Atrioventricular node
Encyclopedia
The atrioventricular node (abbreviated AV node) is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers. The AV node is an area of specialized tissue
between the atria and the ventricles
of the heart
, specifically in the posteroinferior region 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 mm). 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 membraneous part of the interatrial septum.
The AV node may also be (rarely) referred to as the Aschoff-Tawara node named so after Ludwig Aschoff
and Sunao Tawara
.
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. The atrioventricular node delays impulses by approximately 0.12s. 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 (see below).
The AV node receives two inputs from the atria: posteriorly, via the crista terminalis
, and anteriorly, via the interatrial septum
.
AV conduction during normal cardiac rhythm occurs through two different pathways:
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
.
The AV node's normal intrinsic firing rate without stimulation (like from the SA node) is 40-60 times/minute.
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.
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
between the atria and the ventricles
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
of the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, specifically in the posteroinferior region of the interatrial septum
Interatrial septum
The interatrial septum is the wall of tissue that separates the right and left atria of the heart.-Development:The interatrial septum forms during the first and second months of fetal development. Formation of the septum occurs in several stages...
near the opening of the coronary sinus
Coronary sinus
The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the myocardium of the heart. It is present in all mammals, including humans...
, 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—a triangle enclosed by the septal leaflet of the tricuspid valve, the coronary sinus, and the membraneous part of the interatrial septum.
The AV node may also be (rarely) referred to as the Aschoff-Tawara node named so after Ludwig Aschoff
Ludwig Aschoff
Karl Albert Ludwig Aschoff was a German physician and pathologist. He is considered to be one of the most influential pathologists of the early 20th century and is regarded as the most important German pathologist after Rudolf Virchow.Aschoff was born in Berlin, Prussia...
and Sunao Tawara
Sunao Tawara
, M.D., Ph.D., was a Japanese pathologist.Tawara was born in Aki and studied at the Imperial University in Tokyo, graduating in 1901 and receiving his degree in 1908. The years 1903 to 1906 he spent in Marburg studying pathology and pathological anatomy with Ludwig Aschoff. It was here he...
.
Function
Contraction of myocytes (heart muscle cells) requires depolarizationDepolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
and repolarization
Repolarization
In neuroscience, repolarization refers to the change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value. Repolarization results from the movement...
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
Sinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...
through the atria along specialized conduction channels. This activates the AV node. The atrioventricular node delays impulses by approximately 0.12s. 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 (see below).
The AV node receives two inputs from the atria: posteriorly, via the crista terminalis
Crista terminalis
The Crista Terminalis 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 incorporated with and form a part of the adult right atrium...
, and anteriorly, via the interatrial septum
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
.
AV conduction during normal cardiac rhythm occurs through two different pathways:
- the first “pathway” has a slow conduction velocity but shorter refractory periodRefractory periodIn physiology, a refractory period is a period of time during which an organ or cell is incapable of repeating a particular action, or the amount of time it takes for an excitable membrane to be ready for a second stimulus once it returns to its resting state following an excitation...
- 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
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
or atrial flutter
Atrial flutter
Atrial flutter is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia , and falls into the category of supra-ventricular tachycardias. While this rhythm occurs most often in individuals with...
.
The AV node's normal intrinsic firing rate without stimulation (like from the SA node) is 40-60 times/minute.
Blood supply
The blood supply can vary.- The blood supply of the AV node is from the posterior interventricular artery, which is a branch of the right coronary arteryRight coronary arteryThe right coronary artery originates above the right cusp of the aortic valve. It travels down the right atrioventricular groove, towards the crux of the heart.At the origin of the RCA is the conus artery....
in right-dominant individuals.
- In the remainder of individuals, the AV node is still supplied by the posterior interventricular artery, but that artery is a branch of the left circumflex arteryLeft circumflex arteryThe "LCX", or left circumflex artery is an artery of the heart.-Course:...
; the coronary circulationCoronary circulationCoronary circulation is the circulation of blood in the blood vessels of the heart muscle . The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries...
of these individuals is considered left-dominant.
Disorders
- Atrioventricular (AV) conduction disease (AV block) describes impairment of the electrical continuity between the atria and ventricles. It occurs when the atrial depolarization fail to reach the ventricles or is conducted with a delay. It can result from an injury or be a genetically inherited disorder.
- Atrioventricular nodal re-entry tachycardia
- Cystic tumour of atrioventricular nodal region (CTAVN) CTAVN is of endodermal origin and occurs exclusively in the area of the AV node, tricuspid valveTricuspid valveThe tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles. They are connected to the papillary muscles by the chordae...
, and interatrial septumInteratrial septumThe interatrial septum is the wall of tissue that separates the right and left atria of the heart.-Development:The interatrial septum forms during the first and second months of fetal development. Formation of the septum occurs in several stages...
.
Development
BMP (Bone morphogenetic protein) cell signalingCell signaling
Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue...
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.
External links
- "The conduction system of the heart."- http://www.healthyheart.nhs.uk/heart_works/heart03.shtml