Longitudinal Strength Differs Between Stents
Longitudinal Strength Differs Between Stents
November 30, 2011 (Rochester, Minnesota)— A new bench study attempting to address the issue of stent longitudinal integrity suggests that stents with just two connectors, which are used to hold the hoops of the coronary stent together, have less longitudinal strength than stents that use more connectors [1].
The independent study, which assessed the force required to compress and elongate seven contemporary stents, showed that the Element and Omega (Boston Scientific) coronary stents, as well as the Driver (Medtronic) stent, required significantly less force to be compressed 5 mm and elongated 1 mm when compared with stents that had more connectors, such as the now-defunct CypherSelect (Cordis/Johnson & Johnson) stent. Dr John Ormiston (Mercy Angiography, Auckland, New Zealand), along with colleagues Drs Bruce Webber and Mark Webster (Mercy Angiography), published the data in the December 2011 issue of the Journal of the American College of Cardiology: Cardiovascular Interventions and previously presented their findings at TCT 2011 in San Francisco, CA.
"This study sheds light on the increasingly recognized clinical problem of disruption of stent longitudinal integrity leading to distortion that can be marked," write the authors. "There were significant differences between seven contemporary stent designs subjected to a standardized compression or elongation force. Those stents with only two connectors, the Element and the Driver, were more likely to distort under longitudinal loads than those with three or more connectors."
Now-Defunct Cypher Held Up Best
As reported previously by heartwire, the issue of stent compression, a rare but potentially devastating phenomenon that can result in major adverse cardiac events, has gained traction with the interventional community. The concern is that in the pursuit of deliverability and flexibility, some of the newer stents might have compromised longitudinal strength, with the devices compressing along their longitudinal axis, a phenomenon that has been described as a concertina or accordion effect--folding, wrinkling, pushed or bunched together rings--or deformation. It is believed that the use of the postdilating balloon, intravenous ultrasound (IVUS) catheter, guide catheters, or thrombectomy catheters, among others, can cause longitudinal compression.
In their bench analysis of seven different stents, which involved the compression of the stents 5 mm, the least amount of force was required for the Omega and Driver stents, each requiring 0.40 N and 0.71 N of force, respectively. The Cypher stent required 1.33 N of force to compress 5 mm, a significant difference compared with the Omega and Driver stents. The Integrity (Medtronic), Liberté (Boston Scientific), Vision (Abbott Vascular), and MultiLink (Abbott Vascular) stents all required significantly more force to compress 5 mm compared with the Omega stent. When 0.5 N of force was applied to the Cypher stent it did not shorten, while little shortening was observed with the Vision and MultiLink stents, and the most distortion with the Driver and Omega stents.
When the researchers applied force to elongate the stents 1 mm, the Omega and Driver stents were more easily deformed, while the force needed to elongate the Liberté and Integrity stents was similar and significantly greater than the force needed to alter the structure of the Driver stent. All the stents were equivalent in terms of the amount of force needed to stretch the stent a full 5 mm, with exception of the Cypher stent, which required significantly more force.
"Stent deliverability, strongly influenced by flexibility, is the property that cardiologists desire most, and designs that have high longitudinal integrity may not have high flexibility and deliverability," write Ormiston, Webber, and Webster. "We show that the earlier-generation Cypher Select, a six-connector design, had the greatest resistance to longitudinal distorting forces. This stent is no longer widely used because other designs have better flexibility, deliverability, crossing profile, radiopacity, side-branch access, and freedom from strut fracture."
The alignment of the connectors along the longitudinal axis also appears to be important for stent integrity, add the investigators. If longitudinal distortion of the stent is observed, Ormiston and colleagues say that careful postdilation should be considered, and in situations where distortion is more likely, such as ostial locations, "the interventional cardiologist may choose to select a stent with higher longitudinal strength."
November 30, 2011 (Rochester, Minnesota)— A new bench study attempting to address the issue of stent longitudinal integrity suggests that stents with just two connectors, which are used to hold the hoops of the coronary stent together, have less longitudinal strength than stents that use more connectors [1].
The independent study, which assessed the force required to compress and elongate seven contemporary stents, showed that the Element and Omega (Boston Scientific) coronary stents, as well as the Driver (Medtronic) stent, required significantly less force to be compressed 5 mm and elongated 1 mm when compared with stents that had more connectors, such as the now-defunct CypherSelect (Cordis/Johnson & Johnson) stent. Dr John Ormiston (Mercy Angiography, Auckland, New Zealand), along with colleagues Drs Bruce Webber and Mark Webster (Mercy Angiography), published the data in the December 2011 issue of the Journal of the American College of Cardiology: Cardiovascular Interventions and previously presented their findings at TCT 2011 in San Francisco, CA.
"This study sheds light on the increasingly recognized clinical problem of disruption of stent longitudinal integrity leading to distortion that can be marked," write the authors. "There were significant differences between seven contemporary stent designs subjected to a standardized compression or elongation force. Those stents with only two connectors, the Element and the Driver, were more likely to distort under longitudinal loads than those with three or more connectors."
Now-Defunct Cypher Held Up Best
As reported previously by heartwire, the issue of stent compression, a rare but potentially devastating phenomenon that can result in major adverse cardiac events, has gained traction with the interventional community. The concern is that in the pursuit of deliverability and flexibility, some of the newer stents might have compromised longitudinal strength, with the devices compressing along their longitudinal axis, a phenomenon that has been described as a concertina or accordion effect--folding, wrinkling, pushed or bunched together rings--or deformation. It is believed that the use of the postdilating balloon, intravenous ultrasound (IVUS) catheter, guide catheters, or thrombectomy catheters, among others, can cause longitudinal compression.
In their bench analysis of seven different stents, which involved the compression of the stents 5 mm, the least amount of force was required for the Omega and Driver stents, each requiring 0.40 N and 0.71 N of force, respectively. The Cypher stent required 1.33 N of force to compress 5 mm, a significant difference compared with the Omega and Driver stents. The Integrity (Medtronic), Liberté (Boston Scientific), Vision (Abbott Vascular), and MultiLink (Abbott Vascular) stents all required significantly more force to compress 5 mm compared with the Omega stent. When 0.5 N of force was applied to the Cypher stent it did not shorten, while little shortening was observed with the Vision and MultiLink stents, and the most distortion with the Driver and Omega stents.
When the researchers applied force to elongate the stents 1 mm, the Omega and Driver stents were more easily deformed, while the force needed to elongate the Liberté and Integrity stents was similar and significantly greater than the force needed to alter the structure of the Driver stent. All the stents were equivalent in terms of the amount of force needed to stretch the stent a full 5 mm, with exception of the Cypher stent, which required significantly more force.
"Stent deliverability, strongly influenced by flexibility, is the property that cardiologists desire most, and designs that have high longitudinal integrity may not have high flexibility and deliverability," write Ormiston, Webber, and Webster. "We show that the earlier-generation Cypher Select, a six-connector design, had the greatest resistance to longitudinal distorting forces. This stent is no longer widely used because other designs have better flexibility, deliverability, crossing profile, radiopacity, side-branch access, and freedom from strut fracture."
The alignment of the connectors along the longitudinal axis also appears to be important for stent integrity, add the investigators. If longitudinal distortion of the stent is observed, Ormiston and colleagues say that careful postdilation should be considered, and in situations where distortion is more likely, such as ostial locations, "the interventional cardiologist may choose to select a stent with higher longitudinal strength."
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