**2. Aortic root anatomy**

The aortic valve's function is dependant upon its leaflets, the sinotubular junction (STJ), aortic sinuses and annulus, which together constitute the aortic root. Important geometric relationships exist between several of the aortic root dimensions [1-3].

Valve-Sparing Aortic Root Replacement and Aortic Valve Repair 89

Therefore the ideal number of cusps whereby the valve will neither be incompetent nor stenotic is three (trileaflet). By similar arguments, we can understand how if a bileaflet valve is to open properly (i.e. not be stenotic) it will have redundant FM in the closed position, and thus prolapse and become incompetent. On the other hand, if the bileaflet valve is to close properly (i.e. with no prolapse), it will have a smaller diameter than the STJ in the

We can also derive the geometrically ideal FM length in relation to the length of the line of

The line of attachment of the leaflet is approximately a semicircle. Thus in the open position with the free margin of the leaflet hugging the line joining the 2 adjacent commissures, the

**Base** ≈ π/2 × FM ≈ 1.5 × FM

*Reprinted from Heart, Lung and Circulation, 2004;13 Suppl 3, Matalanis G, Valve sparing aortic root repairs--an* 

There are three aortic sinuses corresponding to the respective leaflets. These sinuses play an important role in minimising leaflet stress and strain [4] by helping to evenly distribute the diastolic pressure load across the leaflets and the sinus wall through the formation of a

A spherical surface is the shape that gives the minimal surface area for a given volume, thus

In systole, the sinuses allow the development of eddy currents, which prevent contact between leaflet and aortic wall (Fig. 4). This may also keep the leaflets away from the coronary ostia, however this is not likely to be a major factor as the majority of coronary flow occurs during diastole. In late systole, these currents help the leaflets drift towards the centre, such that they are in contact immediately prior to the onset of diastole [5]. This results in closure prior to the reversal of pressure difference across the valve, thus abolishing

Fig. 3. The relationship between the base and free margin lengths – base ≈ 1.5 x FM

*anatomical approach. S13-18., Copyright (2004), with permission from Elsevier* 

relatively spherical shape together with the valve cusps.

minimising the stress forces on the leaflets in diastole.

early diastolic reguritation.

open position and therefore be stenotic.

FM approximates the diameter of the semicircle. Therefore,

valve attachment.

In clinical practice the aortic annulus is defined as the superior most aspect of the left ventricular outflow tract (LVOT) which connects the aortic cusps and sinuses to the left ventricle. The annulus' perimeter consists of fibrous (55%) and muscular (45%) components. Of the two, the fibrous component is the one that tends to dilate first in aneurysmal disease.

*Reprinted from Heart, Lung and Circulation, 2004;13 Suppl 3, Matalanis G, Valve sparing aortic root repairs--an anatomical approach. S13-18., Copyright (2004), with permission from Elsevier* 

Fig. 2. Dimensions of the aortic valve cusps, whereby R is the radius of the STJ and FM represents the length of the valve cusp free margin

For a trileaflet valve to be competent in the closed position, while not be stenotic in the open position, the length of the free margin (FM) must geometrically be equivalent to the diameter at the STJ (Fig. 2):

> *Valve in Closed position*  **FM** ≈ 2 × R (Radius of STJ) **FM** ≈ D (Diameter of STJ) ………………… c *Valve in Open position*  In order for the valve to hug the perimeter of the STJ in the open position, the circumference of the STJ (C) must be equivalent to the total length FM of the "n" leaflets combined: C ≈ **FM** x n; and thus **FM** ≈ C/n ……………………………… d Combining c and d we get: **D** ≈ C/n From basic geometry we know that C = D x π, therefore: **D** ≈ (D x π) /n π ≈ n since π ≈ 3 hence **n** ≈ 3 ie. trileaflet design works best

Table 1. Why a trileaflet valve is ideal geometric design

In clinical practice the aortic annulus is defined as the superior most aspect of the left ventricular outflow tract (LVOT) which connects the aortic cusps and sinuses to the left ventricle. The annulus' perimeter consists of fibrous (55%) and muscular (45%) components. Of the two, the fibrous component is the one that tends to dilate first in aneurysmal disease.

*Reprinted from Heart, Lung and Circulation, 2004;13 Suppl 3, Matalanis G, Valve sparing aortic root repairs--an* 

For a trileaflet valve to be competent in the closed position, while not be stenotic in the open position, the length of the free margin (FM) must geometrically be equivalent to the

> In order for the valve to hug the perimeter of the STJ in the open position, the circumference of the STJ (C) must be equivalent to the total length FM of the "n" leaflets combined:

From basic geometry we know that C = D x π, therefore:

Fig. 2. Dimensions of the aortic valve cusps, whereby R is the radius of the STJ and FM

*anatomical approach. S13-18., Copyright (2004), with permission from Elsevier* 

**FM** ≈ D (Diameter of STJ) ………………… c

**FM** ≈ C/n ……………………………… d

represents the length of the valve cusp free margin

*Valve in Closed position*  **FM** ≈ 2 × R (Radius of STJ)

*Valve in Open position* 

C ≈ **FM** x n; and thus

**D** ≈ C/n

π ≈ n since π ≈ 3 hence **n** ≈ 3

**D** ≈ (D x π) /n

Combining c and d we get:

ie. trileaflet design works best

Table 1. Why a trileaflet valve is ideal geometric design

diameter at the STJ (Fig. 2):

Therefore the ideal number of cusps whereby the valve will neither be incompetent nor stenotic is three (trileaflet). By similar arguments, we can understand how if a bileaflet valve is to open properly (i.e. not be stenotic) it will have redundant FM in the closed position, and thus prolapse and become incompetent. On the other hand, if the bileaflet valve is to close properly (i.e. with no prolapse), it will have a smaller diameter than the STJ in the open position and therefore be stenotic.

We can also derive the geometrically ideal FM length in relation to the length of the line of valve attachment.

The line of attachment of the leaflet is approximately a semicircle. Thus in the open position with the free margin of the leaflet hugging the line joining the 2 adjacent commissures, the FM approximates the diameter of the semicircle. Therefore,

**Base** ≈ π/2 × FM ≈ 1.5 × FM

*Reprinted from Heart, Lung and Circulation, 2004;13 Suppl 3, Matalanis G, Valve sparing aortic root repairs--an anatomical approach. S13-18., Copyright (2004), with permission from Elsevier* 

Fig. 3. The relationship between the base and free margin lengths – base ≈ 1.5 x FM

There are three aortic sinuses corresponding to the respective leaflets. These sinuses play an important role in minimising leaflet stress and strain [4] by helping to evenly distribute the diastolic pressure load across the leaflets and the sinus wall through the formation of a relatively spherical shape together with the valve cusps.

A spherical surface is the shape that gives the minimal surface area for a given volume, thus minimising the stress forces on the leaflets in diastole.

In systole, the sinuses allow the development of eddy currents, which prevent contact between leaflet and aortic wall (Fig. 4). This may also keep the leaflets away from the coronary ostia, however this is not likely to be a major factor as the majority of coronary flow occurs during diastole. In late systole, these currents help the leaflets drift towards the centre, such that they are in contact immediately prior to the onset of diastole [5]. This results in closure prior to the reversal of pressure difference across the valve, thus abolishing early diastolic reguritation.

Valve-Sparing Aortic Root Replacement and Aortic Valve Repair 91

Nevertheless, in many patients, the aetiology of aortic aneurysms is multifactorial, with additional clinical characteristics such as age, hypertension and male gender among others

Acute or chronic type A dissections of the aorta is also a cause for valve regurgitation, resulting from commissural detachment due to the proximally propagating dissection. Patients with dissection may also have aortic regurgitation secondary to pre-existing

As one of the most common congenital cardiac anomalies, bicuspid aortic valves (BAV) are found in between 1-2% of the population. BAVs may be anatomically or purely 'bicuspid' (Type 0), that is, consisting of two completely developed cusps, sinuses and commissures. However, most BAVs are functionally bicuspid (Type 1), in that three sinuses exist, with two cusps of different sizes whereby the larger cusp contains a median raphe, representing an obliterated or malformed commissure. This raphe extends from the mid-point of the cusp's free margin to the aortic annulus, inserting at a lower level than the other commissures. Patients with BAV are at increased risk of developing aortopathy such as aortic dilatation and acute dissection. This may be due to a combination of 1) genetic predisposition, whereby the aortic tissue weakness and fragility responsible for dilatation is a manifestation of a development defect afflicting both the aortic valve and wall and 2) the haemodynamic abnormality caused by a bicuspid valve such as eccentric turbulence is responsible for aortic dilatation. Although there is widespread support for the genetic theory, some debate still

*Reprinted from Heart, Lung and Circulation, 2004;13 Suppl 3, Matalanis G, Valve sparing aortic root repairs--an* 

Fig. 5. Leaflet prolapse (a) results in reduction of the area of coaptation between the leaflets and thus the security of the "seal" in diastole. Asymmetrical prolapse (b) will result in aortic

*anatomical approach. S13-18., Copyright (2004), with permission from Elsevier* 

regurgitation at a much earlier stage

exists as to which process exerts the most dominant effect [7].

serving as risk factors.

aneurysmal disease.

It has been shown that increased stiffness of the aortic sinuses in advanced age and atherosclerosis contributes towards valve degeneration [6]. With reduced sinus compliance, leaflets may be more inclined to abruptly contact the aortic wall upon opening causing valve damage, while the delay in eddie current formation, with subsequent delay in valve closure may increase the regurgitant volume [3].

*Reprinted from Heart, Lung and Circulation, 2004;13 Suppl 3, Matalanis G, Valve sparing aortic root repairs--an anatomical approach. S13-18., Copyright (2004), with permission from Elsevier* 

Fig. 4. The aortic sinuses form an integral part of the normal aortic valve function both in diastole and systole
