Impact of Atrial Fibrillation During ST-Segment–Elevation Myocardial Infarction on Infarct Characteristics and Prognosis

Background— Atrial fibrillation (AF) is frequently observed in patients with ST-segment–elevation myocardial infarction and associated with worse clinical outcome. However, the mechanisms for this increased risk are not fully understood. The purpose of this study was to investigate the relationship of the presence of AF to cardiac magnetic resonance (CMR) derived myocardial salvage and damage as well as clinical outcomes. Methods and Results— This multicenter CMR study enrolled 786 patients with ST-segment–elevation myocardial infarction. CMR parameters (infarct size, myocardial salvage index, microvascular obstruction, and myocardial function) were assessed 3 (interquartile range [IQR], 2–4) days post-ST-segment–elevation myocardial infarction and compared between patients with or without AF during hospitalization. Major adverse cardiac events were assessed as a composite of all-cause death, reinfarction, and new congestive heart failure at 12 months. AF was documented in 48 (6.1%) patients. There was no significant difference in infarct size (18 [IQR, 9–29]% versus 17 [IQR, 9–25]% of left ventricular mass; P =0.340), myocardial salvage index (51 [IQR, 34–69] versus 51 [IQR, 33–69]; P =0.830), or microvascular obstruction (0.6 [IQR, 0–2.0]% versus 0.0 [IQR, 0–1.8]% of left ventricular mass; P =0.340) between groups. Patients with AF had significantly lower left ventricular (47 [IQR, 34–54]% versus 51 [IQR, 44–58]%; P =0.003) and left atrial (42 [IQR, 17–57]% versus 53 [IQR, 45–59]%; P <0.001) ejection fraction. AF was associated with major adverse cardiac events, even when adjusting for clinical risk factors (odds ratio, 2.48 [95% confidence interval, 1.22–5.03]; P =0.0120) or CMR prognosis markers (odds ratio, 3.77 [95% confidence interval, 1.83–7.79]; P =0.001). Conclusions— This CMR study found no major differences in myocardial salvage, infarct size, or microvascular damage in patients with ST-segment–elevation myocardial infarction or without AF. AF was, however, associated with cardiac dysfunction and independently related to major adverse cardiac events. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00712101.