Impact of Co-Axial Placement of Balloon-Expandable and Self-Expanding Stent on Crush Resistance in Vitro

During venous interventions, coaxial deployment of different types of stents may be required to preserve luminal gain.  We characterized the impact on crush resistance and post-compression stent diameter recovery when balloon-expandable (BE) and self-expanding (SE) stents are deployed coaxially.

Materials and Methods:

Crush resistance of BE and SE, in combination and separately, was investigated using a 14 x 80 mm self-expanding nitinol stent (Venovo, Bard, Temp, AZ) and a 10 x 40 mm BE stent (Palmaz 4010; Cordis/Johnson & Johnson Endovascular, Warren, NJ). Four configurations were tested: a) SE alone; b) BE dilated to 14 mm alone; c) SE inside BE dilated to 14 mm; d) BE inside SE dilated to 14 mm. A universal testing machine (Criterion MTS, Model 42, Eden Prairie, MN) equipped with a 100 N load cell and parallel plates was used to measure crush resistance in a water bath at 37 ± 1℃. The stent configurations were compressed from a fully expanded state to 7 mm, representing 50% diameter reduction in that single direction, at a speed of 6 mm/minute. Stent outer diameter after release of compression was recorded. Six compression cycles were performed for each stent configuration.

Results:

Coaxial deployment in both configurations (SE inside BE and BE inside SE) demonstrated significantly higher crush resistances compared to each stent individually or simple mathematical summation. At 50% diameter reduction SE inside BE exhibited a crush resistance of 11.33 ± 0.25 N/cm, similar to BE inside SE at 11.24 ± 0.17 N/cm (p > 0.05). Both were significantly higher compared to 8.96 ± 0.12 N/cm and 1.30 ± 0.01 N/cm for BE alone and SE alone, respectively (ANOVA p < 0.0001, pairwise comparison p-values < 0.01). Compared to the configuration of BE inside SE, the configuration of SE inside BE showed lower initial rise in crush resistance per amount of compression (26.95 ± 0.01 N/cm² vs. 31.30 ± 0.01 N/cm², p < 0.0001) but significantly higher post-compression diameter recovery (48.7 ± 1.9% vs. 31.8 ± 0.7%, percent recovery compared to stent outer diameter at 50% diameter reduction, p = 0.0001).

Conclusion:

Coaxial deployment of a self-expanding stent inside a balloon-expandable stent is the optimal configuration for maximal crush resistance and post-compression luminal recovery using currently available stents.