What segment of an ecg tracing represents the end of the atrial action potential?

Ecg: The ecg represents the surface recording of electrical vectors produced by the summated electrical forces through time produced by the cells of the heart. As such there are millions of atrial action potentials summated in each portion. Roughly the end of the P wave and the rest of theQRS-T would correlate with atrial repolarization and depolarization would be present as the P wave appears