Tachyarrhythmia Medication Protocol

Tachyarrhythmia (heart rate over 100 beats each minute) is treated by the patient's stability. Adverse features (shock, syncope, ischaemia, heart failure) call for synchronised cardioversion. A stable patient is treated by the rhythm: regular narrow, irregular narrow, or wide complex.

Rhythm check. Obtain a 12-lead ECG, correct oxygen, potassium (aim for 4.0 to 5.0 mmol/L) and magnesium (aim for 1.0 mmol/L or more), and look for causes (sepsis, thyrotoxicosis, drugs, haemorrhage).

Pre-excited atrial fibrillation. Avoid drugs that block the atrioventricular node.

Unstable. Synchronised direct current cardioversion under sedation or anaesthesia.

Regular narrow (supraventricular tachycardia). Vagal manoeuvre, then adenosine, then verapamil or a beta blocker.

Atrial fibrillation or flutter. Rate control (beta blocker, diltiazem, digoxin or amiodarone), and cardioversion for recent onset or instability. Anticoagulate by risk.

Wide complex (ventricular tachycardia). Amiodarone, or cardioversion. Assume ventricular tachycardia unless supraventricular with a bundle branch block is certain.

Torsades de pointes. Magnesium sulphate and correction of potassium.

Special groups.

• Children: adenosine and cardioversion doses by weight.

• Pregnancy: adenosine and cardioversion are safe, and use specialist advice for other drugs.

• Heart failure: amiodarone or digoxin, and avoid verapamil, diltiazem and beta blockers in decompensation.

• East Africa: atrial fibrillation with rheumatic mitral stenosis needs warfarin, not a direct oral anticoagulant. Check thyroid function.

• Cardioversion: synchronised, 70 to 120 joules biphasic for regular narrow rhythms, 120 to 150 joules for atrial fibrillation and ventricular tachycardia, escalating if unsuccessful. Children 1 joule/kg, then 2 joules/kg.

• Adenosine: 6 mg by rapid intravenous bolus with a flush, then 12 mg, then 12 mg. Use 3 mg through a central line or in patients on dipyridamole or carbamazepine. Children 0.1 mg/kg (maximum 6 mg), then 0.2 mg/kg (maximum 12 mg).

• Verapamil: 2.5 to 5 mg intravenously over 2 minutes.

• Metoprolol: 2.5 to 5 mg intravenously over 2 minutes, repeated up to 3 times.

• Diltiazem: 0.25 mg/kg intravenously over 2 minutes, then 5 to 15 mg/h.

• Digoxin: 500 micrograms intravenously over 30 minutes, with further doses to a total of 0.75 to 1.5 mg over 24 hours.

• Amiodarone: 300 mg intravenously over 10 to 60 minutes (central line preferred), then 900 mg over 24 hours. Children 5 mg/kg.

• Magnesium sulphate: 2 g (8 mmol) intravenously over 10 to 15 minutes for torsades.

• Flecainide: 2 mg/kg intravenously (maximum 150 mg) for recent-onset atrial fibrillation in structurally normal hearts.

• Procainamide: 10 to 17 mg/kg intravenously for stable wide complex tachycardia or pre-excited atrial fibrillation, where available.

Monitoring. Continuous ECG, blood pressure and oxygen saturation. Repeat 12-lead ECG after treatment, with potassium, magnesium and thyroid function.

Stop rules. Stop an antiarrhythmic infusion with hypotension, bradycardia or QT prolongation. Limit amiodarone to short courses when thyroid or liver disease is present.

Referral and escalation. Seek cardiology review after cardioversion, for recurrent or refractory arrhythmia, structural heart disease, or suspected pre-excitation, and electrophysiology for ablation.

Common errors. Giving verapamil or diltiazem in wide-complex tachycardia or heart failure, missing pre-excitation, cardioverting atrial fibrillation of unknown duration without anticoagulation planning, and giving adenosine too slowly.