• A rapid atrial rate overrides the SA node and becomes the dominant pacemaker.
• Some ST segment and T wave abnormalities may be present.

Rate: 150–250 bpm

Rhythm: Regular

P Waves: Normal (upright and uniform) but differ in shape from sinus P waves

PR Interval: May be short (less than 0.12 sec) in rapid rates

QRS: Normal (0.06–0.10 sec) but can be aberrant at times