Number of Stent Connectors Could Explain Longitudinal Weakness

It may be the number of connectors in a stent that determines whether or not it is more susceptible to longitudinal compression, according to a new study.

Researchers at Mercy Ascot Hospital (Auckland, New Zealand) conducted a bench analysis of seven different stents, which involved the compression of the stents by 5 mm. The researchers found that the least amount of force was required to compress the Omega (Boston Scientific) and Driver (Medtronic) stents, each requiring 0.40 N and 0.71 N of force, respectively. The Integrity (Medtronic), Liberté (Boston Scientific), Vision (Abbott Vascular), and MultiLink (Abbott Vascular) stents all required significantly more force to compress 5 mm, when compared with the Omega stent. The soon-to-be-discontinued Cypher stent (Cordis; Bridgewater Township, NJ, USA) was the hardest to compress, requiring 1.33 N. Conversely, 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 by 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. The researchers suggest that a stent design change ensuring three connectors, especially at the proximal end of a stent, should increase longitudinal integrity, but perhaps at the expense of stent flexibility. The study was published in the December 2011 issue of Cardiovascular Interventions.

“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,” concluded lead author John Ormiston, MBChB, and colleagues. “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.”
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Stent compression is a potentially devastating phenomenon that can result in major adverse cardiac events. Some of the newer stents, in search of improved flexibility, might have compromised their longitudinal strength, compressing along their longitudinal axis, thus causing folding, wrinkling, bunching together of rings, or other forms of deformation. The use of the postdilating balloon, intravenous ultrasound (IVUS) catheter, guide catheters, or thrombectomy catheters could cause longitudinal compression.

Related Links:
Mercy Ascot Hospital
Cordis