Sinus arrhythmias may show a pattern consistent with normal sinus rhythm, but the pattern also includes an irregularity of the R-R interval. The following characteristics of sinus arrhythmia should be kept in mind when monitoring Lead II:

1. P waves are followed by QRS complexes.
2. P waves have a positive deflection.
3. The rate is 60–100 bpm.
4. The R-R interval is irregular. 
5. The PR interval is normal (120–200 milliseconds) and consistent.
6. The QRS complexes measure < 120 milliseconds.

In a true sinus arrhythmia, the irregular R-R interval is evident.