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This post is an answer to the ECG Case 338

• Rate: 48 bpm
• Rhythm: Regular, sinus rhythm
• Axis: Normal
• Intervals:
  • PR – Normal (~160ms)
  • QRS – Normal (100ms)
  • QT – 480ms (QTc Bazette 430 ms)
    • Note the ECG machine calculated the QT 500ms / QTc 480ms
    • Likely due to low T wave voltage plus T-U fusion

• Additional:
  • Subtle ST depression in leads II, aVF
  • U wave visible in leads V2-3
  • T waves globally flat
  • Relatively long ST segment

Changes consistent with electrolyte abnormality – differentials: 

• Hypokalaemia – U waves, T-U fusion with QT prolongation, ST depression, low voltage T waves
• Hypomagnesaemia – associated with hypokalaemia
• Hypocalcaemia – causes long QT due to ST segment lengthening

What happened next ?

The patient’s potassium (K) was 2.7 mmol/L with a low-normal magnesium and low-normal calcium. Following IV electrolyte replacement the patients ECG changes resolved and her symptoms of weakness also resolved. 

READ ALSO:

• Hypokalemia ECG Changes [With Examples]
• Disorders of Potassium Homeostasis (Hypokalemia and Hyperkalemia)

SIMILAR CASES:

• Hypokalemia in a Man With Generalized Weakness
• Hypokalemia as a result of Anorexia Nervosa and Diarrhea