# PR interval

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{{Short description|Period in electrocardiography}}
[[Image:SinusRhythmLabels.svg|right|thumb|Schematic representation of a normal [sinus rhythm](/source/sinus_rhythm) EKG wave|300x300px]] 

In [electrocardiography](/source/electrocardiography), the '''PR interval''' is the period, measured in milliseconds, that extends from the beginning of the [P wave](/source/P_wave_(electrocardiography)) (the onset of [atrial](/source/Atrium_(heart)) [depolarization](/source/depolarization)) until the beginning of the [QRS complex](/source/QRS_complex) (the onset of [ventricular](/source/Ventricle_(heart)) 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](/source/atrioventricular_node) (AV node).<ref name=":0">{{Cite book|title=Clinical cardiac electrophysiology in clinical practice|others=Huang, David T.,, Prinzi, Travis|isbn=978-1-4471-5433-4|location=Berlin|oclc=897466910|date = December 2014}}</ref> This is known as [first degree heart block](/source/first_degree_heart_block).<ref name=":0" /> Prolongation can be associated with [fibrosis](/source/fibrosis) of the AV node, high [vagal tone](/source/vagal_tone), medications that slow the AV node such as [beta-blockers](/source/Beta_blocker), [hypokalemia](/source/hypokalemia), [acute rheumatic fever](/source/acute_rheumatic_fever), or [carditis](/source/carditis) associated with [Lyme disease](/source/Lyme_disease).<ref name="pmid21933462">{{cite journal |vauthors = Karacan M, Ceviz N, Olgun H |title=Heart rate variability in children with acute rheumatic fever |journal=Cardiol Young |volume=22 |issue=3 |pages=285–92 |year=2012 |pmid=21933462 |doi=10.1017/S1047951111001429 |s2cid=25845504 }}</ref><ref>{{cite journal |doi=10.1542/peds.2008-3058 |pmid=19403477 |title=Lyme Carditis in Children: Presentation, Predictive Factors, and Clinical Course |journal=Pediatrics |volume=123 |issue=5 |pages=e835–41 |year=2009 |last1=Costello |first1=J. M. |last2=Alexander |first2=M. E. |last3=Greco |first3=K. M. |last4=Perez-Atayde |first4=A. R. |last5=Laussen |first5=P. C. |s2cid=25270378 }}</ref>
** A short PR interval (of less than 120ms) may be associated with a [Pre-excitation syndrome](/source/Pre-excitation_syndrome)s such as [Wolff–Parkinson–White syndrome](/source/Wolff%E2%80%93Parkinson%E2%80%93White_syndrome) or [Lown–Ganong–Levine syndrome](/source/Lown%E2%80%93Ganong%E2%80%93Levine_syndrome), and also junctional arrhythmia like [atrioventricular reentrant tachycardia](/source/atrioventricular_reentrant_tachycardia) or [junctional rhythm](/source/junctional_rhythm).
** A variable PR interval may indicate other types of [heart block](/source/heart_block).{{fact|date=May 2015}}
* PR segment depression may indicate atrial injury<ref>{{cite book |first1=B.N. Vijay Raghawa |last1=Rao |year=2009 |chapter=Evolution of ECG Changes |chapter-url=https://books.google.com/books?id=_IGGF2Etes8C&pg=PT575 |pages=561–2 |title=Clinical Examinations in Cardiology |isbn=978-81-312-0964-6}}</ref> or [pericarditis](/source/pericarditis).<ref>{{cite journal |pmid=11989495 |year=2002 |last1=Pedley |first1=D. K. |title=P-R segment depression: An early diagnostic feature in acute pericarditis: A telephone survey of UK accident and emergency departments |journal=European Journal of Emergency Medicine |volume=9 |issue=1 |pages=43–5 |last2=Brett |first2=C |last3=Nichol |first3=N |doi = 10.1097/00063110-200203000-00010|s2cid=22919251 }}</ref>
[[File:Heart electrical conduction system (PQ segment).svg|thumb|PQ segment divided into parts corresponding to the location in heart's [electrical conduction system](/source/Electrical_conduction_system_of_the_heart)|230x230px]]

==See also==
* [P wave](/source/P_wave_(electrocardiography))

==References==
{{reflist}}

{{Cardiovascular physiology}}

{{DEFAULTSORT:Pr Interval}}
Category:Cardiac electrophysiology
Category:Diagnostic cardiology

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Adapted from the Wikipedia article [PR interval](https://en.wikipedia.org/wiki/PR_interval) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/PR_interval?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.