Longitudinal deformation of contemporary coronary stents: an integrated analysis of clinical experience and observations from the bench

Side-branch expansion capacity of contemporary DES platforms

Background

Percutaneous coronary interventions (PCI) of bifurcation stenoses are both complex and challenging. Stenting strategies share that the stents’ side cells must be carefully explored and appropriately prepared using balloons or stents. So far, stent manufacturers have not provided any information regarding side-branch expansion capacity of their stent platforms.

Aims

Given that drug-eluting stent (DES) information regarding their mechanical capacity of side-branch expansion is not available, we aimed to evaluate contemporary DES (Orsiro, BIOTRONIK AG; Xience Sierra, Abbott Vascular; Resolute Integrity, Medtronic; Promus Premier Select, Boston Scientific; Supraflex Cruz, Sahajan and Medical Technologies) by their side-branch expansion behavior using in vitro bench testing.

Methods

In this in vitro study, we analyzed five commercially available DES (diameter 3.0 mm), measuring their side-branch expansion following inflation of different high-pressure non-compliant (NC) balloons (balloon diameter: 2.00–4.00 mm), thereby revealing the morphological characteristics of their side-branch expansion capacities.

Results

We demonstrated that all tested contemporary DES platforms could withstand large single-cell deformations, up to 4.0 mm. As seen in our side-branch experiments, DES designs consisting of only two connectors between strut rings did not only result in huge cell areas, but also in larger cell diameters following side-branch expansion compared with DES designs using three or more connectors. Furthermore, the stent cell diameter attained was below the balloon diameter at normal pressure.

Conclusions

We recommend that the expansion capacity of side-branches should be considered in stent selection for bifurcation interventions.

Longitudinal stent elongation or shortening after deployment in the coronary arteries: which is dominant?

Background

Stent manufacturers always record stent shortening data while they do not record stent elongation data. The aim of this study is to identify both stent shortening and elongation occurring after deployment in the coronary arteries and know their percentage.

Results

The length of coronary stents was measured by intravascular ultrasound (IVUS) by (1) edge-to-edge (E-E) length, measured from the appearance of the first distal strut to the last proximal strut, and (2) area-to-area (A-A) length, measured from the first distal struts seen at more than one IVUS quadrant to the last proximal struts seen at more than one IVUS quadrant. Stent shortening was defined as both E-E and A-A lengths were shorter than the manufacturer box-stated length (shortened group). Stent elongation was defined as both E-E and A-A lengths were longer than the manufacturer box-stated length (elongated group), otherwise unchanged group. Consecutive 102 stents deployed in ischemic patients were included. Stent elongation was detected in 67.6% (69 stents), and shortening was detected in 15.7% (16 stents), while unchanged stents were detected in 16.7% (17 stents). Although the 3 groups had similar box-stated length and predicted foreshortened length, they had significantly different measurements by IVUS, p<0.001 for each comparison. Differences from box-stated length were 1.9±1.4mm, −1.4±0.4mm, and 0.4±0.3mm, respectively, p<0.001. The elongated group had significantly longer differences from the corresponding box-stated and predicted foreshortened lengths, while the shortened group had significantly shorter differences from the corresponding box-stated length and similar foreshortened length. By multinomial regression analysis, the plaque-media area and stent deployment pressure were the independent predictors of the stent length groups, p=0.015 and p=0.026, respectively.

Conclusions

Change in stent length is not only shortening—as mentioned in the manufacturer documents—but also stent elongation. Stent elongation is dominant, and the most important predictors of longitudinal stent changes are plaque-media area and stent deployment pressure.

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.

In vivo measurement of stent length by using intravascular ultrasound

Background

What happens to stent length when deployed in a coronary artery? It is the aim of this study.

Results

Consecutive 95 balloon-expandable stents (BES) were studied by intravascular ultrasound (IVUS) imaging. The stent length was measured from the longitudinal view in two ways: (1) edge-to-edge length (E-E) measured between distal and proximal stent frames located at one IVUS quadrant and (2) area-to-area length (A-A) measured between distal and proximal stent frames located at two or more IVUS quadrants. IVUS measurements were compared with the manufacturer-stated length (M-L). The median E-E length was significantly longer than M-L, 18.76 mm [interquartile range (IQR) 15.65–23.60] versus 18.00 mm (IQR 15.00–23.00), respectively, p < 0.0001. Also, the median A-A length was significantly longer, 18.36 mm (IQR 15.19–23.47), p < 0.0001, than M-L. Moreover, the E-E length was significantly different from A-A length, p < 0.0001. Among the stent groups, the differences were significantly present in all drug-eluting stent and bare metal stent (BMS) comparisons, p < 0.0001, except the A-A length versus M-L in BMS only. By multivariate analysis, the predictors of difference in stent length were as follows: lesion length, p = 0.01; pre-intervention minimal diameter of the external elastic membrane (EEM), p = 0.03; lesions present in the left anterior descending branch, p = 0.03; and M-L, p = 0.04.

Conclusions

In the present study, the length of BES measured by IVUS was significantly different from the manufacturer-stated length. In addition to the manufacturer length, other important factors such as lesion length, pre-intervention diameter of EEM, and affected vessel determine the stent length.

First-in-man pulmonary artery stenting in children using the Bentley® BeGrow™ stent system for newborns and infants

BACKGROUND

Stent implantation into growing vessels is a common treatment option in infants and children with congenital heart disease (CHD) and corresponding vessel lesions. After stent implantation in small children, repetitive stent redilations are frequently necessary to accommodate for somatic growth. Until now, all available stents have limited final expansion diameters.

MATERIAL AND RESULTS

The new Bentley BeGrow™ stent system for newborns and infants is a L605 cobalt‑chromium, pre-mounted, balloon expandable stent, which is compatible with a 4 French sheath and 0.014 inch guide wire thus allowing implantation in small vessels (4-6 mm). It offers a new, unique stent design that allows post-dilation steps up to Ø11.5 mm. While re-dilating up to Ø11.5 mm this new stent maintains radial force and shows uniform expansion with only minimal foreshortening. Predetermined breaking points allow the stent struts to break in a controlled manner when exceeding a diameter of 11.5 mm. Residual radial force maintains even after stent opening due to spiral arrangement of the predetermined breaking points. The 2 first-in-man pulmonary artery stent implantations in a newborn with univentricular circulation and a toddler with biventricular circulation are reported as part of the currently performed licencing trial (ClinicalTrials.govNCT03287024).

CONCLUSION

The low-profile BeGrow™ stent system offers new treatment options for transcatheter stent implantations in newborns and infants. In our first experience, it can be effectively implanted. Longer follow-up will evaluate multiple, stepwise redilations and controlled stent strut breakage, which have the potential to accommodate for somatic vessel growth and/or subsequent implantation of larger stents.

The potential hazard of a non-slip element balloon causing distal longitudinal stent deformation: the first clinical experience and in vitro assessment

BACKGROUND

A new complication, longitudinal stent deformation (LSD), is increasingly reported with recent intracoronary stent designs. There have been experiences of unusual cases of distal LSD caused by entrapment of a Lacrosse® non-slip element (NSE) balloon (Goodman Co., Ltd., Nagoya, Japan), which has three flexible nylon elements to prevent slippage. Accordingly, the aim of this study is to report the clinical experience of distal LSD caused by the NSE in the documented center and to investigate the incidence and mechanisms involved.

METHODS

Coronary intervention cases were retrospectively reviewed using the NSE balloon in hospital between May 2014 and June 2017. In bench testing, distal LSD was reproduced in a silicon tube model to identify its mechanism.

RESULTS

A total of 95 patients with 107 lesions underwent coronary interventions with NSE. Of these, 72 lesions (12 de-novo lesions and 60 in-stent restenosis) were treated using in-stent dilatation. Two distal LSD cases occurred, representing an incidence of 2.78% (2/72) among all procedures; 16.7% (2/12) of the de-novo lesions developed LSD. In vitro experimentation allowed indentification of the mechanisms involved and bailout strategies.

CONCLUSIONS

This is the first study to evaluate NSE balloon catheter entrapment complicated by distal LSD in which reconstruction of the deformed stent and retrieval of the NSE could be achieved successfully. There is a potential hazard for distal LSD during post-dilatation using the NSE balloon due to its structural characteristics. Careful assessment is needed to prevent this complication.

Coronary Stent Failure: Fracture, Compression, Recoil, and Prolapse

Current-generation coronary drug-eluting stents are associated with low rates of restenosis and target lesion revascularization. However, several mechanisms of stent failure remain clinically important. Stent fracture may occur in areas of excessive torsion or angulation. Longitudinal stent deformation is related to axial stent compression owing to extrinsic forces or secondary devices that disrupt stent architecture. Stent recoil occurs when a stent does not deploy at its optimal cross-sectional area. Tissue prolapse between stent struts may also predispose patients to adverse outcomes. Prevention, recognition, and treatment of these stent failures are necessary to optimize patient outcomes after percutaneous coronary interventions.

Impact of stent platform on longitudinal stent deformation: an in vivo frequency domain optical coherence tomography study

Recently, longitudinal coronary stent deformation has been highlighted as a possible cause of drug-eluting stent failure. Although bench tests and in vivo studies have demonstrated difference in longitudinal stent strength among the stents with different platforms, its clinical impact is still unknown. Furthermore, it is unknown if modified stent platform favorably affect the incidence of stent deformation. The aim of this study was to investigate the longitudinal deformation of the everolimus-eluting stents (EES) with different stent platforms by using frequency domain optical coherence tomography (FD-OCT). Seventy-eight lesions treated with EES (Xience Prime: n = 26, Promus element: n = 29, Promus premier: n = 23) were studied. After successful stent implantation, FD-OCT was performed and stent length was measured using three-dimensional reconstruction of the images in vivo. Percent longitudinal stent shortening (%SS) was defined as the in vivo stent length divided by nominal stent length. Longitudinal stent deformation was defined as  %SS > 10 %. Patients' and procedural characteristics were similar among 3 EESs. There was no difference in mean  %SS between Xience Prime, Promus Element and Promus Premier (1.0 ± 5.8, 2.9 ± 6.7 and 0.8 ± 3.7 %, p = 0.322). Incidence of the longitudinal stent deformation was significantly higher in Promus Element than the other stents (0, 13.8 and 0 %, p = 0.028). Incidence of longitudinal stent deformation was different between EESs with different stent platforms. Stent material, stent design and/or stent delivery balloon may affect longitudinal stent deformation.

Clinical, angiographic and procedural characteristics of longitudinal stent deformation

Recently, longitudinal stent deformation (LSD) has been reported increasingly. Even though the reported cases included almost all stent designs, most cases were seen in the Element™ stent design (Boston Scientific, Natick, MA, USA). It is considered that stent design, lesion and procedural characteristics play a role in the etiology of LSD. Yet, the effect of LSD on long-term clinical outcomes has not been studied well. Element stents implanted between January 2013 and April 2015 in our hospital were examined retrospectively. Patients were grouped into two according to the presence of LSD, and their clinical, lesion and procedural characteristics were studied. Twenty-four LSD's were detected in 1812 Element stents deployed in 1314 patients (1.83 % of PCI cases and 1.32 % of all Element stents). LMCA lesions (16.7 % vs 1.6 %, p < 0.001), complex lesions (75 % vs 35.1 %, p < 0.001), bifurcation lesions (37.5 % vs 18.3 %, p = 0.017), ostial lesions (33.3 % vs 12.8 %, p = 0.003), using of extra-support guiding catheter (54.2 % vs 22.3 %, p < 0.001) and extra-support guidewire (37.5 % vs 16.2 %, p = 0.005) were found to be more frequent in cases with LSD than in cases without it. In addition, the number of stents, stent inflation pressure and the use of post-dilatation were significantly different between the two groups. Two patients had an adverse event during the follow-up period. LSD is a rarely encountered complication, and is more common in complex lesions such as ostial, bifurcation and LMCA lesions. The use of extra-support guiding catheter, extra-support guidewires and low stent inflation pressure increases the occurrence of LSD. Nevertheless, with increased awareness of LSD and proper treatment, unwanted long-term outcomes can be successfully prevented.

Incidence and mechanisms of longitudinal stent deformation associated with Biomatrix, Resolute, Element, and Xience stents: Angiographic and case-by-case review of 1,800 PCIs

BACKGROUND

There is conflicting evidence regarding the incidence of longitudinal stent deformation (LSD) in contemporary practice.

METHODS AND RESULTS

To assess the incidence and mechanism of LSD across commonly used DES platforms, we performed a case-by-case review of 1,800 PCI cases involving 450 consecutive procedures using Biomatrix Flex, Resolute Integrity, Promus Element, and Xience V stents, respectively, between January 2009 and December 2011. LSD was detected in a higher proportion with Promus Element [15 (3.1%)] compared with other platforms (Xience V [4 (0.9%)], Biomatrix [3 (0.7%)], Resolute [3 (0.7%)]; P = 0.002). LSD was characterized as guide catheter/guide extension induced, or as impact from secondary devices such as postdilatation balloons or IVUS catheters. The incidence of guide catheter/guide extension LSD was similar across platforms; (Promus Element [5 (1.1%)], Xience V [4 (0.9%)], Biomatrix [3 (0.7%)], Resolute [3 (0.7%)]; P = 0.85). Secondary device LSD occurred exclusively with Promus Element (9/450 cases [2%] (P < 0.0001). Re-entering the deformed stent was more difficult in cases of secondary device LSD (6/9 compared with 0/12 treated cases; P < 0.001). Univariate predictors of LSD were previous CABG, culprit vessel, ostial involvement, and lesion tortuosity. Multivariate predictors of LSD were the Promus Element stent (OR 5.53 CI[1.54-19.85]), Guideliner use (OR 22.09 CI[4.73-103]), postdilation balloons (OR 5.47 CI[1.31-22.81]) and number of stents deployed (OR 2.06 CI[1.45-2.9].

CONCLUSION

LSD is more common than previously reported. LSD by a guide catheter/guide extension occurred equally with all platforms, however, LSD associated with secondary devices only occurred with the Element stent. These findings have important implications regarding current and future stent designs.

[Longitudinal stent deformation during bifurcation lesion treatment]

Longitudinal stent deformation is defined as a compression of stent length after its implantation. It's a rare complication but dangerous seen with several stents. We reported a case of longitudinal stent deformation during bifurcation lesion treatment with a Promus Element(®) and we perform a short review of this complication.

Third-generation zotarolimus-eluting and everolimus-eluting stents in all-comer patients requiring a percutaneous coronary intervention (DUTCH PEERS): a randomised, single-blind, multicentre, non-inferiority trial

BACKGROUND

Third-generation, permanent-polymer-based drug-eluting stents with novel, flexible designs might be more easily delivered than previous generations of stents in complex coronary lesions, but might be less longitudinally stable. We aimed to assess the safety and efficacy in all-comer patients of two third-generation stents that are often used clinically, but that have not yet been compared, and one of which has not previously been assessed in a randomised trial.

METHODS

In this investigator-initiated, single-blind, multicentre, randomised, two-arm, non-inferiority trial, patients aged 18 years and older who required a percutaneous coronary intervention with implantation of a drug-eluting stent were recruited from four study sites in the Netherlands. We randomly assigned patients by independently managed computer-generated allocation sequences in a 1:1 ratio to receive either cobalt-chromium-based zotarolimus-eluting stents (Resolute Integrity, Medtronic, Santa Rosa, CA, USA) or platinum-chromium-based everolimus-eluting stents (Promus Element, Boston Scientific, Natick, MA, USA). Patients and analysts were masked to the allocated stent, but treating clinicians were not. The primary endpoint of target-vessel failure was a composite of safety (cardiac death or target-vessel-related myocardial infarction) and efficacy (target-vessel revascularisation) at 12 months, analysed by intention to treat (with a non-inferiority margin of 3·6%). This trial is registered with ClinicalTrials.gov, number NCT01331707.

FINDINGS

Between Nov 25, 2010, and May 24, 2012, 1811 eligible all-comer patients, with 2371 target lesions, were enrolled in the study. 370 (20%) patients presented with ST-elevation myocardial infarction and 447 (25%) with non-ST-elevation myocardial infarction. 906 patients were assigned to receive zotarolimus-eluting stents and 905 to receive everolimus-eluting stents. Ease of stent delivery was shown by very low numbers of patients requiring treatment other than their assigned study treatment (six [1%] in the zotarolimus-eluting stent group vs five [1%] in the everolimus-eluting stent group; p=0·22). 12-month follow-up results were available for 1810 patients (one patient in the zotarolimus-eluting stent group withdrew consent). The primary endpoint was met by 55 (6%) of 905 patients in the zotarolimus-eluting stent group and 47 (5%) of 905 in the everolimus-eluting stent group. The zotarolimus-eluting stent was non-inferior to the everolimus-eluting stent (absolute risk difference 0·88%, 95% CI -1·24% to 3·01%; upper limit of one-sided 95% CI 2·69%; non-inferiority p=0·006). We noted no significant between-group differences in individual components of the primary endpoint. Definite stent thrombosis occurred in three (0·3%) patients in the zotarolimus-eluting stent group and six (0·7%) patients in the everolimus-eluting stent group (p=0·34). Longitudinal stent deformation was seen only in the everolimus-eluting stent group (nine [1·0%] of 905 vs 0 of 906, p=0·002; nine of 1591 [0·6%] everolimus-eluting stents implanted became deformed), but was not associated with any adverse events.

INTERPRETATION

Both stents were similarly efficacious and safe, and provided excellent clinical outcomes, especially in view of the large number of patients who presented with acute myocardial infarctions.

FUNDING

Boston Scientific, Medtronic.

In vivo evaluation of axial integrity of coronary stents using intravascular ultrasound: Insights on longitudinal stent deformation

OBJECTIVE

To evaluate the axial integrity of different coronary stents using intravascular ultrasound (IVUS).

BACKGROUND

Longitudinal stent deformation was recently reported.

METHODS

Consecutive patients who underwent IVUS analysis after drug-eluting stent (DES) implantation for de novo coronary lesions were evaluated. Stent length was compared with label length for calculation of absolute change and relative difference (absolute change divided by label length).

RESULTS

A total of 233 DES utilizing five different platforms were included. The median absolute change in stent length was 0.90 mm (interquartile range [IQR] 0.48-1.39) and the relative difference was 5.24% (IQR 2.55-8.29). There was no significant difference among the groups in median absolute or relative change: Cypher 0.89 mm/3.89%, Taxus 0.88 mm/5.39%, Endeavor 1.16 mm/6.77%, Xience V 0.86 mm/5.80%, and PROMUS Element 0.79 mm/5.34% (P = 0.085, P = 0.072, respectively). Multivariate logistic regression revealed that the Cypher stent was independently correlated with a lower change in length, whereas stent label length and deployment pressure were correlated with higher absolute change.

CONCLUSION

The axial integrity of DES platforms examined in vivo was high, with only mild changes in stent length after implantation. While there are differences between first- and second-generation DES, axial integrity among second-generation DES was similar.