Incidence, Mechanisms, Predictors, and Clinical Impact of Acute and Late Stent Malapposition After Primary Intervention in Patients With Acute Myocardial Infarction An Intravascular Ultrasound Substudy of the Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction (HORIZONS-AMI) Trial

Background-The incidence and mechanisms of acute and late stent malapposition after primary stent implantation in ST-segment elevation myocardial infarction remain unclear. Methods and Results-The Harmonizing Outcomes with Revascularization and Stents in Acute Myocardial Infarction (HORIZONS-AMI) trial was a dual-arm, factorial, randomized trial comparing paclitaxel-eluting stents (PES) and otherwise equivalent bare metal stents (BMS) in ST-segment elevation myocardial infarction patients. The intravascular ultrasound substudy enrolled 241 patients with 263 native coronary lesions (201 PES, 62 BMS) with baseline and 13-month follow-up imaging. Postintervention acute stent malapposition (ASM) occurred in 34.3% PES-and 40.3% BMS-treated lesions. Of these, 39.1% PES-and 40.0% BMS-treated lesions resolved at follow-up, especially within the stent body (66.7%); complete resolution was accompanied by a reduction in external elastic membrane area. An ASM area > 1.2 mm(2) best separated persistent from resolved ASM. At follow-up, a higher frequency of late stent malapposition was detected in PES-treated lesions (46.8%) mainly because of more late acquired stent malapposition (30.8%) compared with BMS-treated lesions. Late acquired stent malapposition area correlated to the decrease of peri-stent plaque in the subset of lesions without positive remodeling and only to change in external elastic membrane in the group with positive remodeling. Independent predictors of late acquired stent malapposition were plaque/thrombus protrusion (odds ratio, 5.60; 95% confidence interval [CI], 2.32 to 13.54) and PES use (odds ratio, 6.32; 95% CI, 2.15 to 18.62). Conclusions-The incidence of ASM was similar in PES-and BMS-treated lesions, but late acquired stent malapposition was more common in PES-treated lesions. The reason for resolved ASM was negative remodeling, with larger ASM areas separating persistent from resolved ASM. Late acquired stent malapposition was due mainly to positive remodeling and plaque/thrombus resolution.