Overview

• 1st Degree AV Block → prolonged conduction through the AV node
• 2nd Degree AV Block
  • Mobitz Type I → progressive prolongation of AV node conduction resulting in one atrial impulse failing to be conducted through AV node.
  • Mobitz Type II → intermittent or regular failure of conduction through the AV node.
• 3rd Degree (Complete) AV Block → no relationship between atrial and ventricular contraction.

Aetiology → MI or IHD (most common), infection (rheumatic fever or infective endocarditis), drugs (digoxin), metabolic (hyperkalaemia)

• Complete heart block following MI ⇒ Right Coronary Artery occlusion (supplies AV node)

Making Diagnosis

Clinical Features:

• 1st & 2nd degree usually asymptomatic
• Mobitz Type II & 3rd Degree → may cause Stokes-Adams Attacks (syncope, dizziness, palpitations, chest pain). May also show signs of reduced cardiac output (ie. hypotension)
• Complete Heart Block → JVP may show cannon A waves, syncope, regular bradycardia (30-50 bpm)

Investigations:

• ECG
  • First Degree → fixed prolonged PR interval (>0.2s/200ms = 1 large square)
    • Normal variant in athlete (asymptomatic), hence doesn’t require tx in that case (as is mobitz I)
  • Mobitz Type I → progressively prolonged PR interval, then eventually dropped beat
    • Also normal variant in athlete
  • Mobitz Type II → intermittently a P wave is not followed by a QRS (PR interval is constant)
  • Complete Heart Block → no relationship between P waves and QRS complexes (complete AV dissociation)
  • ECGs

Management Plan

• Chronic Block (definitive management) → permanent pacemaker