Atrioventricular node

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Atrioventricular node
Reizleitungssystem 1.png
Image showing the conduction system of the heart. The AV node is labelled 2.
Details
System Electrical conduction system of the heart
Artery Atrioventricular nodal branch
Identifiers
Latin nodus atrioventricularis
Acronym(s)AV node
MeSH D001283
TA98 A12.1.06.004
TA2 3954
FMA 9478
Anatomical terminology

The atrioventricular node or AV 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. [1] 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 mm). [2]

Contents

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 mm). [2] 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. [3]

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. [4] [5] [6] 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 (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. [7]

Function

Isolated heart conduction system showing atrioventricular node ConductionsystemoftheheartwithouttheHeart-en.svg
Isolated 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. [8]

Contraction of 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. [1] 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. [9]

This also protects the ventricles from excessively fast rate response to atrial arrhythmias (see below). [10]

AV conduction during normal cardiac rhythm occurs through two different pathways:

An important property that is unique to the AV node is decremental conduction, [12] 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. [13] 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

See also

Related Research Articles

<span class="mw-page-title-main">Bradycardia</span> Heart rate below the normal range

Bradycardia is a medical term used to describe a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from a variety of pathologic processes, it is commonly a physiologic response to cardiovascular conditioning, or due to asymptomatic type 1 atrioventricular block. Resting heart rates less than 50 BPM are often normal during sleep in young and healthy adults, and in athletes. In large population studies of adults without underlying heart disease, resting heart rates of 45-50 BPM appear to be the lower limits of normal, dependent on age and sex. Bradycardia is most likely to be discovered in the elderly, as both age and underlying cardiac disease progression contribute to its development.

<span class="mw-page-title-main">Heart</span> Organ found inside most animals

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 to the lungs. In humans, the heart is approximately the size of a closed fist and is located between the lungs, in the middle compartment of the chest, called the mediastinum.

<span class="mw-page-title-main">Systole</span> Part of the cardiac cycle when a heart chamber contracts

Systole is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood.

<span class="mw-page-title-main">Bundle of His</span> Collection of heart muscle cells

The bundle of His (BH) or His bundle (HB) ( "hiss") is a collection of heart muscle cells specialized for electrical conduction. As part of the electrical conduction system of the heart, it transmits the electrical impulses from the atrioventricular node to the point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinje fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval.

<span class="mw-page-title-main">Cardiac conduction system</span> Aspect of heart function

The cardiac conduction system transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the body's circulatory system. The pacemaking signal travels through the right atrium to the atrioventricular node, along the bundle of His, and through the bundle branches to Purkinje fibers in the walls of the ventricles. The Purkinje fibers transmit the signals more rapidly to stimulate contraction of the ventricles.

<span class="mw-page-title-main">Supraventricular tachycardia</span> Abnormally fast heart rhythm

Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower chambers of the heart. There are four main types of SVT: atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff–Parkinson–White syndrome. The symptoms of SVT include palpitations, feeling of faintness, sweating, shortness of breath, and/or chest pain.

<span class="mw-page-title-main">AV nodal reentrant tachycardia</span> Medical condition

AV-nodal reentrant tachycardia (AVNRT) is a type of abnormal fast heart rhythm. It is a type of supraventricular tachycardia (SVT), meaning that it originates from a location within the heart above the bundle of His. AV nodal reentrant tachycardia is the most common regular supraventricular tachycardia. It is more common in women than men. The main symptom is palpitations. Treatment may be with specific physical maneuvers, medications, or, rarely, synchronized cardioversion. Frequent attacks may require radiofrequency ablation, in which the abnormally conducting tissue in the heart is destroyed.

<span class="mw-page-title-main">Atrium (heart)</span> Part of the human heart

The atrium is one of the two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular mitral and tricuspid heart valves.

<span class="mw-page-title-main">Atrioventricular block</span> Medical condition

Atrioventricular 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 sinoatrial node produces an electrical signal to control the heart rate. The signal travels from the SA node to the ventricles through the atrioventricular node. In an AV block, this electrical signal is either delayed or completely blocked. When the signal is completely blocked, the ventricles produce their own electrical signal to control the heart rate. The heart rate produced by the ventricles is much slower than that produced by the SA node.

<span class="mw-page-title-main">Cardiac cycle</span> Performance of the human heart

The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, called systole. After emptying, the heart relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems. A normally performing heart must be fully expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 second to complete the cycle.

In cardiology, the cardiac skeleton, also known as the fibrous skeleton of the heart, is a high-density homogeneous structure of connective tissue that forms and anchors the valves of the heart, and influences the forces exerted by and through them. The cardiac skeleton separates and partitions the atria from the ventricles .The heart's cardiac skeleton comprises four dense connective tissue rings that encircle the mitral and tricuspid atrioventricular (AV) canals and extend to the origins of the pulmonary trunk and aorta. This provides crucial support and structure to the heart while also serving to electrically isolate the atria from the ventricles.

Lown–Ganong–Levine syndrome (LGL) is a pre-excitation syndrome of the heart. Those with LGL syndrome have episodes of abnormal heart racing with a short PR interval and normal QRS complexes seen on their electrocardiogram when in a normal sinus rhythm. LGL syndrome was originally thought to be due to an abnormal electrical connection between the atria and the ventricles, but is now thought to be due to accelerated conduction through the atrioventricular node in the majority of cases. The syndrome is named after Bernard Lown, William Francis Ganong, Jr., and Samuel A. Levine.

<span class="mw-page-title-main">Bachmann's bundle</span> Anatomical cardiac structure

In the heart's conduction system, Bachmann's bundle is a branch of the anterior internodal tract that resides on the inner wall of the left atrium. It is a broad band of cardiac muscle that passes from the right atrium, between the superior vena cava and the ascending aorta. Bachmann's bundle is, during normal sinus rhythm, the preferential path for electrical activation of the left atrium. It is therefore considered to be part of the "atrial conduction system" of the heart.

<span class="mw-page-title-main">Sinoatrial nodal artery</span> Artery of the heart which supplies the sinoatrial node

The sinoatrial nodal artery, sinuatrial nodal artery or sinoatrial artery is an artery of the heart which supplies the sinoatrial node, the natural pacemaker center of the heart. It is usually a branch of the right coronary artery. It passes between the right atrium, and the opening of the superior vena cava.

An accessory pathway is an additional electrical connection between two parts of the heart. These pathways can lead to abnormal heart rhythms or arrhythmias associated with symptoms of palpitations. Some pathways may activate a region of ventricular muscle earlier than would normally occur, referred to as pre-excitation, and this may be seen on an electrocardiogram. The combination of an accessory pathway that causes pre-excitation with arrhythmias is known as Wolff-Parkinson-White syndrome.

<span class="mw-page-title-main">Junctional ectopic tachycardia</span> Medical condition

Junctional ectopic tachycardia (JET) is a rare syndrome of the heart that manifests in patients recovering from heart surgery. It is characterized by cardiac arrhythmia, or irregular beating of the heart, caused by abnormal conduction from or through the atrioventricular node. In newborns and infants up to 6 weeks old, the disease may also be referred to as His bundle tachycardia or congenital JET.

<span class="mw-page-title-main">Arrhythmia</span> Group of medical conditions characterized by irregular heartbeat

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 – is called tachycardia, and a resting heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath, chest pain, or decreased level of consciousness. While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.

Cardiac physiology or heart function is the study of healthy, unimpaired function of the heart: involving blood flow; myocardium structure; the electrical conduction system of the heart; the cardiac cycle and cardiac output and how these interact and depend on one another.

<span class="mw-page-title-main">Heart development</span> Prenatal development of the heart

Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is the first functional organ in vertebrate embryos.

The heart is a muscular organ situated in the mediastinum. It consists of four chambers, four valves, two main arteries, and the conduction system. The left and right sides of the heart have different functions: the right side receives de-oxygenated blood through the superior and inferior venae cavae and pumps blood to the lungs through the pulmonary artery, and the left side receives saturated blood from the lungs.

References

  1. 1 2 Gray, Huon H.; Keith D. Dawkins; Iain A. Simpson; John M. Morgan (2002). Lecture Notes on Cardiology. Boston: Blackwell Science. p.  135. ISBN   978-0-86542-864-5.
  2. 1 2 Full Size Picture triangle of-Koch.jpg. Retrieved on 2008-12-22
  3. ↑ Harrison's Principles of Internal Medicine, 17e” Section 3: Disorders of Rhythm Archived July 7, 2011, at the Wayback Machine
  4. ↑ Van der Hauwaert LG, Stroobandt R, Verhaeghe L (October 1972). "Arterial blood supply of the atrioventricular node and main bundle". British Heart Journal. 34 (10): 1045–1051. doi:10.1136/hrt.34.10.1045. PMC   458545 . PMID   5086972.
  5. ↑ Pejković, B.; Krajnc, I.; Anderhuber, F.; Kosutić, D. (2008). "Anatomical aspects of the arterial blood supply to the sinoatrial and atrioventricular nodes of the human heart". The Journal of International Medical Research. 36 (4): 691–698. doi: 10.1177/147323000803600410 . PMID   18652764.
  6. ↑ Saremi, F.; Abolhoda, A.; Ashikyan, O.; Milliken, J. C.; Narula, J.; Gurudevan, S. V.; Kaushal, K.; Raney, A. (2007). "Arterial Supply to Sinuatrial and Atrioventricular Nodes: Imaging with Multidetector CT". Radiology. 246 (1): 99–107, discussion 108–109. doi:10.1148/radiol.2461070030. PMID   18024438.
  7. ↑ Stroud DM, Gaussin V, Burch JB, et al. (November 2007). "Abnormal Conduction and Morphology in the Atrioventricular Node of Mice With Atrioventricular Canal–Targeted Deletion of Alk3/Bmpr1a Receptor". Circulation. 116 (22): 2535–2643. doi:10.1161/CIRCULATIONAHA.107.696583. PMC   2947829 . PMID   17998461.
  8. ↑ Fuster V, Rydén LE, Asinger RW, et al. (October 2001). "ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation" (PDF). Journal of the American College of Cardiology. 38 (4): 1231–1266. doi: 10.1016/S0735-1097(01)01587-X . PMID   11583910.
  9. ↑ Campbell, N., & Reece, J. (2002). Biology. 6th ed. San Francisco: Benjamin Cummings[ page needed ][ ISBN missing ]
  10. ↑ Gray, Huon H.; Keith D. Dawkins; Iain A. Simpson; John M. Morgan (2002). Lecture Notes on Cardiology. Boston: Blackwell Science. p.  136. ISBN   978-0-86542-864-5.
  11. 1 2 Gray, Huon H.; Keith D. Dawkins; Iain A. Simpson; John M. Morgan (2002). Lecture Notes on Cardiology. Boston: Blackwell Science. p.  157. ISBN   978-0-86542-864-5.
  12. ↑ Patterson E, Scherlag BJ (October 2002). "Decremental conduction in the posterior and anterior AV nodal inputs". Journal of Interventional Cardiac Electrophysiology. 7 (2): 137–148. doi:10.1023/A:1020833604423. PMID   12397223. S2CID   22728910.
  13. ↑ Guyton, Arthur C.; John E. Hall (2006). Textbook of Medical Physiology (11 ed.). Philadelphia: Elsevier Saunders. p.  120. ISBN   978-0-7216-0240-0.
  14. ↑ Benson DW (October 2004). "Genetics of atrioventricular conduction disease in humans". The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology. 280 (2): 934–939. doi: 10.1002/ar.a.20099 . PMID   15372490.
  15. ↑ "Dual Atrioventricular Nodal Physiology - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2022-11-14.
  16. ↑ Sharma G, Linden MD, Schultz DS, Inamdar KV (January 2009). "Cystic tumor of the atrioventricular node: an unexpected finding in an explanted heart". Cardiovascular Pathology. 19 (3): e75–e78. doi:10.1016/j.carpath.2008.10.011. PMID   19144541.
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