30-year old patient presenting with generalised weakness.
Describe and interpret this ECG
ECG ANSWER and INTERPRETATION
- The ECG shows widespread ST segment abnormalities
- There is a biphasic appearance to the ST segments and T waves, with initial negative deflection (= ST segment depression / T wave inversion) followed by a terminal positive deflection (= U wave)
- All these waves merge into each other and it is difficult to tell where one wave ends and the other begins
- There is gross prolongation of the QU interval (= time from onset of QRS complex to end of T/U wave)
The combination of…
- Widespread ST depression / T wave inversion
- Prominent U waves
- Long QU interval (> 500 ms)
…. is highly suggestive of severe hypokalaemia.
This patient had a serum K of 1.7 mmol/L in the context of decompensated Conn’s syndrome (primary aldosteronism).
The push-pull effect
- Hypokalaemia creates the illusion that the T wave is “pushed down”, with resultant T-wave flattening/inversion, ST depression, and prominent U waves
- In hyperkalaemia, the T wave is “pulled upwards”, creating tall “tented” T waves, and stretching the remainder of the ECG to cause P wave flattening, PR prolongation, and QRS widening
Biphasic T waves: Wellens or hypokalaemia?
The main differentiating factor (apart from the clinical picture) is the direction of the T waves:
- Wellens: – biphasic T waves go UP then DOWN.
- Hypokalaemia: – T waves go DOWN then UP.