Atrial Fibrillation | Reference Guide.

EKG Features

Rate: Very fast (> 350 bpm) for Atrial, but ventricular rate may be slow, normal or fast
Rhythm: Irregular
P Wave: Absent - erratic waves are present
PR Interval: Absent
QRS: Normal but may be widened if there are conduction delays

Atrial fibrillation is a common type of supraventricular tachycardia (SVT) arrhythmia, characterized by chaotic, quivering atria. These atrial fibrillations result in atrial contractions that are ineffective and out of coordination with the ventricles.
External Source: http://www.nhlbi.nih.gov/health/health-topics/topics/af/
National Institutes of Health