PR interval

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Period in electrocardiography

title: "PR interval" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["cardiac-electrophysiology", "diagnostic-cardiology"] description: "Period in electrocardiography" topic_path: "science/biology" source: "https://en.wikipedia.org/wiki/PR_interval" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Period in electrocardiography ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/9/9e/SinusRhythmLabels.svg" caption="Schematic representation of a normal [[sinus rhythm]] EKG wave"] ::

In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarization); it is normally between 120 and 200 ms in duration. The PR interval is sometimes termed the PQ interval.

Interpretation

Variations in the PQ interval can be associated with certain medical conditions:

Duration
- A long PR interval (of over 200 ms) indicates a slowing of conduction between the atria and ventricles, usually due to slow conduction through the atrioventricular node (AV node). This is known as first degree heart block. Prolongation can be associated with fibrosis of the AV node, high vagal tone, medications that slow the AV node such as beta-blockers, hypokalemia, acute rheumatic fever, or carditis associated with Lyme disease.
- A short PR interval (of less than 120ms) may be associated with a Pre-excitation syndromes such as Wolff–Parkinson–White syndrome or Lown–Ganong–Levine syndrome, and also junctional arrhythmia like atrioventricular reentrant tachycardia or junctional rhythm.
- A variable PR interval may indicate other types of heart block.
PR segment depression may indicate atrial injury or pericarditis. ::figure[src="https://upload.wikimedia.org/wikipedia/commons/9/9b/Heart_electrical_conduction_system_(PQ_segment).svg" caption="electrical conduction system]]"] ::

References

(December 2014). "Clinical cardiac electrophysiology in clinical practice".
(2012). "Heart rate variability in children with acute rheumatic fever". Cardiol Young.
(2009). "Lyme Carditis in Children: Presentation, Predictive Factors, and Clinical Course". Pediatrics.
(2009). "Clinical Examinations in Cardiology".
(2002). "P-R segment depression: An early diagnostic feature in acute pericarditis: A telephone survey of UK accident and emergency departments". European Journal of Emergency Medicine.

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