Hyperkalemia and ECG

The earliest sign of hyperkalemia on the ECG is a change in the T wave. It usually is described as tall, narrow, and “peaked” or “tented” in appearance (Fig. 17-36). As the serum potassium level increases, the P-wave amplitude decreases and the PR interval is prolonged. Atrial asystole occurs, along with a widening of the QRS complex. At high, near-lethal potassium levels, the widened QRS complex merges with the T wave and starts to resemble a sine wave. Various dysrhythmias may occur during this time, with progression to VF and asystole. Clinically, the described changes in T waves begin to appear at serum levels of 6 to 7 mEq/L, and QRS complex widening is seen at serum levels of 8 to 9 mEq/L. Vigorous treatment must be instituted to reverse the condition at this point because sudden death may occur at any time after these levels are reached.

The ECG changes in hyperkalemia also may be associated with other conditions. Tall, peaked T waves may be a normal finding or may occur in the early stages of MI. QRS complex widening may be seen with quinidine and procainamide toxicity.