Late Catch-up In-Stent Restenosis and Stent Thrombosis for 2nd Generation Biodegradable Polymer Drug Eluting Stents

Second generation drug-eluting stents (DES) have reduced the rate of in-stent restenosis (ISR) to < 10% [1, 2] in patients undergoing PCI. However, late catch-up in-stent restenosis remains an issue despite the advent in drug-eluting stent technology from 1st to 2nd generation drug eluting stents. The late catch-up phenomenon has been associated with serious consequences and adverse events and remains an important issue in modern practice, despite medical advances with more biocompatible and biodegradable polymers, as well as new therapeutic agents and thinner scaffolds in the development of 2nd generation DES polymer systems. The idea behind biodegradable polymers has been to provide a more controlled elution profile for DES drugs, allowing for long-term therapeutic, but sub-toxic, drug levels in the arterial tissue to prevent ISR and stent thrombosis. However, the late catch-up phenomenon remains an issue resulting in 2ndary revascularization beyond the first year of primary PCI, as it is defined as ISR >1 year. Late stent thrombosis (<1 year) and very late stent thrombosis (>1 year) also remain an issue for biodegradable polymer systems. A long-term presence of the polymer can cause inflammation and thrombogenesis, which is dependent upon polymer degradation kinetics in case of biodegradable polymer DES systems. However, the cause of late catch-up restenosis and stent thrombosis is multi-factorial from a drug-in-polymer formulation perspective of drug release kinetics, e.g., drug elution profile, drug physiochemical properties, and polymer degradation kinetics. It appears that the focus should be on controlling burst release for both late catch-up restenosis and stent thrombosis phenomena.