This ECG was obtained from a patient who had a serum potassium level of 7.4 mEq/L. It shows some of the earliest ECG signs of hyperkalemia. There are tall, sharply-peaked T waves in many leads. The P waves have not yet widened and lost amplitude, but they will soon flatten out and disappear. At this level of hyperkalemia, we can expect to see conduction disturbances (first-degree AV block in this case) and bradycardia (not yet). It is a bit surprising that the QRS complexes have not yet widened at this serum K level. Caution: hyperkalemia can progress and become life-threatening very quickly.
Potassium is primarily an intracellular electrolyte. It is necessary for proper electrical functioning of the heart. Extracellular serum potassium can rise due to renal failure, or taking potassium supplements, potassium-sparing diuretics, or ACE inhibitors. Occasionally, serum K levels may be artificially elevated by drawing the blood with too much syringe pressure, or using too small a needle, as the red blood cells can be damaged and release intracellular K into the serum.
ECG signs may vary among people with hyperkalemia, but in general:
Serum K levels of 5.5 mEq/L or greater can cause repolarization abnormalities like tall, peaked T waves.