Which of the following is the earliest ECG abnormality expected as serum potassium rises above 5.5 mEq/L?

• A Shortening of the PR interval
• B Loss of P waves with sine wave pattern
• C Widening of the QRS complex
• D Peaked, narrowed T waves ✓

Explanation

Hyperkalaemia produces a predictable ECG sequence: tall peaked narrow-based T waves appear first (around 5.5 to 6.5 mEq/L), followed by flattening of P waves and PR prolongation, then QRS widening, and finally a merging of QRS and T into a sine wave before ventricular fibrillation or asystole. Recognising peaked T waves as the earliest sign matters because it prompts calcium gluconate before conduction deteriorates. Sine wave morphology is a pre-arrest finding, not an early one.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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