What is the primary physiological event represented by the U wave?

The U wave is primarily indicative of the repolarization of the Bundle of His and Purkinje fibers within the heart. This wave typically appears after the T wave on an electrocardiogram (ECG) and can be observed under certain physiological conditions. It reflects the recovery phase of the cardiac conduction system associated with the contraction of the ventricles.

The reason this choice is correct lies in the timing and physiological actions during the cardiac cycle. After the ventricles contract and repolarization occurs — which is represented by the T wave — additional repolarization of the conducting pathways in the heart, particularly those related to the Purkinje fibers and the Bundle of His, can lead to the formation of the U wave.

In contrast, the other options represent different events or phases of cardiac electrical activity that are not linked to the U wave. Atrial repolarization corresponds to events that occur before the QRS complex and does not produce a visible wave in healthy ECGs. Ventricular depolarization is displayed by the QRS complex, not the U wave, reflecting contraction rather than repolarization. The activation of pacemaker cells is represented by the P wave, indicating atrial depolarization, and is unrelated to the U