Aortic Stenosis

How AS Severity Is Measured on TTE

Aortic Valve Area (AVA) by continuity equation:
AVA = (π × (LVOT diameter ÷ 2)² × LVOT VTI) ÷ AV VTI
- Severe if ≤ 1.0 cm²
Mean gradient:
CW Doppler mean pressure difference across the valve during systole
- Severe if ≥ 40 mmHg
Peak velocity (Vmax):
Highest CW Doppler velocity through the aortic valve
- Severe if ≥ 4.0 m/s
Dimensionless/VTI ratio (DVI):
LVOT VTI ÷ AV VTI
- Severe if ≤ 0.25
Stroke volume index (SVI):
(LVOT area × LVOT VTI) ÷ BSA
- Low flow if < 35 mL/m²
Ejection fraction (EF):
Used to subtype LFLG:
- Classic LFLG if EF < 50%
- Paradoxical LFLG if EF ≥ 50% with low SVI

AS Severity Patterns

Severe AS without LFLG (normal flow):

AVA ≤ 1.0 cm²
Mean gradient ≥ 40 mmHg
Vmax ≥ 4.0 m/s
SVI ≥ 35 mL/m²
VTI ratio <0.25

Low-Flow, Low-Gradient Severe AS:

AVA ≤ 1.0 cm²
Mean gradient < 40 mmHg
Vmax < 4.0 m/s
SVI < 35 mL/m²
VTI ratio <0.25

Subtypes:

Classic LFLG: EF < 50% → low contractility → low flow
Paradoxical LFLG: EF ≥ 50% but small/stiff LV (concentric remodeling, diastolic dysfunction) → low flow despite preserved EF

Examples

Phenotype	AVA (cm²)	Mean Gradient (mmHg)	Vmax (m/s)	SVI (mL/m²)	EF (%)	VTI Ratio	Interpretation
Severe AS, normal flow	0.8	45	4.2	≥ 35	60	0.20	Severe by AVA, velocity, gradient, and DVI
Classic LFLG	0.8	28	3.3	27	35	0.22	Severe AVA with low flow → low gradients
Paradoxical LFLG	0.7	19	2.7	24.1	60	0.32	Severe AVA; DVI borderline → correlate with anatomy, consider DSE/CT calcium

AS Severity + Flow Status Calculator

Aortic Valve Area (AVA) — cm²

Mean Gradient — mmHg

Peak Velocity (Vmax) — m/s

Stroke Volume Index (SVI) — mL/m²

Left Ventricular EF — %

VTI Ratio (LVOT VTI ÷ AV VTI)

Metric	Value	Cutoffs	Interpretation

Severity grading uses the most severe category among available metrics: • AVA: ≤1.0 severe; 1.0–1.5 moderate; >1.5 mild/none. • Mean gradient: ≥40 severe; 20–39 moderate; <20 mild/none. • Vmax: ≥4.0 severe; 3.0–3.9 moderate; 2.6–2.9 mild; <2.6 none. • DVI: ≤0.25 severe; 0.26–0.50 moderate; >0.50 mild/none. Flow status: “low-flow low-gradient” if SVI <35 mL/m² AND mean gradient <40 AND Vmax <4.0; otherwise “normal flow”. EF (cut at 50%) helps subtype classic vs paradoxical, but flow label here focuses on physiology (low-flow + low-gradient).