Clinical Scenario:
A 10-year-old boy is admitted with diabetic ketoacidosis (DKA). Treatment is initiated with intravenous fluids and insulin. A few hours later, an ECG is performed and shows mild ST-segment depression, prominent U waves, and QT interval prolongation. Laboratory investigations reveal the following:
| Investigation | Result |
|---|---|
| Serum sodium | 137 mmol/L |
| Serum potassium | 3.8 mmol/L |
| Random blood glucose | 310 mg/dL |
What is the most likely cause of these ECG changes?
A. Hyponatremia
B. Hypernatremia
C. Hypokalemia
D. Hyperkalemia
E. Hypocalcemia
Correct answer & Explanation:
Answer: C. Hypokalemia
Explanation: ECG changes in hypokalemia
The ECG findings of ST-segment depression, prominent U waves, and QT prolongation are classic features of hypokalemia. In diabetic ketoacidosis, there is a significant total body potassium deficit due to osmotic diuresis and potassium loss in urine. Although the serum potassium level may initially be normal or even elevated, it does not accurately reflect total body potassium stores. Once insulin therapy is started, potassium shifts into the cells, making hypokalemia more apparent. ECG changes are often a more reliable indicator of clinically significant potassium depletion.
Why not the other options?
- A. Hyponatremia: Usually does not produce characteristic ECG changes. Severe hyponatremia may rarely cause conduction abnormalities but not the ECG pattern seen here.
- B. Hypernatremia: Typically does not cause specific ECG abnormalities, and the serum sodium level is normal in this patient.
- D. Hyperkalemia: Characteristically causes tall peaked T waves, shortened QT interval, widening of the QRS complex, and eventually sine-wave changes in severe cases.
- E. Hypocalcemia: Causes QT prolongation by prolonging the ST segment but does not produce prominent U waves or the typical ECG findings seen in hypokalemia.
