Longitudinal deformation bench testing using a coronary artery model: a new standard?

Fluid-Structure Interaction in Coronary Stents: A Discrete Multiphysics Approach

Stenting is a common method for treating atherosclerosis. A metal or polymer stent is deployed to open the stenosed artery or vein. After the stent is deployed, the blood flow dynamics influence the mechanics by compressing and expanding the structure. If the stent does not respond properly to the resulting stress, vascular wall injury or re-stenosis can occur. In this work, a Discrete Multiphysics modelling approach is used to study the mechanical deformation of the coronary stent and its relationship with the blood flow dynamics. The major parameters responsible for deforming the stent are sorted in terms of dimensionless numbers and a relationship between the elastic forces in the stent and pressure forces in the fluid is established. The blood flow and the stiffness of the stent material contribute significantly to the stent deformation and affect its rate of deformation. The stress distribution in the stent is not uniform with the higher stresses occurring at the nodes of the structure. From the relationship (correlation) between the elastic force and the pressure force, depending on the type of material used for the stent, the model can be used to predict whether the stent is at risk of fracture or not after deployment.

Comparison of the Physical Characteristics of Support Stents for Cerebral Aneurysm Embolization

Objective

There is a limited understanding of the characteristics of individual intracranial stents used for aneurysm treatment. We used an experimental model to evaluate the physical characteristics of support stents for aneurysm embolization.

Methods

Enterprise 2 VRD 4.0 × 39 mm, Neuroform Atlas 4.5 × 21 mm, and LVIS 4.5 × 32 mm stents were: 1) observed under light microscopy and subjected to measurements of 2) circumferential radial force, 3) strut tension, 4) stent compression, and 5) conformability upon bending.

Results

1) Light microscopy showed a large structural difference between laser-cut (Enterprise 2 VRD, Neuroform Atlas) and braided (LVIS) stents. 2) Within the range of indicated blood vessel diameters, the radial force of Enterprise 2 VRD was higher than that of Neuroform Atlas. An extremely large force was required to decrease the LVIS diameter. 3) Neuroform Atlas easily deformed compared to Enterprise 2 VRD, while LVIS was extended with a smaller traction force than that required for Neuroform Atlas. 4) The compression strength was in the order of Enterprise 2 VRD >Neuroform Atlas >LVIS. 5) Enterprise 2 VRD showed a decreased cell area on the concave side, and Neuroform Atlas showed deformation with overlapping struts on the concave side. LVIS naturally adhered to the wall of the blood vessel model.

Conclusion

Laser-cut and braided stents showed different physical characteristics that were visualized and shown as numerical data. These findings improve the understanding of the proper use of these stents in clinical applications.

Impact of stent designs of second-generation drug-eluting stents on long-term outcomes in coronary bifurcation lesions

OBJECTIVES

We compared the long-term clinical outcomes of four different types of second-generation drug-eluting stents (DESs) in coronary bifurcation lesions.

BACKGROUND

Clinical outcomes of different designs of second-generation DESs are not well known in bifurcation lesions.

METHODS

Patients who underwent percutaneous coronary intervention with second-generation DESs for coronary bifurcation lesion were enrolled from 21 centers in South Korea. A total of 2,526 patients was evaluated and divided into four treatment groups according to DES type: bioabsorbable polymer biolimus-eluting stent (BP-BES group, n = 514), platinum chromium everolimus-eluting stent (PtCr-EES group, n = 473), cobalt nickel zotarolimus-eluting stent (CoNi-ZES group, n = 736), or cobalt chromium everolimus-eluting stent (CoCr-EES group, n = 803). Primary outcome was target lesion failure (TLF, defined as a composite of cardiac death, target vessel myocardial infarction, or target lesion revascularization). Inverse probability of treatment weighting (IPTW) was performed to reduce selection bias and potential confounding factors.

RESULTS

For 5 years of follow-up, the rates of TLF among the four DES groups were not significantly different (6.2% for BP-BES group, 8.2% for PtCr-EES group, 6.5% for CoNi-ZES group, and 8.6% for CoCr-EES group, p = .434). The results were consistent after IPTW adjustment (6.8, 8.4, 6.0, and 7.5%, respectively, p = .554). In subgroup analysis, the similarity of long-term outcomes among the four different types of second-generation DES was consistent across subgroups regardless of side branch treatment (p for interaction = .691).

CONCLUSION

There seems to be no significant difference in long-term clinical outcomes among patients who received different types of second-generation DES for coronary bifurcation lesion.

Long and short of optimal stent design

The ideal stent must fulfil a broad range of technical requirements. Stents must be securely crimped onto the delivery balloon and, in this form, must have a low profile and be sufficiently flexible to facilitate deliverability to the lesion site without distortion or displacement. Following expansion, stents must exert sufficient radial force on the vessel wall to overcome lesion resistance and elastic recoil. To achieve an optimal lumen diameter, the lesion must be uniformly and adequately scaffolded, with minimal tissue prolapse between struts but without compromising side-branch access. Furthermore, the deployed stent must conform to the vessel curvature to minimise vessel distortion, particularly at the stent edges. Radio-opacity is also important to guide safe positioning, adequate deployment and postdilataion and to permit assessment of optimal stent expansion. Equally though, the stent lumen must also be sufficiently visible to allow radiographic assessment of flow dynamics and restenosis. Efforts to optimise one characteristic of stent design may have detrimental effects on another. Thus, currently available stents all reflect a compromise between competing desirable features and have subtle differences in their performance characteristics. Striving to achieve stents with optimal deliverability, conformability and radial strength led to a reduction in longitudinal strength. The importance of this parameter was highlighted by complications occurring in the real-world setting where percutaneous coronary intervention is often undertaken in challenging anatomy. This review focuses on aspects of stent design relevant to longitudinal strength.