**1. Introduction**

[123] Chlenski A, Liu S, Crawford SE, Volpert OV, DeVries GH, Evangelista A, et al. SPARC is a key Schwannian-derived inhibitor controlling neuroblastoma tumor an‐

[124] Sage H. Pieces of eight: bioactive fragments of extracellular proteins as regulators of

[125] Kalluri R, Zeisberg E. Controlling angiogenesis in heart valves. *Nature Medicine*. 2006

giogenesis. *Cancer Research*. 2002 Dec 15;62(24):7357–63.

angiogenesis. *Trends in Cell Biology*. 1997 May;7(5):182–6.

Oct;12(10):1118–9.

30 Calcific Aortic Valve Disease

Recently, the interest in the anatomy of the normal aortic valve complex has augmented, mostly because of the increasing use of conservative surgical techniques for repairing or re‐ placing cardiac valves. The knowledge of the anatomy also has important implications in the manufacture of prostheses that must conform to this anatomical configuration.

#### **1.1. Historical perspective**

The earliest documented interest in the anatomy of the aortic valvular complex stems from the Renaissance, with the description and drawings by Leonardo da Vinci. [1]

Leonardo da Vinci had an almost perfect understanding of the physiology of the human heart. But he had no inkling of the circulation of the blood, and the existence of one-way valves was incompatible with the ancient belief that the heart simply churned blood in and out of the ventricles, thus generating heat and 'vital spirit'. Unable to reconcile what he had observed with what he believed to be true, Leonardo reached an impasse. He became trap‐ ped in describing the motion of the blood through the valves in even more detail. And there, it seems, his anatomical work came to an end. [2]

The next anatomist to study the aortic valve was Andreas Vesalius. Then, for almost 400 years the study of the human heart was very sporadic and limited.

The 19th century brought in the era of anatomic dissection and the knowledge on the aortic valve grew wider. Henle was the first to introduce the term "arterial root". During the first

half of the 20th century the rise in autopsy rates in Europe and North America facilitated the study of cardiac anatomy. [3]

Annulus is conventionally described as the virtual ring, formed by joining the basal attach‐

Anatomy and Function of Normal Aortic Valvular Complex

http://dx.doi.org/10.5772/53403

33

Nodule of Arantius is the small fibrous mound that forms at the center of each leaflet when

Between the free and closing edges, to each side of the nodule are two crescent-shaped areas known as the lunulae, which represent the sites of cusp apposition during valve closure. [6]

The development of the aortic valve complex is extremely complicated and not yet fully

The heart begins as a single tube that separates into two tubes and begins to twist rightward

Cells from the primary cardiac crescent, formed bilaterally within the embryonic disc, mi‐ grate into the cervical region of the developing embryo to form the primary heart tube. With further growth, cells from a second cardiogenic area, located posterior to the dorsal wall of the developing pericardial cavity, migrate into the cardiac region. The cells from this secon‐

The heart tube is composed of an outer layer of myocardium and an inner lining of endocar‐ dial cells, separated by an extensive extracellular matrix referred to as the cardiac jelly. After rightward looping of the heart, the cardiac jelly overlying the future atrioventricular canal

Subsequent to looping, the outflow tract possesses a characteristic dog-leg bend which di‐

The cushions contained within the myocardial wall go through significant changes. In addition to the cushions that have fused to separate the proximal outflow tract into prospective aortic and pulmonary components, two further intercalated cushions have grown in the opposite quadrants of the common outflow tract. Formation of cavities in the fused distal parts of the proximal cushions, along with similar cavitation in the intercalated cushions, now produces the primordiums of the arterial valvular leaflets and sinuses. These structures, therefore, are formed in the most distal part of the proximal outflow tract, immediately upstream relative to the developing sinotubular junction. The cavitation of the cushions leaves the central luminal part of each cushion to form the arterial valvular leaflets, with the peripheral part arterialising to form the wall of the supporting valvular sinuses. The rightward and inferior of the interca‐ lated cushions forms one sinus of the aortic valve, while the opposite leftward and superior in‐ tercalated cushion forms the non-adjacent sinus of the pulmonary valve. The adjacent sinuses and valvular leaflets, in contrast, are excavated from the fused distal parts of the proximal cushions, with each of the two fused cushions forming one sinus and leaflet of the aortic valve,

dary heart field populate the outflow tract and the aortic arches. [7]

and outflow tract expands into swellings known as cardiac cushions. [8]

together with the adjacent sinus and leaflet of the pulmonary valve. [7]

The definitive fetal cardiac structure is developed by 8 weeks.

vides the outflow tract into proximal and distal portions.

ment points of the leaflets within the left ventricle.

the closing edge meets the free edge.

onto itself, called "d" looping.

**1.3. Embryology**

understood.

**Figure 1.** Leonardo da Vinci - The aortic valve, from the Royal Collection © Her Majesty Queen Elizabeth II - http:// www.royalcollection.org.uk/collection/919082/the-aortic-valve

Nowadays the need to understand the anatomy of the aortic valve is crucial, therefore the books and articles devoted to this topic are numerous.

#### **1.2. Definitions**

There is still no consensus on the best way to describe the anatomy of the aortic root [4].

The term "aortic root" refers to the aortic valve from its position at the left ventricular outlet to its junction with the ascending portion of the aorta. [5] It is the direct continuation of the left ventricular outflow tract.

Aorto-ventricular junction refers to the junction between the left ventricular structures and the aortic valvular sinuses, this representing the anatomic junction, or the semilunar lines of attachment of the arterial valvular leaflets, this locus representing the haemodynamic ven‐ triculo-arterial junction [4].

Annulus is conventionally described as the virtual ring, formed by joining the basal attach‐ ment points of the leaflets within the left ventricle.

Nodule of Arantius is the small fibrous mound that forms at the center of each leaflet when the closing edge meets the free edge.

Between the free and closing edges, to each side of the nodule are two crescent-shaped areas known as the lunulae, which represent the sites of cusp apposition during valve closure. [6]

#### **1.3. Embryology**

half of the 20th century the rise in autopsy rates in Europe and North America facilitated the

**Figure 1.** Leonardo da Vinci - The aortic valve, from the Royal Collection © Her Majesty Queen Elizabeth II - http://

Nowadays the need to understand the anatomy of the aortic valve is crucial, therefore the

There is still no consensus on the best way to describe the anatomy of the aortic root [4].

The term "aortic root" refers to the aortic valve from its position at the left ventricular outlet to its junction with the ascending portion of the aorta. [5] It is the direct continuation of the

Aorto-ventricular junction refers to the junction between the left ventricular structures and the aortic valvular sinuses, this representing the anatomic junction, or the semilunar lines of attachment of the arterial valvular leaflets, this locus representing the haemodynamic ven‐

www.royalcollection.org.uk/collection/919082/the-aortic-valve

**1.2. Definitions**

left ventricular outflow tract.

triculo-arterial junction [4].

books and articles devoted to this topic are numerous.

study of cardiac anatomy. [3]

32 Calcific Aortic Valve Disease

The development of the aortic valve complex is extremely complicated and not yet fully understood.

The heart begins as a single tube that separates into two tubes and begins to twist rightward onto itself, called "d" looping.

Cells from the primary cardiac crescent, formed bilaterally within the embryonic disc, mi‐ grate into the cervical region of the developing embryo to form the primary heart tube. With further growth, cells from a second cardiogenic area, located posterior to the dorsal wall of the developing pericardial cavity, migrate into the cardiac region. The cells from this secon‐ dary heart field populate the outflow tract and the aortic arches. [7]

The heart tube is composed of an outer layer of myocardium and an inner lining of endocar‐ dial cells, separated by an extensive extracellular matrix referred to as the cardiac jelly. After rightward looping of the heart, the cardiac jelly overlying the future atrioventricular canal and outflow tract expands into swellings known as cardiac cushions. [8]

Subsequent to looping, the outflow tract possesses a characteristic dog-leg bend which di‐ vides the outflow tract into proximal and distal portions.

The cushions contained within the myocardial wall go through significant changes. In addition to the cushions that have fused to separate the proximal outflow tract into prospective aortic and pulmonary components, two further intercalated cushions have grown in the opposite quadrants of the common outflow tract. Formation of cavities in the fused distal parts of the proximal cushions, along with similar cavitation in the intercalated cushions, now produces the primordiums of the arterial valvular leaflets and sinuses. These structures, therefore, are formed in the most distal part of the proximal outflow tract, immediately upstream relative to the developing sinotubular junction. The cavitation of the cushions leaves the central luminal part of each cushion to form the arterial valvular leaflets, with the peripheral part arterialising to form the wall of the supporting valvular sinuses. The rightward and inferior of the interca‐ lated cushions forms one sinus of the aortic valve, while the opposite leftward and superior in‐ tercalated cushion forms the non-adjacent sinus of the pulmonary valve. The adjacent sinuses and valvular leaflets, in contrast, are excavated from the fused distal parts of the proximal cushions, with each of the two fused cushions forming one sinus and leaflet of the aortic valve, together with the adjacent sinus and leaflet of the pulmonary valve. [7]

The definitive fetal cardiac structure is developed by 8 weeks.
