What is aortic stenosis?

Aortic Stenosis: Definition and Clinical Implications

Aortic stenosis (AS) is a congenital or acquired disorder of the aortic valve characterized by abnormal narrowing of the valve orifice, resulting in increased impedance to blood flow from the left ventricle into the aorta, which can lead to significant morbidity and mortality if left untreated. 1

Anatomical and Pathophysiological Features

Aortic stenosis can occur at three distinct levels:

1. Valvular stenosis - The most common form, involving the aortic valve leaflets
2. Subvalvular stenosis - Can present as:
   • Fibromuscular shelf
   • Fibromuscular tunnel
   • Other subvalvular obstructions 1
3. Supravalvular stenosis - Can present as:
   • Diffuse narrowing
   • Fibrous membrane
   • Hourglass deformity 1

Valve Morphology

• Tricuspid valve: Calcification is most prominent in central and basal parts of each cusp with a stellate-shaped systolic orifice
• Bicuspid valve: Often presents with asymmetric calcification; most commonly results from fusion of right and left coronary cusps (80% of cases) 1
• Rheumatic AS: Characterized by commissural fusion with a triangular systolic orifice; almost always affects the mitral valve as well 1

Classification and Severity

Severe aortic stenosis is defined by:

• Peak velocity ≥4.0 m/s
• Mean gradient ≥40 mmHg
• Aortic valve area (AVA) <1.0 cm² (or indexed AVA <0.6 cm²/m²) 2

The American College of Cardiology/American Heart Association staging system:

• Stage A: At risk (bicuspid valve, sclerosis)
• Stage B: Progressive AS
• Stage C: Asymptomatic severe AS
• Stage D: Symptomatic severe AS 2

Clinical Manifestations

The natural history of AS typically involves a long asymptomatic period during which stenosis gradually worsens. Once symptoms develop, prognosis deteriorates dramatically. The classic triad of symptoms includes:

1. Syncope - Often exertional
2. Angina pectoris - Due to increased myocardial oxygen demand and decreased supply
3. Dyspnea - Resulting from heart failure 1

The risk of sudden cardiac death is low (3-5%) in asymptomatic patients but increases significantly (8-34%) once symptoms develop 1.

Diagnostic Evaluation

Transthoracic echocardiography is the primary diagnostic tool for AS evaluation:

• Measures valve area, transvalvular gradients, and left ventricular function
• Assesses valve morphology and calcification
• Evaluates for concurrent valvular disease 1

Additional imaging modalities may be necessary in cases of discordant measurements:

• Dobutamine stress echocardiography
• CT calcium scoring
• CMR for aortic assessment, particularly in patients with bicuspid valves 2, 1

Disease Progression and Complications

Aortic stenosis is characterized by:

• Progressive valve calcification and narrowing
• Left ventricular hypertrophy as a compensatory mechanism
• Eventually, left ventricular dysfunction and heart failure 3

Complications include:

• Heart failure
• Arrhythmias and sudden cardiac death
• Endocarditis
• Thromboembolism

Management Considerations

The definitive treatment for severe symptomatic AS is aortic valve replacement, which improves survival and relieves symptoms. Options include:

• Surgical Aortic Valve Replacement (SAVR)
• Transcatheter Aortic Valve Replacement (TAVR)

The choice between SAVR and TAVR depends on surgical risk, patient characteristics, and valve anatomy 1.

For asymptomatic patients with severe AS, valve replacement is appropriate if:

• Ejection fraction is <50%
• Disease progression is rapid
• AS is very severe (aortic velocity >5 m/s) 4

Special Considerations

• Exercise/sports: Patients with severe symptomatic or asymptomatic AS and those with moderate stenosis due to bicuspid valves should avoid strenuous or isometric exercise and competitive sports 1

• Pregnancy: Contraindicated in severe symptomatic AS; treatment should be performed before conception. In asymptomatic patients with severe AS and a normal exercise test, pregnancy may be possible with careful monitoring 1

• Hypertension: Should be recorded during echocardiographic examinations as it can alter peak velocity and mean gradient measurements 2

Aortic stenosis is a progressive disease that requires regular monitoring and timely intervention to prevent the significant morbidity and mortality associated with advanced disease.