A 45-year-old man with chronic kidney disease has serum potassium of 7.2 mEq/L. He is asymptomatic. Which electrocardiographic change is expected to appear EARLIEST as potassium rises?
- A Flattening of the P wave
- B Widening of the QRS complex
- C Tall, narrow, peaked T waves ✓
- D Sine wave pattern leading to ventricular fibrillation
Correct answer: C. Tall, narrow, peaked T waves
Explanation
Hyperkalemia accelerates terminal ventricular repolarization, so tall, narrow, peaked T waves are the earliest electrocardiographic change, appearing around 5.5 to 6.5 mEq/L. Progressive elevation then flattens the P wave, widens the QRS, and finally merges QRS and T into a sine wave before cardiac arrest. Recognizing the peaked T wave allows intervention before conduction deteriorates.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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