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In vivo evaluation of stent strut distribution patterns in the bioabsorbable everolimus-eluting device: an OCT ad hoc analysis of the revision 1.0 and revision 1.1 stent design in the ABSORB clinical trial.

AIMS
The ABSORB Cohort A clinical study has shown the feasibility and safety of the fully bioabsorbable everolimus-eluting structure (BVS, revision 1.0). However, the study also demonstrated somewhat higher acute and late recoil with the BVS structure compared to metallic drug eluting stents. Based on these clinical observations, modifications to the stent design (BVS, revision 1.1) were introduced for the ABSORB Cohort B study in order to decrease recoil. The aim was to compare in vivo the strut distribution between the BVS revision 1.0 (Cohort A), and BVS revision 1.1 (Cohort B) designs.


METHODS AND RESULTS
OCT analysis was performed by two independent analysts in four patients from each cohort of the ABSORB study. Strut distribution was assessed in cross-section, and longitudinally in a frameby-frame analysis. Variables recorded included inter-strut angle, maximum inter-strut angle and number of frames with < or =3 struts. The inter-observer correlation coefficient was also assessed. For both designs, on a patient level there was no significant difference in the number of analysed struts corrected for the length of the scaffold (p=0.78). Likewise, on a frame by frame analysis mean stent area, number of struts per frame, mean maximum inter-strut angle, and mean inter-strut angle were similar for both groups. However, in both structures there was a cyclical variation in the maximum number of struts per frame. The frequency of this variation was significantly higher in Cohort B. The inter-observer correlation coefficient for strut counts, inter-strut angle and maximum inter-strut angle was 0.91, 0.87 and 0.74 respectively.


CONCLUSIONS
This ad hoc analysis confirms that the revision 1.1 BVS design has a different longitudinal strut distribution to the revision 1.0 BVS design, indicating that the new design has a reduced maximum circular unsupported cross sectional area.