From the Guidelines
Unstable torsades de pointes requires immediate treatment with electrical cardioversion at 120-200 joules (biphasic) and administration of IV magnesium sulfate 2g over 1-2 minutes, followed by an infusion of 2-4g over 1-2 hours, regardless of serum magnesium levels, as recommended by the 2017 AHA/ACC/HRS guideline 1.
Treatment Approach
The treatment approach for unstable torsades de pointes involves several key steps:
- Electrical cardioversion to immediately convert the arrhythmia
- Correction of electrolyte abnormalities, particularly magnesium and potassium, to prevent recurrence
- Discontinuation of any QT-prolonging medications
- Consideration of temporary transvenous pacing or isoproterenol infusion to increase the heart rate and shorten the QT interval if torsades recurs
Electrolyte Correction
Correcting hypokalemia to maintain potassium levels between 4.5-5.0 mEq/L is crucial, as hypokalemia can exacerbate QT prolongation 1. Additionally, magnesium repletion to normal values (e.g., ≥2.0 mmol/L) is beneficial in suppressing the arrhythmia 1.
Refractory Cases
For refractory cases, consideration of lidocaine 1-1.5 mg/kg IV bolus followed by infusion at 1-4 mg/minute may be necessary, although this is not explicitly recommended in the 2017 AHA/ACC/HRS guideline 1. The use of magnesium sulfate in cardiac arrest is not recommended unless torsades de pointes is present, as noted in the 2010 American Heart Association guidelines 1.
Key Recommendations
- Administer IV magnesium sulfate 2g over 1-2 minutes, followed by an infusion of 2-4g over 1-2 hours, regardless of serum magnesium levels 1
- Correct hypokalemia to maintain potassium levels between 4.5-5.0 mEq/L
- Discontinue any QT-prolonging medications immediately
- Consider temporary transvenous pacing or isoproterenol infusion to increase the heart rate and shorten the QT interval if torsades recurs 1
From the FDA Drug Label
5.4 Proarrhythmia Like all antiarrhythmic agents, amiodarone may cause a worsening of existing arrhythmias or precipitate a new arrhythmia sometimes leading to fatal outcomes [see Adverse Reactions ( 6-6. 2)]. Proarrhythmia, primarily torsade de pointes (TdP), has been associated with prolongation, by intravenous amiodarone, of the QTc interval to 500 ms or greater. The FDA drug label does not answer the question.
From the Research
Treatment for Unstable Torsades de Pointes (TdP)
The treatment for unstable Torsades de Pointes (TdP) includes:
- Withdrawal of any precipitating agents 2
- Intravenous administration of magnesium sulfate, potassium supplements, and lidocaine 2
- Adequate sedation 2
- Transvenous ventricular pacing at rapid rates to shorten the QT interval, eliminate the pauses that precipitate TdP, and prevent further bursts of arrhythmias 2
- Acceleration of the basic heart rate with isoproterenol, which should only be used when TdP is due to an acquired LQTS, the underlying rhythm is slow, and torsades is clearly "pause dependent", and transvenous pacing cannot be immediately implemented 2
- Intravenous administration of magnesium sulphate, terminating prolonged episodes using electrical cardioversion 3
- Increasing the underlying heart rate using isoproterenol (isoprenaline) or transvenous pacing in refractory cases of recurrent TdP 3
- Correction of electrolyte abnormalities and hypoxia, with potassium concentrations maintained in the high normal range 3
Dosage of Magnesium Sulfate
The optimal dosage of magnesium sulfate for TdP in children with long QT syndrome is:
- A bolus injection of 3 to 12 mg/kg, followed by continuous infusion at rates of 0.5 to 1.0 mg/kg/hr 4
- Serum magnesium (SMg) concentration of 3 to 5 mg/dL 4
Effectiveness of Magnesium Sulfate
Magnesium sulfate is a very effective and safe treatment for TdP associated with acquired long QT syndrome (LQTS) in adults 5, 6, 3 and children 4