Mobitz type II

Description

Single or intermittent nonconducted P waves without QRS complexes The PR interval remains constant. The conduction of atrial impulses to the ventricles typically follows a regular pattern, e.g.:

• 3:2 block: regular AV block with 3 atrial depolarizations but only 2 atrial impulses that reach the ventricles (heart rate = ⅔ SA node rate)
• 4:3 block: regular AV block with 4 atrial depolarizations but only 3 atrial impulses that reach the ventricles (heart rate = ¾ SA node rate) While 2:1 block follows a regular pattern, it cannot be classified as Mobitz type I or II and is classified separately (see “2:1 AV block”). Risk of progression to complete heart block: high (> 50%), as it is typically due to infranodal block (usually in the His-Purkinje system)

2:1 AV block 

• Description
  • Inhibited conduction of every second atrial depolarization (P wave) to the ventricles (heart rate = ½ SA node rate)
  • Cannot be classified as Mobitz I or Mobitz II as only one PR interval is observed before the subsequent dropped complex (can fit into both types)
  • Often a transient rhythm occurring on a baseline Mobitz I or Mobitz II rhythm
• Risk of progression to complete heart block: depends on level of block 
  • Block at the level of the AV node (more common): low
  • Infranodal block (less common): high

Ventriculophasic sinus arrhythmia

Sinus rate variation of this type with complete heart block is called ventriculophasic sinus arrhythmia.