What is aortic stenosis?

Definition of Aortic Stenosis

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

Types of Aortic Stenosis

Aortic stenosis can be categorized based on location:

1. Valvular aortic stenosis: Narrowing at the level of the aortic valve leaflets

   • Most common form
   • Can be congenital or acquired (degenerative calcification)

2. Subvalvular aortic stenosis: Narrowing below the aortic valve

   • May be due to:
     • Fibromuscular shelf
     • Fibromuscular tunnel
     • Other indeterminate types 1

3. Supravalvular aortic stenosis: Narrowing above the aortic valve

   • May present as:
     • Diffuse narrowing of the proximal aorta
     • Fibrous membrane within the aortic lumen
     • Hourglass deformity
     • Other indeterminate types 1

Severity Classification

Aortic stenosis severity is classified based on hemodynamic parameters:

• Severe AS:

  • 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

• Flow-gradient patterns in severe AS:

  • Classic severe AS: AVA <1.0 cm², mean gradient ≥40 mmHg, stroke volume index ≥35 mL/m²
  • Low-flow/low-gradient AS: AVA <1.0 cm², mean gradient <40 mmHg, stroke volume index <35 mL/m² 2

Pathophysiology

Aortic stenosis involves two key pathological processes:

1. Progressive valve narrowing:

   • Characterized by inflammation, fibrosis, and calcification of the valve leaflets 3
   • Results in increased resistance to left ventricular outflow

2. Left ventricular response:

   • Development of left ventricular hypertrophy as a compensatory mechanism
   • Eventually leads to myocardial fibrosis and potential decompensation 4

Clinical Staging

The American College of Cardiology/American Heart Association guidelines propose a staging system:

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

Clinical Manifestations

Classic symptoms of severe AS include:

• Angina
• Dyspnea
• Syncope 5

These symptoms typically develop late in the disease process and indicate a poor prognosis without intervention.

Diagnostic Considerations

• Echocardiography is the primary diagnostic tool
• Proper measurement technique is crucial to avoid errors in AVA calculation
• Discordant measurements between AVA and gradient may require additional testing (dobutamine stress echo, CT calcium scoring)
• Hypertension can alter peak velocity/mean gradient measurements 2

Management Implications

• Symptomatic severe AS requires valve replacement (surgical or transcatheter)
• Management of asymptomatic severe AS remains controversial
• No medical therapy has been proven to delay or halt disease progression 6
• Low-flow/low-gradient AS with reduced ejection fraction carries a worse prognosis than normal-flow/high-gradient AS 2

Conclusion

Aortic stenosis represents a spectrum of disease involving both valve obstruction and myocardial response. Understanding its definition, classification, and pathophysiology is essential for appropriate clinical management and timing of intervention.