Which sequence best describes ECG progression in untreated severe hyperkalemia?

Which sequence best describes ECG progression in untreated severe hyperkalemia?

• A. ST segment changes progress to Q waves
• B. Flattened T waves followed by U waves
• C. Tall peaked T waves → Wide QRS → Sine-wave pattern
• D. Normal ECG

Answer: (C)

In severe hyperkalemia, the heart’s electrical activity changes in a distinct, progression-driven way because high extracellular potassium alters cardiac myocyte excitability and conduction. Early on, elevated potassium speeds repolarization, so the T waves become tall and peaked. As potassium rises further, conduction slows: the PR interval lengthens and the P waves may flatten, and the QRS complex widens as ventricular depolarization takes longer. If potassium remains very high, the QRS and T waves can merge into a sine-wave pattern, a dangerous rhythm that can lead to cardiopulmonary arrest. This sequence—tall peaked T waves followed by widening of the QRS and then a sine-wave pattern—best fits the described progression. Other options don’t fit this pattern: ST changes progressing to Q waves are more typical of myocardial infarction; flattened T waves with a U wave point to hypokalemia; a normal ECG would not occur in untreated severe hyperkalemia.

In severe hyperkalemia, the heart’s electrical activity changes in a distinct, progression-driven way because high extracellular potassium alters cardiac myocyte excitability and conduction. Early on, elevated potassium speeds repolarization, so the T waves become tall and peaked. As potassium rises further, conduction slows: the PR interval lengthens and the P waves may flatten, and the QRS complex widens as ventricular depolarization takes longer. If potassium remains very high, the QRS and T waves can merge into a sine-wave pattern, a dangerous rhythm that can lead to cardiopulmonary arrest. This sequence—tall peaked T waves followed by widening of the QRS and then a sine-wave pattern—best fits the described progression.

Other options don’t fit this pattern: ST changes progressing to Q waves are more typical of myocardial infarction; flattened T waves with a U wave point to hypokalemia; a normal ECG would not occur in untreated severe hyperkalemia.