Interatrial block (IAB) may be manifested by a number of changes in the P wave. P wave interatrial block is associated with an increased risk of developing atrial fibrilation.
Pathophysiology: fibrosis of the interatrial conduction pathways, primarily in the Cahmann region
In complete IAB there is a complete blockage of the interatrial conduction pathways. The left atrium is activated in a caudocranial direction, causing a biphasic P wave in the inferior leads.
With incomplete IAB the transmission along the interatrial conduction pathways is prolonged, with an increase in the P wave duration.
Parameters:
(1) morphology of P wave in the inferior leads (II, III, aVF)
(2) duration of the P wave in milliseconds
Parameter
Finding
Interpretation
P wave morphology
monophasic
not complete IAB block
biphasic
complete IAB block
P wave duration
< 120 ms
not incomplete IAB block
>= 120 ms
at least incomplete IAB block
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