Incidence and predictors of myocardial infarction among patients with atrial fibrillation

OBJECTIVES We sought to evaluate the utility of excluding myocardial infarc tion (MI) in patients presenting to the emergency department (ED) with atri al fibrillation (AF) and to identify predictors of MI in this group. BACKGROUND Patients with AF are frequently admitted to the hospital, in par t, to exclude an associated MI. There are no prospective data on unselected patients to support this common practice. METHODS We conducted a prospective cohort study of all patients who present ed to a single-center ED with the primary diagnosis of AF. RESULTS Of a total of 255 patients, 190 (75%) were admitted to the hospital , and 109 of them underwent a standard "rule-out MI" protocol. Of these 109 patients, six (5.5%) were identified as having an acute MI at the time of admission. Chest pain was present in 39% of patients, with a sensitivity an d specificity for the occurrence of MI of 100% and 65%, respectively. ST se gment elevation or depression was present in 43% of patients, with a sensit ivity and specificity of 100% and 51%. The presence of either major ST segm ent depression (>2 mm) or elevation on the admission electrocardiogram (ECG ) was present in 6%, with a sensitivity of 100% and a specificity of 99%. T he resulting positive and negative predictive values were 86% (95% confiden ce interval [CI] 42% to 99%) and 100% (95% CI 96% to 100%), respectively. U se of this criterion would have reduced the number of rule-out MIs in our s tudy group by 94%, with no loss of sensitivity. CONCLUSIONS Chest pain and ST segment depression are extremely common findi ngs in patients presenting to the ED with AF and have limited power to pred ict MI. In contrast, ECG evidence of ST segment elevation or depression >2 mm appears to be a reliable discriminator of which patients are at risk for MI. Patients without significant ST segment changes are at very low risk f or MI and may not require performance of the rule-out MI protocol or hospit al admission ii clinically stable. CT Am Coil Cardiol 2000;36:1223-7) (C) 2 000 by the American College of Cardiology.