Overview of bradyarrhythmias

Writing Committee Members, 2019

Bradycardia is defined as a heart rate of less than 60 beats per minute. However, a slow heart rate may be physiologically normal for some people (sinus bradycardia), especially at rest or if very fit. Junctional escape rhythm and Wenckebach block are also seen in the general population and are usually asymptomatic. People with asymptomatic bradycardia usually need no treatment.

Note: People with asymptomatic bradycardia usually need no treatment.

Intermittent severe bradycardia can cause syncope. Chronic bradycardia can cause fatigue, shortness of breath on exertion, and dizziness.

Bradycardia can result in haemodynamic compromise with signs of poor perfusion, leading to hypotension and syncope, altered conscious state, ischaemic chest pain and heart failure. Look for contributing factors such as myocardial infarction or poor ventricular function and treat if present. Also, exclude other reversible causes such as hypothyroidism, raised intracranial pressure, electrolyte disorders and drugs.

In patients with symptomatic bradycardia, identify drugs that cause bradycardia (eg digoxin, beta blockers, verapamil, diltiazem, amiodarone) and withhold them if possible; however, these drugs may be needed to treat coexistent tachyarrhythmias or other conditions. Avoid combinations of drugs that block the atrioventricular (AV) node, such as a beta blocker plus verapamil or diltiazem.

Bradycardia can be due to sinus node dysfunction (formerly called sick sinus syndrome), which is characterised by sinus bradycardia, sinus pauses and junctional or ventricular escape rhythms. It is often associated with paroxysmal atrial fibrillation (‘tachy-brady’ syndrome). Chronic sinus node dysfunction associated with symptoms is an indication for permanent pacing but rarely requires acute intervention.

Bradycardia may be associated with AV block, which is classified as:

  • third-degree block (complete heart block), which is due to complete interruption of AV conduction, and may or may not be symptomatic
  • second-degree block, which has intermittent AV conduction (ie intermittent dropped beats). This can be:
    • Mobitz 1 or Wenckebach block, which is at the level of the AV node and is usually transient, asymptomatic and benign
    • Mobitz 2 block, which is at the level of the His-bundle and distal conduction system. It is usually symptomatic and progresses on to complete heart block
    • Block of a 2:1 ratio, which can be either Mobitz 1 or 2 and requires careful evaluation
  • first-degree block (with a prolonged PR interval [more than 0.2 seconds]), which is usually benign and does not require treatmentKwok, 2016.

Refer patients with haemodynamic compromise, syncope or other symptoms due to bradycardia for urgent consideration of pacemaker implantation.

Patients with chronic symptomatic bradycardia and some patients with asymptomatic but significant bradyarrhythmias require a permanent pacemaker. See the European Society of Cardiology (ESC) guidelines on cardiac pacing and cardiac resynchronisation therapy for the indications for implanting a permanent pacemaker.