Scenario: The top ECG strip (lead V1) was a routine ECG strip in a 75-year-old man 2 days after a stent was placed in the left anterior descending coronary artery for acute anterioseptal myocardial infarction. Currently, the patient is intubated and nonresponsive. The bottom ECG strip was obtained at 2 PM when the nurse noted the ST segment in V1 “seemed different.”

Interpretation: The top ECG strip shows normal sinus rhythm with 1st-degree atrioventricular block and right bundle branch block (RBBB) pattern. The bottom ECG strip shows normal sinus rhythm with RBBB and acute ST elevation of >2mm.

Right bundle branch block is the result of a conduction delay or block within the right bundle branch. Causes include right ventricular hypertrophy or strain, coronary artery disease, pulmonary embolism, Wolff-Parkinson-White syndrome, myocarditis, and idiopathic causes. The typical QRS complex pattern, best seen in lead V1, is...

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