A client is admitted with a serum potassium of 6.2 mEq/L. Which finding requires the nurse's MOST urgent attention?

HYPERKALEMIA (K+ above 5.0 mEq/L) produces a predictable progression of ECG changes that correlates with potassium level and toxicity: K+ 5.5-6.5 mEq/L: PEAKED T WAVES — tall, narrow, symmetrical T waves; this is the first ECG sign; K+ 6.5-7.5 mEq/L: prolonged PR interval, widened QRS, loss of P waves; K+ above 7.5 mEq/L: sinusoidal wave pattern → VENTRICULAR FIBRILLATION → asystole. THE URGENCY: Peaked T waves indicate the cardiac conduction system is being affected and the patient is at immediate risk of fatal dysrhythmia; this takes priority over subjective symptoms like weakness. NURSING PRIORITIES WITH PEAKED T WAVES: (1) CONTINUOUS CARDIAC MONITORING — apply immediately if not already in place; (2) NOTIFY PROVIDER IMMEDIATELY; (3) PREPARE FOR EMERGENCY TREATMENT: Calcium gluconate IV — cardiac membrane stabiliser; does not lower K+ but protects the heart; fastest-acting intervention; Sodium bicarbonate IV — drives K+ into cells (alkalosis shifts K+ intracellularly); Dextrose 50% + Regular insulin — drives K+ into cells (faster-acting); Kayexalate (sodium polystyrene) — GI potassium binder; removes K+ from body; slower (hours); Dialysis for severe refractory hyperkalemia. CAUSES OF HYPERKALEMIA: Renal failure (most common); ACE inhibitors; potassium-sparing diuretics; excessive supplementation; acidosis; tissue destruction (rhabdomyolysis, haemolysis).