Escape atrial beats

The 4th and 5th beats are escape atrial beats. The rate of the atrial escape rhythm is slower than that of the sinus node (first 3 beats) and the P wave morphology differs from that of the sinus P wave, depending upon the location of the ectopic atrial focus.

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.