Ectopic atrial rhythm

Ectopic atrial rhythm occurs when the dominant pacemaker is an ectopic focus in the atrium. The direction of atrial activation may be altered when an atrial rhythm is present since the pacemaker focus is within the atrial myocardium. In this tracing, the P wave is inverted due to retrograde atrial activation from a pacemaker focus in the low atrium, the area of the coronary sinus, or the left atrium. The QRS complexes of an atrial tachycardia resemble those seen during sinus rhythm, since myocardial activation is via the His-Purkinje system.

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.