Torsades de pointes: ECG features and long QT triggers
THE CONTEXT
Torsades de pointes is a form of polymorphic ventricular tachycardia associated with prolonged ventricular repolarisation and a prolonged QT interval.
ECG features and course
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The ECG shows rapid, irregular complexes that appear to twist around the baseline as the mean QRS axis changes.
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The arrhythmia is usually non-sustained and repetitive, but it may degenerate into ventricular fibrillation.
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During sinus rhythm, the corrected QT interval is usually prolonged: greater than 0.44 seconds in men and greater than 0.46 seconds in women when corrected to a heart rate of 60/min.
Predisposition and congenital triggers
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Torsades de pointes is more common in women and is often triggered by a combination of factors, such as QT-prolonging medication and hypokalaemia.
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Congenital long QT syndromes involve mutations in genes encoding cardiac potassium or sodium channels.
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Vigorous exercise causing adrenergic stimulation is a common trigger in long QT type 1. Sudden noise may trigger arrhythmias in type 2, while arrhythmias during sleep are more common in type 3.
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Subtype-specific triggers are important when counselling patients.