A 52-year-old man with chronic kidney disease (eGFR 18 mL/min/1.73m²) presents with muscle weakness and palpitations. Serum potassium is 6.8 mEq/L. An ECG shows peaked T waves and prolonged PR interval. Which investigation is most appropriate to confirm the cardiac manifestation of hyperkalemia?

Explanation

## Investigation of Choice for Cardiac Manifestations of Hyperkalemia ### Role of ECG in Hyperkalemia **Key Point:** The 12-lead electrocardiogram (ECG) is the gold-standard investigation to detect and confirm cardiac toxicity from hyperkalemia. It provides real-time evidence of the electrolyte disturbance's effect on myocardial conduction and repolarization. ### ECG Changes in Hyperkalemia (Progressive) | Serum K⁺ (mEq/L) | ECG Finding | | --- | --- | | 5.5–6.5 | Peaked (tented) T waves, tall and narrow | | 6.5–8.0 | Prolonged PR interval, widened QRS complex | | > 8.0 | Flattened P wave, ST depression, sine-wave pattern | | > 10 | Ventricular fibrillation, cardiac arrest | **High-Yield:** Peaked T waves are the earliest ECG sign of hyperkalemia and appear at K⁺ ~5.5–6.0 mEq/L. They are symmetrical, narrow-based, and confined to precordial leads. ### Why ECG Over Other Tests 1. **Serum potassium level** — Confirms the biochemical abnormality but does NOT assess cardiac safety or urgency of treatment. 2. **ECG** — Directly visualizes the functional cardiac consequence; guides urgency and intensity of intervention. 3. **Chest X-ray** — Non-specific; does not evaluate conduction or repolarization abnormalities. 4. **Echocardiography** — Assesses structural and functional cardiac pathology, not electrolyte-induced conduction disturbances. **Clinical Pearl:** A patient with K⁺ > 6.5 mEq/L and ECG changes (peaked T waves, prolonged PR, widened QRS) requires **immediate** treatment with calcium gluconate (membrane stabilization) regardless of symptoms. **Mnemonic:** **PEAKED** — PR prolongation, Peaked T waves, Absence of P wave, Widened QRS, ECG is the key diagnostic tool, Danger of dysrhythmia. ### Clinical Decision-Making In this case, the patient has: - Serum K⁺ = 6.8 mEq/L (confirmed hyperkalemia) - Clinical symptoms (muscle weakness, palpitations) - ECG findings already noted (peaked T waves, prolonged PR) The ECG **confirms** the cardiac manifestation and justifies emergency treatment. Repeat or confirmatory ECG may be done to assess response to therapy.