Assessment of Aortic Stenosis
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Introduction
Aortic stenosis (AS) is the most common valvular heart disease requiring intervention in adults. It results from progressive narrowing of the aortic valve opening, leading to obstruction of left ventricular outflow. This increases left ventricular pressure, causes compensatory hypertrophy, and eventually results in heart failure, syncope, or sudden cardiac death if untreated.
Accurate assessment of aortic stenosis is essential for determining disease severity, timing of intervention, and prognosis. Echocardiography remains the cornerstone of evaluation, supported by clinical assessment and additional imaging when required.
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Etiology of Aortic Stenosis
The major causes include:
Degenerative (Calcific) Aortic Stenosis
Most common cause in elderly patients due to progressive calcification of the valve.
Bicuspid Aortic Valve
Congenital abnormality leading to earlier valve degeneration.
Rheumatic Heart Disease
Leads to leaflet thickening, fusion, and calcification.
Less common causes include radiation-induced valve disease and congenital unicuspid valves.
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Clinical Assessment
Symptoms are critical in determining management.
Classic triad of symptomatic severe AS includes:
Angina
Due to increased myocardial oxygen demand and reduced coronary perfusion.
Syncope
Occurs during exertion due to fixed cardiac output.
Dyspnea
Results from elevated LV filling pressures and heart failure.
Other findings may include fatigue, reduced exercise tolerance, and palpitations.
Physical Examination
Important signs include:
Slow rising carotid pulse (pulsus parvus et tardus)
Harsh ejection systolic murmur best heard at the right upper sternal border
Radiation of murmur to carotid arteries
Soft or absent second heart sound in severe disease
Presence of an S4 due to left ventricular hypertrophy
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Role of Echocardiography
Transthoracic echocardiography (TTE) is the primary diagnostic tool for assessing aortic stenosis.
It provides information about:
Valve morphology
Valve calcification
Severity of stenosis
Left ventricular function
Associated valve disease
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Key Echocardiographic Parameters
Severity of AS is determined using three major parameters.
Peak Aortic Jet Velocity
Measured using continuous wave Doppler across the aortic valve.
Mild AS
2.6 – 2.9 m/s
Moderate AS
3.0 – 3.9 m/s
Severe AS
≥ 4.0 m/s
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Mean Transvalvular Gradient
Calculated from Doppler velocities using the Bernoulli equation.
Mild
< 20 mmHg
Moderate
20 – 39 mmHg
Severe
≥ 40 mmHg
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Aortic Valve Area (AVA)
Calculated using the continuity equation.
Normal AVA
3 – 4 cm²
Severe AS
≤ 1.0 cm²
Very severe AS
≤ 0.6 cm²
Indexed AVA ≤ 0.6 cm²/m² also suggests severe stenosis.
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Continuity Equation
The continuity equation is based on the principle of conservation of flow.
Flow through the LVOT equals flow through the aortic valve.
AVA = (LVOT area × LVOT VTI) / AV VTI
Where
LVOT area = Ο (LVOT diameter/2)²
This is the most reliable method for calculating valve area.
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Low-Flow Low-Gradient Aortic Stenosis
Some patients may have severe AS with lower gradients.
Types
Classical Low Flow Low Gradient
Reduced EF (<50%)
Paradoxical Low Flow Low Gradient
Preserved EF but reduced stroke volume index (<35 ml/m²)
Dobutamine stress echocardiography helps differentiate:
True severe AS
Pseudo severe AS
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Dimensionless Index
Also known as the Doppler Velocity Index.
DVI = LVOT VTI / Aortic Valve VTI
Interpretation
DVI > 0.50 → Mild AS
DVI 0.25 – 0.50 → Moderate AS
DVI < 0.25 → Severe AS
This parameter is useful when LVOT measurement is uncertain.
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Additional Imaging Modalities
CT Aortic Valve Calcium Scoring
Useful when echo findings are discordant.
Severe AS likely when calcium score exceeds:
Men
> 2000 Agatston units
Women
> 1200 Agatston units
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Cardiac MRI
Helpful for:
Assessing LV function
Evaluating myocardial fibrosis
Assessing flow when echo images are poor
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Cardiac Catheterization
Now rarely required for diagnosis.
Indications include:
Discordant non-invasive findings
Evaluation before valve surgery
Assessment of coronary artery disease
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Staging of Aortic Stenosis
According to ACC/AHA guidelines:
Stage A
At risk (bicuspid valve or sclerosis)
Stage B
Progressive mild-moderate AS
Stage C
Severe AS but asymptomatic
Stage D
Symptomatic severe AS
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Follow-Up Recommendations
Mild AS
Echo every 3–5 years
Moderate AS
Echo every 1–2 years
Severe AS
Echo every 6–12 months
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When to Consider Intervention
Intervention is indicated in:
Symptomatic severe AS
Severe AS with LV dysfunction (EF <50%)
Severe AS undergoing other cardiac surgery
Very severe AS with abnormal exercise test
Options include surgical aortic valve replacement (SAVR) or transcatheter aortic valve implantation (TAVI).
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Key Takeaways
Aortic stenosis is a progressive disease that requires careful clinical and echocardiographic assessment.
Peak velocity, mean gradient, and valve area are the primary parameters used to determine severity.
Low-flow states can mask severe disease and require advanced evaluation.
Timely recognition of severe AS is essential because once symptoms develop, prognosis without intervention is poor.
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