Hyperkalemia ECG vs Hypokalemia ECG
How to tell Hyperkalemia ECG and Hypokalemia ECG apart when a board question makes them look alike.
Hyperkalemia: peaked T waves progressing to a widened QRS; hypokalemia: flattened T waves with prominent U waves.
Side by side
Tall peaked T waves can progress to PR prolongation, P-wave flattening/disappearance, QRS widening, sine-wave rhythm, ventricular arrhythmia, and arrest.
Flattened T waves, ST depression, prominent U waves, and apparent QT/QU prolongation.
High extracellular potassium alters cardiac membrane potentials and progressively slows conduction as levels rise.
Low extracellular potassium delays repolarization and makes U waves more prominent, increasing arrhythmia risk.
Kidney failure, potassium-sparing drugs, acidosis, tissue breakdown, peaked T waves, or widening QRS points hyperkalemia.
Loop/thiazide use, vomiting, diarrhea, alkalosis, flattened T waves, ST depression, or U waves points hypokalemia.
The trap
Both can cause weakness and arrhythmias, so read the T-QRS-U sequence instead of symptoms alone.
Watch it explained
The repair move
For potassium ECGs, scan in order: T wave height, P wave visibility, QRS width, then U waves.
Try a free question
CoreA patient with kidney failure has weakness and an ECG with tall peaked T waves, PR prolongation, small P waves, and widening QRS complexes. Which electrolyte abnormality is most likely?
Show answer and explanation
Answer: A. Hyperkalemia. Hyperkalemia classically causes peaked T waves and can progress to P-wave flattening/disappearance, PR prolongation, QRS widening, and sine-wave rhythm.
Why the other choices are tempting
- B. Hypokalemia causes flattened T waves, ST depression, and prominent U waves.
- C. Hypocalcemia prolongs the QT interval.
- D. Hypernatremia causes neurologic water-balance symptoms, not peaked T waves.
- E. Hypomagnesemia can predispose to arrhythmias but does not create the classic hyperkalemia pattern.
Flashcards
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What is the early ECG clue for hyperkalemia?
Tall peaked T waves are the classic early clue before conduction slowing becomes severe.
What ECG progression signals severe hyperkalemia?
P waves flatten or disappear, PR may prolong, QRS widens, and a sine-wave pattern can develop.
Quick answers
What is the fastest way to tell Hyperkalemia ECG from Hypokalemia ECG?
Hyperkalemia: peaked T waves progressing to a widened QRS; hypokalemia: flattened T waves with prominent U waves.
What is the key clue for Hyperkalemia ECG?
Tall peaked T waves can progress to PR prolongation, P-wave flattening/disappearance, QRS widening, sine-wave rhythm, ventricular arrhythmia, and arrest.
What is the key clue for Hypokalemia ECG?
Flattened T waves, ST depression, prominent U waves, and apparent QT/QU prolongation.
What is the common trap with Hyperkalemia ECG vs Hypokalemia ECG?
Both can cause weakness and arrhythmias, so read the T-QRS-U sequence instead of symptoms alone.