What is aortic stenosis?

What is Aortic Stenosis

Aortic stenosis is a congenital or acquired disorder of the aortic valve that causes abnormal narrowing of the valve orifice, leading to increased impedance to blood flow from the left ventricle into the aorta. 1

Pathophysiology and Disease Mechanism

Aortic stenosis represents a progressive disease affecting both the valve and myocardium, characterized by:

• Progressive valve narrowing that obstructs left ventricular outflow, with secondary development of left ventricular hypertrophy in response to the increased afterload 2
• Inflammation, fibrosis, and calcification driving progressive valve narrowing, ultimately leading to left ventricular decompensation and transition to heart failure 2
• Left ventricular outflow obstruction that can occur at subvalvular, valvular, or supravalvular levels 3

Etiology and Valve Morphology

The underlying causes vary by age and geography:

Calcific Aortic Stenosis (Most Common in Developed Countries)

• Calcific stenosis of a tricuspid valve is the most frequent etiology in Europe and North America, representing a manifestation of aging that becomes more prevalent as populations age 1, 4
• Calcification is most prominent in the central and basal parts of each cusp without commissural fusion, resulting in a stellate-shaped systolic orifice 1
• Degenerative AS involves progressive calcification of an anatomically normal tricuspid valve attributed to lifelong exposure to multifactorial risk factors and physiological wear-and-tear 3

Bicuspid Aortic Valve

• Bicuspid aortic valve is the most common cause of AS in younger patients due to primary anatomic narrowing, with secondary premature calcification induced by altered hemodynamics 3
• Most commonly results from fusion of the right and left coronary cusps (80% of cases), creating a larger anterior and smaller posterior cusp with both coronary arteries arising from the anterior cusp 1
• Diagnosis is most reliable when two cusps are visualized in systole with only two commissures framing an elliptical systolic orifice 1

Rheumatic Aortic Stenosis

• Rheumatic AS is characterized by commissural fusion resulting in a triangular systolic orifice, with thickening and calcification most prominent along the edges of cusps 1
• Nearly always affects the mitral valve concurrently, so rheumatic aortic valve disease is accompanied by rheumatic mitral valve changes 1

Other Causes

• Congenital AS from a unicuspid aortic valve is rare in adults, typically showing marked dysmorphic features with severe thickening, calcification, and associated significant aortic regurgitation 1
• Radiation-induced AS presents a special challenge as the aortic valve is often heavily calcified in younger populations 1

Hemodynamic Severity Classification

Severe aortic stenosis is defined by specific hemodynamic criteria:

• Peak aortic jet velocity ≥4.0 m/s 1
• Mean transvalvular gradient ≥40 mmHg 1
• Aortic valve area <1.0 cm² (or indexed area <0.6 cm²/m²) 1
• Velocity ratio <0.25 1

High gradient severe AS specifically refers to peak velocity ≥4 m/s or mean gradient ≥40 mmHg, usually accompanied by valve area ≤1.0 cm² 1

Clinical Significance and Natural History

The disease carries profound prognostic implications:

• Symptomatic severe disease is universally fatal if left untreated, yet is consistent with typical lifespan when mechanical relief is provided in a timely fashion 4
• Patients with advanced symptoms (angina, dyspnea, syncope) have much higher mortality rates than asymptomatic patients 5
• AS is now one of the most common valvular heart diseases with increased life expectancy and aging populations, representing the most prevalent valvular disease in developed countries 6, 4
• AS is the most frequent valvular disease requiring intervention, with aortic valve replacement being the standard treatment for severe or symptomatic disease 3

Associated Complications

The disease process affects multiple cardiac structures:

• Left ventricular hypertrophy develops secondary to chronic pressure overload 2
• Heart failure occurs as left ventricular hypertrophy decompensates 2
• Pulmonary hypertension may develop in advanced disease 1
• Coronary artery disease frequently coexists and must be managed according to revascularization guidelines 1