Metabolic Mayhem

The ECG shows:

• Sinus rhythm at around 70 bpm
• Normal axis
• PR interval 200ms (upper limit of normal)
• Long QT (640ms, QTc 700ms)
• Widespread downsloping ST depression / T wave inversion
• Prominent U waves, especially in the precordial leads

NB. Note that the long QT in this case is an ‘apparent’ long QT due to fusion of the T wave and U wave (see comments below).

The combination of a markedly prolonged QT interval, widespread ST depression and T wave inversion with prominent U waves is pathognomonic of severe hypokalaemia.

• This patient’s potassium was 1.7 mmol/L (she had recently stopped taking her spironalactone).
• The muscle pain was rhabdomyolysis secondary to hypokalaemia.
• She was treated in the high-dependency area for 3 days on a continuous potassium drip and made a good recovery.

Full review of the ECG features of hypokalaemia

The ECG shows:

• Sinus tachycardia at 120 bpm
• Inferior axis (+90 degrees)
• Normal intervals
• Markedly peaked T waves, particularly in V3-4

Hyperkalaemia secondary to diabetic ketoacidosis (this patient’s potassium was 8.5 mmol/L)

This is his ECG after treatment, by which time the potassium was 5.5 mmol/L:

Full review of the ECG features of hyperkalaemia

• Hampton, JR. The ECG In Practice, 6e
• Mattu A, Brady W. ECG’s for the Emergency Physician 1
• Mattu A, Brady W. ECGs for the Emergency Physician 2
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
• Wagner, GS. Marriott’s Practical Electrocardiography 12e

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