Conduction blocks

First degree AV block: Prolonged PR interval (> 1 big or 5 small boxes), normal P waves, QRS complexes

Second degree AV block: Some P waves fail to pass through AV node.

· Mobitz type I: Progressive prolongation of PR interval until there is a non-conducted P wave causing missed beat (no QRS complex).

· Mobitz type II: Missed beats (no QRS complex) occur every few beats, but PR Interval remains constant

Third degree AV block: No P waves pass through AV node leading to complete AV dissociation, no correlation between P waves and QRS complexes. Depending on the level of block, QRS complexes can be narrow or wide.

Right bundle branch block: Rsr', rsR', or rSR' (“M” pattern) in V1, V2; and wide QRS (> 3 small boxes)

Left bundle branch block: Broad notched R wave (“M” pattern) in leads I, aVL, V5, V6; and wide QRS