What typically happens to the QRS complex in the presence of hyperkalemia?

In the presence of hyperkalemia, the QRS complex typically widens. This occurs because elevated potassium levels can have a profound impact on the cardiac conduction system. Specifically, hyperkalemia affects the resting membrane potential of cardiac myocytes, making it less negative, which alters the excitability and conduction velocity of cardiac action potentials.

As potassium levels rise, the decreased excitability leads to slower conduction through the His-Purkinje system and ventricular myocardium, resulting in a prolonged depolarization phase. This prolongation manifests as widening of the QRS complex on the ECG. In more severe cases of hyperkalemia, the QRS may take on a "tombstone" appearance, indicating significant changes in the ventricular depolarization process.

This widening is an important ECG change to recognize, as it may indicate the risk for more serious arrhythmias and potentially life-threatening cardiac events.