Acute stent recoil: in vivo evaluation of different stent designs

Role of invasive imaging in acute and long-term assessment of bioresorbable scaffold technology

Fully bioresorbable scaffolds (BRS) represent a novel approach for the percutaneous treatment of coronary artery stenosis, providing temporary vessel scaffolding with drug-eluting capability during the restenosis-prone phase of the vascular healing. Beyond this initial critical period, when mechanical scaffolding support is no longer necessary, the device is bioresorbed, restoring the normal vascular physiology with the aim to eliminate the long-term safety concerns related to permanent metallic implants. Nonetheless, current BRS technology suffers from limited mechanical properties as compared to available metallic platforms, requiring careful attention to lesion preparation, accurate vessel sizing, and implantation technique. Intravascular imaging has played an important role in providing knowledge on the acute effects after BRS deployment, and it helped refine the current technique of BRS implantation. In addition, extensive work with multiple intravascular imaging modalities have also contributed to the understanding of the unique dynamic vascular changes that are experienced in the treated segment from post-implantation up to complete device bioresorption. In this manuscript, we review the role of invasive imaging modalities-from angiography to sound- and light-based techniques-to guide BRS implantation procedures, to assess its acute results postimplantation, and the changes experienced in the long-term until complete bioresorption has ensued. © 2016 Wiley Periodicals, Inc.

Microwave spectrometry for the evaluation of the structural integrity of metallic stents

PURPOSE

To assess the feasibility of a method based on microwave spectrometry to detect structural distortions of metallic stents in open air conditions and envisage the prospects of this approach toward possible medical applicability for the evaluation of implanted stents.

METHODS

Microwave absorbance spectra between 2.0 and 18.0 GHz were acquired in open air for the characterization of a set of commercial stents using a specifically design setup. Rotating each sample over 360°, 2D absorbance diagrams were generated as a function of frequency and rotation angle. To check our approach for detecting changes in stent length (fracture) and diameter (recoil), two specific tests were performed in open air. Finally, with a few adjustments, this same system provides 2D absorbance diagrams of stents immersed in a water-based phantom, this time over a bandwidth ranging from 0.2 to 1.8 GHz.

RESULTS

The authors show that metallic stents exhibit characteristic resonant frequencies in their microwave absorbance spectra in open air which depend on their length and, as a result, may reflect the occurrence of structural distortions. These resonances can be understood considering that such devices behave like dipole antennas in terms of microwave scattering. From fracture tests, the authors infer that microwave spectrometry provides signs of presence of Type I to Type IV stent fractures and allows in particular a quantitative evaluation of Type III and Type IV fractures. Recoil tests show that microwave spectrometry seems able to provide some quantitative assessment of diametrical shrinkage, but only if it involves longitudinal shortening. Finally, the authors observe that the resonant frequencies of stents placed inside the phantom shift down with respect to the corresponding open air frequencies, as it should be expected considering the increase of dielectric permittivity from air to water.

CONCLUSIONS

The evaluation of stent resonant frequencies provided by microwave spectrometry allows detection and some quantitative assessment of stent fracture and recoil in open air conditions. Resonances of stents immersed in water can be also detected and their characteristic frequencies are in good agreement with theoretical estimates. Although these are promising results, further verification in a more relevant phantom is required in order to foresee the real potential of this approach.

Effect of structural remodeling (retraction and recoil) of the pipeline embolization device on aneurysm occlusion rate

BACKGROUND AND PURPOSE

During endovascular treatment of unruptured aneurysms with the Pipeline Embolization Device, an oversized device is often selected to achieve better wall apposition; however, this device oversizing could be related to overelongation and possible delayed enlargement of the stented region. The purpose of this study is to investigate the relationship between oversize and treatment outcome.

MATERIALS AND METHODS

The DynaCT images of 14 aneurysms treated by a single Pipeline Embolization Device were retrospectively analyzed. 3D images of the deployed device were compared with those acquired at the 6-month follow-up for qualitative and quantitative evaluation. The diameter and length of the Pipeline Embolization Device were measured at both time points and compared for determination of the device changes.

RESULTS

Structural changes of the device have been observed, and it was found that the Pipeline Embolization Device influences the vessel curvature in some cases. On average, it increases its diameter by 0.23 mm and decreases its length by 2.88 mm within 6 months of initial deployment. Excessive elongation beyond its nominal length is correlated with a lower aneurysm occlusion rate at the 6-month follow-up.

CONCLUSIONS

Not only does a Pipeline Embolization Device reconstruct the aneurysm and parent artery, but its entire structure goes through a gradual remodeling process. The relative deformation between the device and the artery indicates suboptimal wall apposition. Device oversizing does not have a direct effect on shortening or recoil. The aneurysm occlusion rate, however, is lowered by overelongation of the Pipeline Embolization Device.

Stents: material, surface texture and design, in theory and practice

Intravascular stenting has become standard practice in cardiology and interventional radiology. As part of their daily routine, interventional therapists have to choose from more than 50 different coronary stents for the optimal treatment of patients. Striking advances in biomedical engineering have triggered the production of numerous new and improved stent models, whose theoretical benefits have not yet been confirmed by large-scale clinical trials. Selecting appropriate stents for individual patients is frequently subject to the personal and, therefore, subjective experience of the interventional therapist. This paper reviews different stent materials and designs used in current trials and clinical practice. The theoretical benefits of individual parameters are discussed and correlated with up-to-date clinical results, particularly with a view to considering their favourable impact on intervention outcomes.

Stent expansion: a combination of delivery balloon underexpansion and acute stent recoil reduces predicted stent diameter irrespective of reference vessel size

BACKGROUND

There is a strong inverse relationship between final vessel diameter and subsequent risk of treatment failure after coronary stent deployment. The aim of this study was to investigate the magnitude by which stent delivery balloon underexpansion and stent elastic recoil contributed to suboptimal final vessel geometry.

METHODS

A prospective angiographic study recruiting 499 lesions (385 patients) undergoing coronary stent implantation was performed. Quantitative coronary angiography (QCA) was used to measure the minimal lumen diameters of the delivery balloon during stent deployment (MLD1) and of the stented segment following balloon deflation (MLD2). The expected balloon diameter for the deployment pressure was determined from the manufacturer's reference chart. Delivery balloon deficit was measured by subtracting the MLD1 from the expected balloon size and stent recoil was calculated by subtracting MLD2 from MLD1. Delivery balloon deficit and stent recoil were examined as a function of reference vessel diameter (RVD) and balloon-vessel (BV) ratio.

RESULTS

The final stent MLD was a mean 27.2% (SD = 7.2) less than the predicted diameter. The mean delivery balloon deficit was 0.65 mm (SD = 0.27) and the mean stent recoil was 0.28 mm (SD = 0.17). Percentage delivery balloon deficit and stent recoil were independent of RVD. Delivery balloon deficit increased with higher BV ratios. Stent recoil was independent of BV ratio and the use of predilatation.

CONCLUSION

Failure to achieve predicted final stent diameter is a real problem with contribution from delivery balloon underexpansion and stent recoil. On average the final stent MLD is only 73% of the expected diameter, irrespective of vessel size.

Impact of stent design on clinical outcome after coronary stent implantation

Coronary stents have considerably improved both immediate and late results after coronary angioplasty, by limiting elastic recoil and vascular remodeling, but their use does not eliminate restenosis, caused mainly by neointimal hyperplasia. Stents are now implanted in over 70% of percutaneous coronary interventions. More than 50 coronary stents have already been approved in Europe and over 20 stents are commercially available in the USA, raising the question: which device is best suitable for which lesion? Several in vitro experiments revealed significant differences in expansion characteristics of coronary stents, related to the strut design and metallic composition. Animal studies were performed to determine the influence of stent design on the patterns and extent of neointimal hyperplasia. However, the clinical results of randomized trials comparing stent types in humans have not always reflected laboratory findings. This article is a critical overview of experimental and clinical data concerning the impact of stent design on the early and late clinical outcome after coronary stent implantation.

Compliance matching stent placement in the carotid artery of the swine promotes optimal blood flow and attenuates restenosis

OBJECTIVES

We assessed the value of a gradient-compliant stent in an animal model.

METHODS

Bilateral carotid arteries were stented with nitinol stents having variable-oversizing, variable-stiffness, and with (CMS, 10 animals) and without (SMART, four animals) compliance-matching endings. Angiography, hemodynamic, scanning-electron-microscopic and histological analyses were performed at 3-month. The protocol was completed in 14 among 19 swines.

RESULTS

Transient (1-month) exaggerated recoil, attributable to stress-induced phasic inhibition of vasorelaxation, developed at CMS endings. At mid-term, all stents were endothelialized; CMS-stents, but not SMART-stents, were incorporated into walls (one-strut-thickness). Restenosis developed outside SMART-stents (cell migration+wall-compensatory enlargement) whereas CMS-stents elicited no or focalized cell-accumulations at endings that bulged vascular walls radially outward. SMART-stents were blood-flow neutral, whereas CMS-stents favored (higher-stiffness, higher-oversizing) or opposed (lower-stiffness, less-oversizing) carotid blood flow.

CONCLUSIONS

Direct carotid stenting with stents having compliance-matched endings and specific requirements of stiffness and oversizing can optimize blood flow to the brain and restrict local restenosis.

Preliminary experience with the Tsunami coronary stent: immediate and six-month clinical and angiographic results

The Tsunami is a new, balloon-expandable, stainless steel, tubular coronary stent whose design is based on a number of radial, diamond-shaped cells joined by double connectors. The aim of this two-centre, prospective, nonrandomized study was to examine the procedural, in-hospital, and long-term clinical and angiographic outcomes of patients undergoing angioplasty with the Tsunami stent. Sixty-one consecutive unselected patients were treated by means of the implantation of 74 Tsunami stents in 72 coronary lesions. Most of the patients (64%) had unstable angina or acute myocardial infarction. The baseline lesion morphology was complex in 76% of cases, and the mean lesion length was 14 +/- 6 mm. The procedural success rate was 98%. Mean percentage diameter of the stenosis decreased after the intervention from 79 +/- 12% to 10 +/- 6%. The in-hospital major adverse cardiac event rate was 3.3%. During the six-month follow-up, there was one cardiac death and nine subjects (14.5%) underwent target vessel revascularization. The six-month event-free survival rate was 80%. The angiographic restenosis rate was 17%: a focal or limited pattern (class I or II) was found in 43% of cases, whereas the remaining 57% had a proliferative morphology (class III or IV). In conclusion, this study indicates the good clinical and angiographic performance of the Tsunami coronary stent system in consecutive unselected patients.

Long-term clinical outcomes after coronary angioplasty using long stents in small coronary vessels

The role of coronary stenting in challenging situations, such as small vessels and long lesions, remains controversial. The aim of this study was to examine the procedural, in-hospital, and long-term clinical outcomes of patients undergoing angioplasty with long stents in small coronary vessels. We evaluated the procedural success rate and clinical outcomes in 252 consecutive subjects treated by means of the implantation of a single coronary stent in vessels with a mean reference diameter of < 2.5 mm; 128 patients received a short stent (< or = 16 mm) and 124 a long stent (> or = 18 mm). Lesion morphology was more complex in patients treated with long stents (P < 0.05). The mean stent length was 14 +/- 2 mm in the short-stent group and 25 +/- 3 mm in the long-stent group (P < 0.001). The overall procedural success rate (98.4% vs. 97.6%; P = NS) and the rate of major in-hospital adverse events (death, acute myocardial infarction, or target vessel revascularization; 1.6% vs. 2.4%; P = NS) was similar in the two groups. After 11.7 +/- 7 months of follow-up, there was no difference in the incidence of mortality and myocardial infarction (5% vs. 6.6%; P = NS), but revascularization tended to occur more frequently in the patients treated with long stents (21.7% vs. 13.9%; P = NS). In conclusion, the procedural success rate of single short or long stents in small coronary vessels was similar. Although the incidence of target vessel revascularization tended to be higher in the patients treated with longer stents, 2-year event-free survival was equivalent in the two groups (65% vs. 70%; P = NS).

Patterns of in-stent restenosis after placement of NIR gold-coated stents in unselected patients

The aim of this study was to assess the incidence and angiographic patterns of in-stent restenosis 6 months after the implantation of NIR gold-coated stents in an unselected patient population. One hundred and sixteen consecutive patients were treated with the implantation of 149 NIR gold-coated stents. The majority of the patients (52%) had unstable angina or acute myocardial infarction. The baseline lesion morphology was complex in 78% of cases; the mean lesion length was 18 +/- 5 mm. The procedural success rate was 97%. Subacute stent thrombosis occurred in three patients (2.6%). During the 6-month follow-up, there were 2 deaths and 22 subjects (19.5%) underwent target vessel revascularization. The 6-month event-free survival was 60%. The angiographic restenosis rate was 32%. In 83% of the cases, the morphology of the restenosis was proliferative; in the remaining 17%, it presented as total occlusion. In conclusion, the restenosis rate after NIR gold-coated stent implantation in high-risk patients is similar to that reported using other stent designs. However, restenosis was always diffuse, involving the overall stent length and extending beyond the margins, thus indicating a greater proliferative neointimal response to this device.