Answer
A: Atrial fibrillation
Educational Objective
Identify atrial fibrillation on electrocardiogram.
Critique
This electrocardiogram is characteristic of atrial fibrillation, with an irregularly irregular rhythm and no discernible P waves. Atrial fibrillation can present with a rapid ventricular response, with an average rate of more than 120/min; a controlled ventricular response, with an average rate between 70/min and 110/min; or a slow ventricular response, with an average rate of less than 60/min. The tracing shows an average rate of approximately 100/min.