In AV nodal delay PR interval should increase or PR segment?
PR interval increases in AV nodal delay - not just the PR segment.
Here's the distinction:
- PR segment = from end of P wave to start of QRS (reflects conduction through AV node + Bundle of His)
- PR interval = from start of P wave to start of QRS (includes the P wave itself + PR segment)
In AV nodal delay, the conduction slows within the AV node, which falls in the PR segment anatomically. However, on the ECG report and in clinical practice, we measure and report the PR interval as the overall marker of AV conduction time.
So:
- What actually gets prolonged anatomically = PR segment (the AV nodal conduction time)
- What we measure on ECG to diagnose AV delay = PR interval (> 200 ms = 1st degree AV block)
The reason we use PR interval clinically is simply because it's easier to measure precisely (P wave onset is a clear landmark; the exact end of the P wave is harder to define).
Bottom line: AV nodal delay directly prolongs the PR segment, but clinically this manifests as and is diagnosed by a prolonged PR interval.
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