GOLDEN RULES OF ELECTROPHYSIOLOGY

1. The ventricular rate depends on how healthy the AV node is.

2. The sinus node is reset by retrograde P waves. These retrograde P waves can be found within the QRS. The next sinus beat is determined by adding the usual P-P interval to the time at which the R wave occurred.
e.g. R wave at 3:05:09pm. P-P interval 1 second in a patient with a heart rate of 60bpm. Therefore expect to see the next P wave at 3:05:10pm.

3. Usually in CHB you will see P's at twice the speed as the R's, i.e. 2P for every R. If there is almost 1:1 then this is called "CHB with isorhythmic dissociation".