Morphological changes and clinical impact of unstable plaques within untreated segments of acute myocardial infarction patients during a 3-year follow-up: an analysis from the HORIZONS-AMI trial.

OBJECTIVES:Plaque ruptures and attenuated plaques are considered to be unstable and have been identified in both culprit and nonculprit lesions of patients with ST-segment elevation myocardial infarction (STEMI). However, there are limited data available on the natural evolution of these plaques and their long-term clinical outcome. We investigated the natural evolution and long-term impact of plaque ruptures and attenuated plaques in untreated segments of infarct-related arteries in patients with STEMI. METHODS:In the Harmonizing Outcomes with Revascularization and Stents in Acute Myocardial Infarction trial, 389 patients with 429 lesions underwent intravascular ultrasound (IVUS) at baseline. Follow-up IVUS at 13 months was conducted in 245 patients. Three-year follow-up data were available for all patients. RESULTS:Segments not treated between baseline and follow-up were compared. Baseline IVUS identified 29 plaque ruptures in 27 patients (7%). Of 11 plaque ruptures with follow-up IVUS, four healed and seven persisted. Conversely, through follow-up IVUS, nine new plaque ruptures in nine patients (4%) were identified. Attenuated plaques were identified in 31 of 38 plaque ruptures (81.5%), of which 24 were in the same circumferential segment as the ruptured cavity and seven were within 5 mm proximal or distal to the plaque rupture. Morphologic changes during follow-up, including new plaque ruptures and changes in the attenuated plaque frequency and distribution, were not accompanied by either serious lumen compromise or clinical events. CONCLUSION:Serial IVUS analysis demonstrated that the morphology of unstable plaques within untreated segments in STEMI patients treated with optimal systemic therapies markedly changed during the 13-month follow-up period, without lumen compromise or clinical events at the 3-year follow-up.