Calcified plaque rupture and very late stent thrombosis after bare-metal stent implantation

Very late stent thrombosis (>1 year: VLST) is a major concern in the drug-eluting stent (DES) era. VLST occurs not only in patients implanted with DESs but also in those implanted with bare-metal stents (BMSs). We examined intravascular ultrasound (IVUS) findings in patients with VLST after BMS implantation. Five consecutive patients presented with VLST as ST elevation myocardial infarction. VLST occurred at a mean of 9.5 years after BMS implantation. In the IVUS findings, the minimum stent area was 7.8 ± 1.2 mm². None of the patients had incomplete stent apposition or stent underexpansion, which was defined as a stent expansion index of <0.8. The mean stent expansion index was 1.01. Calcium deposits in the previous stented segment were observed in 4 patients (80%), and a total of 14 calcium deposits were observed in all patients. The calcification pattern was superficial (78.5%) and spotty (57.1%) within a calcium arc of <90°. The mean calcium arc was 72.5° ± 88.5°. A ruptured plaque with an intraluminal flap was detected in all cases. According to the IVUS findings of ruptured plaque and calcium deposits, VLST after BMS might be caused by a thrombus formation subsequent to a calcified atherosclerotic plaque rupture.