third-degree atrioventricular (AV) block (complete heart block)

Etiology

• drug toxicity: digitalis
• myocardial scarring secondary to infarction
• conduction system disease
• infiltrative diseases
  • amyloidosis
  • sarcoidosis
• rheumatologic disorders
  • polymyositis
  • scleroderma
  • rheumatoid nodules
• infectious diseases
  • Chagas' disease
  • Lyme disease
• inadvertant surgical interruption of conduction system
• calcific aortic stenosis
• endocarditis
• metastatic disease
• Stokes-Adams-Morgagni syndrome

Pathology

• absence of transmission of atrial impulses to the ventricles
• in congenital heart block, the site of conduction block is within the AV node
• in acquired heart block, the conduction block is within the His bundle or Purkinje system

Clinical manifestations

• depends upon underlying escape rhythm
• light-headedness
• dyspnea
• angina
• syncope & near-syncope

Diagnostic procedures

• electrocardiogram:
  • atrial rate exceeds ventricular rate
  • atrial/ventricular dissociation
  • ventricular escape rhythm is usually regular

Differential diagnosis

• competitive AV dissociation

Management

• symptomatic patients
  • transcutaneous pacemaker first priority
    • transvenous pacemaker second priority
  • atropine 0.5-2.0 mg IV
    • unlikely to be of benefit in wide-complex bradyarrhythmias
  • bradycardia refractory to atropine & transcutaneous pacemaker not available
    • dopamine 5-20 ug/kg/min
    • epinephrine 2-20 ug/min
    • isoproterenol 2-10 ug/min
• permanent pacemaker for all patients with 3rd degree AV block

More general terms

• atrioventricular (AV) block
• hemodynamic instability (compromise)

Additional terms

• Stokes-Adams-Morgagni syndrome