Atrial fibrillation

Atrial fibrillation is an irregularly irregular rhythm without regular or organized atrial activity. Atrial activation is rapid (generally greater than 320 beats per minute) and of various amplitudes. No discrete P waves are seen on this tracing. Instead, rapid, irregular, variable and low-amplitude oscillating fibrillatory waves are observed between the QRS complexes. When the arrhythmia is of long duration, the fibrillatory waves may be inapparent.

The normal P wave in sinus rhythm is slightly notched since activation of the right atrium precedes that of the left atrium. The P wave is upright in a positive direction in leads I and II. A P wave with a uniform morphology precedes each QRS complex. The rate is between 60 and 100 beats per minute and the cycle length is uniform between sequential P waves and QRS complexes. In addition, the P wave morphology and PR intervals are identical from beat to beat.