The aortic valve regulates blood flow from the left ventricle into the aorta. It is a semilunar valve that must withstand the highest pressure in the cardiovascular system. The valve and its surrounding structures form the aortic root complex, which serves as the anatomic and hemodynamic junction between the left ventricle and the systemic arterial system.
Location and Relations
The aortic valve is located at the junction of the left ventricle and the ascending aorta, posterior and to the right of the pulmonary valve. It is positioned centrally within the cardiac silhouette, deep to the sternum at the level of the third intercostal space.
The aortic valve is related to:
- Inferiorly: Left ventricular outflow tract (LVOT)
- Superiorly: Ascending aorta
- Posteriorly: Left atrium and left atrial appendage
- Anteriorly: Pulmonary trunk and right ventricular infundibulum
- Right: Right atrium and superior vena cava
- Left: Left atrial appendage and left main coronary artery
- Fibrous continuity: With the anterior leaflet of the mitral valve via the aortomitral curtain
The Aortic Root Complex
The aortic valve is part of a functional unit called the aortic root, which includes:
- Aortic annulus
- Aortic valve cusps (leaflets)
- Aortic sinuses (sinuses of Valsalva)
- Sinotubular junction
- Interleaflet triangles
Aortic Annulus
The aortic annulus is a crown-shaped fibrous structure that anchors the valve cusps. It consists of three semicircular attachments arranged in a three-dimensional crown-like configuration.
Components:
- Three scalloped fibrous attachments for each cusp
- The intervalvular fibrosa between adjacent cusps
- Fibrous continuity with the mitral valve (aortomitral curtain)
The annulus is not a simple ring but a complex three-dimensional structure. The surgical annulus (measured during valve replacement) differs from the hemodynamic annulus (the virtual ring at the ventriculoarterial junction measured by echocardiography).
Aortic Sinuses (Sinuses of Valsalva)
The aortic wall dilates behind each cusp, forming three bulges. These sinuses are critical for valve function and coronary perfusion.
Left Coronary Sinus:
- Located posteriorly and to the left
- Contains the left coronary ostium at or below the sinotubular junction
- Gives rise to the left main coronary artery
Right Coronary Sinus:
- Located anteriorly
- Contains the right coronary ostium
- Gives rise to the right coronary artery
Non-Coronary Sinus (Posterior):
- Located posteriorly and to the right
- Does not contain a coronary ostium
- Adjacent to the interatrial septum
Functions of the sinuses:
- Prevent coronary ostial occlusion by the cusps during systole
- Generate vortices that initiate valve closure before forward flow ceases
- Distribute mechanical stress across the aortic wall
- Provide space for coronary blood flow during systole
Sinotubular Junction
The sinotubular junction is the ridge where the three aortic sinuses meet the tubular portion of the ascending aorta. It marks the distal boundary of the aortic root.
- Forms the physiologic waist of the aortic root
- Dilation of the sinotubular junction causes aortic regurgitation by splaying the commissures and preventing cusp coaptation
- The coronary ostia are typically located at or below this junction
Interleaflet Triangles
Three fibrous triangles occupy the spaces between the cusps, extending from the annulus to the sinotubular junction.
- Left-Non coronary triangle: In fibrous continuity with the anterior mitral leaflet (aortomitral curtain)
- Right-Non coronary triangle: Adjacent to the membranous interventricular septum; the atrioventricular bundle (Bundle of His) passes through this region
- Right-Left triangle: Adjacent to the pulmonary root
These triangles are thin, fibroelastic structures that are the weakest part of the aortic root. They allow the aortic root to expand during systole and contract during diastole.
Cusps of the Aortic Valve
The three semilunar cusps are named for their associated coronary sinuses:
Left Coronary Cusp:
- Supports the left coronary ostium
- Adjacent to the left atrial wall and left atrial appendage
- The left main coronary artery originates from the sinus above this cusp
- Triangular shape with a broad base
Right Coronary Cusp:
- Supports the right coronary ostium
- Adjacent to the interventricular septum and right ventricular outflow tract
- The right coronary artery originates from the sinus above this cusp
- Most commonly involved in bicuspid valve fusion
Non-Coronary Cusp:
- Does not give rise to any coronary artery
- Adjacent to the interatrial septum and mitral valve
- Largest of the three cusps in some individuals
- Most commonly involved in unicuspid valves
Microscopic Structure of Each Cusp:
| Layer | Composition | Location |
|---|---|---|
| Fibrosa | Dense collagen | Ventricular side (load-bearing) |
| Spongiosa | Loose connective tissue | Middle layer (shock absorption) |
| Ventricularis | Elastic fibers | Ventricular surface (elastic recoil) |
Each cusp also features:
- Free edge: Contains the nodule of Arantius (central thickening of collagen)
- Lunula: Thin, crescent-shaped area adjacent to the free edge
- Coaptation surface: The area where adjacent cusps overlap during closure (5-8 mm)
Commissures
The three commissures are the peripheral attachment points between adjacent cusps:
| Commissure | Location | Adjacent Structures |
|---|---|---|
| Right-Left | Anterior | Pulmonary root |
| Left-Non | Left posterior | Anterior mitral leaflet |
| Right-Non | Right posterior | Membranous septum |
The height of the commissures relative to the sinotubular junction determines the effective coaptation reserve.
Valve Hemodynamics
The aortic valve is subjected to the highest pressures in the cardiovascular system:
Systole: The valve opens when left ventricular pressure exceeds aortic pressure (typically >80 mmHg). The cusps are displaced outward against the sinus walls, creating a nearly triangular orifice.
Diastole: The valve closes when aortic pressure exceeds left ventricular pressure. Vortices in the sinuses push the cusps toward the center. The closed valve supports a diastolic pressure of 80-120 mmHg without leakage.
Normal flow characteristics:
- Peak flow velocity: 1.0-1.7 m/s
- Mean pressure gradient: < 5 mmHg
- Valve area: 3-4 cm²
- Flow pattern: Laminar, with systolic vortices in the sinuses
Normal Dimensions
| Parameter | Normal Range |
|---|---|
| Annular diameter | 2.0-2.5 cm |
| Sinus diameter | 2.5-3.5 cm |
| Sinotubular junction diameter | 2.0-2.8 cm |
| Valve area | 3.0-4.0 cm² |
| Peak systolic gradient | < 10 mmHg |
| Mean systolic gradient | < 5 mmHg |
| Coaptation height | 5-8 mm |
| Coaptation length | 2-4 mm |
Clinical Significance
Aortic Stenosis (AS)
Narrowing of the aortic valve orifice, the most common valvular heart disease requiring intervention.
Causes and Demographics:
| Etiology | Typical Age | Mechanism |
|---|---|---|
| Calcific degenerative | > 70 years | Progressive calcium deposition on cusps |
| Bicuspid valve | 40-60 years | Accelerated wear on abnormal valve |
| Rheumatic | 20-50 years | Commissural fusion and cusp thickening |
| Congenital (unicuspid) | Childhood | Single functional cusp |
Clinical Triad: Angina, syncope, dyspnea on exertion
Physical Findings:
- Late-peaking systolic ejection murmur at right upper sternal border
- Radiates to carotids
- Parvus et tardus (weak, delayed carotid upstroke)
- S4 gallop
- Reverse splitting of S2 in severe cases
Severity Classification:
| Severity | Valve Area | Mean Gradient | Peak Velocity |
|---|---|---|---|
| Mild | > 1.5 cm² | < 20 mmHg | 2.0-2.9 m/s |
| Moderate | 1.0-1.5 cm² | 20-40 mmHg | 3.0-3.9 m/s |
| Severe | < 1.0 cm² | > 40 mmHg | > 4.0 m/s |
Aortic Regurgitation (AR)
Incomplete coaptation of the valve cusps during diastole, allowing blood to leak from the aorta into the left ventricle.
Acute Causes:
- Infective endocarditis (leaflet perforation or vegetation)
- Aortic dissection (involvement of the aortic root)
- Trauma (deceleration injury)
Chronic Causes:
- Bicuspid aortic valve
- Rheumatic heart disease
- Annuloaortic ectasia (Marfan syndrome, Ehlers-Danlos)
- Syphilitic aortitis
- Ankylosing spondylitis
- Hypertension with aortic root dilation
Physical Findings:
- Decrescendo diastolic murmur at left sternal border
- Corrigan pulse (bounding, collapsing carotid pulse)
- de Musset sign (head bobbing with each heartbeat)
- Quincke pulse (nail bed capillary pulsations)
- Wide pulse pressure
- Austin Flint murmur (diastolic rumble from jet impinging on mitral valve)
Bicuspid Aortic Valve
The most common congenital cardiac anomaly, affecting 1-2% of the population. The valve has two functional cusps, most commonly due to fusion of the right and left coronary cusps.
Types:
- Type 1: Fusion of right and left cusps (most common, ~70%)
- Type 2: Fusion of right and non-coronary cusps (~20%)
- Type 3: Fusion of left and non-coronary cusps (~10%)
Associated Conditions:
- Accelerated calcific aortic stenosis (presents 10-20 years earlier than trileaflet valve)
- Aortic regurgitation (from cusp prolapse or root dilation)
- Ascending aortic aneurysm (independent of valve hemodynamics)
- Coarctation of the aorta
- Aortic dissection (increased risk even without aneurysm)
Aortic Valve in Systemic Diseases
Marfan Syndrome:
- Annuloaortic ectasia with dilation of the sinuses of Valsalva
- Thinning and elongation of the cusps
- Aortic regurgitation from sinotubular junction dilation
Ankylosing Spondylitis:
- Fibrotic thickening of the aortic root
- Nodular thickening of the cusps
- Aortic regurgitation from root involvement
Syphilitic Aortitis:
- Obliterative endarteritis of the vasa vasorum
- Destruction of elastic fibers in the aortic media
- Aortic root dilation and regurgitation (tertiary syphilis, decades after infection)
Rheumatoid Arthritis:
- Nodular accumulation of rheumatoid granulomas at the base of the cusps
- Can cause both stenosis and regurgitation