Scenario: The patient is a 52-year-old woman who presents to her physician’s office with complaints of general malaise and a low-grade fever. The patient presented to an acute care clinic 3 weeks prior for a sore throat, which was diagnosed as strep throat (streptococcal pharyngitis). Appropriately, she was started on oral penicillin but admitted to not finishing the prescription since she “felt better after 4 days of taking the antibiotic.”

Rationale: Nonparoxysmal (gradual-onset) junctional tachycardia is a supraventricular rhythm with narrow QRS complexes and a regular rate, usually between 60–140 bpm. The distinguishing feature of this ECG is retrograde conduction of the atrium causing an inverted P wave, best observed in lead II. In this case, the P waves are also inverted in multiple leads (III, aVF, V3 through V6). Although lead V1, a...

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