Author + information
- Received September 21, 2011
- Revision received November 6, 2011
- Accepted November 7, 2011
- Published online December 1, 2011.
- John A. Ormiston, MBChB⁎ (, )
- Bruce Webber, MHSc and
- Mark W.I. Webster, MBChB
- ↵⁎Reprint requests and correspondence:
Dr. John A. Ormiston, Mercy Angiography, P.O. Box 9911, Newmarket 1023, Auckland, New Zealand
Objectives Standardized bench-top compression and elongation testing was undertaken to assess the longitudinal strength of contemporary stents. Insights gained may improve clinical stent choice and deployment techniques, and facilitate future stent design improvements.
Background The hoops of coronary stents provide radial support, and connectors hold hoops together. Strut material, shape, and thickness, along with connector number and configuration, provide the balance between stent flexibility and longitudinal integrity. Longitudinal distortion manifests as length change, strut overlap, strut separation, malapposition, and luminal obstruction. These may predispose to restenosis and stent thrombosis, obstruct passage of devices, be misinterpreted as strut fracture, and require additional stenting.
Methods The force required to compress and to elongate 7 contemporary stents was measured with an Instron universal testing machine (Norwood, Massachusetts). Stents deployed in a silicone phantom damaged by a balloon or guide catheter were imaged by microcomputed tomography to understand better the appearances and effects of longitudinal distortion.
Results Stents with 2 connectors (Boston Scientific [Natick, Massachusetts] Omega and Medtronic [Santa Rosa, California] Driver) required significantly less force to be compressed up to 5 mm and elongated by 1 mm than designs with more connectors. The 6-connector Cypher Select required significantly more force to be elongated 5 mm than other designs.
Conclusions Stents with 2 connectors between hoops have less longitudinal strength when exposed to compressing or elongating forces than those with more connectors. This independent, standardized study may assist stent selection in clinical situations where longitudinal integrity is important, and may aid future design improvements.
Stent longitudinal strength, the resistance to shortening or elongation, appears related to the number of connectors between hoops. Using a standardized testing protocol, designs with 2 connectors were more likely to shorten or elongate than those with more connectors. Distortion may be recognized clinically as bunching or separation of struts, and may be confused with strut fracture. Without post-dilation or further stent deployment, the patient may be at increased risk for adverse clinical events. A stent design change ensuring 3 connectors, especially at the proximal end of a stent, should increase longitudinal integrity, but perhaps at the expense of stent flexibility.
Supported by the Auckland Heart Group Charitable Trust. Dr. Ormiston is an advisory board member for and has received minor honoraria from Abbott Vascular and Boston Scientific. Drs. Webber and Webster have reported that they have no relationship relevant to the contents of this paper to disclose.
- Received September 21, 2011.
- Revision received November 6, 2011.
- Accepted November 7, 2011.
- American College of Cardiology Foundation