A young woman presented by EMS for weakness.

Here is her ED ECG:

Diagnosis?  See Below.

There is sinus rhythm.  There is a very wide and bizarre PVC.  The arrows point to what appear to be very late T-waves.  The two black lines show how, if these are T-waves, the QT interval is 600ms and the QTc is then 680ms.  This is too long.  When the QT is this long, you are seeing U-waves, not T-waves.  The blue arrows point to U-waves and the Blue lines show them in simultaneous leads.

Here is the prehospital ECG:

This is harder to interpret, except that there are multiple bizarre PVCs demonstrating the cardiac irritability.

U-waves like this are almost always a result of hypokalemia.  They may also be due to drugs that block potassium channels, which simulates hypokalemia.

The patient’s weakness is due to a K of 1.5 mEq/L.  This is very dangerous and can lead to ventricular fibrillation, as in this case.  It is a true Medical Emergency. 

Here are more ECGs of hypokalemia.

The patient’s K was replenished, and this was the ECG 4 hours later with a K of 4.5 mEq/L: