Cases: In Case 1, a 63-year-old woman was admitted with muscular weakness. She had hypertension, diabetes mellitus, and chronic renal failure on hemodialysis. She was taking a beta-blocker. Her pulse rate was 42 b.p.m. (irregular rhythm); serum potassium level was 9.8 mmol/L; electrocardiogram revealed widening of the QRS complex (0.256 s). In Case 2, a 59-year-old man was admitted with muscular weakness. He had hypertension and chronic renal failure, and was taking a renin-angiotensin-aldosterone system inhibitor. His pulse rate was 42 b.p.m. (irregular rhythm); serum potassium level was 10.1 mmol/L; electrocardiogram revealed widening of the QRS complex (0.180 s).
Outcome: Life-threatening arrhythmia did not occur, and patients survived under appropriate treatment.
Conclusion: Chronic renal failure, diabetes mellitus, or medications affecting extrarenal potassium homeostasis can produce a tolerance to hyperkalemia. This tolerance may help prevent life-threatening arrhythmia despite fatal levels of serum potassium.
Keywords: Electrocardiogram; hyperkalemia; potassium homeostasis; tolerance.