Atrioventricular (AV) Block
Atrioventricular (AV) block occurs when atrial impulses fail to conduct to the ventricles because of disease in the AV node, the His bundle, or the distal His-Purkinje system. In the emergency department the priorities are rapid recognition of the block type and anatomical level, assessment of haemodynamic impact, identification and treatment of reversible causes, immediate resuscitation (drugs and pacing as required) and timely cardiology referral for definitive management (often permanent pacing).
Pathophysiology and anatomical level
- The AV conduction system includes the AV node (including proximal His) and the His-Purkinje system (His bundle, bundle branches, Purkinje fibres).
- AV nodal blocks are frequently vagally mediated, rate‑dependent and tend to have narrow‑QRS escape rhythms.
- Infranodal (His‑Purkinje) blocks are more likely to be fixed, to produce wide‑QRS escape rhythms and to progress to complete heart block.
- Common causes:
- Myocardial ischaemia
- Fibrosis or degeneration of the conduction system
- Drugs (β‑blockers, non‑dihydropyridine calcium‑channel blockers, digoxin, some antiarrhythmics)
- Electrolyte disturbances (notably hyperkalaemia)
- Infection and infiltrative disease
- Post‑procedural injury (e.g. after cardiac surgery or ablation)
Clinical presentation and red flags
- Many patients are asymptomatic (particularly with first‑degree or Mobitz I block).
- Symptoms reflect inadequate ventricular rate or output and may include: