Ning Guo1; Akiko Maehara1; Gary S Mintz1; Alexandra J Lansky1; Bernhard Witzenbichler2; Giulio Guagliumi3; Bruce  Brodie4; Mirle A Kellett， Jr.5; Helen Parise6; Roxana Mehran6; Gregg W Stone6
    1 Columbia Univ Med Cntr and the Cardiovascular Rsch Foundation， New York， NY
    2 Charitë Univ Medicine Campus Benjamin Franklin， Berlin， Germany
    3 Ospedali Riuniti di Bergamo， Bergamo， Italy
    4 LeBauer CV Rsch Foundation/Moses Cone Hosp， Greensboro， NC
    5 Maine Med Cntr， Portland， ME
    6 Columbia Univ Med Cntr and the Cardiovascular Rsch Foundation， New York， NY
    Background. The determinants of the magnitude of late stent malapposition (LSM) in pts with acute ST-segment elevation myocardial infarction (STEMI) treated with stent implantation.
    Methods. HORIZONS-AMI was a prospective， dual-arm， factorial， trial in which pts with STEMI were randomized to
1. unfractionated heparin + GPIIb/IIIa inhibition vs bivalirudin (1:1); and
2. paclitaxel-eluting TAXUS stents (PES) vs bare metal EXPRESS stents (BMS) (3:1).
A formal IVUS substudy enrolled 241 pts with 263 native coronary lesions (201 PES and 62 BMS) in whom baseline and 13-month follow-up imaging was completed and analyzed at a blinded core laboratory.
    Results. Post-intervention stent malapposition (ASM) occurred in 33.8% PES and 38.7% BMS-treated lesions (P =0.73)， and persisted at 13 month follow-up in 20.4% PES and 24.2% BMS lesions (p =0.85). At follow-up， a higher frequency of late stent malapposition (LSM) was detected in PES compared to BMS treated lesions (46.3% vs. 29.0%， P =0.001)) mainly due to more late acquired stent malapposition (LASM， 30.8% vs. 8.1%， p =0.001). There was a strong interaction among persistent ASM， LSM， and positive remodeling (late increase in EEM， Figure). LSM area of >3.0mm2 indicated either persistent ASM or LASM with positive modeling， and was not due to thrombus dissolution. The occurrence of LASM was associated with less neointima at 13 month follow-up compared to pts without LASM (3.2% [1.4%， 8.5%] vs 9.0% [4.7%， 17.1%]， p<0.001).
    Conclusions. Large LSM areas either persist after stent implantation or are due to positive remodeling (more commonly with PES than BMS)， whereas small areas of LSM are often due to baseline thrombus dissolution.