Bradyarrhythmia / Complete Heart Block

Symptomatic bradycardia: HR <60 with haemodynamic compromise (hypotension, syncope, heart failure, chest pain). ECG classification: sinus bradycardia, 1st/2nd/3rd degree AV block. Mobitz type II and complete heart block (CHB) are high-risk…

Resuscitation Council UK Bradycardia Algorithm

The pathway

1 · Assess & classify

Is the patient compromised? (SBP <90, HR <40, syncope, chest pain, HF signs)
12-lead ECG: sinus bradycardia, 1st degree (PR >200ms), Mobitz I/Wenckebach (progressive PR lengthening then drop), Mobitz II (sudden P-wave drop), CHB (P and QRS independent, escape rhythm)

2 · Reversible causes

Drugs: beta-blockers, rate-limiting CCBs (diltiazem/verapamil), digoxin, amiodarone — check drug chart, consider reversal (atropine, glucagon for beta-blocker, digoxin-specific antibody fragments)
Inferior MI: right-sided leads, fluids for RV infarction
Hyperkalaemia: ECG sine wave changes
Hypothyroid: TFTs

3 · Atropine

If haemodynamically compromised: atropine 500mcg IV, repeat every 3–5 min to max 3mg total
Do NOT give it in high-degree AV block with a broad QRS — RCUK 2025: ineffective, and may worsen the block. Go to pacing or a chronotrope
Do NOT give it in a transplanted heart — it can cause high-degree AV block or sinus arrest. Use aminophylline 100–200mg slow IV instead
Works where the block is at or above the AV node: sinus bradycardia, 1st degree, Mobitz I
Inferior MI is not a contraindication — the block is often vagally mediated and nodal, and atropine commonly works
The tachycardia raises myocardial oxygen demand, so treat compromise, not the number

4 · Transcutaneous pacing

If atropine fails or Mobitz II/CHB with haemodynamic compromise: Apply pads (anterior-posterior)
Start at 70bpm, 50mA output
Increase mA until electrical capture (pacer spike followed by QRS)
Confirm mechanical capture (pulse)
Sedate with IV morphine/midazolam

5 · Intravenous chronotropes

If pacing not immediately available: adrenaline infusion 2–10mcg/min (broad compromise)
Or isoprenaline 5mcg/min (more specific chronotropy, less vasoconstriction)
Or glucagon 5–10mg IV bolus then infusion (beta-blocker toxicity specifically)
Transplanted heart or spinal cord injury: aminophylline 100–200mg slow IV

6 · Transvenous pacing / definitive treatment

Mobitz II and CHB almost always require transvenous pacing and subsequent permanent pacemaker insertion
Cardiology must be involved early
Post-inferior MI CHB: may recover — temporary wire
Idiopathic CHB: permanent pacemaker
Do not discharge Mobitz II/CHB without cardiology review

Drugs

Drug	Dose	Route	Notes
Atropine	500mcg IV, repeat to max 3mg	IV bolus	Do NOT give in high-degree AV block with broad QRS (ineffective, may worsen it) or in a transplanted heart (use aminophylline) — RCUK 2025. Inferior MI is not a contraindication.
Adrenaline	2–10mcg/min infusion	IV	Broad haemodynamic support while awaiting pacing.
Aminophylline	100–200mg slow IV	IV	The drug to reach for instead of atropine in a transplanted heart or spinal cord injury (RCUK 2025).
Glucagon	5–10mg IV bolus then 1–5mg/hr	IV	Specific antidote for beta-blocker toxicity causing bradycardia.
Digoxin-specific antibody (Digibind)	Weight and level dependent	IV	For digoxin toxicity causing bradyarrhythmia.

When to escalate

Complete heart block or Mobitz II → cardiology immediately for transvenous pacing,Atropine-resistant haemodynamic compromise → transcutaneous pacing now,Post-inferior MI CHB → cardiac care unit, temporary pacing wire,Beta-blocker/CCB toxicity → toxicology/ITU, glucagon, high-dose insulin protocol,Asystole developing → CPR, ALS algorithm

Reference: Resuscitation Council UK Bradycardia Algorithm 2021

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