Sinus node reentry

Sinus node re-entry is due to continuous activity or re-entry within the sinus node or the sinoatrial junction. This arrhythmia has a sudden onset and offset with a rate that is usually 100 to 160 beats per minute. A P wave proceeds each QRS complex and has a morphology identical to the sinus P wave. The PR interval is also similar to that of sinus rhythm. Thus, it is only the abrupt onset and offset that distinguishes this arrhythmia from sinus tachycardia.

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.