A biphasic P wave in the inferior leads results from interference of the atrial conduction of Bachmann׳s bundle, which in turn results in delayed activation of the left atrium as the impulse propagated from the lower right atrium to the left atrium occurs in a caudo-cranial direction.

What does it mean when there are two P waves?

Bifid P waves (known as P mitrale) indicate left-atrial abnormality – e.g. dilatation or hypertrophy. If at least three different shaped P waves can be seen in a given ECG lead tracing, this implies that even if one of them arises from the SA node, at least two others are arising elsewhere.

What part of the heart has an anomaly if the P wave is abnormal on an ECG?

Morphology [5] Left atrial abnormalities such as hypertrophy and/or dilation are sometimes identifiable on ECG by P wave morphology. Lead V1 can provide useful information about the status of the left atrium. The P wave is often biphasic in this lead.