Overview

• Bradycardia may generally be caused by sinus node dysfunction, atrioventricular block or escape rhythms in the setting of either of the above.

• • Bradyarrhythmias

  • Regular

  • Sinus bradycardia
  • Sinus arrest with escape rhythm
  • Complete heart block with escape rhythm

  • Irregular

  • Sinus arrhythmia
  • Sinus arrest
  • Second or third degree sinoatrial exit block
  • Atrial fibrillation with slow ventricular rate
  • Atrial flutter with variable block
  • Second or third degree AV block

• • Causes of Bradycardia

  • Intrinsic (SA or AV Nodal)

  • Idiopathic degeneration
  • Myocardial infarction
  • Congenital - congenital heart disease, neonatal lupus
  • Infiltrative disease - sarcoidosis, amyloidosis, haemochromatosis
  • Connective tissue disease - SLE, scleroderma, RA
  • Cardiac procedures - valvular surgery, correction of congenital heart disease, catheter ablation
  • Infections - Lyme disease, endocarditis, viral myocarditis

  • Extrinsic

  • Physiologic - sleep, athletes
  • Autonomic - neurocardiogenic syncope, carotid sinus massage, carotid sinus hypersensitivity
  • Drugs - beta blockers, calcium channel blockers, digoxin, adenosine, amiodarone, ivabradine, clonidine, acetylcholinesterase inhibitors
  • Hypothyroidism
  • Hypothermia
  • Hyperkalaemia
  • Obstructive sleep apnoea
  • Raised intracranial pressure

• • Pearls

  • Sinoatrial exit block and sinus arrest present as pauses without P waves or QRS complexes.
  • Escape rhythms are likle to be present if there are pauses or non-conducted P waves followed by bradycardia with junctional or ventricular complexes.
  • Atrial fibrillation with slow ventricular rate produces fibrillation waves without P waves and with irregular QRS complexes.
  • Atrial flutter with variable block manifests as a sawtooth wave at ~300bpm with irregular QRS complexes.
  • Second degree heart block presents with intermittently non-conducted P waves (without a subsequent QRS complex); the pattern of PR interval prolongation determines the type.
  • Complete AV block produces complete dissociation between P waves and QRS complexes.