Evaluation of Aortic Stenosis Severity by Echocardiography

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Contents

The clinical standard for diagnosis of Aortic Stenosis

  • Etiology
  • usually due to calcification of the leaflets
  • Bicuspid AoV (BAV) higher frequency; earlier onset
  • Level of Obstruction
  • Leaflet motion
  • Root anatomy
  • Dimensions
  • Ascending aorta
  • Complications of AS
  • LV dysfunction
  • dilatation


Methods

Aortic Velocity

  • most reproducible measure of severity
  • strongest predictor of clinical outcome
  • Classification:
  • mild: 2.6-3.0 m/s
  • moderate: 3.1-4.0m/s
  • severe: >4.0 m/s


Leaflet calcification and velocity <2.5m/s is called 'aortic 'sclerosis



Maximum Transaortic Pressure Gradient

The Peak Aortic gradient is estimated with the Simplified Bernoulli equation:

delta P = 4v2

The Mean Aortic Gradient is estimated by tracing the CW curve to avg the instantaneous gradients 

Peak      Mild: <25mmHg    Moderate:  25-60 mm Hg   Severe: >60 mm Hg
Mean      Mild: <20mmHg    Moderate:  20-50 mm Hg   Severe: >50 mm Hg

Aortic Valve Area (AVA)

The Aortic Valve Area is Estimated with the Continuity Equation:

Principle: volume flow proximal to orifice equals volume flow that is distal to it

AVA x VTIAV = CSALVOT x VTILVOT
AVA = (CSALVOT x VTILVOT) / VTIAV 
Mild:      1.5-2.0cm2
Moderate:  1.0-1.5
Severe:    <1.0


Dimensionless Index

Relative valve size based on the area of the patient’s outflow tract

Especially Useful in setting of Prosthetic Valve stenosis Due to shadowing and reverberation of mechanical valve.

Velocity Ratio = VLVOT/VAS 
Normal ratio = 1; 0.25 = 25% of normal


Planimetry

Direct visualization of the valve orifice. Can be limited due to calcification, shadowing, reverberation

Effective orifice area not = Anatomical orifice area

  • Contraction of the flow stream as it passes through orifice
  • Especially with 2D valve shape is flat (i.e. calcification)



Time to Peak Velocity

The longer it takes to reach peak velocity, the more severe the stenosis


Common Mistakes

  • Confusing Mitral Regurgitation with Aortic Stenosis
  • Underestimation of gradient
  • Misalignment of Doppler
  • Poor visualization of valve or “envelope”
  • Confusing LVOT obstruction with AS
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