Scenario: This electrocardiogram (ECG) is from a 78-year-old woman who arrived at the emergency department complaining of lightheadedness, dizziness, exertional dyspnea, and generalized fatigue for the past 3 weeks. Her blood pressure was 80/40 mm Hg and respirations were 20/min. Her only medical history was hyperlipidemia and gastroesophageal reflux disease, and she is currently taking gemfibrozil, aspirin, and omeprazole.

Junctional escape rhythm with atrioventricular (AV) dissociation due to complete AV block, with P waves from both the sinus node (upright) and an ectopic location from a lower atrial region (arrows).

AV block refers to an abnormality in the electrical conduction between the atria and ventricles. The location and severity of AV blocks can be identified by examining ECG features. For example, first degree AV block describes impulses originating from the SA node that are conducted but delayed (> 0.2 seconds), and are...

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