169,850 research outputs found
Modelling of blood flow in coronary stented arteries.
No full textAtherosclerosis is the underlying cause of the majority of clinical cardiovascular events in the developed societies. Atherosclerotic lesions in coronary arteries are usually treated with percutaneous procedures which consist of placing wire mesh tubular structures, known as stents, into the diseased vessel. The main clinical complication is the in-stent restenosis (ISR) which is the local reduction in lumen size as a result of neointimal hyperplasia.
Mechanisms and causes of ISR are not fully understood; in addition to stent design, vascular injury caused by device implantation, hemodynamic alterations induced by its presence can be associated with neointimal hyperplasia. Therefore, the study of the fluid dynamics of stented coronary arteries is of extreme importance for a better comprehension of the mechanisms involved in ISR.
In the present chapter a review of the works on the hemodynamics of stented coronary arteries is given, focusing in particular on the computational fluid dynamics (CFD) models. Indeed, CFD allows the investigation of local hemodynamics at a level of detail not always accessible with experimental techniques, calculating fluid flow variables (e.g. wall shear stress) that can be used as indicators to predict sites where neointimal hyperplasia is excessive.
Application of CFD to idealized, population-specific and patient-specific coronary stented models is outlined as wel
Optimal Site for Proximal Optimization Technique in Complex Coronary Bifurcation Stenting: A Computational Fluid Dynamics Study
No full textBackground/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
On the necessity of modelling fluid–structure interaction for stented coronary arteries
No full textAlthough stenting is the most commonly performed procedure for the treatment of coronary atherosclerotic lesions, in-stent restenosis (ISR) remains one of the most serious clinical complications.
An important stimulus to ISR is the altered hemodynamics with abnormal shear stresses on endothelial cells generated by the stent presence.
Computational fluid dynamics is a valid tool for studying the local emodynamics of stented vessels, allowing the calculation of the wall shear stress (WSS), which is otherwise not directly possible to be measured in vivo. However, in these numerical simulations the arterial wall and the stent are assumed to be rigid and fixed, and then influencing the WSS and flow patterns. Therefore, the aim of this work is to perform fluid-structure interaction (FSI) analyses of a stented coronary artery in order to
understand the effects of the wall compliance on the hemodynamic quantities. Two different standard stents are considered: cobalt-chromium (CoCr) and polymeric (poly-L-lactide - PLLA). The results of the FSI and the corresponding rigid-wall models are compared, especially focusing on the analysis of the WSS distribution.
Results showed similar trends in terms of instantaneous and time-averaged WSS between compliant and rigid-wall cases. In particular, the difference between the percentage area exposed to time-averaged WSS lower than 0.4 Pa in the stented region was small for the CoCr (about 1.5%) and PLLA
(about 1.0%) cases.
The results indicate that, for idealized models of stented coronary artery, rigid-wall assumption for fluid dynamic simulations is adequate when the aim of the study is the analysis of near-wall quantities like WSS
Transcatheter Aortic Valve with Embolic Filter: Experiments and Simulations
No full textCerebrovascular events are one of the most critical complications following transcatheter aortic valve replacement. The majority of these events are associated to calcium debris generated by the stenotic valve manipulation. Embolic protection devices were accordingly designed to reduce the risk of these adverse events. Within this context, an innovative transcatheter aortic valve with embolic filter is proposed, which is temporarily released in the ascending aorta, and avoids severe regurgitation while treating the native valve before the replacement. Experimental tests and computational analyses were conducted on a prototype of the Nitinol frame of the device. The frame integrity throughout the clinical procedure was assessed, radial force curves were experimentally measured and used to calibrate a finite element model
Drug release in coronary bifurcation stenting.
No full textThe treatment of coronary bifurcation lesions represents a challenge for the interventional cardiologists due to the lower rate of procedural success and the higher rate of restenosis. The advent of drug eluting stents (DES) has dramatically reduced
restenosis and consequently the request for re-intervention [1]. The aim of the present work is to provide further insight about the effectiveness of DES by means of computational analysis that combine virtual stent implantation, fluid dynamics and drug
release for different stenting protocols used in the treatment of a coronary artery bifurcation. An explicit dynamic finite element model is developed in order to provide realistic configurations of the implanted device used to perform fluid dynamics analysis
by means of a previously developed [2,3] finite element method coupling the blood flow and intramural plasma filtration in rigid arteries. To efficiently model the drug release, a multiscale strategy is adopted, ranging from lumped parameter model
accounting for drug release, to fully 3-D models for drug transport to the artery [4]. Differences in drug delivery to the artery are evaluated with respect to local drug dosage. The model allowed to compare alternative stenting configurations thus
suggesting guidelines in the treatment of coronary bifurcations lesions and addressing clinical issues such as the effectiveness of drug delivery to lesions in the side branch, as well as the influence of incomplete strut apposition and overlapping stents
A comparison between standard and dedicated stents for coronary bifurcations: structural and fluid dynamic numerical simulations
No full textStenting implantation in coronary bifurcations remains a challenging area in interventional cardiology. Nowadays the concurrent use of two devices is limited and the culotte technique is a commonly applied procedure. A new dedicated device has
been proposed on the market to overcome the main drawback of this procedure which is the wide overlap region in the main branch. The aim of this work is to investigate the culotte technique both from a structural and fluid dynamic point of view, comparing the behavior of the dedicated stent with a standard one. Structural simulations of the stenting procedure were carried out by means of a commercial finite element code. Then, obtained realistic final geometrical configurations were used as fluid domains to perform transient CFD analyses. The biomechanical influence of the two-stents culotte technique was investigated in terms of easiness of implantation, von Mises stresses in the device, velocity and wall shear stress (WSS) patterns. Results showed that the dedicated stent facilitates the
access to the main branch in comparison with the standard stent (63.4% of area available for an optimal re-crossing against 10.9%) and reduces the metal-to-artery ratio and the deformation of stent struts. Moreover, the dedicated stent caused a smaller area (28.7% against 35.5%) with WSS lower than 0.1 Pa, values considered critical for the restenosis process.
This work indicates that new dedicated approaches could contribute to improve the biomechanical influence of the current treatment for coronary bifurcations
Biomechanical Evaluation of Different Balloon Positions for Proximal Optimization Technique in Left Main Bifurcation Stenting
No full textBackground: Proximal optimization technique (POT) is a key step during left main (LM) bifurcation stenting. However, after crossover stenting, the ideal position of POT balloon is unclear. We sought to evaluate the biomechanical impact of different POT balloon positions during LM cross-over stenting procedure. Methods: We reconstructed the patient-specific LM bifurcation anatomy, using coronary computed tomography angiography data of 5 consecutive patients (3 males, mean age 66.3 ± 21.6 years) with complex LM bifurcation disease, defined as Medina 1,1,1, evaluated between 1st January 2018 to 1st June 2018 at our center. Finite element analyses were carried out to virtually perform the stenting procedure. POT was virtually performed in a mid (marker just at the carina cut plane), proximal (distal marker 1 mm before the carina) and distal (distal marker 1 mm after the carina) position in each investigated case. Final left circumflex obstruction (SBO%), strut malapposition, elliptical ratio and stent malapposition were evaluated. Results: The use of both proximal and distal POT resulted in a smaller LM diameter compared to the mid POT. SBO was significantly higher in both proximal and distal configurations compared to mid POT: 38.3 ± 5.1 and 29.3 ± 3.1 versus 18.3 ± 3.6%, respectively. Similarly stent malapposition was higher in both proximal and distal configurations compared to mid POT: 1.3 ± 0.4 and 0.82 ± 1.8 versus 0.78 ± 1.2, respectively. Conclusions: Mid POT offers the best results in terms of LCx opening maintaining slightly smaller but still acceptable LM and LAD diameters compared to alternative POT configuration
Drug delivery patterns for different stenting techniques in coronary bifurcations: a comparative computational study
No full textThe treatment of coronary bifurcation lesions represents a challenge for the interventional cardiologists due to the lower rate of procedural success and the higher risk of restenosis. The advent of drug-eluting stents (DES) has dramatically reduced restenosis and consequently the request for re-intervention. The aim of the present work is to provide further insight about the effectiveness of DES by means of a computational study that combines virtual stent implantation, fluid dynamics and drug release for different stenting protocols currently used in the treatment of a coronary artery bifurcation. An explicit dynamic finite element model is developed in order to obtain realistic configurations of the implanted devices used to perform fluid dynamics analysis by means of a previously developed finite element method coupling the blood flow and the intramural plasma filtration in rigid arteries. To efficiently model the drug release, a multiscale strategy is adopted, ranging from lumped parameter model accounting for drug release to fully 3-D models for drug transport to the artery. Differences in drug delivery to the artery are evaluated with respect to local drug dosage. This model allowed to compare alternative stenting configurations (namely the Provisional Side Branch, the Culotte and the Inverted Culotte techniques), thus suggesting guidelines in the treatment of coronary bifurcation lesions and addressing clinical issues such as the effectiveness of drug delivery to lesions in the side branch, as well as the influence of incomplete strut apposition and overlapping stents
Analysis of repairability index to improve disassemblability and serviceability in cooker hoods
No full textProduct design plays a key role in supporting the principles of circular economy and sustainability by improving the repair and disassembly capabilities of products. The EN4555X standard series provides a framework and a set of indicators to evaluate these aspects for energy-related products. This paper focuses on applying the RSS (Repair Scoring System) introduced by the EN45554 standard to kitchen ventilation systems (T-shape cooker hood models). The study investigates the reliability of the repairability index by examining the impact of assumptions made during its assessment, particularly focusing on the data and parameters used for calculations. The methodology involves four key steps: identification of index parameters, experimental analysis, sensitivity analysis (SA) through data variation, and result interpretation. The experimental analysis involves computing the RSS index for the chosen range hoods, encompassing a SA developed by varying index's parameters. Results illustrate that introducing consistent parameter variations across models leads to changes in the Disassemblability Index. However, these alterations remain consistent across all cases, preserving the overall product ranking. Nonetheless, the study also indicates that altering parameter weights may lead to changes in product rankings within the repairability score. This highlights the importance of employing uniform weights within the same product category. In conclusion, this study underscores the importance of employing consistent methodologies and weights to uphold the reliability of repairability indexes when assessing product repairability
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