Atrial fibrillation, like atrial flutter, may be intermittent. Two examples are shown here. In the upper tracing, the first two beats are sinus beats. Third beat is an atrial premature beat. It is followed by a run of 7 beats with slightly irregular RR intervals. This is probably a short burst of atr1al fibrillation. It terminates spontaneously and is followed by a sinus beat and then an atrial premature beat.
In the lower tracing, the QRS complexes preceded by obvious P waves are sinus beats. They are followed by 3 to 4 beats of a rapid irregular rhythm that probably represent short bursts of atrial fibrillation.