Interval PR

The PR interval is the time from the onset of the P wave to the start of the QRS complex. It reflects conduction through the AV node.

·       The normal PR interval is between 120 – 200 ms (0.12-0.20s) in duration (three to five small squares).

·       If the PR interval is > 200 ms, first degree heart block is said to be present.

·       PR interval < 120 ms suggests pre-excitation (the presence of an accessory pathway between the atria and ventricles) or AV nodal (junctional) rhythm.

Prolonged PR Interval – AV block (PR >200ms)

·       Delayed conduction through the AV node

·       May occur in isolation or co-exist with other blocks (e.g., second-degree AV block, trifascicular block)

Short PR interval (<120ms)

A short PR interval is seen with:

·       Preexcitation syndromes

·       AV nodal (junctional) rhythm.

https://litfl.com/pr-interval-ecg-library/

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