A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses electrocardiogram (ECG) interpretation for clinical practice. To send an eLetter or to contribute to an online discussion about this article, visit www.ajcconline.org and click “Respond to This Article” on either the full-text or PDF view of the article. We welcome letters regarding this feature.

Scenario: This electrocardiogram (ECG) was obtained in the emergency department from a 72-year-old male with chest pain and shortness of breath. The patient’s history included hypertension, coronary artery disease, hyperlipidemia, and urinary incontinence that was managed with a bladder stimulator. Given this ECG, the clinicians were concerned his cardiac pacemaker was misfiring, but the patient insisted he did not have a pacemaker.

Normal sinus rhythm, 59/min and no indication of acute ischemia. Consistent small spikes are present in the limb leads. Thus, a differential diagnosis of nonphysiological artifact caused by the...

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