Scenario: A 73-year-old woman presents to the emergency department complaining of dizziness. Her past medical history includes coronary artery disease with controlled hypertension. She is currently under the care of a cardiologist.

Interpretation: Second-degree atrioventricular (AV) block type II.

In second-degree AV block type II (Mobitz II), the PR interval of the conducted P wave will be constant for each QRS complex. Because second-degree AV block occurs in the Purkinje system, an escape rhythm may not develop. Consequently, this may progress to a third-degree heart block or ventricular standstill, making this rhythm dangerous. Causes may include acute anterior myocardial infarction, cardiomyopathy, rheumatic heart disease, coronary artery disease, digitalis, β-blockers, and calcium channel blockers. The ventricular rate will depend on the number of impulses conducted through the AV node and will be less than the atrial rate. In this...

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