Progression of partial to advanced interatrial block.

Interatrial block (IAB), prolonged conduction between the atria, is denoted by P waves of 110 milliseconds or more and may manifest as partial or advanced. Theoretically, partial IAB may progress to its advanced counterpart if conduction delay increases to complete block. However, there have been no reports of such progression, and electrophysiologic studies have not shown this phenomenon. We briefly review the interatrial conducting pathways of IAB and present the first documentation of possible progression of partial to advanced IAB.