Abstract 15562: Impact of Off-time Presentation on the Vulnerability of the Culprit Lesions in ST-elevation Acute Myocardial Infarction

Background: ST-elevation myocardial infarction (STEMI) that occurs during the off hours shows worse clinical status compared to the patients presenting during working hours. Method: We used Virtual Histology Intravascular Ultrasound (VH-IVUS) to assess the complexity of culprit lesion in 193 patients with STEMI. The patients were divided into two groups that presented to the hospital during the working hours (from 8:30 am to 6:00 pm) and the off hours (from 6:00 pm to 8:30 am of the next day). VH-TCFA (thin-capped fibroatheroma) was defined as necrotic core (NC) >10% of plaque area with a plaque burden of >40% and NC in contact with the lumen for ≥3 image slices. Positive remodeling was a remodeling index (lesion/reference EEM [external elastic membrane] area) >1.05. Result: 91(46.0%) pts were visited during working hours, and 102(54.0%) pts during the off hours. Pt age was 60±13 yr in working hour STEMI and off hour STEMI was 61±10 yr. The lesion length, vessel size and minimal lumen area (MLA) were similar. The average and maximum necrotic core area of the off hours STEMI were larger than the working hours STEMI(p=0.025 and p=0.005 respectively). The remodeling index at maximum necrotic core site was also higher in the off hours STEMI than the working hours group respectively (p=0.042). Positive remodeling was 42.9%(39/91) in working hour STEMI and 59.8%(61/102) in off hour STEMI (p=0.028). However, the frequency of TCFA was similar in both group(25.7% vs 26.6%, p=0.123). Conclusion: The culprit lesions of Off-hour STEMI may more vulnerable compared to STEMI occuring during the working hours.