Tachycardia—a fast heart rate—is a rate > 100 bpm. The following characteristics of sinus tachycardia 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 > 100 bpm.
4. The R-R interval is regular. 
5. The PR interval is normal (120–200 milliseconds) and consistent.
6. The QRS complexes measure < 120 milliseconds.