Aortic Stenosis

Aortic Stenosis Severity

Resting TTE

Use the highest reproducible AV CW Doppler signal from multiple windows

Echo
1Peak AV velocity
Highest dense CW envelope
m/s
2Mean gradient
Trace the full systolic CW envelope
mmHg
3LVOT diameter
2D PLAX measurement; area is calculated internally
cm
4LVOT VTI
PW Doppler just proximal to flow acceleration
cm
5AV VTI
CW VTI through the stenotic valve
cm
Reported AVA (optional)
If blank, AVA is calculated by VTI continuity
cm²
LVEF
Needed to classify low-gradient AS
%
Symptoms attributable to AS?
Used for ACC/AHA stage labeling
Flow, velocity ratio, CT calcium
Height
With weight calculates BSA and SVI
cm
Weight
kg
LVOT peak velocity
Optional alternative dimensionless velocity ratio. No separate Vmax AVA mode
m/s
Systolic BP
Useful context in paradoxical low-flow AS
mmHg
Atrial fibrillation?
Average representative Doppler beats
Sex for CT calcium
CT aortic valve calcium
Flow-independent support when echo grading is discordant
AU

Aortic Stenosis Diagnostic Pathway

TTE suspicious for aortic stenosis
1 · Hemodynamics

Peak velocity + mean gradient

Use the highest reproducible CW Doppler signal from multiple windows.

Aortic Valve Anatomy + ACC/AHA Staging

The normal aortic valve has 3 thin cusps. Normal valve area is roughly 3–4 cm², with about 2 cm leaflet opening in systole.

Stage A · At risk
Risk substrate without hemodynamic AS
Examples: BAV, aortic sclerosis, prior rheumatic disease
Stage B · Progressive
Mild–moderate AS
Early calcification/fibrosis
Usually normal EF and no AS symptoms
Stage C · Severe, asymptomatic
C1: LVEF ≥50%
C2: LVEF <50%
Stage D · Severe, symptomatic
D1: High-gradient
D2: Low-flow, low-gradient + reduced EF
D3: Paradoxical low-flow, low-gradient + normal EF

Congenital Valve Morphology

Congenital Valve Morphology

Valve Morphology
Unicuspid aortic valve morphology
Single functional cusp with a small eccentric opening
Clinical Summary

Unicuspid

Rare congenital valve that usually presents with stenosis

  • Very rare
  • Usually causes AS
  • AR is less common
Valve Morphology
Bicuspid aortic valve morphology
Two functional cusps with a fish-mouth opening
Clinical Summary

Bicuspid

Most common congenital aortic valve abnormality

  • ~1–2% of the population
  • AS more common than AR
  • Screen first-degree relatives
  • Common pattern: right-left cusp fusion
Valve Morphology
Quadricuspid aortic valve morphology
Four cusps meeting centrally
Clinical Summary

Quadricuspid

Rare congenital morphology that more often causes regurgitation

  • AR more common than AS
  • May coexist with other congenital lesions
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How to Quantify Aortic Stenosis on Echo

  • The primary things you are looking for are peak AV velocity, mean gradient, AVA and flow
  • The continuity equation which is used to measure the AVA depends on three measurements
    • LVOT diameter
    • LVOT VTI
    • AV VTI

LVOT Diameter · PLAX

  • PLAX view, zoom on AV + LVOT
  • Measure in mid-systole with valve open
  • Inner-edge to inner-edge
  • LVOT area = 0.785 × diameter²
  • Diameter error is amplified because the value is squared
    • Recommend comparing the measured LVOTD with the predicted LVOTD by using the following formula
      • Predicted LVOTD = (5.7 × body surface area) + 12.1
      • This is integrated into my calculator above if discordance arises
PLAX LVOT diameter measurement

LVOT Diameter Check

Quick check for AVA–mean gradient discordance

Measurements

Body surface area
m²
Measured LVOT diameter
PLAX, inner edge to inner edge
mm
Predicted LVOTD = (5.7 × BSA) + 12.1

LVOT VTI · PW Doppler

Represents forward stroke flow before the stenotic valve.

  • Apical 5-chamber or 3-chamber
  • PW Doppler
  • Sample just proximal to flow acceleration, usually ~0.5–1.0 cm below the valve
  • Trace the modal velocity envelope
PW Doppler LVOT VTI measurement

Aortic Valve VTI + Vmax · CW Doppler

  • CW Doppler through the stenotic valve
  • Use multiple windows: apical 5C, apical 3C, right parasternal, suprasternal when useful
  • Use the highest reproducible velocity
  • Trace the full systolic envelope for Vmax, mean gradient and AV VTI
CW Doppler aortic valve VTI measurement

Aortic Valve Area · Continuity Equation

AVA = (LVOT area × LVOT VTI) ÷ AV VTI

  • LVOT area = π × (LVOT diameter ÷ 2)²
  • Continuity assumes flow entering the valve equals flow across the valve
  • Planimetry can be used, but TEE or CT generally defines the orifice better when transthoracic imaging is limited
Aortic valve area continuity equation

Continuity Equation

Flow entering the LVOT = flow crossing the AV

AV Area Effective valve orifice = LVOT Area π × (D / 2)² × LVOT VTI PW Doppler AV VTI CW Doppler
AVA = (LVOT Area × LVOT VTI) ÷ AV VTI   ·   LVOT Area = 0.785 × Diameter²

Dimensionless Index

DI = LVOT VTI ÷ AV VTI

  • ≤0.25 supports severe AS
  • Useful when LVOT diameter is uncertain because diameter is not part of the calculation

Severity Grading

Severity AVA Mean Gradient Vmax
Mild >1.5 cm² <20 mmHg <3.0 m/s
Moderate >1.0–1.5 cm² 20–39 mmHg 3.0–3.9 m/s
Severe ≤1.0 cm² ≥40 mmHg ≥4.0 m/s
Mild
AVA
>1.5 cm²
Mean Gradient
<20 mmHg
Vmax
<3.0 m/s
Moderate
AVA
>1.0–1.5 cm²
Mean Gradient
20–39 mmHg
Vmax
3.0–3.9 m/s
Severe
AVA
≤1.0 cm²
Mean Gradient
≥40 mmHg
Vmax
≥4.0 m/s
Additional severe criteria
AVAi ≤0.6 cm²/m²
DI ≤0.25
Low flow SVI <35 mL/m²

When the Numbers Disagree

  • Vmax ≥4 m/s or mean gradient ≥40 mmHg with AVA slightly >1 cm²: treat the hemodynamics as severe AS and recheck why AVA is discordant
  • AVA ≤1 cm² but Vmax <4 m/s and mean gradient <40 mmHg: first think measurement error or low-flow physiology
  • Recheck the CW Doppler window, LVOT diameter and LVOT PW sample location before calling low-gradient severe AS
  • Then define flow with SVI and EF

1 · Measurement error

Suboptimal CW alignment can underestimate Vmax/MG. A small LVOT diameter can markedly underestimate calculated AVA.

2 · Define flow

Low flow: SVI <35 mL/m². Then use EF to separate classic from paradoxical low-flow AS.

3 · Use a tie-breaker

Dobutamine stress echo for classic LFLG. CT calcium is especially useful when preserved EF or inconclusive DSE leaves uncertainty.

Low-Flow, Low-Gradient Aortic Stenosis

D2 · Classic LFLG

Pattern: AVA ≤1 cm² · Vmax <4 · MG <40 · EF <50% · low flow
Mechanism: weak LV cannot generate enough forward flow to create a high gradient
Next test: low-dose dobutamine stress echo

D3 · Paradoxical LFLG

Pattern: AVA ≤1 cm² · Vmax <4 · MG <40 · EF ≥50% · SVI <35 mL/m²
Mechanism: often a small, thick, stiff LV with low forward stroke volume despite preserved EF
Tie-breaker: CT aortic valve calcium score (Greater than 2000 in men, 1300 in women)

Dobutamine Stress Echo - Is it the valve or the ventricle?

  • Is the valve truly fixed and severe, or does it open when the ventricle generates more flow?
  • Low-dose dobutamine: start around 5 mcg/kg/min and increase in 5-minute stages up to 20 mcg/kg/min
  • Flow reserve: stroke volume increase ≥20%
  • True severe: AVA stays ≤1 cm² while Vmax/mean gradient rises into the severe range
  • Pseudo-severe: AVA increases >1 cm² while gradient remains <40 mmHg
  • If achieved flow is still inadequate, projected AVA at 250 mL/s can help

Once true severe AS is confirmed, the next question is whether symptoms or LV dysfunction establish an indication for aortic valve replacement.

Special Situations

Atrial fibrillation

  • Beat-to-beat variation changes flow and transvalvular gradients
  • Average at least 5 representative Doppler beats

High arterial afterload

  • High afterload can reduce forward flow and diminish the gradient
  • Valvuloarterial impedance estimates total LV systolic load
  • Zva = (systolic BP + mean AV gradient) ÷ SVI

Look above and below the valve

  • Subvalvular: fixed subaortic membrane or dynamic LVOT obstruction can alter the Doppler profile
  • Valvular: usual calcific/congenital aortic stenosis
  • Supravalvular: congenital narrowing above the valve, classically associated with Williams syndrome
References
1
Baumgartner H, Hung J, Bermejo J, et al. Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography. J Am Soc Echocardiogr. 2017;30(4):372-392. doi:10.1016/j.echo.2017.02.009.
View ASE/EACVI recommendations
Echo Assessment
2
Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA guideline for the management of patients with valvular heart disease. Circulation. 2021;143(5):e72-e227. doi:10.1161/CIR.0000000000000923.
View ACC/AHA guideline
Primary Guideline
3
Vahanian A, Beyersdorf F, Praz F, et al. 2021 ESC/EACTS guidelines for the management of valvular heart disease. Eur Heart J. 2022;43(7):561-632. doi:10.1093/eurheartj/ehab395.
View ESC/EACTS guideline
Valvular Guideline
4
Clavel MA, Magne J, Pibarot P. Low-gradient aortic stenosis. Eur Heart J. 2016;37(34):2645-2657. doi:10.1093/eurheartj/ehw096.
View review
Low-Gradient AS
5
Clavel MA, Messika-Zeitoun D, Pibarot P, et al. The complex nature of discordant severe calcified aortic valve disease grading: new insights from combined Doppler echocardiographic and computed tomographic study. J Am Coll Cardiol. 2013;62(24):2329-2338. doi:10.1016/j.jacc.2013.08.1621.
View study
CT Calcium / Discordant AS