Tachyarrhythmias

Manage now— do this, in order

• Unstable, any rhythm — synchronised DC cardioversion: sedate the conscious patient, and confirm the synchronisation markers before *every* shock — most defibrillators revert to unsynchronised mode after each discharge. Paediatric energy 1 J/kg first shock, then 2 J/kg.Doctor / NurseNot available at your setup — Defibrillator.
• If three synchronised shocks fail: amiodarone 300 mg IV over 10–20 minutes, repeat the shock, then amiodarone 900 mg over 24 hours; correct potassium and magnesium and try an anteroposterior pad position.Doctor / NurseNot available at your setup — Defibrillator.
• Stable, narrow, regular — vagal manoeuvres first (terminate 20–50%): modified Valsalva — semi-recumbent at 45°, blow into a 10 mL syringe for at least 15 seconds, then lie flat with legs raised to 45° for 15 seconds. Infants: iced flannel over forehead, eyes and nose bridge for up to 15 seconds.
• Adenosine is the first-line drug (terminates AVNRT/AVRT in ~90%): 6 mg rapid IV push over 1–2 seconds with an immediate 20 mL sodium chloride 0.9% flush into the largest proximal vein; if no effect in 1–2 minutes, 12 mg, then a further 12 mg. Start at 3 mg with a central line, dipyridamole or a transplanted heart. Paediatric: 0.1 mg/kg (max 6 mg), then 0.2 mg/kg, then 0.3 mg/kg (max 12 mg). A defibrillator must be to hand — it provokes AF in up to 12%.Doctor / NurseNot available at your setup — Defibrillator.
• If adenosine fails, choose ONE AV-nodal blocking class and stay within it: verapamil 5–10 mg IV over 5–10 min, or diltiazem 0.25 mg/kg IV over 2 min, or metoprolol 5 mg IV every 5 min (max 15 mg). Never verapamil with a broad QRS, never verapamil with a beta-blocker (or the reverse), and verapamil is contraindicated in infants under 1 year.Doctor / Nurse
• Stable, broad, regular — treat as VT: amiodarone 300 mg IV over 20–60 minutes then 900 mg over 24 hours, diluted in 5% dextrose through the largest vein (paediatric 5 mg/kg over 20–60 minutes); or lidocaine 1 mg/kg IV bolus then 1–4 mg/min. One antiarrhythmic at a time — if the drug fails, sedate and cardiovert rather than adding a second.Doctor / Nurse
• Torsades de pointes: magnesium sulphate 2 g (8 mmol) IV over 10–15 minutes in every case (paediatric 25–50 mg/kg, max 2 g); stop every QT-prolonging drug; correct potassium to 4.0–4.5 mmol/L; raise the rate with overdrive pacing at 90–120/min or isoprenaline 2–20 micrograms/min. Never give amiodarone, sotalol or any QT-prolonging antiarrhythmic in torsades.Doctor / Nurse
• Pre-excited AF: synchronised DC cardioversion is the treatment of choice. Verapamil, diltiazem, digoxin, beta-blockers and adenosine are absolutely contraindicated — they block the protective AV node and precipitate ventricular fibrillation. If genuinely stable and a drug is needed: procainamide 10–17 mg/kg at 20–50 mg/min, or ibutilide 1 mg over 10 minutes repeated once.Doctor / Nurse
• Stable AF — rate control first: metoprolol where there is ischaemia, diltiazem where blood pressure is low, never both classes IV together; targets < 110/min without symptoms, < 80/min if symptoms persist. Cardioversion without anticoagulation only if AF < 48 hours (Davidson's: 24 hours — prefer the safer figure); otherwise anticoagulate 3 weeks before or exclude thrombus by transoesophageal echo, and continue at least 4 weeks after. Correct potassium, magnesium, hypoxia and acidosis in parallel — nothing works in an uncorrected patient.Doctor / Nurse