Dynamic nature of nonculprit coronary artery lesion morphology in STEMI: a serial IVUS analysis from the HORIZONS-AMI trial.

OBJECTIVES: The authors sought to report the temporal stability of an untreated, nonculprit lesion phenotype in patients presenting with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND: The temporal stability of the untreated, nonculprit lesion phenotype has been studied using intravascular ultrasound-virtual histology (IVUS) in patients with stable ischemic heart disease, but not in STEMI patients.

METHODS: As part of a formal substudy of the HORIZONS-AMI (Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction) trial, baseline and 13-month follow-up IVUS was performed in 99 untreated nonculprit lesions in 63 STEMI patients. Lesions were classified as pathological intimal thickening (PIT), IVUS-derived thin-cap fibroatheroma (TCFA), thick-cap fibroatheroma (ThCFA), fibrotic plaque, or fibrocalcific plaque.

RESULTS: The frequency of TCFA increased from 41% at baseline to 54% at follow-up, whereas ThCFAs decreased from 41% to 34% and PIT decreased from 16% to 8%. Among the 41 lesions classified at baseline as TCFA, at follow-up, 32 (78%) were still classified as TCFA, whereas 9 (22%) were classified as ThCFAs or fibrotic plaques. An additional 21 lesions at follow-up were newly classified as TCFA, developing from either PIT or ThCFA. TCFA at baseline that evolved into non-TCFAs trended toward a more distal location than TCFA that did not change (p = 0.12). In lesions classified as TCFA, the minimum lumen area (MLA) decreased from 8.1 (interquartile range [IQR]: 7.4 to 8.8) mm(2) at baseline to 7.8 (IQR: 7.2 to 8.4) mm(2) at follow-up, p < 0.05; this was associated with an increase in percent necrotic core at the MLA site (14% [IQR: 12 to 16] to 19% [IQR: 17 to 22], p < 0.0001) and over the entire length of the lesion (14% [IQR: 12 to 16] to 18% [IQR: 17 to 20], p < 0.0001).

CONCLUSIONS: Untreated nonculprit lesions in STEMI patients frequently have TCFA morphology that does not change during 13-month follow-up and is accompanied by a decrease in MLA and an increase in necrotic core. (Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction [HORIZONS-AMI]; NCT00433966).