Editing Atrioventricular node (section)

==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.