Hyperkalemia affects up to 10% of hospitalized patients, and in the intensive care setting, the percentage is probably higher. The signs and symptoms of critical illness and hyperkalemia—hypotension, shock, kidney failure, and cardiac dysrhythmias frequently overlap, and therefore clinically, even severe hyperkalemia can be overlooked.4 The lethal effects of hyperkalemia are more closely associated with the rate of rise in serum potassium and the effect of hyperkalemia on the ECG findings than on the absolute laboratory value.5,6 Unfortunately, physicians have poor ability to recognize ECG signs of hyperkalemia.7
In addition to peaking of the T waves, there are several less appreciated ECG signs that should prompt practitioners to consider hyperkalemia. These include widening of the QRS complexes, axis shifts, flattening of the P waves, pseudoinfarction pattern and Brugada-type ST-elevation in the anterior chest leads.8 Most of these changes are associated with hyperkalemia-induced transmembrane sodium-channel blockade. The P waves can be absent even during supraventricular rhythms, a condition referred to as sinoventricular conduction. Wide QRS complex pulseless electrical activity and nonshockable regular wide-complex tachycardia are frequently indicators of extreme hyperkalemia and should prompt immediate treatment with intravenous calcium.9 Recently, it was found that overcounting of the heart rate by ECG interpretation software, especially when combined with wide QRS complexes, can also be an indication of severe hyperkalemia.1- 3