View source for Atrioventricular node

{{Short description|Electrical conducting structure in the heart}}
{{Infobox anatomy
| Name        = Atrioventricular node
| Latin       = nodus atrioventricularis
| Image      = Reizleitungssystem 1.png
| Caption    = Image showing the [[Electrical conduction system of the heart|conduction system of the heart]]. The AV node is labelled '''2'''.
| Precursor   =
| System      = [[Electrical conduction system of the heart]]
| Artery      = [[Atrioventricular nodal branch]]
| Vein        =
| acronym     = AV node
| Nerve       =
| Lymph       =
}}
The '''atrioventricular node''' ('''AV node,''' or '''Aschoff-Tawara node)''' electrically connects the [[heart]]'s atria and ventricles to coordinate beating in the top of the heart; it is part of the [[electrical conduction system of the heart]].<ref name=gray2002p135>{{Cite book |first=Huon H. |last=Gray |author2=Keith D. Dawkins |author3=Iain A. Simpson |author4=John M. Morgan |title=Lecture Notes on Cardiology |publisher=[[Blackwell Science]] |location=[[Boston]] |year=2002 |page=[https://archive.org/details/lecturenotesonca04edunse/page/135 135] |isbn=978-0-86542-864-5 |url=https://archive.org/details/lecturenotesonca04edunse/page/135 }}</ref> The AV node lies at the lower back section of the [[interatrial septum]] near the opening of the [[coronary sinus]], and conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact (~1 x 3 x 5&nbsp;mm).<ref name="medical-dictionary.thefreedictionary.com">[http://medical-dictionary.thefreedictionary.com/_/viewer.aspx?path=dorland&name=triangle_of-Koch.jpg Full Size Picture triangle of-Koch.jpg]. Retrieved on 2008-12-22</ref>

==Structure==
===Location===
The AV node lies at the lower back section of the [[interatrial septum]] near the opening of the [[coronary sinus]], which conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact (~1 x 3 x 5&nbsp;mm).<ref name="medical-dictionary.thefreedictionary.com"/> It is located at the center of [[Koch's triangle]]—a triangle enclosed by the septal leaflet of the tricuspid valve, the coronary sinus, and the membranous part of the interatrial septum.<ref>[http://www.accessmedicine.com/content.aspx?aID=2874462 Harrison's Principles of Internal Medicine, 17e" Section 3: Disorders of Rhythm] {{webarchive |url=https://web.archive.org/web/20110707080333/http://www.accessmedicine.com/content.aspx?aID=2874462 |date=July 7, 2011 }}</ref>

===Blood supply===
The blood supply of the AV node is from the [[atrioventricular nodal branch]]. The origin of this artery is most commonly (80–90% of hearts) a branch of the [[right coronary artery]], with the remainder originating from the [[left circumflex artery]].<ref name="pmid5086972">{{Cite journal|vauthors=Van der Hauwaert LG, Stroobandt R, Verhaeghe L |title=Arterial blood supply of the atrioventricular node and main bundle |journal=British Heart Journal |volume=34 |issue=10 |pages=1045–1051 |date=October 1972 |pmid=5086972 |pmc=458545 |doi=10.1136/hrt.34.10.1045}}</ref><ref>{{Cite journal | last1 = Pejković | first1 = B. | last2 = Krajnc | first2 = I. | last3 = Anderhuber | first3 = F. | last4 = Kosutić | first4 = D. | title = Anatomical aspects of the arterial blood supply to the sinoatrial and atrioventricular nodes of the human heart | journal = The Journal of International Medical Research | volume = 36 | issue = 4 | pages = 691–698 | year = 2008 | pmid = 18652764 | doi=10.1177/147323000803600410| doi-access = free }}</ref><ref>{{Cite journal | last1 = Saremi | first1 = F. | last2 = Abolhoda | first2 = A. | last3 = Ashikyan | first3 = O. | last4 = Milliken | first4 = J. C. | last5 = Narula | first5 = J. | last6 = Gurudevan | first6 = S. V. | last7 = Kaushal | first7 = K. | last8 = Raney | first8 = A. | doi = 10.1148/radiol.2461070030 | title = Arterial Supply to Sinuatrial and Atrioventricular Nodes: Imaging with Multidetector CT | journal = Radiology | volume = 246 | issue = 1 | pages = 99–107; discussion 108–109 | year = 2007 | pmid = 18024438 }}</ref> This is associated with the [[Coronary artery dominance|dominance]] of the coronary artery circulation. In ''right-dominant'' individuals the blood supply is from the right coronary artery while in left dominant individuals it originates from the left circumflex artery.

===Development===
[[Bone morphogenetic protein]] (BMP) [[cell signaling]] plays a key role in diverse aspects of cardiac differentiation and morphogenesis. (BMPs) are multifunctional signaling molecules critical for the development of AV node. BMP influences AV node development through Alk3 receptor (Activin receptor-like kinase 3). Abnormalities seen in BMP and Alk3 are associated with some cardiovascular diseases like Ebstein's anomaly and AV conduction disease.<ref>{{Cite journal|vauthors=Stroud DM, Gaussin V, Burch JB |title=Abnormal Conduction and Morphology in the Atrioventricular Node of Mice With Atrioventricular Canal–Targeted Deletion of Alk3/Bmpr1a Receptor |journal=Circulation |volume=116 |issue=22 |pages=2535–2643 |date=November 2007 |pmid=17998461|pmc=2947829 |doi=10.1161/CIRCULATIONAHA.107.696583|display-authors=etal}}</ref>

==Function==
[[File:ConductionsystemoftheheartwithouttheHeart-en.svg|thumb|Isolated [[Electrical conduction system of the heart|heart conduction system]] showing atrioventricular node]]
The AV node receives two inputs from the right atrium: posteriorly, via the [[crista terminalis]], and anteriorly, via the interatrial [[septum]].<ref>{{Cite journal|vauthors=Fuster V, Rydén LE, Asinger RW |title=ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation |journal=Journal of the American College of Cardiology |volume=38 |issue=4 |pages=1231–1266 |date=October 2001 |pmid=11583910 |doi=10.1016/S0735-1097(01)01587-X |url=http://www.americanheart.org/downloadable/heart/222_ja20017993p_1.pdf|display-authors=etal|doi-access=free }}</ref>

Contraction of [[cardiomyocytes|heart muscle cells]] requires [[depolarization]] and [[repolarization]] of their cell membranes. Movement of ions across cell membranes causes these events. The cardiac conduction system (and AV node part of it) coordinates myocyte mechanical activity. A wave of excitation spreads out from the [[sinoatrial node]] through the atria along specialized conduction channels. This activates the AV node.<ref name=gray2002p135/> The atrioventricular node delays impulses by approximately 0.09s. This delay in the cardiac pulse is extremely important: It ensures that the atria have ejected their blood into the ventricles first before the ventricles contract.<ref>Campbell, N., & Reece, J. (2002). ''Biology''. 6th ed. San Francisco: Benjamin Cummings{{Page needed|date=September 2010}}{{ISBN?}}</ref>

This also protects the ventricles from excessively fast rate response to atrial [[arrhythmias]] (see below).<ref>{{Cite book |first=Huon H. |last=Gray |author2=Keith D. Dawkins |author3=Iain A. Simpson |author4=John M. Morgan |title=Lecture Notes on Cardiology |publisher=[[Blackwell Science]] |location=[[Boston]] |year=2002 |page=[https://archive.org/details/lecturenotesonca04edunse/page/136 136] |isbn=978-0-86542-864-5 |url=https://archive.org/details/lecturenotesonca04edunse/page/136 }}</ref>

AV conduction during normal cardiac rhythm occurs through two different pathways:
* the first "pathway" has a slow conduction velocity but shorter [[refractory period (physiology)|refractory period]]
* the second "pathway" has a faster conduction velocity but longer refractory period.<ref name=gray2002p157>{{Cite book |first=Huon H. |last=Gray |author2=Keith D. Dawkins |author3=Iain A. Simpson |author4=John M. Morgan |title=Lecture Notes on Cardiology |publisher=[[Blackwell Science]] |location=[[Boston]] |year=2002 |page=[https://archive.org/details/lecturenotesonca04edunse/page/157 157] |isbn=978-0-86542-864-5 |url=https://archive.org/details/lecturenotesonca04edunse/page/157 }}</ref>

An important property that is unique to the AV node is ''decremental conduction'',<ref>{{Cite journal|vauthors=Patterson E, Scherlag BJ |title=Decremental conduction in the posterior and anterior AV nodal inputs |journal=Journal of Interventional Cardiac Electrophysiology |volume=7 |issue=2 |pages=137–148 |date=October 2002 |pmid=12397223 |doi=10.1023/A:1020833604423|s2cid=22728910 }}</ref> in which the more frequently the node is stimulated the slower it conducts. This is the property of the AV node that prevents rapid conduction to the ventricle in cases of rapid atrial rhythms, such as [[atrial fibrillation]] or [[atrial flutter]].

The AV node's normal intrinsic firing rate without stimulation (such as that from the SA node) is 40–60 times/minute.<ref>{{Cite book| edition = 11| publisher = Elsevier Saunders| isbn = 978-0-7216-0240-0| page = [https://archive.org/details/textbookmedicalp09guyt/page/n155 120]| last = Guyton| first = Arthur C.|author2=John E. Hall| title = Textbook of Medical Physiology| url = https://archive.org/details/textbookmedicalp09guyt| url-access = limited| location = Philadelphia| year = 2006}}</ref> This property is important because loss of the conduction system before the AV node should still result in pacing of the ventricles by the slower pacemaking ability of the AV node.

==Clinical significance==
* Atrioventricular conduction disease ([[Atrioventricular block|AV block]]) describes impairment of the electrical continuity between the atria and ventricles. It occurs when the atrial depolarization fails to reach the ventricles or is conducted with an abnormally long delay. It can result from an injury or be a genetically inherited disorder.<ref>{{Cite journal|author=Benson DW |title=Genetics of atrioventricular conduction disease in humans |journal=The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology |volume=280 |issue=2 |pages=934–939 |date=October 2004 |pmid=15372490 |doi=10.1002/ar.a.20099|doi-access=free }}</ref>
* [[AV nodal reentrant tachycardia|Atrioventricular nodal re-entry tachycardia]],<ref name=gray2002p157/> which is caused by a dual AV node physiology and AVNRT can only occur in people with it, however almost half of the population have it, though only a few of them will develop AVNRT at some point in life.<ref>{{Cite web |title=Dual Atrioventricular Nodal Physiology - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/medicine-and-dentistry/dual-atrioventricular-nodal-physiology |access-date=2022-11-14 |website=www.sciencedirect.com}}</ref>
* [[Cystic tumour of atrioventricular nodal region]] (CTAVN) CTAVN is of [[endodermal]] origin and occurs exclusively in the area of the AV node, [[tricuspid valve]], and [[interatrial septum]].<ref>{{Cite journal|vauthors=Sharma G, Linden MD, Schultz DS, Inamdar KV |title=Cystic tumor of the atrioventricular node: an unexpected finding in an explanted heart |journal=Cardiovascular Pathology |volume= 19|issue= 3|pages= e75–e78|date=January 2009 |pmid=19144541 |doi=10.1016/j.carpath.2008.10.011}}</ref>

==See also==
{{Anatomy-terms}}
* [[Junctional rhythm]]

==References==
{{Reflist}}

==External links==
* {{SUNYAnatomyFigs|20|06|02}} – "The conduction system of the heart."
* https://web.archive.org/web/20070929080346/http://www.healthyheart.nhs.uk/heart_works/heart03.shtml

{{Heart anatomy}}
{{Authority control}}

{{DEFAULTSORT:Atrioventricular Node}}
[[Category:Cardiac anatomy]]