Mechanical performances of balloon post-dilation for improving stent expansion in calcified coronary artery: Computational and experimental investigations

Finite element analysis predicts a major mechanical role of epicardial adipose tissue in atherosclerotic coronary disease and angioplasty

BACKGROUND

Understanding how atherosclerosis and angioplasty biomechanically affect the coronary artery wall is crucial for comprehending the pathophysiology of this disease and advancing potential treatments. However, acquiring this information experimentally or in vivo presents challenges. To overcome this, different computational methods have been employed. This research assessed the impact of atherosclerosis and angioplasty on the strains of each coronary artery tunic using the finite element method.

METHODS

Anatomical data were used to create two three-dimensional models of the left anterior descending coronary artery: one representing a normal artery and the other with concentric atherosclerosis, which included the surrounding epicardial fat tissue (EFT) and the three arterial tunics (e.g., intima, media, and adventitia). Blood pressure was applied to both models, and angioplasty was performed in the atherosclerotic model. The mean maximum principal and minimum principal strains were obtained for each layer in each case, and the impact of EFT was analyzed by comparing the results of including and omitting it. Furthermore, a sensitivity analysis was conducted for EFT stiffness, EFT volume, and blood pressure.

RESULTS

Noteworthy biomechanical alterations were observed in the atherosclerotic model before and after angioplasty, compared to the healthy state. After angioplasty, strains in the media and adventitia layers increased on average by up to fivefold, whereas the intima layer experienced a comparatively lower impact. Similarly, excluding EFT resulted in an average fourfold increase in strains in the tunics of both the healthy and atherosclerotic models. In addition, in both healthy and atherosclerotic models, a rise in blood pressure caused the most significant increase in arterial tunic strains, followed by reduced EFT stiffness and increased EFT volume, in order of impact.

CONCLUSION

Coronary artery wall strains are significantly altered by atherosclerosis and angioplasty, leading to cellular growth in the media and adventitia layers and subsequent reobstruction of the lumen after the procedure. EFT strongly influences coronary wall biomechanics, with low EFT stiffness and high volume predicted as risk factors for the development and severity of atherosclerosis. However, all the above may be modulated through interventions targeting epicardial adipose tissue.

Interaction of a self-expandable stent with the arterial wall in the presence of hypocellular and calcified plaques

Self-expandable stents manufactured from nitinol alloys are commonly utilized alongside traditional balloon-expandable stents to provide scaffolding to stenosed arteries. However, a significant limitation hampering stent efficacy is restenosis, triggered by neointimal hyperplasia and resulting in the loss of gain in lumen size, post-intervention. In this study, a nonlinear finite element model was developed to simulate stent crimping and expansion and its interaction with the surrounding vessel in the presence of a plaque. The main aim was to determine contact pressures and forces induced at the interface between an artery wall with hypocellular and calcified plaques and an expanded stent. The results demonstrated the drawbacks of plaque calcification, which triggered a sharp contact pressure and radial force surge at the interface as well as a significant rise in von Mises stress within the vessel, potentially leading to rupture and restenosis. A regression line was then established to relate hypocellular and calcified plaques. The adjusted coefficient of determination indicated a good correlation between contact pressures for calcified and hypocellular plaque models. Regarding the directionality of wall properties, contact pressure and force observations were not significantly different between isotropic and anisotropic arteries. Moreover, variations in friction coefficients did not substantially affect the interfacial contact pressures.

Fatigue strength analysis of a new left atrial appendage occluder at different release scales

Owing to its low incidence, small trauma, fast recovery, and high efficiency, left atrial appendage occlusion has become a new strategy for preventing stroke caused by atrial fibrillation. Due to a lack of relevant research information on this emerging technology, the effectiveness, stability, or related complications of occluders are mostly observed from a clinical perspective. However, there are fewer studies on the mechanical properties and safety of these occluders. In this study, a new left atrial appendage occluder is proposed, and a complete numerical simulation analysis framework is established through the finite element method to simulate the actual implantation and service process of the left atrial appendage occluder. Besides, the influence of the structural size and release scale of the occluder on its support performance, occluding effect, and safety is also explored. The results demonstrate that the structural size and release scale exert a significant impact on the support performance, occluding effect, and safety of the occluder. The structural optimization of the occluder contributes to enhancing its mechanical performance, thus ensuring its stability and effectiveness after implantation. Overall, these efforts may lay a scientific foundation for the structural optimization, safety evaluation, and effectiveness prediction of the occluder. Furthermore, these findings also provide effective reference for the application of numerical simulation technology in the research on the left atrial appendage occlusion.

Machine Learning Constructed Based on Patient Plaque and Clinical Features for Predicting Stent Malapposition: A Retrospective Study

BACKGROUND

Stent malapposition (SM) following percutaneous coronary intervention (PCI) for myocardial infarction continues to present significant clinical challenges. In recent years, machine learning (ML) models have demonstrated potential in disease risk stratification and predictive modeling.

HYPOTHESIS

ML models based on optical coherence tomography (OCT) imaging, laboratory tests, and clinical characteristics can predict the occurrence of SM.

METHODS

We studied 337 patients from the Affiliated Hospital of Zunyi Medical University, China, who had PCI and coronary OCT from May to October 2023. We employed nested cross-validation to partition patients into training and test sets. We developed five ML models: XGBoost, LR, RF, SVM, and NB based on calcification features. Performance was assessed using ROC curves. Lasso regression selected features from 46 clinical and 21 OCT imaging features, which were optimized with the five ML algorithms.

RESULTS

In the prediction model based on calcification features, the XGBoost model and SVM model exhibited higher AUC values. Lasso regression identified five key features from clinical and imaging data. After incorporating selected features into the model for optimization, the AUC values of all algorithmic models showed significant improvements. The XGBoost model demonstrated the highest calibration accuracy. SHAP values revealed that the top five ranked features influencing the XGBoost model were calcification length, age, coronary dissection, lipid angle, and troponin.

CONCLUSION

ML models developed using plaque imaging features and clinical characteristics can predict the occurrence of SM. ML models based on clinical and imaging features exhibited better performance.

Surveillance and risk factors for early restenosis following transcarotid artery revascularization

OBJECTIVE

Restenosis after transcarotid artery revascularization (TCAR) is a known complication. When identified in the early postoperative period, it may be related to technique. We evaluated our TCAR experience to identify potentially modifiable factors impacting restenosis.

METHODS

This is a single-institution, retrospective review of patients undergoing TCAR from November 2017 to July 2022. Restenosis was defined as >50% stenosis on duplex ultrasound (DUS) examination or computed tomographic angiography (CTA). Continuous variables were compared using Kruskal-Wallis's test. Categorical variables were compared using the Fisher's exact test.

RESULTS

Of 61 interventions, 11 (18%) developed restenosis within the median follow-up of 345 days (interquartile range, 103-623 days). Among these patients, 82% (9/11) had >50% stenosis, and 18% (2/11) had >80% stenosis. Both patients with high-grade restenosis were symptomatic and underwent revascularization. Diagnosis of post-TCAR restenosis was via DUS examination in 45% (5/11), CTA in 18% (2/11), or both CTA/DUS examination in 36% (4/11). Restenosis occurred within 1 month in 54% (6/11) and 6 months in 72% (8/11) of patients. However, three of the six patients with restenosis within 1 month had discordant findings on CTA vs DUS imaging. Patient comorbidities, degree of preoperative stenosis, medical management, balloon size, stent size, lesion characteristics, and predilatation angioplasty did not differ. Patients with restenosis were younger (P = .02), had prior ipsilateral endarterectomy (odds ratio [OR], 6.5; P = .02), had history of neck radiation (OR, 18.3; P = .01), and lower rate of postdilatation angioplasty (OR, 0.11; P = .04), without an increased risk of neurological events.

CONCLUSIONS

Although post-TCAR restenosis occurred in 18% of patients, only 3% of patients had critical restenosis and required reintervention. Patient factors associated with restenosis were younger age, prior endarterectomy, and history of neck radiation. Although early restenosis may be mitigated by improved technique, the only technical factor associated with restenosis was less use of postdilatation angioplasty. Balancing neurological risk, this factor may have increased application in appropriate patients. Diagnosis of restenosis was inconsistent between imaging modalities; current surveillance paradigms and diagnostic thresholds may warrant reconsideration.

Prediction of stent under-expansion in calcified coronary arteries using machine learning on intravascular optical coherence tomography images

It can be difficult/impossible to fully expand a coronary artery stent in a heavily calcified coronary artery lesion. Under-expanded stents are linked to later complications. Here we used machine/deep learning to analyze calcifications in pre-stent intravascular optical coherence tomography (IVOCT) images and predicted the success of vessel expansion. Pre- and post-stent IVOCT image data were obtained from 110 coronary lesions. Lumen and calcifications in pre-stent images were segmented using deep learning, and lesion features were extracted. We analyzed stent expansion along the lesion, enabling frame, segmental, and whole-lesion analyses. We trained regression models to predict the post-stent lumen area and then computed the stent expansion index (SEI). Best performance (root-mean-square-error = 0.04 ± 0.02 mm2, r = 0.94 ± 0.04, p < 0.0001) was achieved when we used features from both lumen and calcification to train a Gaussian regression model for segmental analysis of 31 frames in length. Stents with minimum SEI > 80% were classified as "well-expanded;" others were "under-expanded." Under-expansion classification results (e.g., AUC = 0.85 ± 0.02) were significantly improved over a previous, simple calculation, as well as other machine learning solutions. Promising results suggest that such methods can identify lesions at risk of under-expansion that would be candidates for intervention lesion preparation (e.g., atherectomy).

Load-sharing characteristics of stenting and post-dilation in heavily calcified coronary artery

In this work, stenting in non-calcified and heavily calcified coronary arteries was quantified in terms of diameter-pressure relationships and load transfer from the balloon to the artery. The efficacy of post-dilation in non-calcified and heavily calcified coronary arteries was also characterized in terms of load sharing and the changes in tissue mechanics. Our results have shown that stent expansion exhibits a cylindrical shape in non-calcified lesions, while it exhibits a dog bone shape in heavily calcified lesions. Load-sharing analysis has shown that only a small portion of the pressure load (1.4 N, 0.8% of total pressure load) was transferred to the non-calcified lesion, while a large amount of the pressure load (19 N, 12%) was transferred to the heavily calcified lesion. In addition, the increasing inflation pressure (from 10 to 20 atm) can effectively increase the minimal lumen diameter (from 1.48 to 2.82 mm) of the heavily calcified lesion, the stress (from 1.5 to 8.4 MPa) and the strain energy in the calcification (1.77 mJ to 26.5 mJ), which are associated with the potential of calcification fracture. Results indicated that increasing inflation pressure can be an effective way to improve the stent expansion if a dog bone shape of the stenting profile is observed. Considering the risk of a balloon burst, our results support the design and application of the high-pressure balloon for post-dilation. This work also sheds some light on the stent design and choice of stent materials for improving the stent expansion at the dog bone region and mitigating stresses on arterial tissues.

Load-sharing characteristics of stenting and post-dilation in heavily calcified coronary artery

In this work, stenting in non-calcified and heavily calcified coronary arteries was quantified in terms of diameter-pressure relationships and load transfer from the balloon to the artery. The efficacy of post-dilation in non-calcified and heavily calcified coronary arteries was also characterized in terms of load sharing and the changes in tissue mechanics. Our results have shown that stent expansion exhibits a cylindrical shape in non-calcified lesions, while it exhibits a dog bone shape in heavily calcified lesions. Load-sharing analysis has shown that only a small portion of the pressure load (1.4 N, 0.8% of total pressure load) was transferred to the non-calcified lesion, while a large amount of the pressure load (19 N, 12%) was transferred to the heavily calcified lesion. In addition, the increasing inflation pressure (from 10 to 20 atm) can effectively increase the minimal lumen diameter (from 1.48 mm to 2.82 mm) of the heavily calcified lesion, the stress (from 1.5 MPa to 8.4 MPa) the strain energy in the calcification (1.77 mJ to 26.5 mJ), which associated with the potential of calcification fracture. Results indicated that increasing inflation pressure can be an effective way to improve the stent expansion if a dog bone shape of the stenting profile is observed. Considering the risk of a balloon burst, our results support the design and application of the high-pressure balloon for post-dilation.

Simulation and Experimental Investigation of Balloon Folding and Inserting Performance for Angioplasty: A Comparison of Two Materials, Polyamide-12 and Pebax

BACKGROUND

A balloon dilatation catheter is a vital tool in percutaneous transluminal angioplasty. Various factors, including the material used, influence the ability of different types of balloons to navigate through lesions during delivery.

OBJECTIVE

Thus far, numerical simulation studies comparing the impacts of different materials on the trackability of balloon catheters has been limited. This project seeks to unveil the underlying patterns more effectively by utilizing a highly realistic balloon-folding simulation method to compare the trackability of balloons made from different materials.

METHODS

Two materials, nylon-12 and Pebax, were examined for their insertion forces via a bench test and a numerical simulation. The simulation built a model identical to the bench test's groove and simulated the balloon's folding process prior to insertion to better replicate the experimental conditions.

RESULTS

In the bench test, nylon-12 demonstrated the highest insertion force, peaking at 0.866 N, significantly outstripping the 0.156 N force exhibited by the Pebax balloon. In the simulation, nylon-12 experienced a higher level of stress after folding, while Pebax had demonstrated a higher effective strain and surface energy density. In terms of insertion force, nylon-12 was higher than Pebax in specific areas.

CONCLUSION

nylon-12 exerts greater pressure on the vessel wall in curved pathways when compared to Pebax. The simulated insertion forces of nylon-12 align with the experimental results. However, when using the same friction coefficient, the difference in insertion forces between the two materials is minimal. The numerical simulation method used in this study can be used for relevant research. This method can assess the performance of balloons made from diverse materials navigating curved paths and can yield more precise and detailed data feedback compared to benchtop experiments.

Rotational Atherectomy or Balloon-Based Techniques to Prepare Severely Calcified Coronary Lesions

BACKGROUND

The comparative efficacy of percutaneous techniques for the preparation of calcified lesions before stenting remains poorly studied.

OBJECTIVES

This study sought to compare the performance of up-front rotational atherectomy (RA) or balloon-based techniques before drug-eluting stent implantation in severely calcified coronary lesions as assessed by angiography and optical coherence tomography (OCT).

METHODS

Patient-level data from the PREPARE-CALC (Comparison of Strategies to Prepare Severely Calcified Coronary Lesions) and ISAR-CALC (Comparison of Strategies to Prepare Severely Calcified Coronary Lesions) randomized trials were pooled. The primary endpoint was stent expansion as assessed by OCT imaging. The secondary endpoints included stent eccentricity, stent asymmetry, angiographic acute lumen gain, strategy success and in-hospital occurrence of cardiac death, target vessel myocardial infarction, and repeat revascularization.

RESULTS

Among 274 patients originally randomized, 200 participants with available OCT data after lesion preparation with RA (n = 63), a modified balloon (MB, n = 103), or a super high-pressure balloon (n = 34) before stenting were analyzed. The use of RA versus MB or a super high-pressure balloon led to comparable stent expansion (73.2% ± 11.6% vs 70.8% ± 13.6% vs 71.8% ± 12.2%, P = 0.49) and stent asymmetry (P = 0.83). Compared with RA or MB, a super high-pressure balloon was associated with less stent eccentricity (P = 0.03) with a numerically higher acute lumen gain, albeit not significantly different (P = 0.08). Strategy success was more frequent with RA versus MB (P = 0.002) and numerically more frequent with RA versus a super high-pressure balloon (P = 0.06). Clinical outcomes did not differ between groups.

CONCLUSIONS

In patients with severely calcified lesions undergoing drug-eluting stent implantation, lesion preparation with RA, MB, or a super high-pressure balloon was associated with comparable stent expansion. A super high-pressure balloon is associated with less stent eccentricity, whereas strategy success is more frequent with RA.

Determination effect of two different NiTi stents on the vessel wall and studying their flexibility using finite element method

Finite element simulation is used to analysis stent designs, extension as well as interaction between a stent and a vessel. In this paper, two different stents with different geometries have been simulated. One is Zilver stent and the other one is Navalis stent. The aim of this study is to determine the effect of stents deployment with various designs that are made of shape memory alloy (SMA) on the distribution of vessel wall stresses by using computational modeling approach. The constitutive model which described the behavior of SMA is based on Microplane model. In addition, SMA stents have been simulated under torsion loading to compare the flexibility of various designs under different conditions. The superelastic behavior and shape memory effect of SMA stents are investigated in this paper. The numerical simulation results show the different geometries of stents have significant effect on the arterial wall. The results show the Navalis stent causes less stress on the arterial wall and it is more flexible than the Zilver stent under the same torsion loading.

Hemodynamic alternations following stent deployment and post-dilation in a heavily calcified coronary artery: In silico and ex-vivo approaches

In this work, hemodynamic alterations in a patient-specific, heavily calcified coronary artery following stent deployment and post-dilations are quantified using in silico and ex-vivo approaches. Three-dimensional artery models were reconstructed from OCT images. Stent deployment and post-dilation with various inflation pressures were performed through both the finite element method (FEM) and ex vivo experiments. Results from FEM agreed very well with the ex-vivo measurements, interms of lumen areas, stent underexpansion, and strut malapposition. In addition, computational fluid dynamics (CFD) simulations were performed to delineate the hemodynamic alterations after stent deployment and post-dilations. A pressure time history at the inlet and a lumped parameter model (LPM) at the outlet were adopted to mimic the aortic pressure and the distal arterial tree, respectively. The pressure drop across the lesion, pertaining to the clinical measure of instantaneous wave-free flow ratio (iFR), was investigated. Results have shown that post-dilations are necessary for the lumen gain as well as the hemodynamic restoration towards hemostasis. Malapposed struts induced much higher shear rate, flow disturbances and lower time-averaged wall shear stress (TAWSS) around struts. Post-dilations mitigated the strut malapposition, and thus the shear rate. Moreover, stenting induced larger area of low TAWSS (<0.4 Pa) and lager volume of high shear rate (>2000 s^-1), indicating higher risks of in-stent restenosis (ISR) and stent thrombosis (ST), respectively. Oscillatory shear index (OSI) and relative residence time (RRT) indicated the wall regions more prone to ISR are located near the malapposed stent struts.