Hypokalemia
critical
Variant
A premature beat on the T-U starts torsades de pointes: give magnesium
Hypokalemia
criticalHR80bpm
RR750msQT589ms
RR750msPR182msQRS94msQT589msQTcF648ms
Pause, then click any lead to inspect itDraws the normal ECG in grey behind every lead. Shortcut: N.Hypokalemia, torsades de pointes
A premature beat, a pause, then a second premature beat on the long T-U starts torsades de pointes: a polymorphic VT that twists around the baseline. Give magnesium, not an antiarrhythmic.
On the trace
Try each step, then check it.
- Find the start.
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In the first columns, a premature beat lands on the T-U. The next sinus beat is lost in its refractory period, so a pause follows. A second premature beat lands on the T-U of the sinus beat after the pause: short, long, short. - Look at the run.
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A wide tachycardia at about 250 per minute, with no P, QRS or T to separate. - Watch the twist.
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In each lead the complexes grow, shrink almost to the baseline and come back pointing the other way: torsades de pointes, "twisting of the points". - Watch it end.
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After about five seconds the cycles slow over the last few complexes and it stops on its own. A pause, then sinus beats with the same long T-U. - Look at the readout.
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No rate or interval while it runs, and none across it.
Telling it apart
| Torsades de pointes | Monomorphic VT | |
|---|---|---|
| Complexes | Changing size and axis, twisting around the baseline | Identical, beat after beat |
| Before it | Long QT or QU; short-long-short start | Usually a scar; the QT normal |
| Course | Usually ends on its own, and recurs | Usually sustained |
| Treatment | Magnesium, potassium, preventing pauses | Cardioversion or antiarrhythmics |
What it means
A peri-arrest rhythm. It usually stops within seconds and comes back while the potassium stays low; any episode can degenerate into VF. Give intravenous magnesium sulfate 2 g whatever the serum magnesium, raise potassium to 4.5 to 5 mmol/L, and prevent pauses by pacing or a faster rate. Defibrillate if it is sustained or pulseless. Antiarrhythmics that lengthen the QT, such as amiodarone, can make it worse.
Full articleHypokalemiaHow to recognise it, why it happens, what it means and what to do.