edition 2011. All rights reserved. Current drug-eluting stents lead to excellent long-term clinical outcomes, with small differences between the most popular products1. This indicates a dominant impact of the drug, and it is therefore not surprising that the design of the stent platforms received less attention during the last few years. Of course, there are a few exceptions here, like the bioabsorbable stents, where the use of unconventional materials requires innovative stent designs, or the dedicated bifurcation stents, designed to fit the complex bifurcation anatomy.

The study aimed to evaluate the adequacy and feasibility of the single string bifurcation stenting technique.Double-stent techniques may be required for complex bifurcations. Currently applied methods all have their morphological or structural limitations with respect to wall coverage, multiple strut layers, and apposition rate.Single string is a novel method in which, first, the side branch (SB) stent is deployed with a single stent cell protruding into the main branch (MB). Second, the MB stent is deployed across this protruding stent cell. The procedure is completed by final kissing balloon dilation. The single string technique was first tested in vitro (n = 20) and next applied in patients (n = 11) with complex bifurcation stenoses.All procedures were performed successfully, crossing a single stent cell in 100%. Procedure duration was 23.0 ± 7.9 min, and the fluoroscopy time was 9.4 ± 3.5 min. The results were evaluated by optical coherence tomography, showing fully apposed struts in 83.0 ± 9.2% in the bifurcation area. Residual area obstruction in the MB was 6.4 ± 5.6% and 25.0 ± 16.9% in the SB, as evaluated by micro computed tomography. All the human cases were performed successfully with excellent angiographic results: the residual area stenosis was 27 ± 8% and 29 ± 10% in the MB and in the SB, respectively, by 3-dimensional quantitative coronary angiography. No relevant periprocedural enzyme increase was observed. During follow-up (6 ± 4 months), no adverse clinical events (death, myocardial infarction, target vessel revascularization) were noted.The single string technique for complex bifurcation dilation was shown to be adequate in vitro and feasible in humans, with favorable results in terms of stent overlap, malapposition rate, and low residual obstruction in both the MB and SB.

Bare-metal stent design influences clinical outcome Stent design matters when using baremetal stents as it affects both immediate and long-term clinical outcome. This clear conclusion was drawn by a randomized clinical study that compared five different uncoated stent designs, all having the same material composition [1]. In this study, the event-free survival rate for the included stent types ranged from 69.4 to 82.4% at 1-year follow-up. However, besides the significant impact of different stent strut patterns, more subtle differences have also been identified as important factors. For example, the Intracoronary Stenting and Angiographic Results: Strut Thickness Effect on Restenosis Outcome (ISARSTEREO) trial evaluated two stents with a very similar design and composed of the same material, but the strut thicknesses of the two devices were 50 and 140 μm [2]. The thin-strut design led to a significantly lower re-intervention rate of 8.6% compared with 13.8% for the thick-strut group.

AIMS We aimed to review the technical characteristics of DES platforms which have been documented to influence bifurcation stenting procedures conducted according to the provisional approach. METHODS AND RESULTS DES platforms have remarkable technical differences (side cell diameter, shape, deformability, etc.). We reviewed the literature data and performed original virtual bench tests to highlight the characteristics of DES platforms which influence the following phases of bifurcation stenting conducted according to the provisional approach: stent implantation in the main vessel across side-branch take-off ("crossover" stenting), proximal optimisation technique, rewiring and kissing balloon inflation. Available data show that the response of different DES platforms to the various procedural steps of provisional stenting is different. CONCLUSIONS When treating bifurcated lesions according to the provisional stenting approach, the search for an ideal matching between individual bifurcated anatomy and DES selection should take into account an articulated series of technical parameters.

This study sought to better understand and optimize provisional main vessel stenting with final kissing balloon dilation (FKBD).Main vessel stenting with FKBD is widely used, but many technical variations are possible that may affect the final result. Furthermore, most contemporary stent designs have a large cell size, making the impact of stent platform selection for this procedure unclear.Finite element simulations were used to virtually deploy and post-dilate 3 stent platforms in 3 bifurcation models. Two FKBD strategies were evaluated: simultaneous FKBD (n = 27) and modified FKBD (n = 27). In the simultaneous FKDB technique, both balloons were simultaneously inflated and deflated. In the modified FKBD technique, the side branch balloon was inflated first, then partially deflated, followed by main branch balloon inflation.Modified FKBD results in less ostial stenosis compared with simultaneous FKBD (15 ± 9% vs. 20 ± 11%; p0.001) and also reduces elliptical stent deformation (ellipticity index, 1.17 ± 0.05 vs. 1.36 ± 0.06; p0.001). The number of malapposed stent struts was not influenced by the FKBD technique (modified FKBD, 6.3 ± 3.6%; simultaneous FKBD, 6.4 ± 3.4%; p = 0.212). Stent design had no significant impact on the remaining ostial stenosis (Integrity [Medtronic, Inc., Minneapolis, Minnesota], 16 ± 11%; Omega [Boston Scientific, Natick, Massachusetts], 17 ± 11%; Multi-Link 8 [Abbott Vascular, Santa Clara, California], 19 ± 8%).The modified FKBD procedure reduces elliptical stent deformation and optimizes side branch access.

The aim of this study is to analyze the shape and flow changes of a patient-specific carotid artery after carotid artery stenting (CAS) performed using an open-cell (stent-O) or a closed-cell (stent-C) stent design. First, a stent reconstructed from micro-computed tomography (microCT) is virtually implanted in a left carotid artery reconstructed from CT angiography. Second, an objective analysis of the stent-to-vessel apposition is used to quantify the lumen cross-sectional area and the incomplete stent apposition (ISA). Third, the carotid artery lumen is virtually perfused in order to quantify its resistance to flow and its exposure to atherogenic or thrombogenic hemodynamic conditions. After CAS, the minimum cross-sectional area of the internal carotid artery (ICA) (external carotid artery [ECA]) changes by +54% (-12%) with stent-O and +78% (-17%) with stent-C; the resistance to flow of the ICA (ECA) changes by -21% (+13%) with stent-O and -26% (+18%) with stent-C. Both stent designs suffer from ISA but the malapposed stent area is larger with stent-O than stent-C (29.5 vs. 14.8 mm(2) ). The untreated vessel is not exposed to atherogenic flow conditions whereas an area of 67.6 mm(2) (104.9) occurs with stent-O (stent-C). The area of the stent surface exposed to thrombogenic risk is 5.42 mm(2) (7.7) with stent-O (stent-C). The computer simulations of stenting in a patient's carotid artery reveal a trade-off between cross-sectional size and flow resistance of the ICA (enlarged and circularized) and the ECA (narrowed and ovalized). Such a trade-off, together with malapposition, atherogenic risk, and thrombogenic risk is stent-design dependent.

Cerebral aneurysms are weakened, balloon like dilations of the intracranial vessels. Rupture of these swelled vessels, with a prevalence of 1 to 5% not uncommon [1], is associated with a high mortality and morbidity [2]. Clipping (by craniotomy) or coiling (passing platinum wires into the aneurysm) is often performed to reduce the risk of rupture. Coiling of wide necked or fusiform aneurysms, which is not easily achieved without risk of coil displacement, is often assisted by placement of intracranial stents, serving as a scaffold for the platinum coils. Cerebral stents can be of either closed or open cell design. Both designs have shown to be successful at assisting coiling, yet each design has its own strengths and weaknesses [3].Copyright © 2012 by ASME

Stenting has become a common procedure in clinical practice to treat arterial stenosis in coronary and peripheral vascular districts such as carotid or superficial femoral arteries.Copyright © 2011 by ASME

In the last years there is an increasing interest in patient-specific simulations of the fluid-structure interaction in aortic aneurysms, a.o. to better understand the growth and development of the aneurysm and to support diagnosis through assessment of its rupture potential. In order to verify these simulations, validation is an important and difficult task. Given ethical constraints, the slow time course of the disease in humans and the absence of true baseline data in a healthy aorta, these studies are difficult to perform in humans. This is particularly true for aneurysm rupture research, as rupture will normally be prevented by surgery and access to post-mortem tissue is not always possible. In order to overcome these problems an AAA mouse model can be used [1].

This study sought to evaluate post-dilation strategies in bifurcation stenting.In bifurcation stenting practice, it is still controversial how post-dilation should be performed and whether the kissing balloon (KB) technique is mandatory when only the main vessel (MV) receives a stent.A series of drug-eluting stents (DES) (n = 26) were deployed in a coronary bifurcation model following a provisional approach. After the deployment of the stent in the MV, post-dilation with the KB technique was compared with a 2-step, sequential post-dilation of the side branch (SB) and MV without kissing.The percentage of the SB lumen area free of stent struts was similar after KB (79.1 ± 8.7%) and after the 2-step sequence (74.4 ± 11.6%, p = 0.25), a considerable improvement compared with MV stenting only without dilation of the stent at the SB ostium (30.8 ± 7.8%, p0.0001). The rate of strut malapposition in the ostium was 21.3 ± 9.2% after KB and 24.9 ± 10.4% after the 2-step sequence, respectively, a significant reduction compared with a simple SB dilation (55.3 ± 16.8%, p0.0001) or MV stenting only (47.0 ± 8.5%, p0.0005). KB created a significant elliptical overexpansion of the MV lumen, inducing higher stress concentration proximal to the SB. KB also led to a higher risk of incomplete stent apposition at the proximal stent edge (30.7 ± 26.4% vs. 2.8 ± 9.6% for 2-step, p = 0.0016).Sequential 2-step post-dilation of the SB and MV may offer a simpler and more efficient alternative to final KB technique for provisional stenting of bifurcations.