Is there atrial enlargement ?
Normal atria: RA depolarization moves towards lead V1 (solid arrow). LA depolarization moves away from lead V1 (dashed arrow).
Both atrial depolarization move towards lead II.
Enlarged RA: Large RA produces stronger depolarization thereby pulling the net electrical vector
towards V1 (positive deflection in first 1/3 of P wave) and
towards II (higher positive deflection of P).
Enlarged LA: Large LA produces stronger depolarization thereby pulling the net electrical vector
away from V1 (negative deflection in last 1/3 of P wave) and
towards towards II (bifid P).
Enlarged RA+LA: Combined effect of enlarged RA and LA