Key Points to Note About Complete Heart Block

Key Points to note about Mobitz I:

• • P-P interval is fairly regular (you can sometimes have sinus arrhythmia that causes mild irregularity)
  • QRS-QRS interval is typically irregular (sometimes causes clumped/grouped beats)
  • The PR interval gradually increases until a non-conducted “lonely” P wave occurs
  • QRS is typically narrow unless there is underlying bundle branch block or aberrant conduction
  • Mobitz I is usually due to an AV nodal problem and responds well to atropine if needed

Key points to note about Mobitz II:

• • P-P interval is clockwork regular (you should NOT have sinus arrhythmia)
  • QRS-QRS interval is typically irregular (sometimes causes clumped or grouped beats)
  • PR intervals are identical before non-conducted P waves
  • QRS complexes are typically wide
  • You can sometimes see 2 or more consecutive lonely P waves (“Mobitz II advanced AV block”)
  • Mobitz II often necessitates permanent pacemaker placement

Key points to note about complete heart block:

• • “AV dissociation” is present 
    • Atrium and ventricle beating independently
    • P-P interval is fairly regular (there may be slight irregularity in the atrial rhythm if sinus arrhythmia is present)
      • Note: sinus arrhythmia can be present in Mobitz I (block at AV node) and complete heart block (block at AV node or below it, including His-Purkinje system with complete dissociation of atrial and ventricular rhythms). In contrast, Mobitz II (infranodal block) is characterized by regular atrial activity without sinus arrhythmia due to the infranodal location of the block. 
  • QRS-QRS interval is typically regular
    • Narrow = junctional escape rhythm (~ 40-60 bpm), has a better prognosis
    • Wide = ventricular escape rhythm (~ 20-40 bpm), worse prognosis, more likely to require a permanent pacemaker
  • PR intervals are randomly changing
  • You can sometimes see 2 or more consecutive lonely P waves (dropped beats)