What does the P wave in an ECG represent?

The P wave in an ECG represents the electrical activity associated with the contraction of the atria. Specifically, it reflects the depolarization of the atrial myocardium as the electrical impulse travels through the atria. This depolarization leads to atrial contraction, which is crucial for pushing blood from the atria into the ventricles before ventricular contraction occurs. Understanding this is essential, as it provides insight into the heart's rhythm and electrical function, which is vital in evaluating cardiac health during dental procedures and anesthesia management.

The other options do not accurately describe the significance of the P wave: the contraction of ventricles is represented by the QRS complex, while the repolarization of ventricles is indicated by the T wave. The interval before ventricular contraction can be observed in the PR interval, which runs from the beginning of the P wave to the beginning of the QRS complex but does not represent the significance of the P wave itself.