The EKG rhythm will appear irregular with heart rate that is fast (200-250 bpm). The P wave is absent and the PR interval is not measurable. The QRS complex will typically be wide (>0.10 sec). Its shape is characterized by a gradual change in the EKG amplitude and a twisting of the QRS complexes around a line.

The EKG rhythm will appear may be irregular with a normal heart rate. The P wave can be observed changing shape and size from beat to beat (at least three different forms). The PR interval is variable in length. The QRS complex will typically be normal (0.06-0.10 sec) and the T wave normal. If heart rate exceeds 100 bpm, then rhythm may be multifocal atrial tachycardia (MAT).