Second degree AV block, advanced 2:1

See brief interpretation of 12 lead EKG above

- two (or more) P waves per QRS complex (conduction ratio 2:1)
- cannot be classified into mobitz I or II heart block as eventual prolongation before the block is impossible to observe

In advanced second degree heart (or atrioventricular, AV) block only every second (2:1 AV block), third (3:1 AV block) or fourth (4:1 AV block) P wave conduct to the ventricles. A conduction ratio of 3:1 or higher is also referred to as high degree or high grade atrioventricular block.

In this 2:1 atrioventricular block also note that the non-conducted P wave nearly fuses with the preceding T wave (detail from 12 lead EKG):

The advanced heart blocks cannot be determined as Mobitz type I or II as it is impossible to observe whether prolongation of the PR interval exist. Though observations of the PR intervals and the width of the conducted QRS intervals may give clues to which block is in question, it is best to avoid classifying these heart blocks into Mobitz types.

– Mathias