These tachycardias are usually ventricular. They are common in acute myocardial infarction.
In acute myocardial infarction, treat non-sustained ventricular tachycardia only if it causes significant haemodynamic compromise.
Ensure the serum potassium level >4 mmol/L.
- Amiodarone, IV, 5 mg/kg infused over 30 minutes. Specialist initiated.
- Amiodarone, oral, 800 mg daily for 7 days.
- Then 600 mg daily for 3 days. o Follow with a maintenance dose of 200–400 mg daily, depending upon clinical judgement.
Precautions: o If on warfarin, halve the dose of warfarin and monitor INR closely, until INR is stable.
- Avoid concomitant digoxin. o Monitor thyroid function every 6months as thyroid abnormalities may develop.
- Ophthalmological examination every 6 months.
Only in haemodynamically stable patients:
- Lidocaine (lignocaine), IV, 50–100 mg (1–2 mg/kg) initially and at 5 minute intervals if required to a total of 200–300 mg. Thereafter, for recurrent ventricular tachycardia only:
- Lidocaine, IV infusion, 1–3 mg/minute for 24–30 hours.
Lidocaine will only terminate ± 30% of sustained ventricular tachycardias, and may cause hypotension, heart block or convulsions.
For emergency treatment of ventricular tachycardia, DC cardioversion is first-line therapy, even if stable.
In the absence of acute ischaemia or infarction, consider torsades de pointes, due to QT prolonging drugs.
TORSADES DE POINTES VENTRICULAR TACHYCARDIA (VT)
Torsades de pointes Ventricular Tachycardia (VT) has a twisting pattern to the QRS complexes and a prolonged QT interval in sinus rhythm. It is usually due to a QT-prolonging drug, and/or hypokalaemia and/or a history of alcohol abuse/malnutrition.
Cardioversion/defibrillation, as necessary.
Torsades complicating bradycardia: temporary pacing.
Stop all QT-prolonging drugs.
Correct serum potassium.
- Magnesium sulphate, IV, 2 g administered over 5–10 minutes. If recurrent episodes after initial dose of magnesium sulphate:
- Magnesium sulphate, IV, 2 g administered over 24 hours.
Torsades complicating bradycardia:
- Adrenaline infusion to raise heart rate to > 100/ minute (if temporary pacing unavailable).
» All cases of wide QRS tachycardia, after resuscitation and stabilization.