Impact of post-dilatation on longitudinal stent elongation: An in vitro study

Open ArchivePublished:November 30, 2017DOI:https://doi.org/10.1016/j.jjcc.2017.11.003

      Highlights

      • Stents were elongated during each step of post-dilatation after implantation.
      • Stent post-dilatation showed uniformly elongation only to the proximal direction.
      • Methods of post-dilatation affected longitudinal stent deformation in tapered model.
      • Incomplete stent apposition was positively correlated with change in stent length.

      Abstract

      Objectives

      To evaluate whether balloon inflation for post-dilatation causes longitudinal stent deformation (LSD).

      Methods and results

      Two stents, sized 2.5 mm × 28 mm and 3.5 mm × 28 mm (Nobori®, biodegradable polymer biolimus-eluting stent; Ultimaster®, biodegradable polymer sirolimus-eluting stent; Terumo Co., Tokyo, Japan), were deployed at nominal pressure in straight and tapered silicon vessel models. Then, post-dilatation was performed in two ways: dilatation from the distal (D-P group) or proximal (P-D group) side of the stent. Microscopic findings showed that the stents were elongated during every step of the procedure regardless of the post-dilatation method and type of vessel model. The D-P group showed linear elongation during each step of post-dilatation (straight model: 28.7 ± 0.3 mm vs. 29.9 ± 0.3 mm, p = 0.002; tapered model: 28.0 ± 0.1 mm vs. 29.9 ± 0.1 mm, p < 0.001). In contrast, in the P-D group, the most significant change was observed in the first step of post-dilatation and only slight changes were observed thereafter (straight model: 28.6 ± 0.1 mm vs. 29.5 ± 0.1 mm, p < 0.001; tapered model: 28.2 ± 0.1 mm vs. 29.5 ± 0.1 mm, p < 0.001). Optical frequency domain imaging analysis showed that the frequency of stent strut malapposition was positively correlated with the percentage change in stent length (r = 0.74, p < 0.0001).

      Conclusion

      LSD was observed during every step of post-dilatation in both the straight and tapered vessel models. However, some differences were observed between the D-P and P-D groups. Minimizing stent strut malapposition may reduce the risk of LSD.

      Keywords

      Introduction

      Recent bench tests and clinical observations have shown the occurrence of longitudinal stent deformation (LSD) with the use of the thin-strut stent platform [
      • Taniguchi N.
      • Mizuguchi Y.
      • Takahashi A.
      Longitudinal stent elongation during retraction of entrapped jailed guidewire in a side branch with balloon catheter support: a case report.
      ,
      • Dvir D.
      • Kitabata H.
      • Barbash I.M.
      • Minha S.
      • Badr S.
      • Loh J.P.
      • et al.
      In vivo evaluation of axial integrity of coronary stents using intravascular ultrasound: insights on longitudinal stent deformation.
      ,
      • Ormiston J.A.
      • Webber B.
      • Webster M.W.I.
      Stent longitudinal integrity bench insights into a clinical problem.
      ,
      • Guler A.
      • Guler Y.
      • Acar E.
      • Aung S.M.
      • Efe S.C.
      • Kilicgedik A.
      • et al.
      Clinical, angiographic and procedural characteristics of longitudinal stent deformation.
      ]. Although LSD is an infrequent complication of percutaneous coronary intervention (PCI), small changes in stent length have been recognized as a common complication in routine clinical PCI [
      • Dvir D.
      • Kitabata H.
      • Barbash I.M.
      • Minha S.
      • Badr S.
      • Loh J.P.
      • et al.
      In vivo evaluation of axial integrity of coronary stents using intravascular ultrasound: insights on longitudinal stent deformation.
      ]. Even small changes in stent length can cause severe problems, especially in stents used for the treatment of ostial or bifurcation lesions. New-generation coronary stents have been designed with improved flexibility, deliverability, and conformability to the vessel wall; however, these improvements come at the cost of longitudinal strength [
      • Ormiston J.A.
      • Webber B.
      • Webster M.W.I.
      Stent longitudinal integrity bench insights into a clinical problem.
      ]. Therefore, the recent changes in stent design may have increased the incidence of LSD during PCI.
      Direct force exerted by pushing and/or pulling of the stent struts together during the delivery of other devices, such as post-dilatation balloon, guide catheter extension system, distal embolic protection device, and intravascular ultrasound catheter, is considered an important cause of LSD [
      • Guler A.
      • Guler Y.
      • Acar E.
      • Aung S.M.
      • Efe S.C.
      • Kilicgedik A.
      • et al.
      Clinical, angiographic and procedural characteristics of longitudinal stent deformation.
      ]. However, under-expansion of the implanted stent is an important factor underlying target-lesion failure [
      • Kastrati A.
      • Dibra A.
      • Mehilli J.
      • Mayer S.
      • Pinieck S.
      • Pache J.
      • et al.
      Predictive factors of restenosis after coronary implantation of sirolimus- or paclitaxel-eluting stents.
      ]. Therefore, post-dilatation of the implanted stent is often performed in clinical settings for optimized functioning [
      • Blackman D.J.
      • Porto I.
      • Shirodaria C.
      • Channon K.M.
      • Banning A.P.
      Usefulness of high-pressure post-dilatation to optimize deployment of drug-eluting stents for the treatment of diffuse in-stent coronary restenosis.
      ], usually from the distal to the proximal side of the stent. The post-dilatation balloon is dilated in the radial axial direction and simultaneously elongated in the longitudinal axial direction. We hypothesized that implanted coronary stents may become elongated as the post-dilatation balloons expand in the longitudinal axis.
      Thus far, few studies have attempted to evaluate the influence of post-dilatation of implanted stents and practical methods of post-dilatation on LSD. Thus, the aim of the present study was to examine the effects of post-dilatation on LSD and to determine how post-dilatation after stent implantation affects this complication.

      Methods

       Experimental models

      In the present study, two types of silicon vessel models (Shonankasei Co., Kanagawa, Japan)—straight and tapered—were used (Fig. 1). The silicon model had a hardness of 5 points based on measurement with a type A durometer. Each silicon model had a stenosis lesion (lesion length, 20 mm), and both edges of the lesions were marked with red lines for confirmation. Biodegradable polymer biolimus-eluting stents (BP-BES) (Nobori®; Terumo Co., Tokyo, Japan) and biodegradable polymer sirolimus-eluting stents (BP-SES) (Ultimaster®; Terumo Co.) were used for the experiments. First, the stents were deployed to adjust the distal marker of the lesion and the distal edge of the stent. Each stent was deployed at a nominal pressure for 20 s. In this in vitro model, 2.5 mm × 28 mm sized stents were deployed in a straight fashion and 3.5 mm × 28 mm sized stents were deployed in a tapered fashion, depending on the vessel model size. Then, we performed post-dilatation by using two methods: dilatation from the distal (D-P group) or proximal (P-D group) site of the stent (Fig. 2A,B ). We planned the method of post-dilatation to resemble the actual clinical procedure. As a result, the number of post-dilatations was different between the D-P and P-D groups.
      • (i)
        Distal–proximal group
        In this group, post-dilatation was performed from the distal to proximal direction of the deployed stents. First, post-dilatation was performed at the proximal marker of the lesion immediately after stent deployment; second, post-dilatation was conducted at the proximal edge of the stent; then, the balloon size was increased, and a third post-dilatation was performed at the proximal edge of the stent.
      • (ii)
        Proximal–distal group
        In this group, post-dilatation was performed from the proximal to distal direction. First, post-dilatation was performed at the proximal edge of the stent. Then, the balloon size was decreased, and a second post-dilatation was performed in the middle of the stent.
      Figure thumbnail gr1
      Fig. 1Characteristics of the silicon vessel models used in this study. Straight (lumen diameter, 2.5 mm) and tapered (lumen diameter, 2.0–5.5 mm) vessel models were used. These models have a 20-mm stenosis lesion. The material of the silicon model reflects the actual vessel frictional resistance and hardness.
      Figure thumbnail gr2
      Fig. 2Study procedure. (A) Experiment with the tapered vessel model. (B) Experiment with the straight vessel model. First, the stent was deployed at a nominal pressure for 20 s. In the D-P group, post-dilatation was performed from the distal to proximal direction of the deployed stents to adjust the proximal marker of the lesion. Then, a second post-dilatation was performed to adjust the proximal edge of the stent and the proximal edge of the balloon. Finally, the balloon size was increased, and the balloon was dilated to adjust the proximal edge of the stent and the proximal edge of the balloon. In the P-D group, post-dilatation was performed from the proximal to the distal direction of the deployed stent to adjust the proximal edge of the stent and the proximal edge of the balloon. Then, the balloon size was decreased, and the balloon was dilated to adjust the proximal marker of the lesion and the proximal edge of the balloon. Both stent size and balloon size were chosen according to the vessel model size. BP-BES, biodegradable polymer biolimus-eluting stents; BP-SES, biodegradable polymer sirolimus-eluting stents.
      We used 2.5 mm × 15 mm and 2.75 mm × 12 mm post-dilatation balloons (Hiryu®; Terumo Co.) for the straight model. For the tapered model, we used 3.5 mm × 15 mm and 4.0 mm × 12 mm post-dilatation balloons (Hiryu®). Every step of post-dilatation was performed at 20 atm for 20 s. We performed the same experimental procedure three times for each stent.

       Microscopy and optical frequency domain imaging

      We used a microscope (SKM-S30B-PC; SaitohKougaku, Yokohama, Japan) to accurately calculate the stent length and check for stent deformation. Optical frequency domain imaging (OFDI) (Terumo Co.) was used to check for stent deformation and malapposition during each step of the procedure (pullback speed, 20 mm/s). Stent apposition was assessed at the cross-sectional level with an interval of 0.5 mm. We measured the distance between the stent surface reflection and the surface of the neighboring visible vessel model; if this distance exceeded the nominal stent strut thickness, the stent strut was considered malapposed (BP-BES: >130 μm; BP-SES: >80 μm) [
      • Tanigawa J.
      • Barlis P.
      • Dimopoulos K.
      • Dalby M.
      • Moore P.
      • Di Mario C.
      The influence of strut thickness and cell design on immediate apposition of drug-eluting stents assessed by optical coherence tomography.
      ]. We calculated the percentages of malapposed stent struts within the site to be dilated in the next step of the procedure. Then, we examined the relationship between the percentage of malapposed struts and the percentage change in stent length during post-dilatation.

       Statistical analysis

      The distribution of continuous variables was examined using the Shapiro–Wilk test. Paired Student's t-test was used to compare the stent length before and after stent post-dilatation during each step of the procedure. Student's t-test was used to compare the differences in the percentage change of stent length during post-dilatation between the D-P and P-D groups. Linear regression and Pearson's correlation statistics were used to examine the correlation between the percentage change of stent length and the frequency of stent malapposition. All analyses were performed with JMP version 5.1 software (SAS Institute, Cary, NC, USA). A p-value of <0.05 was considered statistically significant.

      Results

       Straight model

      In the D-P group, both BP-BES and BP-SES were significantly elongated during the first and second post-dilatations, whereas BP-BES was not significantly elongated during the third post-dilatation. Similarly, in the P-D group, both stents were significantly elongated during the first post-dilatation, whereas BP-BES was not significantly elongated during the second post-dilatation (Table 1). The stent length linearly increased during each step of post-dilatation both in the D-P and P-D groups (Fig. 3A,B ). There was no significant difference in the total percentage change in stent length between the D-P and P-D groups (Table 2). Similarly, in the comparison between different types of stents, no significant difference was observed (Table 3).
      Table 1Change in stent length during each step of procedure.
      Nominal stent length (mm)Immediately after stent deployment (mm)p-value (nominal vs. immediately)After 1st post-dilatation (mm)p-value (immediately vs. 1st)After 2nd post-dilatation (mm)p-value (1st vs. 2nd)After 3rd post-dilatation (mm)p-value (2nd vs. 3rd)p-value (immediately vs. final)
      Straight
       BP-BES
        D-P (n = 3)28.0028.6 ± 0.10.00928.9 ± 0.20.02829.2 ± 0.10.00229.3 ± 0.30.1050.022
        P-D (n = 3)28.0028.6 ± 0.0<0.00129.1 ± 0.20.02829.3 ± 0.40.0900.041
      BP-SES
        D-P (n = 3)28.0028.8 ± 0.20.00529.1 ± 0.30.00830.0 ± 0.60.02730.4 ± 0.70.0030.012
        P-D (n = 3)28.0028.6 ± 0.10.00929.4 ± 0.00.00329.7 ± 0.10.0030.001
      Tapered
       BP-BES
        D-P (n = 3)28.0028.3 ± 0.10.03028.5 ± 0.00.01829.0 ± 0.10.00829.9 ± 0.10.002<0.001
        P-D (n = 3)28.0028.4 ± 0.10.02329.3 ± 0.20.00329.4 ± 0.20.0380.005
       BP-SES
        D-P (n = 3)28.0027.8 ± 0.10.09528.2 ± 0.20.01128.9 ± 0.10.00630.0 ± 0.2<0.001<0.001
        P-D (n = 3)28.0028.1 ± 0.10.60729.5 ± 0.2<0.00129.7 ± 0.10.0770.002
      BP-BES, biodegradable polymer biolimus-eluting stents; BP-SES, biodegradable polymer sirolimus-eluting stents; D, distal; P, proximal.
      A p-value of statistical significance is shown in bold.
      Figure thumbnail gr3
      Fig. 3Change in stent length during each step of post-dilatation. Red lines indicate the change in stent length during each step of post-dilatation in the distal–proximal (D-P) group. Blue lines indicate the change in stent length during each step of post-dilatation in the proximal–distal (P-D) group. (A) In the straight vessel model, biodegradable polymer biolimus-eluting stents (BP-BES) were linearly elongated both in the D-P and P-D groups during each step of post-dilatation. (B) In the straight vessel model, biodegradable polymer sirolimus-eluting stents (BP-SES) were linearly elongated both in the D-P and P-D groups during each step of post-dilatation. (C) In the tapered vessel model, BP-BES were linearly elongated in the P-D group. In the D-P group, the largest change in stent length was observed in the first step of post-dilatation, and only slight changes were observed thereafter. (D) In the tapered vessel model, BP-SES were elongated linearly during each step of post-dilatation in the D-P group. In contrast, the P-D group showed the largest change in stent length in the first step of post-dilatation, and only slight changes were observed thereafter.
      Table 2Comparison of the percent change in stent length between P-D and D-P groups, during post-dilatation.
      D-PP-Dp-value
      Straight model
       Over all4.1 ± 0.8%3.2 ± 0.8%0.431
       BP-BES2.3 ± 0.1%2.4 ± 0.9%0.944
       BP-SES5.4 ± 0.3%4.1 ± 0.4%0.420
      Tapered model
       Overall6.8 ± 0.5%4.6 ± 0.5%0.014
       BP-BES5.7 ± 0.2%3.5 ± 0.6%0.004
       BP-SES7.9 ± 0.0%5.7 ± 0.7%0.005
      BP-BES, biodegradable polymer biolimus-eluting stents; BP-SES, biodegradable polymer sirolimus-eluting stents; D, distal; P, proximal.
      A p-value of statistical significance is shown in bold.
      Table 3Comparison of the percent change in stent length between BP-BES and BP-SES, during post-dilatation.
      BP-BESBP-SESp-value
      Straight model
       D-P2.4 ± 1.2%5.4 ± 1.0%0.096
       P-D2.3 ± 0.5%4.1 ± 0.5%0.125
      Tapered model
       D-P5.7 ± 0.1%7.9 ± 0.1%<0.001
       P-D3.5 ± 0.4%5.7 ± 0.4%0.015
      BP-BES, biodegradable polymer biolimus-eluting stents; BP-SES, biodegradable polymer sirolimus-eluting stents; D, distal; P, proximal.
      A p-value of statistical significance is shown in bold.

       Tapered model

      In the D-P group, both BP-BES and BP-SES were significantly elongated during the first, second, and third post-dilatations. Similarly, in the P-D group, both stents were significantly elongated during the first dilatation, whereas BP-SES was not significantly elongated during the second post-dilatation (Table 1). The stent length linearly increased during each step of post-dilatation in the D-P group. However, in the P-D group, the most significant change in stent length was observed in the first step of post-dilatation; thereafter, only slight changes were observed (Fig. 3C,D).
      The P-D group showed a significantly higher percentage change in stent length than the D-P group during the first step of post-dilatation. Inversely, the P-D group showed a significantly smaller percentage change in stent length during the second dilatation. Furthermore, the D-P group showed a significantly higher total percentage change in stent length than the P-D group (Table 2). In the comparison between the different types of stent (BP-BES and BP-SES), BP-SES showed a significantly higher percentage change in stent length in both the D-P and P-D groups (Table 3).
      During every step of post-dilatation, the stents were longitudinally elongated to the proximal direction but not to the distal direction. Furthermore, the LSD observed in this study appeared as a uniform elongation without geometric distortion (Fig. 4).
      Figure thumbnail gr4
      Fig. 4Optical frequency domain imaging (OFDI) scans taken immediately after stent deployment and after post-dilatation. We used OFDI at every step of post-dilatation to evaluate for stent deformation. Three-dimensional images and carpet views (which reveal the stented segment, reconstructing it as an open structure and displaying the stent mesh work) are shown in the figure. The stents were elongated uniformly without geometric distortion of the struts.
      In the OFDI analysis, strut malapposition was observed in 5.8% (2126 of 36,554 struts) and 46.6% (19,605 of 42,081 struts) in the straight vessel model and tapered vessel model, respectively. Furthermore, the percentage of malapposition within the ballooning segment was positively correlated with the percentage change in stent length, especially in the tapered model (straight model: r = 0.51, p = 0.002; tapered model: r = 0.86, p < 0.001) (Fig. 5).
      Figure thumbnail gr5
      Fig. 5Correlation between the percentage change in stent length and the frequency of malapposition. The frequency of strut malapposition was significantly positively correlated with the percentage change in stent length.

      Discussion

      The principal findings of this study were as follows: (i) the stents were elongated during each step of post-dilatation after implantation; (ii) LSD caused by post-dilatation after stent implantation appeared as a uniform longitudinal elongation only to the proximal direction; (iii) the method of post-dilatation after stent implantation affected LSD in the tapered vessel model; and (iv) incomplete stent apposition was positively correlated with the percentage change in stent length. Our findings revealed that LSD occurred during each step of post-dilatation regardless of the post-dilatation method and type of stent used.
      In the clinical setting, there are various factors that cause LSD, including anatomical factors (lesion length, vessel angulation, cyclic motion of the coronary artery, lesion morphology), device factors (variety of stent and balloon types, size of stent and balloon), and procedural factors (sequence of post-dilatation, duration of balloon inflation, frequency of post-dilatation). Therefore, we conducted this in vitro study by using fixed vessel models, devices, and procedures to evaluate the precise influence of post-dilatation on LSD.
      Previous studies have suggested that the external physical force that compresses or extends the deployed stents in ostial and non-ostial locations when other devices cross the stents is an important cause of LSD [
      • Guler A.
      • Guler Y.
      • Acar E.
      • Aung S.M.
      • Efe S.C.
      • Kilicgedik A.
      • et al.
      Clinical, angiographic and procedural characteristics of longitudinal stent deformation.
      ]. In the present study, we focused on the impact of balloon expansion for post-dilatation on LSD. In the clinical setting, it might be considered that over-expansion of the implanted stents can result in stent shortening. However, interestingly, we found that post-dilatation up to a conceivable expansion range (up to +0.5 mm) beyond the nominal size resulted in stent elongation only longitudinally. During balloon inflation for post-dilatation, the balloon was dilated in the radial axial direction and simultaneously elongated to the longitudinal proximal axial direction. Therefore, we assume that the stents were stretched and pulled by the inflated balloon during post-dilatation.
      Our study also revealed that LSD was associated with incomplete stent apposition. As reported previously, incomplete stent apposition is frequently observed in routine clinical PCI and possibly results in stent thrombosis or stent restenosis [
      • Cook S.
      • Wenaweser P.
      • Togni M.
      • Billinger M.
      • Morger C.
      • Seiler C.
      • et al.
      Incomplete stent apposition and very late stent thrombosis after drug-eluting stent implantation.
      ]. The cut-off point of the distance between the stent strut and vessel wall for the prediction of subsequent adverse events was reported to be >355 μm [
      • Kawamori H.
      • Shite J.
      • Shinke T.
      • Otake H.
      • Matsumoto D.
      • Nakagawa M.
      • et al.
      Natural consequence of post-intervention stent malapposition, thrombus, tissue prolapse, and dissection assessed by optical coherence tomography at mid-term follow-up.
      ]. Furthermore, some reports claim that a small area of malapposition is not a serious problem and most cases resolve at follow-up [
      • Ishida K.
      • Otsuki S.
      • Giacchi G.
      • Ortega-Paz L.
      • Shiratori Y.
      • Freixa X.
      • et al.
      Serial optical coherence tomography assessment of malapposed struts after everolimus-eluting stent implantation. A subanalysis from the HEAL-EES study.
      ]. However, this study found that the frequency of strut malapposition may affect LSD regardless of the area of malapposition. We assume that complete attachment of the stent strut may increase the frictional resistance between the stent strut and vessel wall. As a result, the percentage change in stent length was lower in cases with proper apposition.
      It is popularly believed that BP-BES are one of the most stable stents in terms of LSD because of their peak-to-peak stent design and thin stent strut [
      • Ormiston J.A.
      • Webber B.
      • Ubod B.
      • White J.
      • Webster M.W.I.
      Stent longitudinal strength assessed using point compression: insights from a second-generation, clinically related bench test.
      ]. However, in our experiments, LSD was observed even with the use of BP-BES, similar to when BP-SES is used. We presume that stent post-dilatation had more impact on LSD than the stent design.
      On the contrary, a difference in the percentage change in length between the two different types of stent was simultaneously observed in the tapered vessel experiment. Furthermore, the influence of stent design was observed to be more remarkable during the post-dilatation on the malapposed site of the implanted stent.
      We also examined the influence of the post-dilatation method on LSD. In experiments with the straight vessel model, there was no significant difference between the D-P and P-D groups. In contrast, in the experiment with the tapered vessel model, the D-P group showed a significantly higher total percentage change in stent length than the P-D group. However, the different number of post-dilatations might also have an influence. Therefore, we discuss the procedure in more detail. The P-D group showed a significantly higher change in stent length than the D-P group during the first dilatation. Inversely, during the second dilatation, the P-D group showed a significantly smaller change in stent length than the D-P group. In the straight vessel experiment, the stents were definitely attached to the vessel wall. Therefore, there might be no observable influence of the post-dilatation method. In contrast, in the tapered vessel experiment, stent strut malapposition occurred more frequently in the proximal site of the implanted stent than in the distal site. Moreover, the first post-dilatation in the P-D group and the second and third post-dilatations in the D-P group were the procedures performed on the malapposed site of the implanted stent. Therefore, we assume that the correlation between LSD and incomplete stent apposition might explain these results.
      In the present study, the stents were elongated uniformly as the balloon expanded longitudinally, in contrast to LSD with loss of stent geometry due to a direct external force [
      • Inaba S.
      • Weisz G.
      • Kobayashi N.
      • Saito S.
      • Dohi T.
      • Dong L.
      • et al.
      Prevalence and anatomical features of acute longitudinal stent deformation: an intravascular ultrasound study.
      ,
      • Mamas M.A.
      • Williams P.D.
      Longitudinal stent deformation: insights on mechanisms, treatments and outcomes from the Food and Drug Administration Manufacturer and User Facility Device Experience database.
      ]. We presume that the pulling force from balloon expansion may have been applied uniformly, resulting in stent strut deformity.
      Coronary stents have been dramatically improved in terms of their radial force, conformability, flexibility, plaque scaffold, deliverability, and durability [
      • Mamas M.A.
      • Williams P.D.
      Longitudinal stent deformation: insights on mechanisms, treatments and outcomes from the Food and Drug Administration Manufacturer and User Facility Device Experience database.
      ]. However, these improvements have come at the cost of longitudinal stability. Moreover, stent post-dilatation is widely performed in current clinical practice [
      • Blackman D.J.
      • Porto I.
      • Shirodaria C.
      • Channon K.M.
      • Banning A.P.
      Usefulness of high-pressure post-dilatation to optimize deployment of drug-eluting stents for the treatment of diffuse in-stent coronary restenosis.
      ,
      • Mori F.
      • Tsurumi Y.
      • Hagiwara N.
      • Kasanuki H.
      Impact of post-dilatation with a focal expanding balloon for optimization of intracoronary stenting.
      ]. In view of these points, our results are of great significance. For some lesions, the location of the stent needs to be adjusted precisely, for example, in ostial lesions or lesions just distal to the bifurcation. On the basis of our findings, more attention should be paid to the fact that stent post-dilatation usually causes longitudinal stent elongation. Considering the significant correlation between LSD and incomplete stent apposition, it seems reasonable to conclude that post-dilatation from the proximal site of the stent to minimize strut malapposition is useful for reducing the incidence of LSD.
      This study has some limitations. First, bench testing cannot accurately simulate the physiological conditions. Thus, our study does not completely reflect the actual lesion length, angulation, hardness (calcification), and side branches. In particular, the coefficient of friction between the silicon model and the metallic stent is the most important factor influencing the LSD phenomenon. However, in clinical settings, the vessel frictional resistance varies among different patients. Therefore, we believe that our experimental data obtained under fixed conditions have great significance in assessing the influence of post-dilatation on LSD. Second, our results were based on a limited number of stents, stent sizes, and post-dilatation balloons, and LSD may be affected by the different materials, design, and size of the stents, as well as the types of post-dilatation balloon. Further bench testing with different types of stents and balloons should be conducted to clarify how LSD occurs. Finally, clinical studies examining LSD should also be performed.
      In summary, longitudinal stent elongation was observed during every step of post-dilatation in both straight and tapered vessel models. However, some differences were observed between the D-P and P-D groups especially in the tapered vessel model. Minimizing stent strut malapposition may reduce the risk of LSD. Our study provides a better understanding of the role of stent post-dilatation after implantation on LSD, and the post-dilatation techniques to reduce the risk of LSD.

      Contributions

      Takuya Sumi, Hideki Ishii, Susumu Suzuki, Tomoyuki Ota, Kenji Kada, and Toyoaki Murohara participated in the protocol design, and Takuya Sumi, Hideki Ishii, Akihito Tanaka, Susumu Suzuki, Hiroki Kojima, Naoki Iwakawa, Toshijiro Aoki, Kenshi Hirayama, Takuyuki Mitsuda, Kazuhiro Harada, Yousuke Negishi, Tomoyuki Ota, Kenji Kada, and Toyoaki Murohara were involved in editing the manuscript. Akihito Tanaka, Susumu Suzuki, Hiroki Kojima, Naoki Iwakawa, Toshijiro Aoki, Kenshi Hirayama, Takuyuki Mitsuda, Kazuhiro Harada, Yousuke Negishi, Tomoyuki Ota, and Kenji Kada participated in the collection of clinical information and statistical analysis.

      Funding

      This study was supported by Mitsui Life Social Welfare Foundation .

      Disclosures

      Hideki Ishii received lecture fees from Astellas Pharma Inc., Astrazeneca Inc., Daiichi-Sankyo Pharma Inc., and MSD K. K. Toyoaki Murohara received lecture fees from Bayer Pharmaceutical Co., Ltd., Daiichi-Sankyo Co., Ltd., Dainippon Sumitomo Pharma Co., Ltd., Kowa Co., Ltd., MSD K. K., Mitsubishi Tanabe Pharma Co., Nippon BoehringerIngelheim Co., Ltd., Novartis Pharma K. K., Pfizer Japan Inc., Sanofi-aventis K. K., and Takeda Pharmaceutical Co., Ltd. Toyoaki Murohara received unrestricted research grant for Department of Cardiology, Nagoya University Graduate School of Medicine from Astellas Pharma Inc., Daiichi-Sankyo Co., Ltd., Dainippon Sumitomo Pharma Co., Ltd., Kowa Co., Ltd., MSD K. K., Mitsubishi Tanabe Pharma Co., Nippon BoehringerIngelheim Co., Ltd., Novartis Pharma K. K., Otsuka Pharma Ltd., Pfizer Japan Inc., Sanofi-aventis K. K., Takeda Pharmaceutical Co., Ltd., and Teijin Pharma Ltd. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.

      Acknowledgments

      This study was independently initiated and conducted by the authors. No industry sponsor was received for the study and only the test sample was provided in kind by the Terumo Co. for the experiment. The authors would like to thank the Terumo Co. for accepting to provide test samples for this study.

      Appendix A. Supplementary data

      The following are the supplementary data to this article:

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