Skip to content
Appointments & Referrals

Echo Reference › Aortic Stenosis

Echo Reference — Valve Stenosis

Aortic Stenosis

Severity grading by peak velocity, mean gradient, AVA, indexed AVA, and dimensionless severity index. Integrated stepwise approach for discordant findings including low-flow low-gradient scenarios. AVA calculator by continuity equation.

Algorithm Reference Tables AVA Calculator

Severity Grading

AS severity is determined by an integrated assessment of multiple Doppler parameters. No single parameter should be used in isolation. Discordance between parameters — particularly AVA suggesting severe but mean gradient suggesting moderate — requires a systematic stepwise approach.
Parameter Sclerosis Mild Moderate Severe
Peak velocity (m/s) ≤ 2.5 2.6 – 2.9 3.0 – 3.9 ≥ 4.0
Mean gradient (mmHg) — < 20 20 – 39 ≥ 40
AVA (cm²) — > 1.5 1.0 – 1.5 < 1.0
Indexed AVA (cm²/m²) — > 0.85 0.60 – 0.85 < 0.60
Dimensionless Severity Index — > 0.50 0.25 – 0.50 < 0.25

Key Equations

AVA (continuity equation): AVA = (LVOT area × LVOT VTI) ÷ AV VTI

LVOT area: π × (LVOT diameter ÷ 2)²

Dimensionless Severity Index (DSI): LVOT VTI ÷ AV VTI

Stroke Volume: SV = LVOT area × LVOT VTI

Stroke Volume Index: SVi = SV ÷ BSA (low flow = SVi < 35 mL/m²)

DSI advantage: The dimensionless severity index is independent of LVOT diameter measurement and avoids the squaring error inherent in the continuity equation AVA calculation. A DSI < 0.25 reliably indicates severe AS regardless of body size or LVOT measurement accuracy.

Integrated Stepwise Algorithm — Discordant Findings

When AVA suggests severe AS (< 1.0 cm²) but mean gradient is not in the severe range (< 40 mmHg), a systematic stepwise approach is required to determine whether the patient has true severe AS or moderate AS with measurement error.

Step 1 — Confirm Measurements

Before invoking a low-flow paradigm, verify measurement accuracy. The most common cause of discordant AVA/gradient is LVOT diameter measurement error — a 1 mm error in LVOT diameter produces approximately 0.15 cm² error in AVA due to squaring. Also check: CW Doppler alignment with the AS jet (use multiple windows), LVOT VTI sampling site (immediately below the valve, not in the body of the LVOT), and whether significant aortic regurgitation is present (which increases transvalvular flow and gradients).

Step 2 — Assess Flow State

Flow State SVi Next Step
Normal flow ≥ 35 mL/m² AVA < 1.0 with normal flow and low gradient → most likely moderate AS (or small body size). Check indexed AVA and DSI. If indexed AVA ≥ 0.6 and DSI ≥ 0.25, reclassify as moderate.
Low flow < 35 mL/m² AVA < 1.0 with low flow → proceed to Step 3 to determine cause of low flow.

Step 3 — Classify Low-Flow Low-Gradient AS

Scenario EF Mechanism Next Step
Classical LFLG-AS < 50% Reduced EF → reduced SV → low gradient despite severe AS Low-dose dobutamine stress echo — assess for flow reserve and true vs pseudo-severe AS
Paradoxical LFLG-AS ≥ 50% Small hypertrophied LV, restrictive physiology, or significant diastolic dysfunction → low SV despite preserved EF CT aortic valve calcium scoring — AVC ≥ 2000 AU (men) or ≥ 1200 AU (women) supports severe AS. Also consider indexed AVA < 0.6 and DSI < 0.25.

Step 4 — Dobutamine Stress Echo (Classical LFLG-AS)

DSE Finding Interpretation
SV increases ≥ 20% AND AVA remains < 1.0 with mean gradient rising to ≥ 40 True severe AS — fixed severe stenosis unmasked by improved flow
SV increases ≥ 20% AND AVA increases to > 1.0 with gradient remaining low Pseudo-severe AS — the valve is only moderately stenotic; low resting AVA was due to reduced opening force from low output
SV fails to increase ≥ 20% No flow reserve — test is inconclusive. Consider CT calcium scoring or clinical decision-making based on available data. Absence of flow reserve itself carries poor prognosis.
CT calcium scoring thresholds: For confirming severe AS when echo is inconclusive (particularly in paradoxical LFLG-AS), AVC thresholds are sex-specific: ≥ 2000 Agatston units in men and ≥ 1200 AU in women. An intermediate "likely severe" zone exists (1200–2000 AU in men, 800–1200 AU in women). Below these thresholds, severe AS is unlikely.

AVA Calculator — Continuity Equation

AVA by Continuity Equation

Enter LVOT diameter, LVOT VTI, and AV VTI. BSA (or height/weight) is optional but required for indexed AVA and stroke volume index.

LVOT Area —
AVA (continuity equation) —
AVA Severity —
DSI (LVOT VTI ÷ AV VTI) —
DSI Severity —
Stroke Volume —
BSA —
Indexed AVA —
Stroke Volume Index —
Flow State —

Clinical Context

Measurement Pitfalls

Pitfall Impact
LVOT diameter measurement error The single largest source of error. LVOT diameter is squared in the area calculation — a 1 mm error produces ~7–8% error in area and AVA. Always measure in mid-systole, inner edge to inner edge, in the parasternal long-axis view, parallel and immediately adjacent to the aortic valve.
Non-parallel CW Doppler alignment Underestimates peak AV velocity and mean gradient. Use multiple windows (apical 5-chamber, right parasternal, suprasternal, subcostal) and report the highest velocity obtained.
LVOT VTI sampling too proximal PW sample volume should be immediately below the aortic valve (within 5 mm). Sampling deeper in the LVOT gives lower velocities and overestimates AVA.
Confusing AS jet with MR jet Both are systolic, high-velocity signals in the apical view. The AS jet has a characteristic rounded envelope, while MR is more pan-systolic with a denser signal. Use spectral shape, timing, and colour Doppler to differentiate.
Significant AR inflating gradients Coexisting AR increases transaortic flow volume, raising both Vmax and mean gradient for a given AVA. In moderate or greater AR, gradients overestimate stenosis severity — AVA (or DSI) is more reliable.
Atrial fibrillation Beat-to-beat variability requires averaging ≥ 5 consecutive beats for all Doppler measurements. Short R-R intervals underestimate gradients; long R-R intervals overestimate them.
High-output states Anaemia, thyrotoxicosis, AV fistula — gradients are elevated out of proportion to anatomical severity. AVA and DSI are more flow-independent and should be prioritised.

When to Suspect Discordance

The most common discordant pattern is AVA < 1.0 cm² with mean gradient < 40 mmHg. This occurs in approximately 30% of patients referred for AS assessment. The differential includes: true severe AS with low flow (classical or paradoxical LFLG), moderate AS with measurement error (most commonly LVOT diameter underestimation), moderate AS in a patient with small body habitus (check indexed AVA), and severe AS with significant AR (gradients paradoxically suppressed by the regurgitant volume increasing forward flow). The stepwise algorithm above systematically addresses each of these possibilities.

Progression & Monitoring

Severity Typical Annual Progression Recommended Echo Interval
Mild Vmax increases ~0.3 m/s per year; AVA decreases ~0.1 cm² per year Every 3–5 years (or sooner if symptoms develop)
Moderate Variable — faster if calcific, bicuspid, or associated with renal disease Every 1–2 years
Severe Variable Every 6–12 months, or sooner if symptoms develop. Closer follow-up for very severe AS (Vmax > 5 m/s).
Bicuspid aortic valve: BAV-associated AS tends to present 1–2 decades earlier than calcific trileaflet AS. Always report aortic root and ascending aorta dimensions (see Aortic Dimensions) when BAV is identified, as concomitant aortopathy is common and independently influences surgical timing.

References

  1. Baumgartner H, 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.
  2. Otto CM, et al. 2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease. Circulation. 2021;143(5):e72–e227.
  3. Vahanian A, et al. 2021 ESC/EACTS Guidelines for the Management of Valvular Heart Disease. Eur Heart J. 2022;43(7):561–632.
  4. Clavel MA, et al. Aortic Valve Area Calculation in Aortic Stenosis by CT and Doppler Echocardiography. JACC Cardiovasc Imaging. 2015;8(3):248–257.
← Back to Echo Reference Tools