RN Nursing · Dysrhythmias · Practice question
A patient receiving loop diuretics develops muscle weakness and ECG abnormalities. Serum potassium is 2.8 mEq/L. Which ECG change is most concerning?
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Peaked T waves
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✓
U waves on ECG
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Shortened QT interval
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ST elevation
Answer & explanation
Correct: U waves on ECG
Hypokalemia (serum potassium 2.8 mEq/L) classically produces U waves on the ECG — a positive deflection following the T wave, most visible in the precordial leads. U waves are the hallmark ECG finding associated with low potassium and, when prominent, indicate significant hypokalemia requiring correction. Loop diuretics such as furosemide are a common cause of potassium wasting. Peaked T waves are the hallmark of hyperkalemia, the opposite electrolyte disturbance. A shortened QT interval is also associated with hypercalcemia rather than hypokalemia; hypokalemia actually prolongs the QT interval, increasing the risk of torsades de pointes. ST elevation is the classic finding in myocardial injury or infarction and is not a characteristic finding of hypokalemia. Among the options presented, U waves are the ECG change most specifically associated with hypokalemia and are therefore most concerning in this clinical context, as they confirm the electrolyte abnormality and signal risk for ventricular dysrhythmias.
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