30-year old patient presenting with generalised weakness. 


Describe and interpret this ECG


Main Abnormalities

  • 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?

Biphasic T waves may be seen with both myocardial ischaemia (Wellens syndrome) and 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.

Wellens Syndrome

Biphasic T waves due to ischaemia
Wellens syndrome: biphasic T waves go UP then DOWN


Biphasic T waves due to hypokalaemia
Hypokalaemia: biphasic T waves go DOWN then UP

TOP 100 ECG Series

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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