ATRIAL FIBRILLATION:

Rhythm originating in the atrium at a rate of > 350 beats per minute.

(These rates reflect the rate of atrial beats and not necessarily the rate of the ventricular beats (e.g., There may be atrial fibrillation with a rapid ventricular response indicating the atrial rate is > 350 bpm, and the ventricular rate is > 100 bpm))

Atrial Fibrillation and ventricular response:

Ventricular response <60 BPM            Afib with slow ventricular response.

Ventricular response 60-100 BPM      Afib with controlled ventricular response.

Ventricular response >100 BPM         Afib with rapid ventricular response.