Hyperkalemia can cause which ECG changes?

• A. Prolonged PR interval and widened QRS
• B. Shortened PR interval
• C. ST segment elevation
• D. Prominent U waves

Answer: (A)

Hyperkalemia slows conduction in the heart by changing the electrical environment of cardiac cells. When extracellular potassium rises, the resting membrane potential becomes less negative, which inactivates some of the fast sodium channels responsible for the rapid upstroke of the action potential. This reduces the velocity of depolarization, especially in the atrioventricular (AV) node and ventricles, leading to a longer PR interval (slower AV conduction) and a wider QRS complex (slower ventricular depolarization). Early changes from elevated potassium can include tall, peaked T waves, but as levels rise further, PR prolongation and QRS widening become more prominent, and severe hyperkalemia can progress to a sine-wave pattern with a high risk of fatal rhythm. Among the options, the combination of a prolonged PR interval with a widened QRS best matches the known progression of ECG changes caused by increasing potassium levels. Short PR interval is not typical of hyperkalemia, ST segment elevation points elsewhere (ischemia, pericarditis), and prominent U waves are characteristic of hypokalemia, not hyperkalemia.