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Bradycardia and AV block
In bradycardia first ask whether the patient is symptomatic and whether there is a reversible cause; then decide the level of the block — at the AV node (usually benign) or below it (Mobitz II and complete block), which needs a pacemaker.
Why it matters in the exam
Questions usually show an ECG strip and ask for the type of block: first-degree block (PR above 200 ms), Mobitz I with progressive PR lengthening until a beat drops, Mobitz II with a fixed PR and suddenly dropped beats, and complete block with dissociation between atria and ventricles. The acute treatment of symptomatic bradycardia is also asked: atropine, and if it fails — transcutaneous pacing or an adrenaline infusion.
Some questions test reversible causes: drugs (beta-blockers, calcium blockers, digoxin, amiodarone), hyperkalaemia, hypothyroidism, hypothermia, raised intracranial pressure and inferior infarction. Candidates are also asked what is normal in an athlete (sinus bradycardia, Mobitz I at night), and the difference between block in an inferior infarct — usually transient — and block in an anterior infarct, which signals extensive damage.
Key points
- First-degree block and Mobitz I — at the node and usually benign.
- Mobitz II and complete block — below the node, and need a permanent pacemaker.
- Unstable bradycardia: atropine, and if it fails — transcutaneous pacing or adrenaline.
- Always exclude reversible causes: drugs, hyperkalaemia, hypothyroidism, hypothermia.
- Block in an inferior infarct is usually transient; in an anterior infarct it signals extensive damage.
Summary table
| Type | ECG | Level of block | Treatment |
|---|---|---|---|
| First-degree block | PR above 200 ms, every P wave conducts | AV node | No treatment; review drugs |
| Mobitz I (Wenckebach) | PR lengthens progressively until a beat drops | AV node | Usually none; pacing only if symptomatic |
| Mobitz II | Fixed PR, sudden dropped beat, often wide QRS | Below the node (His-Purkinje) | Permanent pacemaker |
| Complete (third-degree) block | No relation between P and QRS, slow escape rhythm | Node or below | Permanent pacemaker (after excluding a reversible cause) |
| Sick sinus syndrome | Bradycardia, pauses, sometimes with bursts of tachycardia | Sinus node | Pacemaker if symptomatic |
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Sources
- ESC Guidelines on cardiac pacing and cardiac resynchronization therapy, 2021 — Bradycardia and conduction disease: indications for pacing
- European Resuscitation Council Guidelines, 2021 — Adult advanced life support: bradycardia
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Bradyarrhythmias: Disorders of the Sinoatrial Node and of the Atrioventricular Node
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.