The atrioventricular node or AV node electrically connects the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

's atria and ventricles to coordinate beating in the top of the heart; it is part of the

electrical conduction system of the heart The cardiac conduction system (CCS) (also called the electrical conduction system of the heart) transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the ...

. The AV node lies at the lower back section of the

interatrial septum The interatrial septum is the wall of tissue that separates the right and left atria of the heart. Structure The interatrial septum is a that lies between the left atrium and right atrium of the human heart. The interatrial septum lies at angl ...

near the opening of the

coronary sinus In anatomy, the coronary sinus () is a collection of veins joined together to form a large vessel that collects blood from the heart muscle ( myocardium). It delivers deoxygenated blood to the right atrium, as do the superior and inferior ven ...

, and conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact (~1 x 3 x 5 mm).Full Size Picture triangle of-Koch.jpg
Retrieved on 2008-12-22

Structure

Location

The AV node lies at the lower back section of the

near the opening of the

, which conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact (~1 x 3 x 5 mm). It is located at the center of

Koch's triangle Koch's triangle, named after the German pathologist Walter Koch, is an anatomical area located in the superficial paraseptal endocardium of the right atrium, which its boundaries are the coronary sinus orifice, tendon of Todaro, and septal leafle ...

—a triangle enclosed by the septal leaflet of the tricuspid valve, the coronary sinus, and the membranous part of the interatrial septum.

Blood supply

The blood supply of the AV node is from the

atrioventricular nodal branch The atrioventricular nodal branch is a coronary artery that feeds the atrioventricular node, necessary for the excitation of the ventricles. Structure The atrioventricular nodal branch sees significant variation in origin: * proximal posterola ...

. The origin of this artery is most commonly (80–90% of hearts) a branch of the

right coronary artery In the blood supply of the heart, the right coronary artery (RCA) is an artery originating above the right cusp of the aortic valve, at the right aortic sinus in the heart. It travels down the right coronary sulcus, towards the crux of the hear ...

, with the remainder originating from the

left circumflex artery The circumflex branch of left coronary artery, or left circumflex artery or circumflex artery, is a branch of the left coronary artery. Description The left circumflex artery follows the left part of the coronary sulcus, running first to the l ...

. This is associated with the 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 Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of piv ...

(BMP)

cell signaling In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellula ...

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.

Function

ConductionsystemoftheheartwithouttheHeart-en

The AV node receives two inputs from the right atrium: posteriorly, via the

crista terminalis The crista terminalis or terminal crest represents the junction between the sinus venosus and the heart in the developing embryo. In the development of the human heart, the right horn and transverse portion of the sinus venosus ultimately become in ...

, and anteriorly, via the interatrial

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

. Contraction of

heart muscle cells Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle th ...

requires

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is esse ...

and

repolarization In neuroscience, repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential which has changed the membrane potential to a positive value. The repolarizat ...

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 The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...

through the atria along specialized conduction channels. This activates the AV node. 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. This also protects the ventricles from excessively fast rate response to atrial

arrhythmias Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

(see below). AV conduction during normal cardiac rhythm occurs through two different pathways: * the first “pathway” has a slow conduction velocity but shorter refractory period * the second “pathway” has a faster conduction velocity but longer refractory period. An important property that is unique to the AV node is ''decremental conduction'', 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 Atrial flutter (AFL) is a common abnormal heart rhythm that starts in the atrial chambers of the heart. When it first occurs, it is usually associated with a fast heart rate and is classified as a type of supraventricular tachycardia. Atrial f ...

. The AV node's normal intrinsic firing rate without stimulation (such as that from the SA node) is 40–60 times/minute. 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 (

AV block Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatr ...

) 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. * Atrioventricular nodal re-entry tachycardia, 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. *

Cystic tumour of atrioventricular nodal region Cystic tumour of the atrioventricular nodal region is a very rare tumour of the heart in the region of the atrioventricular node. It is also known as ''mesothelioma of the atrioventricular node''. Presentation It may present as a cardiac arrhythm ...

(CTAVN) CTAVN is of

endodermal Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastru ...

origin and occurs exclusively in the area of the AV node,

tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right vent ...

, and

References

External links

* – "The conduction system of the heart." * () * https://web.archive.org/web/20070929080346/http://www.healthyheart.nhs.uk/heart_works/heart03.shtml {{DEFAULTSORT:Atrioventricular Node Cardiac anatomy