Scenario: This ECG was obtained in a 47-year-old man who came to the emergency department with weakness, vomiting, and lethargy. His blood pressure is 100/40 mm Hg. The patient’s only significant history is leukemia, which was diagnosed when he was a teenager. He was treated with chemotherapy, radiation, and a bone marrow transplant. He has been cancer free for more than 20 years.

Type II second degree atrioventricular (AV) block (Mobitz Type II), with ST segment elevation in leads II and III, suggests acute inferior wall myocardial infarction (MI).

In this ECG, there are twice as many P waves as QRS complexes (atrial rate = 75/min; ventricular rate = 37/min). In this situation, the relationship of every P wave to every QRS must be carefully assessed. Whereas the PR interval preceding each QRS is markedly lengthened (0.28), it is consistent, indicating these P...

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