Type II Second Degree AV Block

Type II second degree AV block (Mobitz type II block) is never a normal variant and is always due to cardiac disease.  It occurs secondary to an injury occurring below the AV node and can easily progress into third degree AV block.  To make the diagnosis of type II second degree AV block, there must be at least 2 conducted beats in a row before a dropped beat.  In Mobitz type II AV block, the PR interval of all conducted beats is the same and there is no lengthening of the PR interval as in type I.

If two complexes are not conduced in a row and every other beat is dropped, this can only be called second degree AV block. This is because you only have 1 PR interval to look at and you need two PR intervals in a row to discern type I from type II second degree AV block.

See examples of type II second degree AV block

EKG 74