ECG Case 006

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)

Diagnosis 

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

Hypokalaemia

Further Reading

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.
• Wiesbauer F. Little Black Book of ECG Secrets. Medmastery PDF