Modeling Stented Coronary Arteries: Where We are, Where to Go

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Image-Based Quantification Workflow for Coronary Morphology: A Tool for Use in Next-Generation Bifurcation Stent Design

Coronary artery disease (CAD) occurs in ~200,000 bifurcation lesions annually. Treatment of CAD near bends and bifurcations is challenging and a preferred strategy for bifurcation lesions has yet to be established. However, a favorable treatment option may be elucidated by a more thorough understanding of vessel morphology as well as local hemodynamic alterations caused by current stenting approaches. Computational modeling of human arteries offers an attractive way to investigate the relationships between geometry, hemodynamics and vascular disease. Recent developments also make it possible to perform analysis on realistic geometries acquired noninvasively. The objective of this work was twofold. The first aim was to build on previous work in this area by quantifying hemodynamic alterations introduced by treatment of an idealized coronary bifurcation using several approaches that involve multiple stents. Each model was created using combined computer aided design techniques and computational fluid dynamics (CFD) analysis tools. Resting and hyperemic blood flow conditions were also studied to determine the severity of local hemodynamic alterations and for comparison to previous results. Indices of time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) were quantified for four idealized computational models. The luminal surface exposed to low TAWSS was similar in the main vessel (MV) for all models. Greatest differences were noted between un-stented versus stented side branch vessels (ex. rest: 1% vs. 35%). Sites of elevated OSI (\u3e0.1) were minimal, except under hyperemia conditions in the MV (10% surface area). Flow disturbances were quantified for each provisional technique used, illustrating how stents protruding in main vessels impact flow profiles. Stents without kissing balloon dilation had abnormal flow disturbances, but showed decreased percentage of area exposed to areas of low WSS. A second aim of this work was to design a robust and unbiased method to quantify vessel morphology and representative trends for three bifurcation sites prone to CAD. Computational models of these sites were generated using computed topography images from 22 patients. Models were used to query geometric characteristics from each bifurcation site including area, length, eccentricity, taper, curvature and bifurcation angles. Post-processing was accomplished by a combination of statistical methods and clustering analysis. Vessel length and area were significantly different within and between bifurcation sites. The left main coronary artery (LCA) bifurcation was significantly different from its two daughter bifurcations (left anterior descending and left circumflex arteries). Specifically vessel area and length were significantly different both between and within bifurcation sites. The daughter bifurcation sites were similar for all characteristics. Vessel area and length proved to be the most useful properties for identifying trends within a particular bifurcation site. The outcome of this work provides a workflow for characterizing coronary bifurcations and a strong foundation for elucidating common parameters from normal, healthy coronary arteries. Collectively these results from idealized and patient-specific coronary bifurcations offer additional insight into the impact of current treatment approaches and characteristics associated with current stenting techniques. Flow disturbances and local hemodynamic changes have been quantified for provisional techniques currently used. These methods and results may ultimately be useful in the design of next-generation bifurcation stents

Bioresorbable coronary stents : non-invasive quantitative assessment of edge and intrastent plaque – a 256-slice computed tomography longitudinal study

Les bioresorbable stents (BRS), en français intitulés tuteurs coronariens biorésorbables, sont constitués d’un polymère biorésorbable, plutôt que de métal, et ne créent pas d’artéfacts métalliques significatifs en tomodensitométrie (TDM). Cela permet une meilleure évaluation de la plaque coronarienne sous ces tuteurs en TDM qu’avec les anciens tuteurs qui sont en métal. OBJECTIF: Évaluer l’évolution de la composition de la plaque, sa fraction lipidique (FL)— marqueur de vulnérabilité de la plaque, dans les 3 zones pré-tuteur (bord proximal), intra-tuteur et post-tuteur (bord distal), et le volume de la plaque entre 1 et 12 mois post-implantation de BRS. MÉTHODOLOGIE: Il s’agit d’une étude observationnelle longitudinale réalisée chez 27 patients consécutifs (âge moyen 59,7 +/- 8,6 ans) et recrutés prospectivement pour une imagerie par TDM 256-coupes à 1 et 12 mois post-implantation de BRS (35 tuteurs total). Les objectifs primaires sont: volume de plaque totale et de FL (mm3) comparés entre 1 et 12 mois. Afin de tenir compte de la corrélation intra-patient, des analyses de variance des modèles linéaires mixtes avec ou sans spline sont utilisés avec deux facteurs répétés temps et zone/bloc (1 bloc= 5 mm en axe longitudinal). La valeur % FL= volume absolu du FL/ volume total de la plaque. RÉSULTATS: Notre analyse par bloc ou par spline n’a pas démontré une différence significative dans les volumes de plaque ou des FL dans les zones pre- intra- and post-tuteur entre 1 et 12 mois. CONCLUSION: Notre étude a réussi à démontrer la faisabilité d’une analyse non-invasive quantitative répétée de la plaque coronarienne et de la lumière intra-tuteur avec l’utilisation de TDM 256 coupes. Cette étude pilote n’a pas démontré de différence significative dans les volumes des plaques et atténuation entre 1- et 12- mois de follow-up post-implantation de BRS. Notre méthode pourrait être appliquée à l’évaluation des différents structures ou profils pharmacologiques de ces tuteurs.Coronary bioresorbable stents (BRS) are made of a bioresorbable polymer rather than metal. Unlike metallic stents, BRS do not produce significant artifacts in computed tomography (CT) and are radiolucent in CT, making it possible to evaluate coronary plaque beneath an implanted stent. PURPOSE: The purpose of our study was to evaluate the volumes of plaque and low attenuation plaque components (LAP —a marker of plaque vulnerability) of pre-, intra- and post-stent plaque location between 1 and 12 months post-implantation. METHODS: In our prospective longitudinal study, we recruited 27 consecutive patients (mean age 59.7 +/- 8.6 years) with bioresorbable stents (n=35) for a 256-slice ECG-synchronized CT evaluation at 1 month and at 12 months post stent implantation. Total plaque volume (mm3) as well as absolute and relative (%) LAP volume per block in the pre-, intra- and post-stent zones were analyzed; comparison of 1 and 12 months post BRS implantation. Changes in these variables were assessed using mixed effects models with and without spline, which also accounted for correlation between repeated measurements with factors such as time and zone/block (1 block = 5 mm in longitudinal axis). The value % LAP= LAP absolute volume/ total plaque volume. RESULTS: Our block or spline model analysis showed no significant difference in plaque or LAP volumes in pre-, intra- and post-stent zones measured at 1 month and at 12 months. CONCLUSION: Our study demonstrates the feasibility of repeated non-invasive quantitative analysis of intrastent coronary plaque and in-stent lumen using a 256-channel CT scan. This pilot study did not show significant differences in plaque volume and attenuation between 1- and 12-month follow-up from stent implantation. The method we used could be applied to the evaluation of different stent structures or different pharmacological profiles of bioresorbable stents

Optimal Site for Proximal Optimization Technique in Complex Coronary Bifurcation Stenting: A Computational Fluid Dynamics Study

Background/purpose: The optimal position of the balloon distal radio-opaque marker during the post optimization technique (POT) remains debated. We analyzed three potential different balloon positions for the final POT in two different two-stenting techniques, to compare the hemodynamic effects in terms of wall shear stress (WSS) in patients with complex left main (LM) coronary bifurcation. Methods/materials: We reconstructed the patient-specific coronary bifurcation anatomy using the coronary computed tomography angiography (CCTA) data of 8 consecutive patients (6 males, mean age 68.2± 18.6 years) affected by complex LM bifurcation disease. Subsequently a virtual bench test was performed in each patient using two different double stenting techniques represented by the DK and Nano crush using the reconstruction of Orsiro stents (Biotronik IC, Bulack, Switzerland). Results: A significant reduction in the mean WSS values in all the lesion's sites was observed when the final POT was performed 1 mm distally the carina cut plane in both techniques. Moreover, a significant improvement in the mean WSS values of the entire SB (e.g. LCX) was obtained performing the POT 1 mm distally to the carina cut plane. The proximal POT resulted in larger area of lower WSS values at the carina using both the Nano crush and the DK crush techniques. Conclusions: In patients with complex LM bifurcation disease the use of a final POT performed 1 mm distally to the carina cut plane might results in more favorable WSS patterns (i.e. higher WSS values) along all stented segments and, especially, along the entire LCX lesions