Which wave in the cardiac cycle represents atrial depolarization?

The P wave in the cardiac cycle specifically represents atrial depolarization. This is the electrical activity that occurs in the atria as they prepare to contract and push blood into the ventricles. During this phase, the sinoatrial (SA) node, which is the heart's natural pacemaker, generates an impulse that spreads through the atrial muscle, resulting in depolarization. This depolarization leads to atrial contraction.

In contrast, the QRS wave corresponds to ventricular depolarization, which is a critical part of the cardiac cycle as it leads to the contraction of the ventricles. The T wave represents ventricular repolarization, the process of the ventricles recovering after contraction. The U wave is not always present and its significance is less understood, often associated with certain abnormalities or conditions in the heart.

Therefore, the P wave is distinctly associated with the electrical activity of the atria, marking it as the correct answer in this context. Understanding the different components of the ECG helps in interpreting heart functions and identifying any potential issues in cardiac health.