Bradyarrhythmias

See Cardiac Implantable Electronic Devices for pacemaker indications once bradyarrhythmia is confirmed.

Can result from sinus node dysfunction (formerly “sick sinus syndrome”) — characterised by sinus bradycardia, sinus pauses, and junctional/ventricular escape rhythms — or may be associated with AV block:

• First-degree block (PR interval > 0.2 seconds) — usually benign, no treatment needed.
• Second-degree block — intermittent AV conduction (intermittent dropped beats):
  • Mobitz 1 (Wenckebach) — at the level of the AV node; usually transient, asymptomatic, benign. Progressive PR prolongation culminating in a non-conducted P wave.
  • Mobitz 2 — at the level of the His-bundle/distal conduction system; usually symptomatic and progresses to complete heart block. Intermittent non-conducted P waves without progressive PR prolongation — more likely associated with haemodynamic compromise, severe bradycardia, and progression to 3rd-degree block; needs cardiac monitoring, backup temporary pacing, and ultimately a permanent pacemaker.
  • 2:1 block — can be either Mobitz 1 or 2, and requires careful evaluation.
• Third-degree (complete) heart block — complete absence of AV conduction; may or may not be symptomatic. High risk of ventricular standstill and sudden cardiac death — needs urgent admission for cardiac monitoring, backup temporary pacing, and usually a permanent pacemaker.

Management

Check for and manage other possible causes: raised intracranial pressure, drugs, ischaemic heart disease, hyperkalaemia, hypothermia.

Bradyarrhythmias should only be treated if causing significant haemodynamic compromise with signs of poor perfusion — hypotension, syncope, altered conscious state, ischaemic chest pain, or heart failure.

• In an emergency with severe haemodynamic compromise, transcutaneous pacing may be needed as a temporary measure until transvenous pacing is feasible.
• When bradycardia is due to sinus node dysfunction or AV-node-level block, atropine is the most effective treatment — 0.5mg IV, repeat after 3–5 minutes if necessary, up to a maximum of 3mg. If ineffective, consider transcutaneous or temporary transvenous pacing.
• If pacing is delayed or unavailable, consider isoprenaline 2–5mcg/min IV infusion (titrated to response) or adrenaline 2–10mcg/min IV infusion — adrenaline is preferred if systolic BP is very low (< 80mmHg), since isoprenaline may further reduce BP.