If the cause of a regular narrow complex tachycardia is unclear,  you can unmask the rhythm by transiently increasing AV node block with vagal manoeuvres or adenosine while an recording a 3-lead cardiac tracing.

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; or 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: 2nd degree or complete heart block

Learn more about this in the ECG interpretation section

Drug doses are intended for adults and educational purposes only. Not intended for clinical use.

• Adenosine 6mg IV (can be followed by 12mg then 18mg if unsuccessful) flushed quickly wide-bore cannula in the antecubital fossa 
• Amiodarone 300mg IV over 10-60 minutes
• Atropine 500micrograms IV (repeat every 3-5 minutes to maximum of 3mg if needed; avoid if cardiac transplant, use aminophylline)
• Magnesium sulphate 2g IV over 10 minutes

• 3-lead cardiac monitoring (clockwise from right arm: Ride Your Green Bicycle)
  
  • Red: anterior aspect of right shoulder
  • Yellow: anterior aspect of left shoulder
  • Green: left anterior superior iliac spine
  • Black: not present on defibrillation machine (would go on right anterior superior iliac spine)
• AP defibrillation pads
  • ‘Right’ pad: place longitudinally on left sternal edge
  • ‘Left’ pad: place longitudinally on left paraspinal muscles (in line with anterior pad)

• Anaesthetist/sedation-trained doctor should be present to sedate patient
• Apply 3-lead cardiac monitoring and connect lead to external monitor or defibrillator machine
• Apply defibrillator pads (AP position if atrial dysrhythmia; in anterolateral position if ventricular) after shaving chest if required
• Connect pads lead to defibrillator machine
• Set defibrillator machine monitoring trace to ‘pads’
• Set defibrillator to synchronised mode (synchronises shock with R wave to avoid inducing VF)
• Set energy level (increase as shown if unsuccessful) – energy protocols vary depending on defibrillator and hospital policy. Examples:
  • AF: 200J → 200J → 200J  (biphasic)
  • Broad-complex tachycardia: 150J → 200J → 200J  (biphasic)
• Regular narrow complex tachycardia or atrial flutter: 70J → 100J → 150J  (biphasic)
• Ask anaesthetist to sedate patient and wait until they are happy to proceed
• Ask for oxygen to be removed and everybody to move away from the patient
• Press ‘charge’, then move hand away from button
• Re-check everybody (and oxygen) is away from the patient, announce you are about to shock and, while looking at the patient, hold down the ‘shock’ button until the shock is delivered – it will wait for the R wave
• Re-assess the rhythm and pulse (even if patient reverts to sinus rhythm, ensure you feel pulse to check it is not PEA)
  • If unsuccessful, repeat at next energy (up to 3 attempts)  NB: some defibrilators automatically turn off synchronisation after shock.
  • If successful, reassess patient (ABCDE) and perform another ECG to check rhythm and for any signs of ischaemia
• If cardioversion fails and the patient is unstable, give amiodarone 300 mg IV over 10-20 min and re-attempt electrical cardioversion
• Give all patients who are not anticoagulated therapeutic LMWH or heparin infusion, and continue anticoagulation for at least 4 weeks
• NB: the above is for patients with a pulse. If pulseless, follow cardiac arrest ALS algorithm.

• A conscious patient will require some sedation (ask anaesthetist/sedation-trained doctor)
• Apply the defibrillator machine’s 3-lead cardiac monitoring and defibrillator pads (in standard position) after shaving chest if required
• Ask sedating doctor to sedate patient and wait until they are happy to proceed
• Set defibrillator to pacing (NB: synchronous/demand mode means pacing will only occur if no complex is sensed within given time period; asynchronous/fixed rate mode means pacing will occur at programmed rate regardless of complexes – demand mode usually used)
• Set onscreen pacing rate (default usually 70bpm) and energy (default starting energy usually 30mA)
• Press button to start pacing
• Observe the monitor to see if QRS complexes follow every pacing spike. If not, gradually increase the energy until they do – electrical capture (usually occurs at 50-100mA).
• Next check the patient’s pulse corresponds to the induced QRS complexes – mechanical capture. Now increase the energy by 10mA further.
• Now seek definitive management
• NB: you can touch the patient during pacing

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