Which DES is the most appropriate for very small target vessels? Experimental study of stent expandable performance with SES, PES, ZES and EES

The restenosis rate of coronary stent has significantly decreased by implantation of the drug-eluting stent (DES). We often experienced the DES implantation for very small target vessels. The minimum size of DES in Japan and USA is 2.5 mm-diameter, but there were no reports of the expandability of DESs for the very small target vessels with reference diameter <2.2 mm. We clarify the expandable performance of 2.5 mm-DESs for very small target vessels with reference diameter <2.2 mm in vitro and vivo study. We studied 3 pieces in each kind of DES (Sirolimus-eluting stent; SES, Paclitaxel-eluting stent; PES, Zotarolimus-eluting stent; ZES and Everolimus-eluting stent; EES) in vitro and vivo study of the porcine coronary artery with reference diameter <2.2 mm. By using the delivery balloon, each stent was initially dilated with 3.5 atm. And the pressure of 0.5 atm. was applied until it reached the maximum pressure of 12 atm. The minimum pressure of the full expanded stent balloon was estimated as the minimum expandable pressure. The stent-inner diameter and area on each pressure were measured by IVUS. The average minimum expandable pressure (atm.) in vitro/vivo was 4.7/4.5 in SES, 7.2/6.8 in PES, 4.3/4.5 in ZES and 3.8/3.8 in EES. The inner diameter (mm) in vitro/vivo at minimum expandable pressure was 1.81 ± 0.07/1.84 ± 0.05 in SES, 2.31 ± 0.10/2.13 ± 0.13 in PES, 2.41 ± 0.13/1.98 ± 0.31 in ZES and 2.13 ± 0.11/1.88 ± 0.22 in EES. The stent inner-diameter (mm) of DESs at 8 atm. in vivo was 2.16/2.21/2.45/2.25 in SES/PES/ZES/EES. All kinds of DES could be delivered to very small target vessels with reference diameter <2.2 mm at the minimum expandable pressure in vivo study, but the stent which presented adequate stent inner-diameter at 8 atm. was only SES. We have to implant the 2.5 mm-DESs for very small target vessels according to the data based on this expandability of DESs to bail out threatening occlusion due to coronary dissection or elastic recoil.