What does the P wave represent in an electrocardiogram (ECG)?

The P wave in an electrocardiogram (ECG) specifically represents atrial depolarization. This is the electrical activity that stimulates the atria to contract, thus enabling blood to flow into the ventricles. During this phase of the cardiac cycle, the sinoatrial node (the natural pacemaker of the heart) triggers an impulse that spreads through the atria, causing them to depolarize and subsequently contract.

Understanding the function of the P wave is crucial for interpreting an ECG because it provides insight into the electrical activity of the heart, particularly in the atrial chambers. This knowledge can help identify potential issues such as atrial enlargement or arrhythmias by observing changes in the shape or duration of the P wave. The other options refer to different phases of cardiac electrical activity, with QRS complex indicating ventricular depolarization, the T wave representing ventricular repolarization, and the U wave (if present) sometimes denoting atrial repolarization, further clarifying why the P wave is specifically associated with atrial depolarization.