Background— Stent thrombosis may occur late after drug-eluting stent (DES) implantation, and its cause remains unknown. The present study investigated differences of the stented segment between patients with and without very late stent thrombosis with the use of intravascular ultrasound. Methods and Results— Since January 2004, patients presenting with very late stent thrombosis (>1 year) after DES implantation underwent intravascular ultrasound. Findings in patients with very late stent thrombosis were compared with intravascular ultrasound routinely obtained 8 months after DES implantation in 144 control patients, who did not experience stent thrombosis for ≥2 years. Very late stent thrombosis was encountered in 13 patients at a mean of 630±166 days after DES implantation. Compared with DES controls, patients with very late stent thrombosis had longer lesions (23.9±16.0 versus 13.3±7.9 mm; P <0.001) and stents (34.6±22.4 versus 18.6±9.5 mm; P <0.001), more stents per lesion (1.6±0.9 versus 1.1±0.4; P <0.001), and stent overlap (39% versus 8%; P <0.001). Vessel cross-sectional area was similar for the reference segment (cross-sectional area of the external elastic membrane: 18.9±6.9 versus 20.4±7.2 mm 2 ; P =0.46) but significantly larger for the in-stent segment (28.6±11.9 versus 20.1±6.7 mm 2 ; P =0.03) in very late stent thrombosis patients compared with DES controls. Incomplete stent apposition was more frequent (77% versus 12%; P <0.001) and maximal incomplete stent apposition area was larger (8.3±7.5 versus 4.0±3.8 mm 2 ; P =0.03) in patients with very late stent thrombosis compared with controls. Conclusions— Incomplete stent apposition is highly prevalent in patients with very late stent thrombosis after DES implantation, suggesting a role in the pathogenesis of this adverse event.

Background-Intravascular ultrasound of drug-eluting stent (DES) thrombosis (ST) reveals a high incidence of incomplete stent apposition (ISA) and vessel remodeling. Autopsy specimens of DES ST show delayed healing and hypersensitivity reactions. The present study sought to correlate histopathology of thrombus aspirates with intravascular ultrasound findings in patients with very late DES ST. Methods and Results-The study population consisted of 54 patients (28 patients with very late DES ST and 26 controls).Of 28 patients with very late DES ST, 10 patients (1020Ϯ283 days after implantation) with 11 ST segments (5 sirolimus-eluting stents, 5 paclitaxel-eluting stents, 1 zotarolimus-eluting stent) underwent both thrombus aspiration and intravascular ultrasound investigation. ISA was present in 73% of cases with an ISA cross-sectional area of 6.2Ϯ2.4 mm 2 and evidence of vessel remodeling (index, 1.6Ϯ0.3). Histopathological analysis showed pieces of fresh thrombus with inflammatory cell infiltrates (DES, 263Ϯ149 white blood cells per high-power field) and eosinophils (DES, 20Ϯ24 eosinophils per high-power field; sirolimus-eluting stents, 34Ϯ28; paclitaxel-eluting stents, 6Ϯ6; P for sirolimus-eluting stents versus paclitaxel-eluting stentsϭ0.09). The mean number of eosinophils per high-power field was higher in specimens from very late DES ST (20Ϯ24) than in those from spontaneous acute myocardial infarction (7Ϯ10), early bare-metal stent ST (1Ϯ1), early DES ST (1Ϯ2), and late bare-metal stent ST (2Ϯ3; P from ANOVAϭ0.038). Eosinophil count correlated with ISA cross-sectional area, with an average increase of 5.4 eosinophils per high-power field per 1-mm 2 increase in ISA cross-sectional area. Conclusions-Very