EKG COLUMNRapid Atrial Fibrillation MasqueradeSweeney, Michael MSN, FNP-BC, ENP-BC, NE-BC, CEN, CFRN, CCRN, TCRN, CNRNEditor(s): Davis, Wesley D. DNP, ENP-C, FNP-C, AGACNP-BC, CEN, Column Editor Author Information Chestnut Hill Hospital, Philadelphia, Pennsylvania. Corresponding Author: Michael Sweeney, MSN, FNP-BC, ENP-BC, NE-BC, CEN, CFRN, CCRN, TCRN, CNRN, Chestnut Hill Hospital, 8835 Germantown Pike, Philadelphia, PA 19118 ([email protected]). Disclosure: The author reports no conflicts of interest. Advanced Emergency Nursing Journal: April/June 2021 - Volume 43 - Issue 2 - p 133-137 doi: 10.1097/TME.0000000000000343 Buy Metrics Abstract A 63-year-old man presented to the emergency department for fluttering in the chest. The initial electrocardiogram (ECG) suggested rapid atrial fibrillation with nonspecific RS- and ST-segment abnormalities. Treatment with intravenous β-blocker resulted in conversion to a normal sinus rhythm. The repeat ECG revealed conversion to normal sinus rhythm with an inferior lateral myocardial infarction. This case presentation identifies the importance of an algorithmic approach to identifying narrow complex tachyarrhythmias considering both cardiac and noncardiac causes. Furthermore, evaluating ECG changes when varying rates and rhythms exist on differing ECGs. Identifying the importance of serial ECGs is emphasized by the case presented, concluding with an understanding of arrhythmias associated with myocardial infarctions and clinical pearls. © 2021 Wolters Kluwer Health, Inc. All rights reserved.