Damage to Polymer of a Sirolimus-Eluting Stent
A 75-year-old man with a history of bare-metal stent implantation in the right coronary artery was admitted for unstable angina. Coronary angiography revealed in-stent restenoses of 90% severity in the mid-right coronary artery and the right posterolateral coronary artery (Figure 1A). Attempts to pass a 33-mm sirolimus-eluting stent (Cypher, Cordis, a Johnson & Johnson Company, Miami Lakes, Fla) premounted on a 3.0-mm balloon catheter after predilatation with a 3.0-mm balloon catheter inflated at 16 atm were initially unsuccessful. Additional predilatation and insertion of another guide wire made sirolimus-eluting stent delivery successful. It was then deployed at 18 atm (Figure 1B). An attempt was made to deliver an 18-mm sirolimus-eluting stent premounted on a 2.5-mm balloon catheter into the right posterolateral coronary artery. It would not cross the segment of the sirolimus-eluting stent in the mid-right coronary artery, however. Balloon angioplasty using a 2.5-mm balloon catheter inflated at 16 atm was performed in the right posterolateral coronary artery. The final angiogram showed 25% stenoses in the mid-right coronary artery and the right posterolateral coronary artery (Figure 1C). The undelivered sirolimus-eluting stent was examined using a scanning electron microscope, and the examination demonstrated damage to the polymer of the sirolimus-eluting stent (Figure 2A and 2B).
The sirolimus-eluting stent consists of 3 components: a metallic stent, sirolimus as an antiproliferative agent to inhibit neointimal formation, and a polymer as a drug-carrier vehicle that permits elution of sirolimus into the vessel wall at the required concentration and kinetic profile. Damage to the sirolimus-eluting stent polymer might occur when the sirolimus-eluting stent is delivered through a calcified lesion as well as the segment of a newly deployed stent. It theoretically results in uncontrolled or unsatisfactory sirolimus elution, which might fail to prevent restenosis.