Aortic valve area
AVA (continuity equation) · AVA = [π(LVOT D/2)2 × LVOT VTI] / AV VTI; planimetry by 3D TOE or CT as a cross-check
Normal range & thresholds
Normal 3.0–4.0 cm².
Low-flow states: stroke volume index <35 mL/m². Severe aortic stenosis with a mean gradient <40 mmHg and AVA <1.0 cm² is only confirmed after the flow state is accounted for.[5,6,7]
| Mild | Moderate | Severe | |
|---|---|---|---|
| AVA | >1.5 cm² | 1.0–1.5 cm² | <1.0 cm² |
| AVA index | >0.85 | 0.60–0.85 | <0.6 cm²/m² |
| DVI | >0.25 | <0.25 | |
Pathophysiology
The continuity equation states what conservation of mass requires: the volume passing the LVOT in systole equals the volume passing the valve, so AVA = (LVOT area × LVOT VTI) / AV VTI. It gives an effective orifice area — the area of the vena contracta — which is smaller than the anatomical orifice measured by planimetry, and the two are not interchangeable. The equation’s great virtue is that, unlike gradient, it is theoretically flow-independent; its great weakness is that it depends on the square of a hand-measured LVOT diameter.[5,79]
Raised by
- After valve replacement or valvuloplasty (an intended increase)
- Overestimated by an over-measured LVOT diameter, by sampling LVOT VTI too far from the valve, or by an incompletely interrogated (underestimated) transvalvular jet
Lowered by
- Calcific degenerative aortic stenosis — the dominant cause in adults over 65
- Bicuspid aortic valve — the dominant cause under 65, presenting a decade or two earlier
- Rheumatic aortic valve disease (almost always with mitral involvement)
- Radiation valve disease; chronic kidney disease and dialysis (accelerated calcification); homozygous familial hypercholesterolaemia; Paget disease
- Prosthetic valve stenosis, thrombosis, pannus, or patient–prosthesis mismatch
- Underestimated by an under-measured LVOT diameter — the single commonest reason for a spuriously ‘severe’ valve area in a patient with a modest gradient
Technique & pitfalls
- Measure the LVOT diameter in a zoomed PLAX, mid-systole, inner edge to inner edge, at the annular hinge points — and take the LVOT VTI from the same level. Diameter is squared: a 1 mm error changes AVA by ≈10%.[5]
- Interrogate the transvalvular jet from multiple windows, including the right parasternal; the highest velocity is what belongs in the denominator.
- Report AVA, indexed AVA, mean gradient, Vmax, dimensionless index and stroke volume index together. Any two that disagree mean the study is not yet complete.
- Index AVA to BSA in small patients — but not in the obese, where indexing over-diagnoses severity.
- Use the dimensionless velocity index when the LVOT diameter is unreliable; it removes the diameter entirely.[5]
- Measure at a controlled blood pressure — severe hypertension lowers the gradient and confuses grading.
Pseudo-change & artefact
- LVOT diameter error — the dominant artefact of this parameter, in both directions.
- LVOT VTI sampled in the zone of flow acceleration → falsely large AVA.
- Incomplete interrogation of the jet → falsely large AVA.
- Pressure recovery in a small aorta (<3.0 cm) → Doppler over-estimates severity; the energy loss index corrects it.[5]
- Low-flow, low-gradient states → a genuinely small calculated area in a valve that may be only moderately stenotic (pseudo-severe).
- High-flow states (anaemia, fever, AR, arteriovenous fistula) → over-estimated severity by gradient, under-estimated by area.
- An elliptical LVOT: the circular assumption under-measures the true area, which is why CT-derived areas run larger and TAVI sizing uses CT.[36]
Treatment thresholds
- Severe AS (AVA <1.0 cm²) with symptoms, or with LVEF <50%, or when undergoing other cardiac surgery → aortic valve replacement, class I.[6,7]
- Asymptomatic severe AS → class IIa for AVR when Vmax ≥5.0 m/s, rapid progression, markedly elevated natriuretic peptides, or an abnormal exercise test; supported by RECOVERY, AVATAR and EARLY TAVR.[6,7,61,62,63]
- 2025 ESC/EACTS: the age threshold favouring TAVI over surgery in tricuspid-valve AS has moved from 75 to 70 years.[6]
- Low-flow low-gradient with reduced LVEF: true-severe (AVA remains <1.0 cm² with mean gradient ≥40 mmHg once flow is normalised on dobutamine) → AVR, class I; pseudo-severe → medical therapy and re-assessment.[5,6,7]
- Paradoxical low-flow low-gradient with preserved LVEF: confirm with aortic valve calcium score (≥3000 AU men, ≥1600 AU women) before proceeding.[5,6,80]
- Prosthesis–patient mismatch: indexed effective orifice area ≤0.85 cm²/m² moderate, ≤0.65 severe — anticipated pre-operatively and prevented by root enlargement or a supra-annular prosthesis.[93,107]
Next step
- Next: resolve any discordance — re-measure the LVOT, recheck windows, compute the dimensionless index and the stroke volume index.
- Then: low-dose dobutamine stress echocardiography for low-flow low-gradient AS with reduced LVEF (flow reserve, projected AVA, contractile reserve).[5,28]
- Then: non-contrast CT calcium scoring for paradoxical low-flow low-gradient AS.[5,80]
- Then: exercise testing in the asymptomatic patient; natriuretic peptides; GLS and cardiac damage staging.[58,103]
- Then: Heart Team, coronary assessment, and gated CTA for annulus, access and coronary heights.[6,36]
Drugs
- Nothing halts or reverses aortic stenosis. Statins have been tested and failed; RAAS blockade does not slow calcification.[7]
- Treat hypertension — but grade the valve when the blood pressure is controlled.
- Vasodilators, nitrates and diuretics need care in severe stenosis with a fixed cardiac output.
- Correct anaemia and thyrotoxicosis before finalising severity.
- Beta-blockade lowers the gradient by lowering flow — it does not treat the valve.
Reversibility
0% for the native valve, and progression is the rule: AVA falls by roughly 0.1 cm² per year on average, faster with heavier calcification, renal disease and older age. Relief is mechanical and immediate — effective orifice area jumps to prosthetic values at operation or implantation, limited only by prosthesis–patient mismatch. What is not immediately reversed is the myocardial consequence: LV mass regresses by 20–30% in the first year, but diffuse and replacement fibrosis largely persists, which is the case for intervening before advanced cardiac damage.[58,86,103]