Engineering assessment of the longitudinal compression behaviour of contemporary coronary stents

There have been recently reported clinical observations of significant longitudinal compression or "stent shortening" in certain contemporary drug-eluting stents (DES), when re-crossed with other devices such as post-dilatation balloons, stent delivery systems or intravascular ultrasound (IVUS) catheters. The aim of this study was to understand the effect of stent design on longitudinal compression for coronary stents, when subjected to certain forces in vitro. This goal was achieved by experimentally evaluating the longitudinal strength of 14 contemporary stent designs under a clinically relevant compression force using a bench test method developed for this purpose. The results from the study are intended to provide an indication whether there is a quantifiable difference in the ability of the different stent platform designs to resist longitudinal compression in a deployed configuration.

A test method was developed to evaluate the longitudinal compression behaviour of coronary stents. The test method was used to compare the longitudinal compression of four stent design families including a total of 14 commercialised stent platforms under a clinically relevant longitudinal compression force. The nominal expansion diameter of stents used in this study was 3.0 mm with stent lengths ranging from 28-30 mm. A test method was also developed to estimate a value of the clinically relevant longitudinal compression force to which a deployed stent may be subjected in a situation when a catheter tip is caught while trying to cross a freshly deployed stent. That force was determined to be 50 gram force (gf) (0.49 N). Based on the results of the testing it was noted that three of the four design families (13 of the 14 stents tested) demonstrated a longitudinal compression in the range of 1.25-5.30 mm (longitudinal compression of 4.46%-18.93% compared to the nominal expanded stent length), with the exception of the offset peak-to-peak stent platform having results clearly outside of this grouping. The stent in the offset peak-to-peak design category (Element stent platform) had an average longitudinal compression of 13.20 mm (longitudinal compression of 47.07%), thus demonstrating a markedly lower resistance to longitudinal compression.

Stent design is a primary driver determining the longitudinal compression behaviour of coronary stent platforms. The results of this study comparing the longitudinal compression performance of four different commercial stent design families indicate that the tendency of a deployed stent to undergo longitudinal compression is associated with the stent design concept. It was determined that the particular 2-link offset peak-to-peak design evaluated in this study had the lowest compression resistance compared to the other stent design families.