Cardiac skeleton

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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 (the smaller, upper two chambers) from the ventricles (the larger, lower two chambers).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. [1]

Contents

The unique matrix of connective tissue within the cardiac skeleton isolates electrical influence within these defined chambers. In normal anatomy, there is only one conduit for electrical conduction from the upper chambers to the lower chambers, known as the atrioventricular node. The physiologic cardiac skeleton forms a firewall governing autonomic/electrical influence until bordering the bundle of His which further governs autonomic flow to the bundle branches of the ventricles. Understood as such, the cardiac skeleton efficiently centers and robustly funnels electrical energy from the atria to the ventricles.

Structure

The structure of the components of the heart has become an area of increasing interest. The cardiac skeleton binds several bands of dense connective tissue, as collagen, that encircle the bases of the pulmonary trunk, aorta, and all four heart valves. [2] While not a traditionally or "true" or rigid skeleton, it does provide structure and support for the heart, as well as isolate the atria from the ventricles. This is why atrial fibrillation almost never degrades to ventricular fibrillation. In youth, this collagen structure is free of calcium adhesions and is quite flexible. With aging, calcium and other mineral accumulation occur within this skeleton. Distensibility of the ventricles is tied to variable accumulation of minerals which also contributes to the delay of the depolarization wave in geriatric patients that can take place from the AV node and the bundle of His. [3]

Fibrous rings

Fibrous rings of heart
Gray495.png
Transverse section of the heart showing the fibrous rings surrounding the valves
Details
Identifiers
Latin anulus fibrosus dexter cordis, anulus fibrosus sinister cordis
Anatomical terminology
Fibrous trigone
Details
Identifiers
Latin trigonum fibrosum dextrum cordis, trigonum fibrosum sinistrum cordis, trigona fibrosa
Anatomical terminology

The right and left fibrous rings of heart (annuli fibrosi cordis) surround the atrioventricular and arterial orifices. The right fibrous ring is known as the annulus fibrosus dexter cordis, and the left is known as the annulus fibrosus sinister cordis. [3] The right fibrous trigone is continuous with the central fibrous body. This is the strongest part of the fibrous cardiac skeleton.

The upper chambers (atria) and lower (ventricles) are electrically divided by the properties of collagen proteins within the rings. The valve rings, central body, and skeleton of the heart consisting of collagen are impermeable to electrical propagation. The only channel allowed (barring accessory/rare preexcitation channels) through this collagen barrier is represented by a sinus that opens up to the atrioventricular node and exits to the bundle of His. The muscle origins/insertions of many of the cardiomyocytes are anchored to opposite sides of the valve rings. [3]

The atrioventricular rings serve for the attachment of the muscular fibers of the atria and ventricles, and for the attachment of the bicuspid and tricuspid valves. [3]

The left atrioventricular ring is closely connected, by its right margin, with the aortic arterial ring; between these and the right atrioventricular ring is a triangular mass of fibrous tissue, the fibrous trigone, which represents the os cordis seen in the heart of some of the larger animals, such as the ox. [3]

Lastly, there is the tendinous band, already referred to, the posterior surface of the conus arteriosus. [3]

The fibrous rings surrounding the arterial orifices serve for the attachment of the great vessels and semilunar valves, they are known as The aortic annulus. [3]

Each ring receives, by its ventricular margin, the attachment of some of the muscular fibers of the ventricles; its opposite margin presents three deep semicircular notches, to which the middle coat of the artery is firmly fixed. [3]

The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externally, and by the endocardium internally. [3]

From the margins of the semicircular notches, the fibrous structure of the ring is continued into the segments of the valves. [3]

The middle coat of the artery in this situation is thin, and the vessel is dilated to form the sinuses of the aorta and pulmonary artery. [3]

Os cordis

In some animals, the fibrous trigone can undergo increasing mineralization with age, leading to the formation of a significant os cordis (heart bone), or two (os cordis sinistrum and os cordis dextrum, the latter being the larger one). [4] The os cordis is thought to serve mechanical functions. [5] In humans, two paired trigones (left and right) are seen in this essential view of anatomy. As a surgical purchase point, the Trigones risk much in AV propagation.

It has been known since Classical times in deer [6] and oxen and was thought to have medicinal properties and mystical properties. It is occasionally observed in goats, [7] but also in other animals such as otters. [8] It was recently also discovered in chimpanzees, the only great ape so far to known to have os cordis. [9]

Against the opinion of his time, Galen wrote that the os cordis was also found in elephants. [10] The claim endured up to the nineteenth century and was still treated as fact in Gray's Anatomy, although it is not the case.

Function

Electrical signals from the sinoatrial node and the autonomic nervous system must find their way from the upper chambers to the lower ones to ensure that the ventricles can drive the flow of blood. The heart functions as a pump delivering an intermittent volume of blood, incrementally delivered to the lungs, body, and brain.

The cardiac skeleton ensures that the electrical and autonomic energy generated above is ushered below and cannot return. The cardiac skeleton does this by establishing an electrically impermeable boundary to autonomic electrical influence within the heart. Simply put, the dense connective tissue within the cardiac skeleton does not conduct electricity and its deposition within the myocardial matrix is not accidental.

The anchored and electrically inert collagen framework of the four valves allows normal anatomy to house the atrioventricular node (AV node) in its center. The AV node is the only electrical conduit from the atria to the ventricles through the cardiac skeleton, which is why atrial fibrillation can never degrade into ventricular fibrillation.

Throughout life, the cardiac collagen skeleton is remodeled. Where collagen is diminished by age, calcium is often deposited, thus allowing readily imaged mathematical markers which are especially valuable in measuring systolic volumetrics. The inert characteristics of the collagen structure that blocks electrical influence also make it difficult to attain an accurate signal for imaging without allowing for an applied ratio of collagen to calcium.

History

Boundaries within the heart were first described and greatly magnified by Drs. Charles S. Peskin and David M. McQueen at the Courant Institute of Mathematical Sciences.[ citation needed ]

See also

Related Research Articles

<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 mediastinum.

<span class="mw-page-title-main">Heart valve</span> A flap of tissue that prevent backflow of blood around the heart

A heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. A heart valve opens or closes according to differential blood pressure on each side.

<span class="mw-page-title-main">Mitral valve</span> Valve in the heart connecting the left atrium and left ventricle

The mitral valve, also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one-way valves allowing blood flow in just one direction. The mitral valve and the tricuspid valve are known as the atrioventricular valves because they lie between the atria and the ventricles.

<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. The term originates, via New Latin, from Ancient Greek συστολή (sustolē), from συστέλλειν, and is similar to the use of the English term to squeeze.

<span class="mw-page-title-main">Ventricle (heart)</span> Chamber of the heart

A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper heart that is smaller than a ventricle. Interventricular means between the ventricles, while intraventricular means within one ventricle.

<span class="mw-page-title-main">Wolff–Parkinson–White syndrome</span> Medical condition

Wolff–Parkinson–White syndrome (WPWS) is a disorder due to a specific type of problem with the electrical system of the heart involving an accessory pathway able to conduct electrical current between the atria and the ventricles, thus bypassing the atrioventricular node. About 60% of people with the electrical problem developed symptoms, which may include an abnormally fast heartbeat, palpitations, shortness of breath, lightheadedness, or syncope. Rarely, cardiac arrest may occur. The most common type of irregular heartbeat that occurs is known as paroxysmal supraventricular tachycardia.

<span class="mw-page-title-main">Atrioventricular node</span> Part of the electrical conduction system of the heart

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. 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.

<span class="mw-page-title-main">Atrial flutter</span> Medical condition

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 flutter is characterized by a sudden-onset (usually) regular abnormal heart rhythm on an electrocardiogram (ECG) in which the heart rate is fast. Symptoms may include a feeling of the heart beating too fast, too hard, or skipping beats, chest discomfort, difficulty breathing, a feeling as if one's stomach has dropped, a feeling of being light-headed, or loss of consciousness.

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

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 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">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 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 valves.

<span class="mw-page-title-main">Chordae tendineae</span> Inelastic cords of fibrous connective tissue connecting papillary muscles to heart valves

The chordae tendineae (tendinous cords), colloquially known as the heart strings, are inelastic cords of fibrous connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart.

<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. There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously. At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract, and each atrium pumps blood into the ventricle below it. During ventricular systole the ventricles are contracting and vigorously pulsing two separated blood supplies from the heart—one to the lungs and one to all other body organs and systems—while the two atria are relaxed. This precise coordination ensures that blood is efficiently collected and circulated throughout the body.

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

Atrioventricular septal defect (AVSD) or atrioventricular canal defect (AVCD), also known as "common atrioventricular canal" or "endocardial cushion defect" (ECD), is characterized by a deficiency of the atrioventricular septum of the heart that creates connections between all four of its chambers. It is a very specific combination of 3 defects:

The following outline is provided as an overview of and topical guide to cardiology, the branch of medicine dealing with disorders of the human heart. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in cardiology are called cardiologists.

<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 or chest pain. 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>

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

PD-icon.svgThis article incorporates text in the public domain from page 536 of the 20th edition of Gray's Anatomy (1918)

  1. ↑ "Cardiac Skeleton - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-04-01.
  2. ↑ Martini Anatomy and Physiology, 5th ed. Band theory within the ventricular myocardium first suggested by Dr. Francisco Torrent-Guasp (1931-2005) closely follows the band structure above. The interface of a relatively rigid series of valve rings attached to an incredibly compliant set of individual strings of myocardium below opposed at 180 degrees on valve rings was first introduced by Drs. Charles Peskin and David McQueen in a speech regarding Cray research and computational science at the National Museum of History at the Smithsonian Institution, Washington DC 5/4/1994.
  3. 1 2 3 4 5 6 7 8 9 10 11 Gray, Henry (1918). "The Heart". Gray's Anatomy (1918 ed.). London: Longmans. ISBN   978-613-0-24743-0.
  4. ↑ Schummer, August; Wilkens, Helmut; Vollmerhaus, Bernd; Habermehl, Karl-Heinz (1981). The Circulatory System, the Skin, and the Cutaneous Organs of the Domestic Mammals. Springer. p. 21. ISBN   9781489971029 . Retrieved 10 April 2018.
  5. ↑ Nasoori, Alireza (2020). "Formation, structure, and function of extra‐skeletal bones in mammals". Biological Reviews. 95 (4): 986–1019. doi:10.1111/brv.12597. PMID   32338826. S2CID   216556342.
  6. ↑ Dupuy, Gérard (2011). La croix du cerf. L'os du cœur du cerf. Paris: Montbel. Retrieved 10 April 2018.
  7. ↑ Smith, Mary C.; Sherman, David M. (2009). Goat Medicine (2 ed.). Wiley-Blackwell. ISBN   9781119949527 . Retrieved 10 April 2018.
  8. ↑ Egerbacher, Monika; Weber, Heike; Hauer, Silke (April 2000). "Bones in the heart skeleton of the otter (Lutra lutra)". Journal of Anatomy. 196 (3): 485–491. doi:10.1046/j.1469-7580.2000.19630485.x. PMC   1468091 . PMID   10853970.
  9. ↑ Moittié, Sophie; Baiker, Kerstin; Strong, Victoria; Cousins, Emma; White, Kate; Liptovszky, Mátyás; Redrobe, Sharon; Alibhai, Aziza; Sturrock, Craig J.; Rutland, Catrin Sian (2020-06-10). "Discovery of os cordis in the cardiac skeleton of chimpanzees (Pan troglodytes)". Scientific Reports. 10 (1): 9417. doi:10.1038/s41598-020-66345-7. ISSN   2045-2322. PMC   7286900 . PMID   32523027.
  10. ↑ Salas, Luis Alejandro (2014). "Fighting with the Heart of a Beast: Galen's Use of the Elephant's Cardiac Anatomy against Cardiocentrists". Greek, Roman and Byzantine Studies. 54 (4): 698–727. Retrieved 10 April 2018.
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