ECG: regular with P waves before each QRS complex; variable rate)

Management: treat cause

Occurs due to an entire re-entry conduction circuit in AV node

ECG: regular, often without discernible P waves because they may be buried in the QRS; fast, e.g. 150-200bpm

Management: vagal manoeuvres (1st), adenosine (2nd; not in severe asthma – use Ca2+ channel blocker, e.g. verapamil), β-blocker (3rd)

Occurs due to an accessory conduction pathway allowing conduction re-entry between atrium and ventricle, e.g. in Wolff-Parkinson-White syndrome

ECG: regular, often without discernible P waves because they may be buried in the QRS or retrograde; fast, e.g. 150-200bpm

NB: this refers to orthodromic AVRT. Antidromic AVRT looks more like VT.

Management: vagal manoeuvres (1st), adenosine (2nd; not in severe asthma – use Ca2+ channel blocker, e.g. verapamil), β-blocker (3rd)

Occurs due to abnormal depolarising focus in atrium

ECG: regular with abnormal P waves; variable rate; irregular with abnormal p waves with differing morphology if ‘multifocal’ atrial tachycardia

Occurs due to fluttering atria

ECG: regular with saw-tooth baseline; usually around 150bpm; irregular if ‘variable block’

Management: rate or rhythm control and treating cause and therapeutic anticoagulation (offer if CHA₂DS₂-VASc score ≥2 and consider if male with score of 1)

Occurs due to fibrillating atria

ECG: irregular with no P waves

Management: rate or rhythm control and treating cause and therapeutic anticoagulation (offer if CHA₂DS₂-VASc score ≥2 and consider if male with score of 1)

Occurs due to an abnormal depolarising focus in ventricles or a re-entry circuit within the ventricles

ECG: regular broad complex tachycardia

Management: amiodarone if haemodynamically stable; synchronised DC cardioversion if unstable or adverse signs

NB: may be due to ACS

Torsades de pointes is rhythmic polymorphic VT related to ↑QT, due to prolonged ventricular repolarisation

ECG: VT with rhythmic varying amplitude

Management: magnesium sulphate

Examples: SVT or AF with L/RBBB 

ECG: looks like VT but see box for how to distinguish; irregular if due to AF

Management: treat as supraventricular if definitely sure. If any doubt, treat as VT if regular or below if irregular.

Example: in Wolff-Parkinson-White syndrome

ECG: irregular broad complex tachycardia and with different size complexes due to different AV conduction pathways) 

Management: usually managed with synchronised DC cardioversion (don’t use AV nodal blocking medications – they will increase accessory path conduction and may cause VF) 

May be caused by: drugs (e.g. β-blockers, digitalis), neutrally mediated syndromes (e.g. carotid sinus hypersensitivity, vasovagal syncope), hypothermia, hypothyroidism, SA node dysfunction

Occurs when the SA node fails to depolarise.

May result in: sinus bradycardia, sinus pauses, or sinoatrial arrest with an ‘escape rhythm’

Escape rhythms may be initiated by the AV node (ECG: ‘ junctional rhythm’ – no p waves but normal QRS at 40-60bpm) or ventricles (ECG: ‘ventricular escape rhythm’ – no p waves and abnormal broad QRS at 20-40bpm)

Occurs when the AV note fails to conduct electric depolarisations between the atria and ventricles.

Examples: 2^nd degree or complete heart block

Learn more about this in the ECG interpretation section