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CLINICAL STUDY: MYOCARDIAL INFARCTION

Incidence and predictors of myocardial infarction among patients with atrial fibrillation

^a Cardiovascular Division, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA

Manuscript received December 27, 1999; revised manuscript received March 21, 2000, accepted May 1, 2000.

Reprint requests and correspondence: Dr. Peter J. Zimetbaum, Cardiovascular Division (GZ-435), Beth Israel-Deaconess Medical Center, 330 Brookline Avenue, Boston, Massachusetts 02115
pzimetba{at}caregroup.harvard.edu

OBJECTIVES

We sought to evaluate the utility of excluding myocardial infarction (MI) in patients presenting to the emergency department (ED) with atrial fibrillation (AF) and to identify predictors of MI in this group.

BACKGROUND

Patients with AF are frequently admitted to the hospital, in part, 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 presented 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 and specificity for the occurrence of MI of 100% and 65%, respectively. ST segment elevation or depression was present in 43% of patients, with a sensitivity and specificity of 100% and 51%. The presence of either major ST segment depression (>2 mm) or elevation on the admission electrocardiogram (ECG) was present in 6%, with a sensitivity of 100% and a specificity of 99%. The resulting positive and negative predictive values were 86% (95% confidence interval [CI] 42% to 99%) and 100% (95% CI 96% to 100%), respectively. Use of this criterion would have reduced the number of rule-out MIs in our study group by 94%, with no loss of sensitivity.

CONCLUSIONS

Chest pain and ST segment depression are extremely common findings in patients presenting to the ED with AF and have limited power to predict 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 for MI and may not require performance of the rule-out MI protocol or hospital admission if clinically stable.

Abbreviations and Acronyms   AF = atrial fibrillation   CI = confidence interval   CPK-MB = creatine phosphokinase, MB isoenzyme   ECG = electrocardiogram or electrocardiographic   ED = emergency department   MI = myocardial infarction

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