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Vascular OnlineFirst, published on June 3, 2015 as doi:10.1177/1708538115590040
Original Article
Radial force measurement of endovascular stents: Influence of stent design and diameter
Vascular 0(0) 1–6 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1708538115590040 vas.sagepub.com
Takuya Matsumoto1, Yutaka Matsubara1, Yukihiko Aoyagi1, Daisuke Matsuda1, Jun Okadome1, Koichi Morisaki1, Kentarou Inoue1, Shinichi Tanaka1, Tomoko Ohkusa2 and Yoshihiko Maehara1
Abstract Background and purpose: Angioplasty and endovascular stent placement is used in case to rescue the coverage of main branches to supply blood to brain from aortic arch in thoracic endovascular aortic repair. This study assessed mechanical properties, especially differences in radial force, of different endovascular and thoracic stents. Material and methods: We analyzed the radial force of three stent models (EpicTM, E-LuminexxÕ and SMARTÕ ) stents using radial force-tester method in single or overlapping conditions. We also analyzed radial force in three thoracic stents using MylarÕ film testing method: conformable GoreÕ -TAGÕ , RelayÕ, and ValiantÕ Thoracic Stent Graft. Results: Overlapping SMART stents had greater radial force than overlapping Epic or Luminexx stents (P < 0.01). The radial force of the thoracic stents was greater than that of all three endovascular stents (P < 0.01). Conclusions: Differences in radial force depend on types of stents, site of deployment, and layer characteristics. In clinical settings, an understanding of the mechanical characteristics, including radial force, is important in choosing a stent for each patient.
Keywords Endovascular stent, radial force, thoracic stent graft
Introduction Intra-arterial stenting is rapidly becoming the modality of choice for the management of occlusive, degenerative, and aneurysmal disease, and various endovascular stent designs have recently been developed. Complications associated with stents have increased with their use and include restenosis or passive stenosis because of the presence of other stents.1 The most serious complication of carotid angioplasty and stent placement is stroke in the setting of emboli or hemodynamic depression.2–8 Some studies of the safety and efficacy of different types of carotid stents have reported patency rates achieved after carotid angioplasty and stent placement;9,10 however, it is difficult to analyze results of these studies because of insufficient detail regarding composition of the plaque. Therefore, the results may be influenced by patient-related factors, and the complications can be partially attributed to the physiological and mechanical properties of the stents.
In any structure, physiological properties play a key role in structural performance. In theory, patency rates are ascribed primarily to the radial force of a stent. In the clinical setting, to rescue the obstructed carotid arteries in thoracic endovascular aortic repair, although the patency rates of angioplasty and stent placement might be influenced by patient-related pathophysiological factors, information about the mechanical characteristics of stents, such as the 1 Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan 2 Kirameki Project Career Support Center, Kyushu University Hospital, Fukuoka, Japan
Corresponding author: Takuya Matsumoto, Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Email: [email protected]
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influence of the proximity of an intravascular stent to a thoracic stent, could be of value when choosing an appropriate stent for a given lesion. Although a number of animal and clinical studies have been performed to determine the usefulness of intravascular stents, only a few studies have examined the mechanical properties of stents. In particular, only rarely has the difference in radial force between peripheral stents and thoracic stents been investigated. The purpose of this study was to assess the mechanical properties of the six stent types used most often in clinical settings in Japan.
Methods Stents In this study, we tested three nitinol endovascular stents: EpicTM (Boston Scientific, Marlborough, MA, USA), E-LuminexxÕ (Bard Peripheral Vascular, Tempe, AZ, USA), and SMARTÕ (SMART; Cordis Corp., Bridgewater, NJ, USA). The stents investigated
were 60-mm long and ranged in diameter from 8 to 12 mm. The three thoracic stents tested were the Conformable GoreÕ -TAGÕ Thoracic Endoprosthesis (c-TAG; W.L. Gore & Associates, Flagstaff, AZ, USA), RelayÕ Thoracic Stent-Graft (Bolton Medical, Barcelona, Spain), and ValiantÕ Thoracic Stent Graft (Medtronic, Inc., Santa Rosa, CA, USA).
Radial force measurement We analyzed the characteristics of radial force of nitinol stents using radial force-tester method as previously described.11 In this study, RX-500 (Machine Solutions Inc., Flagstaff, AZ, USA) was used. Three types of stents were fully deployed and set into the RX-500, respectively. The tester was programmed to reduce the stent diameter from unconstrained to predetermined 5 mm and recommended diameter of each stents (1 mm compression) at center or 10 mm from the edge, then gradually and simultaneously fully expanded at 0.5 mm/s (Figure 1). Testing was performed in a booth maintained at a temperature of
Figure 1. Schematic drawing of deformation characteristics of a 10-mm-diameter stent during a loading/unloading cycle. A Starting point, B the stent is loaded, C the stent is loaded to 2 mm stenosis, D the stent is then unloaded, E nominal outer diameter.
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37 2 C. Measurements were collected in triplicate for each stent. The following equation was used to calculate the radial force of stents RF ¼ 2 HF=L
ð1Þ
where RF ¼ radial force (N/mm), HF ¼ Hoop Force (N) and L ¼ stent length (mm). To analyze thoracic stents, we used MylarÕ (DuPont, Wilmington, DE, USA) film-testing method for radial force measurement, as previously described.12 In this study, polytetrafluoroethylene (PTFE) film was used instead of Mylar film. Three types of thoracic stents were fully deployed and set into the apparatus. The film was displaced to reduce the thoracic stent diameter from unconstrained to 12 mm or 4 mm (recommended diameter), then return until fully expand at 0.5 mm/s. Testing was performed in a water bath maintained at a constant temperature of 37 2 C. Measurements were collected in triplicate for each stent.
Statistical analysis Data were presented as mean standard deviation. The effects of stent position, number, and type of stent on radial force were assessed using three-way analysis of variance. All analyses were performed using JMPÕ , Version 9.0 (SAS Institute Inc., Cary, NC, USA). P values
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[1–6] [PREPRINTER stage]
Vascular OnlineFirst, published on June 3, 2015 as doi:10.1177/1708538115590040
Original Article
Radial force measurement of endovascular stents: Influence of stent design and diameter
Vascular 0(0) 1–6 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1708538115590040 vas.sagepub.com
Takuya Matsumoto1, Yutaka Matsubara1, Yukihiko Aoyagi1, Daisuke Matsuda1, Jun Okadome1, Koichi Morisaki1, Kentarou Inoue1, Shinichi Tanaka1, Tomoko Ohkusa2 and Yoshihiko Maehara1
Abstract Background and purpose: Angioplasty and endovascular stent placement is used in case to rescue the coverage of main branches to supply blood to brain from aortic arch in thoracic endovascular aortic repair. This study assessed mechanical properties, especially differences in radial force, of different endovascular and thoracic stents. Material and methods: We analyzed the radial force of three stent models (EpicTM, E-LuminexxÕ and SMARTÕ ) stents using radial force-tester method in single or overlapping conditions. We also analyzed radial force in three thoracic stents using MylarÕ film testing method: conformable GoreÕ -TAGÕ , RelayÕ, and ValiantÕ Thoracic Stent Graft. Results: Overlapping SMART stents had greater radial force than overlapping Epic or Luminexx stents (P < 0.01). The radial force of the thoracic stents was greater than that of all three endovascular stents (P < 0.01). Conclusions: Differences in radial force depend on types of stents, site of deployment, and layer characteristics. In clinical settings, an understanding of the mechanical characteristics, including radial force, is important in choosing a stent for each patient.
Keywords Endovascular stent, radial force, thoracic stent graft
Introduction Intra-arterial stenting is rapidly becoming the modality of choice for the management of occlusive, degenerative, and aneurysmal disease, and various endovascular stent designs have recently been developed. Complications associated with stents have increased with their use and include restenosis or passive stenosis because of the presence of other stents.1 The most serious complication of carotid angioplasty and stent placement is stroke in the setting of emboli or hemodynamic depression.2–8 Some studies of the safety and efficacy of different types of carotid stents have reported patency rates achieved after carotid angioplasty and stent placement;9,10 however, it is difficult to analyze results of these studies because of insufficient detail regarding composition of the plaque. Therefore, the results may be influenced by patient-related factors, and the complications can be partially attributed to the physiological and mechanical properties of the stents.
In any structure, physiological properties play a key role in structural performance. In theory, patency rates are ascribed primarily to the radial force of a stent. In the clinical setting, to rescue the obstructed carotid arteries in thoracic endovascular aortic repair, although the patency rates of angioplasty and stent placement might be influenced by patient-related pathophysiological factors, information about the mechanical characteristics of stents, such as the 1 Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan 2 Kirameki Project Career Support Center, Kyushu University Hospital, Fukuoka, Japan
Corresponding author: Takuya Matsumoto, Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Email: [email protected]
Downloaded from vas.sagepub.com at University of Otago Library on July 26, 2015
XML Template (2015) [2.6.2015–11:20am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/VASJ/Vol00000/150042/APPFile/SG-VASJ150042.3d
(VAS)
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influence of the proximity of an intravascular stent to a thoracic stent, could be of value when choosing an appropriate stent for a given lesion. Although a number of animal and clinical studies have been performed to determine the usefulness of intravascular stents, only a few studies have examined the mechanical properties of stents. In particular, only rarely has the difference in radial force between peripheral stents and thoracic stents been investigated. The purpose of this study was to assess the mechanical properties of the six stent types used most often in clinical settings in Japan.
Methods Stents In this study, we tested three nitinol endovascular stents: EpicTM (Boston Scientific, Marlborough, MA, USA), E-LuminexxÕ (Bard Peripheral Vascular, Tempe, AZ, USA), and SMARTÕ (SMART; Cordis Corp., Bridgewater, NJ, USA). The stents investigated
were 60-mm long and ranged in diameter from 8 to 12 mm. The three thoracic stents tested were the Conformable GoreÕ -TAGÕ Thoracic Endoprosthesis (c-TAG; W.L. Gore & Associates, Flagstaff, AZ, USA), RelayÕ Thoracic Stent-Graft (Bolton Medical, Barcelona, Spain), and ValiantÕ Thoracic Stent Graft (Medtronic, Inc., Santa Rosa, CA, USA).
Radial force measurement We analyzed the characteristics of radial force of nitinol stents using radial force-tester method as previously described.11 In this study, RX-500 (Machine Solutions Inc., Flagstaff, AZ, USA) was used. Three types of stents were fully deployed and set into the RX-500, respectively. The tester was programmed to reduce the stent diameter from unconstrained to predetermined 5 mm and recommended diameter of each stents (1 mm compression) at center or 10 mm from the edge, then gradually and simultaneously fully expanded at 0.5 mm/s (Figure 1). Testing was performed in a booth maintained at a temperature of
Figure 1. Schematic drawing of deformation characteristics of a 10-mm-diameter stent during a loading/unloading cycle. A Starting point, B the stent is loaded, C the stent is loaded to 2 mm stenosis, D the stent is then unloaded, E nominal outer diameter.
Downloaded from vas.sagepub.com at University of Otago Library on July 26, 2015
XML Template (2015) [2.6.2015–11:20am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/VASJ/Vol00000/150042/APPFile/SG-VASJ150042.3d
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37 2 C. Measurements were collected in triplicate for each stent. The following equation was used to calculate the radial force of stents RF ¼ 2 HF=L
ð1Þ
where RF ¼ radial force (N/mm), HF ¼ Hoop Force (N) and L ¼ stent length (mm). To analyze thoracic stents, we used MylarÕ (DuPont, Wilmington, DE, USA) film-testing method for radial force measurement, as previously described.12 In this study, polytetrafluoroethylene (PTFE) film was used instead of Mylar film. Three types of thoracic stents were fully deployed and set into the apparatus. The film was displaced to reduce the thoracic stent diameter from unconstrained to 12 mm or 4 mm (recommended diameter), then return until fully expand at 0.5 mm/s. Testing was performed in a water bath maintained at a constant temperature of 37 2 C. Measurements were collected in triplicate for each stent.
Statistical analysis Data were presented as mean standard deviation. The effects of stent position, number, and type of stent on radial force were assessed using three-way analysis of variance. All analyses were performed using JMPÕ , Version 9.0 (SAS Institute Inc., Cary, NC, USA). P values
