Echo Made Simple: Mastering Aortic Stenosis Assessment in One Watch

 

Echocardiographic Assessment of Aortic Stenosis (AS)

Aortic stenosis is a progressive valvular disease, and echocardiography is the cornerstone for diagnosis, grading severity, determining mechanism, and guiding timing of intervention.

1. Goals of Echocardiographic Assessment

• Confirm presence of AS

• Identify valve morphology and etiology

• Quantify severity

• Assess left ventricular (LV) response

• Detect associated lesions

• Resolve discordant or low-gradient AS

2. Valve Morphology and Etiology

2D echocardiography is used to assess:

• Number of cusps

– Tricuspid (degenerative/calcific AS)

– Bicuspid (younger patients, eccentric opening, raphe)

• Degree and distribution of calcification

• Cusp mobility and thickness

• Associated aortopathy (especially in bicuspid valve)

Parasternal short-axis view at the level of the aortic valve is key for cusp number and opening pattern.

3. Doppler Hemodynamic Assessment (Core of AS Evaluation)

A. Peak Aortic Jet Velocity (Vmax)

Measured using continuous-wave (CW) Doppler from multiple windows (apical, right parasternal, suprasternal).

Use the window with highest velocity.

Severity grading:

• Mild: 2.6–2.9 m/s

• Moderate: 3.0–3.9 m/s

• Severe: ≥4.0 m/s

• Very severe: ≥5.0 m/s

B. Mean Transvalvular Gradient

Calculated from the CW Doppler velocity-time integral (VTI).

Severity grading:

• Mild: <20 mmHg

• Moderate: 20–39 mmHg

• Severe: ≥40 mmHg

Mean gradient is preferred over peak gradient for clinical decision-making.

C. Aortic Valve Area (AVA) – Continuity Equation

AVA = (LVOT area × LVOT VTI) / Aortic VTI

LVOT area = π × (LVOT diameter/2)²

LVOT diameter is measured in parasternal long-axis during mid-systole.

Severity grading:

• Mild: >1.5 cm²

• Moderate: 1.0–1.5 cm²

• Severe: <1.0 cm²

• Indexed AVA severe: <0.6 cm²/m²

Continuity equation is flow dependent and sensitive to LVOT measurement error.

4. Dimensionless Index (Velocity Ratio)

Useful when LVOT measurement is unreliable.

Dimensionless Index = LVOT VTI / Aortic VTI

Severity grading:

• Mild: >0.50

• Moderate: 0.25–0.50

• Severe: <0.25

5. Left Ventricular Assessment

A. LV Systolic Function

• Measure LVEF

• Reduced EF suggests advanced disease or low-flow AS

B. LV Hypertrophy

• Concentric LV hypertrophy is typical

• Measure wall thickness and LV mass

C. Diastolic Function

• Diastolic dysfunction is common

• Elevated filling pressures may explain symptoms

6. Stroke Volume and Flow Status

Stroke Volume Index (SVI) = Stroke volume / BSA

Low flow is defined as:

• SVI <35 mL/m²

Flow status is essential for classifying discordant AS.

7. Classification of Severe AS Phenotypes

A. High-gradient Severe AS

• AVA <1.0 cm²

• Mean gradient ≥40 mmHg

• Vmax ≥4.0 m/s

B. Low-flow, Low-gradient Severe AS with Reduced EF

• AVA <1.0 cm²

• Mean gradient <40 mmHg

• LVEF <50%

• SVI <35 mL/m²

Dobutamine stress echo is used to:

• Differentiate true severe vs pseudo-severe AS

• Assess contractile reserve

True severe AS: AVA remains <1.0 cm² with increased gradient.

C. Paradoxical Low-flow, Low-gradient Severe AS (Preserved EF)

• AVA <1.0 cm²

• Mean gradient <40 mmHg

• LVEF ≥50%

• SVI <35 mL/m²

Often associated with:

• Small LV cavity

• Concentric remodeling

• Hypertension

8. Stress Echocardiography in AS

Indications:

• Asymptomatic severe AS

• Low-flow, low-gradient AS

Abnormal findings:

• Increase in mean gradient ≥20 mmHg

• Failure of LV contractile reserve

• Development of symptoms

9. Associated Findings to Evaluate

• Aortic regurgitation

• Mitral valve disease

• Pulmonary hypertension (TR jet velocity)

• Ascending aorta size

• LV strain (reduced GLS indicates subclinical dysfunction)

10. Common Pitfalls in Echo Assessment

• Underestimation of LVOT diameter

• Inadequate Doppler alignment

• Failure to use multiple acoustic windows

• Ignoring flow status

• Blood pressure not controlled during study

11. Reporting Checklist for AS

A complete echo report should include:

• Valve morphology and calcification

• Peak velocity, mean gradient

• AVA and indexed AVA

• Dimensionless index

• LVEF and LV geometry

• Stroke volume index

• Flow-gradient category

• Associated valvular and aortic pathology

Echocardiography remains the primary tool for comprehensive assessment of aortic stenosis, but accurate interpretation requires integration of valve hemodynamics, flow status, and ventricular response rather than reliance on a single parameter.