CET Electrolyte Imbalances & ECG Changes 2 — Questions and Answers
Question 1: What is the FIRST ECG change seen as serum potassium rises in progressive hyperkalemia?
- Absent P waves
- Widened QRS complex
- Peaked T waves (Correct answer)
- Sine wave pattern
Correct answer: Peaked T waves
Peaked T waves are the earliest manifestation of hyperkalemia, appearing before any conduction abnormalities such as PR prolongation or QRS widening.
Question 2: A patient with end-stage renal disease presents with absent P waves and a widened QRS. The most likely cause is:
- Atrial fibrillation from hypomagnesemia
- Hypocalcemia
- Severe hyperkalemia (Correct answer)
- Digoxin toxicity
Correct answer: Severe hyperkalemia
Absent P waves and widened QRS in a renal failure patient indicate severe hyperkalemia impairing both atrial depolarization and ventricular conduction.
Question 3: The QTc interval is most reliably prolonged in which electrolyte condition?
- Hyperkalemia
- Hypercalcemia
- Hypermagnesemia
- Hypocalcemia (Correct answer)
Correct answer: Hypocalcemia
Hypocalcemia specifically prolongs the ST segment (isoelectric portion), extending the QTc and increasing risk of torsades de pointes.
Question 4: Which electrolyte imbalance is the first-line treatment target when a patient develops torsades de pointes?
- Hyperkalemia correction
- Hypomagnesemia correction (Correct answer)
- Hypercalcemia correction
- Hypernatremia correction
Correct answer: Hypomagnesemia correction
IV magnesium sulfate is the first-line treatment for torsades de pointes; hypomagnesemia facilitates the QT prolongation that initiates this arrhythmia.
Question 5: How does hyperkalemia progressively affect the PR interval on ECG?
- Shortens it below 120 ms
- Has no effect on the PR interval
- Prolongs it beyond 200 ms (Correct answer)
- Creates a delta wave at the start of QRS
Correct answer: Prolongs it beyond 200 ms
Hyperkalemia slows AV nodal conduction, causing PR interval prolongation that can progress to complete AV block if potassium continues to rise.
Question 6: A patient on furosemide develops ST depression, T wave flattening, and prominent U waves. The most likely electrolyte cause is:
- Hyponatremia
- Hypercalcemia
- Hypermagnesemia
- Hypokalemia (Correct answer)
Correct answer: Hypokalemia
Loop diuretics like furosemide cause renal potassium wasting; hypokalemia classically produces ST depression, T wave flattening, and prominent U waves.
Question 7: Which emergency medication stabilizes the cardiac membrane in hyperkalemia WITHOUT lowering the serum potassium level?
- Sodium bicarbonate
- Regular insulin with dextrose
- Calcium gluconate (Correct answer)
- Sodium polystyrene sulfonate
Correct answer: Calcium gluconate
Calcium gluconate directly antagonizes hyperkalemia's membrane effects within minutes, providing temporary cardiac protection without redistributing or removing potassium.
CET Electrolyte Imbalances & ECG Changes 2
What is the FIRST ECG change seen as serum potassium rises in progressive hyperkalemia?