Which ECG change is associated with hypomagnesemia?

Hypomagnesemia, or lower-than-normal levels of magnesium in the blood, can significantly affect the heart's electrical activity. One of the key ECG changes associated with this condition is a prolonged PR interval. This occurs because magnesium plays a vital role in maintaining normal cardiac conduction and excitability. When magnesium levels drop, it can lead to disturbances in the conduction system of the heart, particularly affecting the atrioventricular (AV) node, which is responsible for transmitting electrical impulses from the atria to the ventricles. This results in a delayed conduction time, hence the prolonged PR interval on the ECG.

While other options may be seen in various cardiac conditions, they are not specifically tied to hypomagnesemia. For instance, a shortened QT interval is typically associated with hypercalcemia rather than hypomagnesemia, indicating a relationship with calcium levels rather than magnesium. Bradycardia and atrial fibrillation can occur due to various causes and are not direct indicators of low magnesium levels. Thus, the presence of a prolonged PR interval is a critical ECG finding that reflects the effects of hypomagnesemia on cardiac conduction.