Scenario: This 12-lead electrocardiogram (ECG) was obtained by paramedics from a 69-year-old man who called 911 because he was experiencing chest pressure and palpitations. The patient has a medical history of chronic obstructive pulmonary disease, myocardial infarction, and atrial fibrillation. The patient was alert, had palpable pulses, and had a blood pressure of 95/70 mm Hg.

Atrial fibrillation at about 150 beats per minute, frequent premature ventricular contractions (beats 12-13 and 18-20), progressing into ventricular tachycardia (V-tach) as fast as 300 beats per minute (last 5 beats). The ST segment is depressed in the inferior leads, which is suggestive of acute ischemia but could also be due to the rapid heart rate.

A 10-second rhythm strip, often lead II and/or V1, is typically displayed at the bottom of a standard 12-lead ECG. This rhythm strip is extremely helpful with rhythm interpretation, which is exemplified in highly dynamic...

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