Entrainment in typical atrial flutter with right atrial pacing with the rate of recording by the ECG machine being slowed by one-half

The spontaneous rhythm, in which the flutter waves are not clearly apparent, is shown in the left side of panel A. The right atrium is then paced at just under 400 beats/min; entrainment is achieved at the asterisk when there is a sudden change in atrial morphology as the flutter rate matched the pacing rate. Cessation of pacing led to conversion to sinus rhythm (panel B).

Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright.