What is the normal PA interval?

• A. 25-55
• B. 15-30
• C. 40-60
• D. 60-90

Answer: (A)

The PA interval measures intra-atrial conduction time: from the site where the atrial impulse is generated (the pacing stimulus) to the first atrial electrogram recorded at the other atrial site. It reflects how quickly the atrial myocardium conducts the impulse.

A normal PA interval is about 25 to 55 milliseconds. This range captures typical healthy atrial conduction across the atria, including through pathways like Bachmann’s bundle. If the interval is longer than about 60 ms, it suggests slowed intra-atrial conduction, which can occur with atrial disease or scarring. If it’s much shorter (well below 25 ms), that would generally be unusual and may reflect a recording setup that places the recording site very close to the pacing site or measurement error.

So the value around 25–55 ms best represents normal intra-atrial conduction.