Aortic Valve

The aortic valve has three cusps/leaflets, separated by three commissures and supported by a fibrous annulus.

Cusps are slightly thickened at the tips = node of Arantius; cusps meet centrally when closed, and leaflet overlap during diastole ensures a tight seal.

Behind each cusp is an aortic root outpouching = sinus of Valsalva.

• RCC — in front of the right coronary sinus, where the right coronary artery arises.
• LCC — in front of the left sinus, where the left coronary artery arises.
• NCC — in front of the non-coronary sinus, where no coronary artery arises.

• PLAX: cusp opposite the RVOT = RCC; the other cusp is either LCC or NCC.
• PSAX: cusp opposite the RVOT = RCC; cusp opposite the interatrial septum = NCC; remaining cusp = LCC.

Coronary arteries may not be well seen in adult TTE, but cusps can still be identified.

The RCC is always placed at the 6 o'clock position, whether viewed from the aorta or LVOT perspective.

Most common causes of valvular AS:

1. Degenerative bicuspid AV — commonest in age <65 years.
2. Degenerative calcification of a trileaflet AV due to aging — commonest in age >75 years.
3. Rheumatic AV.

Degeneration pattern helps determine etiology:

• Bicuspid AV: degeneration starts at leaflet tips and raphe if present.
• Age-related degeneration: leaflet body is commonly involved.
• Rheumatic AV: degeneration mainly occurs at commissures and leaflet tips.

• Most common etiology in elderly patients.
• Accelerated by hypertension and chronic renal failure.
• Severe calcification can convert a trileaflet AV into an acquired morphologic bicuspid valve.
• Thickening/calcification without stenosis = "aortic sclerosis."

• Starts at commissures and leaflet tips.
• Extremely rare not to have mitral valve rheumatic involvement.

Congenital cusp number abnormalities:

• Bicuspid AV — most common, prevalence 1–2% of congenital heart disease; caused by fusion of two cusps at one commissure.
• Unicuspid AV — rare; caused by fusion at two commissures; the fusion line is called a raphe.
• Acommissural unicuspid valve — extreme form with no commissure and no commissure-aorta meeting point.
• Quadricuspid AV — also associated with abnormal AV function.

Best method to identify cusp number:

• Count commissure-aorta meeting points during fully opened AV in short-axis view.
• Counting leaflets in diastole is not recommended and can be misleading.

• Type 1: RCC/LCC fusion — most common.
• Type 2: RCC/NCC fusion.
• Type 3: LCC/NCC fusion — rarest.
• Type 4: NCC fused with either LCC or RCC without raphe to distinguish which one.
• Type 1: identified by raphe between RCC/LCC, or if no raphe, both coronary ostia arise from the fused leaflets.
• Types 2/3: raphe identification is mandatory; if no raphe is identified, it is type 4 when fusion involves NCC and the other leaflet is uncertain.

• Coronary cusp fusion (CCF): RCC/LCC fusion; valve mostly anterior-posterior/horizontal in PSAX; both coronaries arise from the anterior cusp.
• Mixed cusp fusion (MCF): mostly right-left/vertical orientation in PSAX; coronaries arise from RCC and LCC.
• Leaflet orientation is primary; with atypical orientation, use coronary ostium and adjacent structures.
• MCF type is an independent risk factor for hemodynamically significant AS and aortopathy.

When reporting bicuspid AV, always comment on:

• Bicuspid phenotype
• Ascending aorta size
• Coarctation of the aorta — known association.

Associated aortic dilation:

• Most common: tubular dilatation starting at the sinotubular junction.
• Root phenotype (marfanoid) can also occur.

Echocardiographic clues for bicuspid AV:

• Systolic doming of leaflets due to incomplete opening from fusion; related to ejection click.
• Asymmetric aortic valve closure line on M-mode.
• Absence of these clues does not exclude bicuspid AV.

AS severity is assessed fundamentally by:

1. AS peak velocity
2. Mean transvalvular pressure gradient
3. AV area

• Use CW Doppler.
• Use multiple acoustic windows and a Pedoff/non-imaging probe, especially suprasternal and right parasternal windows.
• Sinus rhythm: report the highest velocity and incorporate it into calculations.
• Irregular rhythm: average 5–8 consecutive beats from the highest-velocity window.

• Measured from the properly obtained velocity.
• Use the short simplified Bernoulli equation as standard.
• Use the long simplified Bernoulli equation when proximal velocity is >1–1.5 m/s, e.g., concomitant subaortic stenosis or LVOT dynamic obstruction.

• Flow passing through a stenotic AV increases velocity and decreases pressure: pressure energy → kinetic energy.
• Distal to the narrowing, turbulent flow in the aortic root prevents significant pressure recovery.
• In the small ascending aorta, velocity decreases and pressure recovers.
• Depends on the ratio of valve area/EOA to ascending aorta area; the smaller the ascending aorta, the greater the recovery.
• Echo/CW measures the highest pressure between LVOT and just distal to the AV; invasive cath measures LV-to-ascending aorta gradient, which is smaller because of pressure recovery. Both are accurate, but invasive measurement is more clinically relevant.
• Usually not significant in native AV compared to a bileaflet mechanical valve, but important when ascending aorta diameter is <30 mm.

• EOA = effective orifice area/AV area.
• AoA = ascending aorta area = πr², where r = radius at the sinotubular junction.

AVA standard method: continuity equation.

• A small error in linear LVOT measurement is squared when calculating area.
• Circular LVOT assumption can be an occasional error; 3D/biplane planimetry of LVOT area is helpful.
• LVOT VTI is another potential error source.

Measurement sites:

• LVOT diameter measured in PLAX.
• LVOT VTI measured in apical views because Doppler angle dependency prevents VTI measurement at the PLAX diameter site.

In AS, turbulence proximal to AV can cause spectral broadening:

• Place sample volume near the AV, then gradually move apically until laminar flow is obtained.
• Ideal Doppler signal shows the AV closure click but not the opening click; an opening click means the sample volume is too deep into the LVOT.

If no good PW LVOT signal:

• CW through the AV may show two overlapping systolic signals: slower = LVOT signal, higher = AV signal.
• Decreasing Doppler gain helps separate them.

Alternative stroke volumes:

• If no significant MR or PR, mitral or pulmonic stroke volume can be used instead of LVOT as a second choice, but with higher technical error.

• DVI = LVOT VTI / AV VTI or LVOT peak velocity / AV peak velocity.
• Eliminates LVOT area error.
• Normal ≈1; decreasing DVI = more severe stenosis.
• Helps distinguish high velocity/gradient from hyperdynamic circulation (e.g., AR, where DVI is normal) from true stenosis (DVI reduced).

Grading should also incorporate valve morphology and degree of AV opening.

Discordant parameters: first check for measurement errors in:

• LVOT area
• LVOT VTI
• AV peak velocity

If discordance persists, determine the pattern:

1. Gradient/peak velocity in severe range but AVA ≥1 cm²:
   • Consider high transvalvular flow; stroke volume and DVI are most helpful.
   • Causes: aortic regurgitation, shunt lesion, anemia, other high cardiac output states.
   • Treat the cause of high flow, not the aortic stenosis.
2. Gradient/peak velocity in moderate range but AVA <1 cm²:
   • Systemic hypertension can lower Doppler velocity/gradient; repeat exam when BP is normal.
   • If BP normal and discordance persists, assess for low-flow state:
     • True severe AS = AVA truly severe but low flow lowers velocity/gradient = low-flow low-gradient severe AS.
     • Pseudosevere AS = low flow did not open the AV maximally.

Low-flow, low-gradient AS with reduced EF is defined as:

• AVA <1.0 cm²
• Mean AV systolic gradient <40 mmHg
• LV EF <50%
• SV index <35 ml/m²

In this condition, dobutamine stress echocardiography helps distinguish true severe from pseudosevere AS.

• Start at 2.5–5 μg/kg/min.
• Increase by 5 μg/kg/min every 3–5 minutes.
• Maximum 20 μg/kg/min.

Stop infusion when any of the following occurs:

• Maximum dobutamine dose reached: 20 μg/kg/min.
• Heart rate rises 10–20 bpm over baseline or exceeds 100 bpm.
• Symptoms, blood pressure fall, or significant arrhythmia.
• Positive result obtained:
  • AVA increases to >1.0 cm², or
  • AS peak velocity increases to ≥4 m/s or mean gradient to ≥40 mmHg, or
  • >20% increase in SV from baseline.

AV severity interpretation:

1. True severe AS: peak velocity increases to ≥4 m/s or mean gradient ≥40 mmHg with AVA <1 cm².
2. Pseudosevere/moderate AS: AVA increases to ≥1.0 cm².
3. Absence of flow reserve: no significant change in AVA and velocity/gradient; severity cannot be assessed by this method.

Flow reserve:

• ≥20% increase in SV = flow reserve present.
• <20% increase in SV = absent flow reserve; predicts poor surgical and long-term outcome, but does not predict LV function improvement after intervention.

If AVA and velocity do not change significantly with dobutamine:

• Aortic valve calcium score by CT is recommended.
• Projected AVA is also helpful.

Predicted valve area at a presumed normal flow of 250 ml/sec.

• Q = flow rate = SV / LV ejection time (seconds by Doppler).
• AVA(proj) ≤1.0 cm² identifies true severe AS.

• AVA <1.0 cm²
• Mean AV systolic gradient <40 mmHg
• LV EF ≥50%
• SV index <35 ml/m²

Infrequent; carefully check for technical error in AVA measurement.

Causes: reduced transvalvular flow from LV hypertrophy with small cavity, severe MR, or severe TR.

Dobutamine stress is not helpful; calcium score by CT is recommended.

• AVA <1.0 cm²
• Mean AV systolic gradient <40 mmHg
• LV EF ≥50%
• SV index ≥35 ml/m²

This combination is unlikely to be true; technical errors, especially in AVA measurement, are common.

General rule: true severe AS is unlikely when peak velocity <3 m/s and mean gradient <20 mmHg.

• Rare acquired lesion with genetic predisposition.
• Associated with other congenital heart disease: coarctation of the aorta, bicuspid AV, ASD, VSD.
• May be part of Shone complex: parachute mitral valve, supra-mitral stenosis, and coarctation.
• Morphologic types:
  • Discrete subaortic membrane — 90%
  • Tunnel-like muscular ring — 10%
• Membrane is thin and easily missed; best clue is systolic flow turbulence proximal to the aortic valve.
• Exaggerated aortoventricular angle speeds progression; angle >130° is a risk factor for faster progression.
• High-velocity jet hitting the AV causes AV degeneration and aortic regurgitation.
• Multiple views with manipulation may show the membrane.
• Surgery:
  • Recommended with severe obstruction and peak gradient 60 mmHg or mean gradient 40 mmHg.
  • In children, lower threshold: mean gradient 30 mmHg to avoid progression.
  • Earlier resection may be considered with significant AR to avoid AV replacement.
  • Restenosis is not uncommon.

Etiology by mechanism/genetics:

1. Leaflet abnormalities:
   • Congenital: bicuspid, unicuspid, quadricuspid.
   • Acquired: senile degeneration, infective endocarditis, rheumatic valve, radiation, toxin-induced valvulopathy.
2. Aortic root abnormalities:
   • Congenital: Loeys-Dietz, Ehlers-Danlos, Marfan syndrome, osteogenesis imperfecta.
   • Acquired: idiopathic, systemic hypertension, autoimmune diseases (SLE, ankylosing spondylitis, Reiter's syndrome), aortitis (syphilitic, Takayasu's arteritis), aortic dissection, trauma.

In aortic root disease, leaflets/motion are normal and the regurgitant jet is central.

Knowing the mechanism is important for repair vs replacement.

• Mild AR is not physiological; evaluate valve anatomy and aortic root for etiology.
• Severe chronic AR causes LV volume overload and LV dilatation; continued overload impairs LV systolic function.
• Significant AR jet may hit the anterior mitral leaflet, causing fluttering, best seen on M-mode.

• Identify three jet components: flow convergence, vena contracta, jet area.
• Jet area and vena contracta measured in PLAX; flow convergence measured in apical views because axial resolution is better than lateral resolution.
• Vena contracta (VC):
  • Narrowest jet area through the valve.
  • Measured in PLAX; independent of flow and driving pressure gradient.
  • <0.3 cm mild, 0.3–0.6 cm moderate, >0.6 cm severe.
• Jet width/LVOT diameter ratio:
  • AR jet width measured 1 cm proximal to VC, divided by LVOT diastolic diameter.
  • For centrally directed jets in PLAX.
  • <25% mild, 25–64% moderate, ≥65% severe.
• Jet area/LVOT diastolic area ratio can be used in PSAX, with different cutoffs; biplane guidance necessary.
• Jet width and area are not validated in eccentric jets.

• Sample volume in descending aorta (suprasternal) and abdominal aorta (subcostal).
• Brief diastolic flow reversal can be normal.
• Holodiastolic flow reversal is abnormal.
  • Descending aorta = at least moderate AR.
  • Abdominal aorta = severe AR.
• Other causes: upper extremity A-V fistula, patent ductus arteriosus, ruptured sinus of Valsalva.

• Signal density:
  • Weak/incomplete = trace or mild AR.
  • Strong, dense signal matching forward flow = severe AR.
• Pressure half-time (PHT):
  • More severe AR → faster LV filling → LV diastolic pressure rises → aorta-LV gradient drops → steeper deceleration slope.
  • >500 ms mild, 200–500 ms moderate, <200 ms severe.
  • PHT depends on LV compliance/chronicity: severe AR with dilated compensated LV may show moderate PHT; mild AR with severe LV diastolic impairment may show short PHT.

Quantitative methods are most accurate/dependable; use them whenever AR is more than mild.

• LVOT SV includes regurgitant volume + effective forward volume.
• Volumetric method: subtract nonregurgitant valve SV from LVOT SV.
  • Use pulmonic or mitral SV if no shunt is present.
• EROA method: obtain EROA first, then multiply by AV regurgitation VTI from CW.

Regurgitant fraction (RF): Percentage of regurgitant volume from LVOT SV.

EROA:

• Usually calculated as regurgitant volume ÷ AV regurgitant flow VTI.
• PISA method: apical views recommended; lower the Nyquist limit to obtain a good hemispheric shape.
  • Early peak regurgitant velocity typically used; for accuracy, match color and spectral Doppler timing.
• 3D planimetry: align orthogonal planes through the vena contracta to directly planimeter vena contracta area, which correlates with EROA.

• Exclude measurement errors; assess other qualitative parameters such as LV size and BP.
• Wide pulse pressure suggests severe AR.
• If conflict persists, weight: RF > RV > EROA.
• Example: severe mitral stenosis decreases LVOT SV, so RV may be <60 ml even in severe AR, but RF maintains correct severity.

• Chronic parameters are validated in chronic AR; in acute AR, the LV has not adapted.
• Diastolic aorto-LV equilibrium occurs early, so a smaller regurgitation can cause severe hemodynamic compromise.
• LV diastolic pressure rises quickly → brief diastolic jet with steep deceleration slope and early mitral valve closure on M-mode.
• Early mitral valve closure = mitral valve closure before QRS onset.
  • Type A: mitral valve closes after the echocardiographic "A" wave on mitral M-mode.
  • Type B: more severe; mitral valve closes in mid-diastole with absence of the "A" wave.