Scenario: The electrocardiogram (ECG) here (lead V1) was obtained from a 66-year-old woman who arrived in the emergency department with palpitations and chest pain. The patient has no cardiac history and takes no medications. She is a smoker and states that she has recently been under a lot of stress at work. The nurse admitting the patient identified the rhythm shown here as atrial fibrillation on the basis of the irregular heart rate and the lack of P waves.

Yes, sinus P waves are present except for beats 3, 6, and 9, which are premature atrial beats.

Sinus rhythm with frequent premature atrial contractions (PACs). P-wave amplitude in lead II may suggest right atrial enlargement (> 2.5 mm); however, P waves suggestive of atrial enlargement are not seen in V1. Hence, evaluation with a standard 12-lead ECG and...

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