Tachyarrhythmias
Torsades de pointes
Polymorphic VT twisting around the baseline, on a background of a long QT.
What you see
- Rapid polymorphic ventricular tachycardia whose amplitude waxes and wanes in spindles.
- The QRS axis twists around the isoelectric line every 5–20 beats.
- The preceding sinus beats show a prolonged QTc, often with prominent U waves.
- Frequently initiated by a short–long–short RR sequence.
Why it looks like that
Delayed repolarisation lengthens the QT and allows early afterdepolarisations to reach threshold. These trigger re-entry in tissue whose refractory periods now vary widely across the ventricle, so the activation wavefront meanders and the axis rotates.
What to do
- Magnesium sulphate 2 g IV, regardless of the serum magnesium.
- Stop every QT-prolonging drug and correct potassium and calcium.
- Increase the heart rate to shorten the QT — isoprenaline or overdrive pacing at 90–110.
- Defibrillate if it degenerates into ventricular fibrillation.
The trap
Amiodarone is the wrong reflex here: it prolongs the QT further. And in congenital long QT, isoprenaline is contraindicated — beta blockade is the treatment. Establish whether the long QT is acquired or congenital before choosing.
More in tachyarrhythmias
Atrial fibrillation
Irregularly irregular narrow complexes with no P waves and a wandering baseline.
Atrial flutter
Sawtooth flutter waves at about 300 per minute, usually conducted 2:1 to give a ventricular rate near 150.
AV nodal re-entrant tachycardia
Regular narrow complex tachycardia around 180 with P waves hidden inside or just after the QRS.
Monomorphic ventricular tachycardia
Broad, regular, identical complexes — assume VT in any broad complex tachycardia until you have proved otherwise.