Interatrial Block, Bayés Syndrome, Left Atrial Enlargement, and Atrial Failure.

Interatrial block (IAB) is defined by the presence of a P-wave ≥120 ms. Advanced IAB is diagnosed when there is also a biphasic morphology in inferior leads. The cause of IAB is complete block of Bachmann's bundle, resulting in retrograde depolarization of the left atrium from areas near the atrioventricular junction.