Heart Blocks & Bradycardias

Heart blocks & bradycardias

(Arrhythmias and Conduction Disorders)

This section covers recognition, initial assessment and emergency management of atrioventricular (AV) conduction block and clinically important bradycardias in the emergency department. Focus is on identifying patterns that require urgent intervention (drugs, transcutaneous pacing, escalation to transvenous or permanent pacing), recognising reversible causes, and organising appropriate disposition and cardiology involvement.

Clinical context: lesions range from benign first‑degree AV block to high‑degree AV block (Mobitz II, 2:1 with infra‑Hisian disease, complete heart block) that can cause syncope, hypotension, ischaemia and cardiac arrest. Early identification of Mobitz II, new bifascicular block, high‑degree block or complete heart block warrants senior/cardiology escalation and consideration of pacing (Resuscitation Council UK ALS; NICE TA88/TA324).

Quick electrophysiology refresher

• SA node - the primary pacemaker; atrial depolarisation produces the P wave.
• Atrial conduction - Bachmann’s bundle transmits the impulse to the left atrium.
• AV node - introduces delay that determines the PR interval; AV‑nodal block is usually nodal, tends to produce narrow QRS complexes and may respond to vagolytic therapy.
• His-Purkinje system - bundle of His divides to the right bundle branch (RBB) and left bundle branch (LBB, which splits into anterior and posterior fascicles); infra‑Hisian disease usually produces a wide QRS and is less likely to respond to atropine.
• Ventricular depolarisation - produces the QRS complex; block below the...