Author + information
- Hao-Ming Hsiao, PhD⁎ ()
- ↵⁎National Taiwan University, Department of Mechanical Engineering, Roosevelt Road, No.1, Sec.4, Taipei, 10617, Taiwan
Interventional cardiologists at TCT 2011 debated over an emerging clinical issue called longitudinal stent compression (LSC), a new failure mode not previously observed and reported in coronary stents. This phenomenon occurs when the clinician attempts to cross the deployed stent with other devices, such as dilation balloons or intravascular ultrasound catheters, causing the stent to dramatically shorten when the 2 devices are accidentally entangled (1–4). The perspective of Ormiston et al., “Stent Longitudinal Integrity: Bench Insights Into a Clinical Problem,” (5) provided an excellent longitudinal compression analysis by comparing 7 contemporary drug-eluting stents. Results demonstrated that the new Omega/Element stents (Boston Scientific, Natick, Massachusetts) were the least resistant to longitudinal compression, whereas the Cypher Select stents (Cordis, Miami, Florida) were the most resistant.
The Omega/Element stent is not a new design. In fact, its design pattern is very similar to several old stent platforms being used extensively in the current peripheral market, such as Smart (Cordis) for superficial femoral artery indications and Precise (Cordis) for carotid indications. In addition, Boston Scientific also had an old coronary stent called Radius (approved by the Food and Drug Administration in 1998) that looks very similar to the Omega/Element. This type of stent can be classified as the so-called “offset peak-to-peak” stent family (4), and Omega/Element represents the only major coronary stent belonging to this family. From an engineering standpoint, it is not difficult to understand why this stent family is the least resistant to longitudinal compression: its offset peak-to-peak design allows the crowns to travel longitudinally with higher degrees of freedom, whereas the crown movement of other stent families is significantly limited by the presence of long connectors (peak-to-valley family) or neighboring crowns (peak-to-peak family). Although the Radius stent may be considered obsolete in coronary indications, the Smart stent and the Precise stent are still heavily used today for the treatment of peripheral artery diseases . Therefore, if longitudinal stent compression is an important clinical issue, why has such a failure mode never been observed and reported previously with Smart and Precise? The key factor may lie in the basic materials chosen for making these stents.
The Omega/Element stent is made of platinum–chromium (Pt–Cr) material that could undergo large plastic deformation, whereas the Smart/Precise/Radius stent is made of nickel–titanium (Ni–Ti) material that exhibits superelastic properties. It is likely that the Smart/Precise stent may encounter similar LSC issues clinically during procedures; however, Ni–Ti stents are able to fully recover back to their original shapes or lengths even if such a phenomenon occurs. By contrast, Pt–Cr stents are not able to recover due to their material nature and may suffer permanent deformations if the stent design with lower longitudinal compression integrity happens to trigger the LSC issue. Therefore, we are perhaps witnessing an interesting story: an unexpected new clinical issue with an old stent design simply by changing its constitutive material.
- American College of Cardiology Foundation