Background: Very late stent thrombosis (VLST) after drug-eluting stent (DES) implantation emerges as the hottest issue in DES ear, because the optimal duration and combination of antiplatelet therapy to prevent VLST have not been established yet. Some lesson may come from the long-term follow-up results of intracoronary radiation therapy. Methods: From SPARE trial, which was a prospective randomized trial to evaluate the efficacy of intracoronary radiation therapy, we selected 103 patients treated with new bare-metal stents (BMS) during the index procedure (radiation group: n=51, control group: n=52). Radiation was performed using 188Re-DTPA-filled balloon system and the dose into 1.0mm depth of the vessel wall was 17.6Gy. Following radiation, all patients received dual antiplatelet therapy at least for 1 month. We analyzed VLST-free survival and incidence of VLST according to combination of antiplatelet therapy. Results: Mean duration of observation was 5.3±2.2 years for radiation group and 5.4±2.5 years for control group. Five cases of definite/probable VLST by ARC definition were documented in the radiation group, ranging from 1.6 year to 6.7 year but no case was documented in control group. Among 5 cases of VLST, one case occurred during no antiplatelet therapy, one during the use of aspirin alone, one during the use of clopidogrel alone, and two during the use of aspirin plus cilostazol combination but no case occurred during the use of aspirin plus thienopyridine combination. VLST-free survival distribution was significantly different between the two groups (p=0.02) despite much longer use of multiple antiplatelets in the radiation group. Conclusions: Intracoronary radiation therapy on new BMS was associated with higher VLST risk which persisted at least 6.7 years. Aspirin plus thienopyridine combination was more effective than any other single or other combinations, suggesting that aspirin plus clopidogrel combination should be given indefinitely to these patients. These lessons may also be applied to the patients with DES implantation.
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