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 case, the block is continuous with a 3 to 1 conduction...

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