The atrioventricular node (AV node, or Aschoff-Tawara node) electrically connects the

heart The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...

'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 Cardiac action potential, signals generated by the sinoatrial node – the heart's Cardiac pacemaker, pacemaker, to cause the heart musc ...

. 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 ang ...

near the opening of the

coronary sinus The coronary sinus () is the largest vein of the heart. It drains over half of the deoxygenated blood from the heart muscle into the right atrium. It begins on the backside of the heart, in between the left atrium, and left ventricle; it begi ...

, 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, also known as the triangle of Koch, is named after the German pathology, pathologist Walter Koch (physician), Walter Koch. It is an anatomical area located at the base of the right atrium, and its boundaries are the coronary sin ...

—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 supplies arterial blood to the atrioventricular node, which is responsible for initiating muscular contraction of the ventricles. The AV nodal branch is most often a branch of the right ...

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

right coronary artery In the coronary circulation, blood supply of the heart, the right coronary artery (RCA) is an artery originating above the right cusp of the aortic valve, at the Aortic sinus, right aortic sinus in the heart. It travels down the right coronary su ...

, with the remainder originating from the

left circumflex artery The circumflex branch of left coronary artery (also known as the left circumflex artery or circumflex artery) is a branch of the left coronary artery. It winds around the left side of the heart along the atrioventricular groove (coronary sulc ...

. 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. Professor Marshall Urist and Professor Hari Reddi discovered their ability to induce the formation of bone and cartilage, BMPs are now ...

(BMP)

cell signaling In biology, cell signaling (cell signalling in British English) is the Biological process, process by which a Cell (biology), cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all Cell (biol ...

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 (also known as the terminal crest, or crista terminalis of His) is a vertical ridge on the posterolateral inner surface of the adult right atrium extending between the superior vena cava, and the inferior vena cava. The cris ...

, and anteriorly, via the interatrial

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

. Contraction of heart muscle cells requires

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

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, sinus node or Keith–Flack node) is an ellipse, oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of Cell (biology), cells known as pa ...

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, are irregularities in the heartbeat, including when it is too fast or too slow. Essentially, this is anything but normal sinus rhythm. A resting heart rate that is too fast – above 100 beats ...

(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 Atrial fibrillation (AF, AFib or A-fib) is an Heart arrhythmia, abnormal heart rhythm (arrhythmia) characterized by fibrillation, rapid and irregular beating of the Atrium (heart), atrial chambers of the heart. It often begins as short periods ...

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 (SVT). ...

. 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) 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