ECG progression of hyperkalemia by severity
Hyperkalemia produces a predictable ECG progression that correlates roughly with serum potassium levels, though individual variability means ECG changes can occur at lower levels than expected — particularly in patients with chronic kidney disease, diabetes, or concurrent acidosis.
Mild hyperkalemia (5.5–6.5 mEq/L): Tall, peaked, narrow-based T waves are the earliest ECG change. These T waves have a characteristic morphology — symmetric, narrow-based, and pointed — most prominent in the precordial leads V2–V5. This distinguishes them from the tall T waves of hyperacute STEMI (which are broad-based and asymmetric) and LV volume overload.
Moderate hyperkalemia (6.5–7.5 mEq/L): P waves flatten and widen as atrial conduction slows. The PR interval lengthens. QRS begins to widen. The sinoatrial node continues to fire but atrial conduction is impaired — producing a pattern that resembles junctional rhythm or AV block.
Severe hyperkalemia (>7.5 mEq/L): QRS widens progressively until it merges with the T wave — the sine-wave pattern. This is a preterminal pattern and represents impending cardiac arrest. VF or asystole follows without immediate treatment.
Treatment-ECG correlation: what to give based on ECG findings
Calcium gluconate is the first-line treatment for severe hyperkalemia with ECG changes — specifically QRS widening. Calcium does not lower potassium; it stabilizes the myocardial membrane by raising the threshold potential. The ECG effect occurs within minutes: QRS narrows, rhythm stabilizes. One to two ampules IV over 5–10 minutes, with repeat dosing if ECG changes persist.
Insulin + dextrose shifts potassium intracellularly. Regular insulin 10 units IV with 25g dextrose (50 mL of D50). Onset 15–30 minutes, effect lasts 1–2 hours. Monitor for hypoglycemia. Sodium bicarbonate shifts potassium intracellularly through an ion-exchange mechanism — useful when metabolic acidosis is concurrent.
Definitive treatment requires potassium removal: Kayexalate (sodium polystyrene sulfonate) or Lokelma (sodium zirconium cyclosilicate) exchange resins, loop diuretics with adequate urine output, or dialysis for severe or refractory hyperkalemia. Dialysis is the fastest and most reliable method for removing large potassium loads.