Aortic valve

Article written and reviewed by Dr Luca Moretti

The aortic valve is the semilunar structure that separates the left ventricular outflow tract from the aortic root and makes systemic ejection unidirectional. More than a simple diaphragm, it represents the mobile component of a dynamic root formed by the ventriculoarterial junction, interleaflet triangles, cusps, sinuses of Valsalva and sinotubular junction, whose coordinated geometry permits wide opening with minimal energy loss and rapid, competent diastolic closure.

The normal configuration comprises three cusps, the right coronary, left coronary and noncoronary cusps, named in relation to the sinuses from which the coronary arteries originate. The lines of insertion are crown-shaped and reach the commissures; the fibrous triangles extending between the insertions place the root in relation with surrounding structures. This three-dimensional anatomy explains why two-dimensional measurements may not adequately describe the annulus and root.

The main diseases are aortic stenosis, in which opening is reduced, and aortic regurgitation, in which diastolic coaptation is incomplete. Disease may involve the cusps, the root or both; it may be congenital, degenerative, rheumatic, infectious, inflammatory, iatrogenic or secondary to aortic disease.

Bicuspid aortic valve is a distinct condition because it combines abnormal valve morphology, risk of early stenosis or regurgitation and possible aortopathy. Its recognition modifies surveillance, family screening and the choice among repair, surgical replacement and transcatheter treatment.

Anatomy and development

The aortic root extends from the ventricular outflow tract to the sinotubular junction. The term aortic annulus is used clinically to indicate the virtual plane connecting the nadirs of the three cusps, especially in CT planning, but the anatomical insertion is not a circular ring. The plane is often elliptical and varies during the cardiac cycle.

Each aortic cusp has a basal portion, a thin body and a free margin. At the center of the margin lies the nodule of Arantius, with the lunules on either side; coaptation occurs over a surface rather than along a simple line. Fenestrations near the commissures may be acquired or age-related findings and become relevant when they rupture or compromise the free margin.

The sinuses of Valsalva facilitate cusp dynamics and contain the right and left coronary ostia. Vortices forming in the sinuses during and after ejection help prepare closure without imposing traumatic impact. The sinotubular junction maintains the relationship between the commissures; its dilation separates the margins and can cause regurgitation even when the cusps are relatively normal.

The noncoronary cusp is continuous with the anterior mitral leaflet through the mitral-aortic fibrous continuity, whereas the right sinus lies close to the membranous septum and conduction system. These relationships explain why, during surgery and TAVI, calcium, sutures or prosthesis expansion may involve not only the valve but also the conduction system, coronary ostia and mitral apparatus.

Histologically, the cusps have organized layers: the collagen-rich fibrosa on the aortic side, the proteoglycan-rich spongiosa and the elastin-rich ventricularis on the ventricular side. Endothelial cells sense different shear forces on the two surfaces; interstitial cells maintain and remodel the matrix. Disruption of this homeostasis is central to calcific and myxomatous degeneration.

The valve develops from the endocardial cushions of the outflow tract and the conotruncal ridges through remodeling, excavation and thinning. Defects in separation and modeling can produce unicuspid, bicuspid or quadricuspid valves and may be associated with abnormalities of the arch or aorta. Bicuspid morphology is not a single entity and includes phenotypes with different fusion patterns and raphes.

Root dimensions vary with age, sex and body surface area, so every measurement should specify technique, phase of the cardiac cycle and anatomical level. Because echocardiography, CT and magnetic resonance imaging may use different conventions, serial comparison is truly reliable only when plane, method and modality are maintained and significant increases are confirmed with tomographic imaging.

The ascending aorta is not part of the valve, but its geometry influences function and treatment. Dilation may be primary, associated with bicuspid valve or connective tissue disease, or result from hemodynamic and degenerative factors. The root and tubular segment should be described separately because phenotype, risk and surgical thresholds are not identical.

The virtual annulus connecting the nadirs is distinct from the anatomical ventriculoarterial junction and the crown-shaped insertion line. Terminology matters: surgery, echocardiography and CT may refer to different levels when reporting diameter. In transcatheter planning, the area and perimeter of the basal plane are preferred to a single diameter because the cross-section is elliptical.

The commissures reach the sinotubular junction and their height contributes to the coaptation surface. Geometric cusp height and effective height, meaning the vertical distance of the free margin from the basal plane, are not equivalent. Reduced effective height indicates prolapse and guides repair of regurgitation at experienced centers.

The coronary ostia are located in the right and left sinuses with variable height and orientation. Cusps, calcium and prostheses may approach the ostia during TAVI or valve-in-valve procedures; small sinuses, low ostia and a narrow junction increase the risk of obstruction. Coronary anatomy must be interpreted as part of the root and of the reintervention strategy.

Bicuspid anatomy is described by the number of functional commissures, presence and position of the raphe, and cusp orientation. Phenotypes with right-left or right-noncoronary fusion have different jets and aortic associations, but morphology alone does not predict the course. Evaluation includes coarctation, the arch, root and ascending aorta and may extend to first-degree relatives.

Physiology and biomechanics

During systolic opening, when ventricular pressure exceeds aortic pressure, the cusps open passively and move toward the sinuses. The effective orifice area is smaller than the geometric area because flow continues to converge and reaches its smallest cross-section just beyond the orifice, at the vena contracta. In a normal valve the gradient is minimal even at high flow rates.

During diastolic closure, aortic pressure again exceeds ventricular pressure and vortices within the sinuses promote central movement of the cusps. Coaptation distributes the load over a broad surface; closure generates the dicrotic notch of the aortic pressure waveform. Diastolic coronary flow originates from the coronary sinuses while the valve remains closed.

The cusps withstand millions of cycles of flexion and tension through a matrix in which oriented collagen provides strength, elastin restores shape and proteoglycans permit sliding between layers. This matrix is not inert: cells continuously respond to load and repair microdamage, but age, inflammation and biochemical abnormalities can transform an adaptive response into a fibrotic and calcific process.

The shape of the sinuses reduces stress and permits opening without adhesion to the wall. A root that is excessively dilated or deformed alters the commissural angle and effective height of the margins, reducing coaptation. Conversely, calcification and fusion restrict excursion and concentrate flow into a high-velocity jet.

The transvalvular gradient arises from flow acceleration: Doppler measures velocity and applies the simplified Bernoulli relationship, whereas the mean gradient integrates pressure differences throughout ejection. Because both measures increase with flow, they should be interpreted together with valve area calculated by the continuity equation and with the dimensionless index.

Stenosis imposes pressure overload. The ventricle develops concentric hypertrophy, end-diastolic pressure rises and coronary reserve decreases. The obstruction is not the only afterload: arterial impedance and systemic pressure add to the valvular load, particularly in older patients with a stiff aorta.

Regurgitation imposes volume overload because the ventricle simultaneously receives mitral inflow and retrograde aortic volume. In chronic regurgitation, dilation and eccentric hypertrophy preserve forward output; in acute regurgitation, the rise in end-diastolic pressure causes premature mitral valve closure and severe congestion.

When stenosis and regurgitation coexist, area, gradient and regurgitant volume must be integrated. Increased volume passing through the valve can raise the gradient even when the area is not critically reduced, whereas stenosis limits regurgitant volume. The ventricular consequence may be more severe than suggested by separate classification of the two components.

Coronary perfusion occurs predominantly during diastole, when the closed valve separates the ventricle from aortic pressure. High end-diastolic pressure, hypertrophy and shortening of diastole reduce the subendocardial perfusion gradient. For this reason, stenosis can cause angina even without epicardial coronary stenosis, and severe regurgitation can impair aortic diastolic pressure.

Pressure recovery occurs when part of the kinetic energy of the jet is reconverted distal to the vena contracta. In a small root, the Doppler gradient, which reflects maximal acceleration, may exceed the net energy loss measured invasively. The phenomenon does not make Doppler incorrect, but requires understanding which pressure and which site were compared.

Valvuloarterial impedance considers mean gradient and systolic pressure together in relation to indexed stroke volume and describes the overall load on the ventricle. It may be elevated in an older hypertensive patient even when the valvular gradient is not extreme. It does not replace stenosis thresholds, but helps explain symptoms and remodeling when both the valve and arterial tree contribute.

The myocardial response is heterogeneous. Some ventricles develop marked hypertrophy, others little increase in mass but substantial fibrosis; sex, blood pressure, coronary artery disease, amyloidosis and genetics modify adaptation. Longitudinal strain and reserve decline before ejection fraction, whereas replacement fibrosis represents less reversible damage even after implantation of a perfectly functioning prosthesis.

Diseases and clinical manifestations

Calcific stenosis progresses from thickening and microcalcification to confluent nodules that reduce opening. Aortic valve sclerosis describes a thickened or calcified valve without hemodynamically significant obstruction; it is a possible precursor, not a miniature form of severe stenosis. Progression varies widely among individuals.

Bicuspid stenosis presents earlier because the eccentric jet and abnormal distribution of stress accelerate fibrosis and calcification. Rheumatic aortic stenosis is usually associated with commissural fusion and mitral valve disease. Subvalvular and supravalvular forms are not cusp diseases and must be distinguished from valvular stenosis.

Primary aortic regurgitation results from prolapse, fenestrations, retraction, perforation, endocarditis or trauma. Secondary root regurgitation results from dilation of the functional annulus, sinuses or sinotubular junction. In bicuspid valve, cusp prolapse and aortic dilation may coexist, requiring a detailed mechanistic description.

The acute form is caused mainly by endocarditis, dissection, trauma or procedural complications. Patients present with sudden dyspnea, pulmonary edema, hypotension or shock. The diastolic murmur may be short and not loud because aortic and ventricular pressures equalize rapidly; severity must not be excluded on the basis of a modest auscultatory finding.

In the chronic form, symptoms develop after a long compensated phase. Dyspnea, reduced exercise capacity, angina and palpitations are common; awareness of pulsations and a wide pulse pressure suggest regurgitation. In stenosis, the classic triad of angina, syncope and heart failure belongs to the advanced symptomatic phase and should not be awaited before surveillance is initiated.

On examination, stenosis produces a systolic ejection murmur radiating to the carotids, a small and delayed pulse, and reduced aortic component of the second heart sound in calcific forms. Regurgitation produces a decrescendo diastolic murmur along the sternal border and peripheral signs of increased pulse pressure. Low flow, tachycardia and vascular stiffness modify these findings.

Extravalvular damage includes hypertrophy, atrial dilation, secondary mitral regurgitation, pulmonary hypertension and right ventricular dysfunction. Myocardial fibrosis may be diffuse or replacement fibrosis and is associated with worse outcomes. Recognition of concomitant amyloidosis in an older patient with stenosis requires attention to wall thickening, low voltage and other clues.

Aortopathy may remain asymptomatic until dissection occurs. Sudden chest or back pain, pulse deficits, neurological signs or new aortic regurgitation require urgent imaging. The presence of a bicuspid valve or connective tissue syndrome modifies pretest probability and family surveillance.

Aortic endocarditis can perforate a cusp, destroy coaptation or extend to the root, mitral-aortic continuity and membranous septum. Abscess, fistula and conduction block indicate perivalvular extension. The combination of infection and acute regurgitation requires an assessment that is not limited to quantifying the jet.

Calcific sclerosis is distinct from stenosis because velocity and gradient do not indicate significant obstruction. It nevertheless represents a marker of biological age and cardiovascular risk and may progress. The rate of increase is not constant: calcific burden, renal failure and baseline severity are associated with faster progression, but the individual trajectory requires serial measurements.

Rheumatic disease, unicuspid and quadricuspid valves, radiation injury and aortitis are less common than calcific degeneration. Commissural fusion suggests a rheumatic or congenital etiology, whereas calcification of the cusp bodies without fusion more often characterizes the degenerative form. Mechanism influences repairability, age at presentation and associated lesions.

Acute chest pain with new regurgitation requires exclusion of aortic root dissection, even if the murmur is short or absent. Dissection can dilate the junction, detach a commissure or prolapse through the orifice. Hypotension, pulse differences, tamponade and coronary ischemia constitute an aortic emergency, not an acute exacerbation of chronic valvular heart disease.

Investigations and diagnosis

Transthoracic echocardiography assesses cusp number and mobility, calcification, raphe, jet direction, ventricular dimensions and diameters of the root and proximal aorta. Continuous-wave Doppler must be acquired from multiple windows to avoid underestimating velocity; pulsed-wave Doppler measures flow in the outflow tract and permits use of the continuity equation.

In stenosis, peak velocity, mean gradient, area and dimensionless index are integrated. Severe high-gradient disease requires concordance of the following parameters:

• Peak velocity at least 4.0 m/s.
• Mean gradient at least 40 mmHg.
• Valve area no greater than 1.0 cm².

Discordant findings require technical verification, definition of flow status and additional imaging. The most severe value should not be selected in isolation to assign severity because misalignment, outflow tract measurement error and flow variations produce apparently discordant combinations.

In regurgitation, the assessment describes mechanism, vena contracta, flow convergence, holodiastolic aortic flow reversal, Doppler signal density and deceleration, regurgitant volume and fraction, and ventricular response. No single parameter is an absolute reference standard. Blood pressure and heart rate should be considered during quantification.

Transesophageal echocardiography defines cusps, fenestrations, vegetations and the mechanism of regurgitation and guides repair. It is not the preferred method for gradient measurement when TTE is adequate, but can clarify anatomy and provide three-dimensional measurement of the root. During the procedure it verifies competence, residual gradient and complications.

Noncontrast CT quantifies valve calcium in cases of discordant stenosis. CT angiography describes the annulus, sinuses, sinotubular junction, coronary ostia, aorta, calcium distribution and vascular access and is the standard for TAVI planning. In bicuspid valve it defines the raphe, symmetry and aortopathy.

Cardiac magnetic resonance imaging measures ventricular volumes and mass, aortic flow and regurgitant fraction, and characterizes fibrosis. It is indicated when echocardiography is inconclusive or ventricular dilation appears disproportionate. Magnetic resonance imaging or CT completes evaluation of the aorta when the ascending segment is not visible on TTE.

Exercise testing is useful in apparently asymptomatic severe stenosis and can reveal symptoms or an abnormal blood pressure response. Low-dose dobutamine echocardiography is reserved for low-flow stenosis with reduced ejection fraction. In chronic regurgitation, exercise objectively assesses capacity and ventricular response but does not replace anatomical and functional thresholds.

Catheterization is indicated when noninvasive findings and the clinical picture remain incongruent and an invasive measurement may change management. Coronary angiography, invasive or by CT, is selected according to age, coronary risk and the planned intervention. Retrograde crossing of a stenotic valve is not routine and carries risks.

The differential diagnosis includes fixed subvalvular obstruction, hypertrophic obstructive cardiomyopathy, supravalvular stenosis and high-output states for systolic murmurs; pulmonary regurgitation, fistulas and vascular sounds for diastolic murmurs. Integration of morphology, Doppler and tomographic imaging avoids attributing to the valve physiology that originates elsewhere.

In stenosis, Doppler quality is checked with multiwindow acquisition and a dedicated transducer; the highest velocity represents the best-aligned jet. Stroke volume is derived from outflow tract diameter and VTI, whereas the dimensionless index avoids diameter measurement. Discordance requires verification of blood pressure, rhythm, flow and geometry before severity is assigned.

In regurgitation, diagnosis integrates mechanism, vena contracta, flow convergence, signal density, holodiastolic aortic flow reversal, regurgitant area and volume, and ventricular response. Eccentric jets may appear small because of adherence to the wall; pressure half-time varies with compliance and pressure. No isolated measurement is sufficient when findings are discordant.

The noncontrast CT calcium score helps when stenosis area and gradient do not agree, with different thresholds according to sex. Dobutamine echocardiography is reserved mainly for low-flow states with reduced ejection fraction to distinguish true severe from pseudo-severe stenosis. These tests answer complementary questions, one anatomical and the other functional.

The root and aorta are measured at defined levels and compared using a consistent method. If echocardiography does not visualize the entire segment or detects dilation, CT or magnetic resonance imaging confirms diameters perpendicular to the vessel axis. Assessment of growth rate requires reproducible measurements; an uncertain change should not automatically be interpreted as rapid progression.

Treatment, follow-up and complications

A normal aortic valve requires no specific intervention; treatment concerns the disease and conditions that influence its load. Blood pressure, heart failure and coronary artery disease should be treated, but no drug has been shown to halt calcific stenosis. Symptomatic therapy must not delay indicated valve replacement.

In severe calcific stenosis, correction consists of valve replacement. Surgery removes the cusps and implants a prosthesis, whereas TAVI expands a bioprosthesis within the native valve. Age, risk, anatomy, transfemoral access, bicuspid valve, aorta, coronary arteries and expected durability determine the choice within the Heart Team.

In severe regurgitation, surgery is standard when symptoms or defined ventricular abnormalities develop. Repair or a valve-sparing procedure may be appropriate in selected patients with good-quality cusps and aortopathy, provided it is performed at highly experienced centers. TAVI for pure regurgitation is limited to selected cases with high risk and suitable anatomy.

Prosthesis selection considers durability and anticoagulation. A mechanical prosthesis is generally favored in a younger patient who can take a vitamin K antagonist; a bioprosthesis is favored at older age or when permanent anticoagulation is contraindicated. The strategy includes the risk of mismatch and feasibility of future valve-in-valve procedures.

Balloon valvuloplasty has a durable role in congenital noncalcific stenosis, but in adults with calcific stenosis it provides transient benefit and carries risks of regurgitation, stroke and vascular complications. It may be considered as a bridge in unstable patients or before urgent noncardiac surgery when immediate replacement is not possible.

Follow-up depends on the lesion and its severity. In asymptomatic severe stenosis, assessment at least every six months allows recognition of symptoms and changes in function; in moderate stenosis, follow-up is generally at least annual and more frequent with marked calcification. In severe regurgitation, volumes, diameters and ejection fraction are monitored and the interval is shortened near intervention thresholds.

The aorta should be measured serially. An initial diameter greater than 45 mm requires confirmation at six months and then annual surveillance according to the 2025 ESC/EACTS guidelines, with tomographic validation of increases greater than 3 mm. Operative thresholds depend on diameter, phenotype, etiology, growth, family history and concomitant valve surgery.

Complications of stenosis include heart failure, angina, syncope, arrhythmias, sudden death and shock in the terminal stage. Regurgitation causes dilation, systolic dysfunction, arrhythmias and congestion. Endocarditis and aortopathy can complicate both and produce acute regurgitation or dissection.

Procedures may cause conduction block, pacemaker implantation, stroke, bleeding, kidney injury, paravalvular leak, coronary obstruction, mismatch and endocarditis. TAVI is more often associated with leak, vascular complications and pacemaker implantation; surgery more often with severe bleeding, atrial fibrillation and early kidney injury. The differences depend on the device and the patient.

Over the long term, bioprostheses may degenerate and mechanical prostheses may thrombose or develop pannus; both may become infected or develop leaks. A baseline echocardiogram after implantation is essential for comparison. The onset of new symptoms, a change in the murmur or an increase in gradient requires earlier reassessment and multimodality imaging.

Prognosis after timely correction is generally good, but depends on the presence of fibrosis, ventricular dysfunction, pulmonary hypertension, coronary artery disease and frailty. Optimal success is not merely a valve with a low gradient and no regurgitation, but a patient with functional recovery and a sustainable strategy for the entire life expectancy.

The lifetime strategy considers durability and reintervention. Age, annular size, coronary access, the possibility of valve-in-valve treatment, risk of mismatch and presence of aortopathy guide the first treatment. A solution that is optimal in the immediate term may preclude future options; planning should anticipate at least the next realistically necessary procedure.