Hyperkalemia, the sine wave
The QRS has widened until it runs into the T: one broad, smooth wave per beat, with no P, no ST segment and nothing left to measure. A peri-arrest rhythm.
On the trace
- Look at the shape. One broad, smooth wave per beat, with no sharp deflection in it: the QRS runs straight into the T. There is no P, no ST segment and no point where one wave ends and the next begins.
- Check the rate. Regular, 120 per minute. The beat starts in the ventricles now, not the sinus node.
- Look at the readout. PR, QRS, QT and QTc all show a dash. With no J point there is nowhere to measure them from, and the inspect box offers only the full beat.
- Look at the chest leads. Largest in V2 and V3, about 23 mm from peak to trough, and large in every chest lead.
- Compare II with aVR. Mostly positive in II, mostly negative in aVR.
Telling it apart
| Sine wave | Ventricular tachycardia | |
|---|---|---|
| Complex | Smooth and rounded throughout | Usually sharper deflections within the QRS |
| ST and T | Merged into the complex | Usually separate from the QRS |
| Setting | Kidney failure, a drug that raises potassium, rhabdomyolysis | Structural heart disease, scar |
| Treatment | Calcium | Cardioversion or antiarrhythmics |
What it means
A peri-arrest rhythm: ventricular fibrillation or asystole can follow within minutes. It is often mistaken for VT. Give intravenous calcium at once and repeat it until the complexes narrow, then shift and remove the potassium. Antiarrhythmics such as amiodarone and lidocaine slow conduction further and can precipitate arrest.
Full articleHyperkalemiaHow to recognise it, why it happens, what it means and what to do.