CET Electrolyte Imbalances & ECG Changes 1 — Questions and Answers
Question 1: Which ECG change is the hallmark finding of hyperkalemia?
- Prominent U waves
- Peaked (tall, narrow) T waves (Correct answer)
- Shortened QT interval
- Delta waves
Correct answer: Peaked (tall, narrow) T waves
Hyperkalemia causes tall, narrow, peaked T waves due to altered ventricular repolarization from elevated extracellular potassium.
Question 2: Hypokalemia on a 12-lead ECG is most commonly identified by:
- Shortened PR interval
- ST elevation in V1-V4
- Prominent U waves with T wave flattening (Correct answer)
- Widened QRS complex
Correct answer: Prominent U waves with T wave flattening
Hypokalemia produces T wave flattening and prominent positive U waves (deflection after the T wave) most visible in leads V2-V3.
Question 3: Hypercalcemia typically produces which ECG finding?
- Prolonged QT interval
- Prominent U waves
- Shortened QT interval (Correct answer)
- Peaked T waves
Correct answer: Shortened QT interval
Hypercalcemia shortens the ST segment and QT interval because elevated calcium accelerates ventricular repolarization.
Question 4: Which electrolyte abnormality is most strongly associated with a prolonged QT interval and risk of torsades de pointes?
- Hyperkalemia
- Hypermagnesemia
- Hypocalcemia (Correct answer)
- Hypernatremia
Correct answer: Hypocalcemia
Hypocalcemia prolongs the ST segment and QTc interval by extending the plateau phase of the action potential, increasing torsades de pointes risk.
Question 5: In severe hyperkalemia, the ECG 'sine wave' pattern results from:
- Atrial flutter with variable block
- QRS widening merging with the T wave (Correct answer)
- Accelerated junctional rhythm
- Complete right bundle branch block
Correct answer: QRS widening merging with the T wave
As hyperkalemia worsens, progressive QRS widening causes the complex to merge with the T wave, creating a sinusoidal pattern that precedes cardiac arrest.
Question 6: In which leads are U waves most prominently seen in hypokalemia?
- aVR and aVL
- II, III, and aVF
- V2 and V3 (Correct answer)
- V5 and V6
Correct answer: V2 and V3
U waves in hypokalemia are best visualized in the mid-precordial leads V2 and V3, where they appear as a positive deflection after the T wave.
Question 7: Hypomagnesemia on ECG most closely mimics which other electrolyte abnormality?
- Hyperkalemia
- Hypercalcemia
- Hypokalemia (Correct answer)
- Hypernatremia
Correct answer: Hypokalemia
Hypomagnesemia causes T wave flattening and prominent U waves similar to hypokalemia, and the two deficiencies frequently coexist.
CET Electrolyte Imbalances & ECG Changes 1
Which ECG change is the hallmark finding of hyperkalemia?