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Aortic Valve Stenosis

 

Primary vs. Secondary Findings:
  • A primary finding refers to the primary cause of the abnormality
  • EX: atherosclerosis formation on the aortic valve causes the stenosis
  • A secondary finding refers to other abnormalities caused by the primary abnormality
  • EX: aortic stenosis causes thickening of the LV wall and post-stenotic dilatation of the aortic root

Considerations When Evaluating Cardiac Valves:
  1. How many valve leaflets are present?
  2. Do you see abnormal masses, thickening or calcification attached to the valve leaflets?
  3. Is leaflet mobility normal, restricted or hypermobile?
  4. What are the associated abnormalities of the cardiac chambers and other cardiac valves?
Aortic Stenosis - Atherosclerosis:
  • Most common primary heart valve disease
  • Echocardiography is the preferred noninvasive imaging method for evaluation of suspected AS
  • Degenerative disease is the most common cause of aortic stenosis
  • Degenerative changes of a tri-leaflet valve begin at the sinus and spread toward the center of the valve, without commissural fusion
  • Calcification of a bicuspid valve is often more asymmetric
  • Rheumatic AS is characterized by commissural fusion and raphe formation; it is usually accompanied by rheumatic MS
  • Systemic inflammatory diseases like ankylosing spondylitis, systemic lupus erythematosus, cause leaflet thickening and aortic aneurysm formation
  • Hypertrophy of the muscle wall of the ventricle will occur as it adapts to the chronic pressure overload
Clinical Symptoms:
  • Dyspnea/Shortness of breath most common symptom
  • Orthopnea
  • Palpitations
  • Fatigue
  • Dizziness and syncope due to decreased cardiac output
  • Harsh systolic crescendo-decrescendo murmur best heard at the right upper sternal border
  • Systolic ejection click
  • Significant stenosis can lead to angina due to reduced cardiac output to the aorta and coronary arteries
  • Significant stenosis can lead to a cerebral infarct/ischemia caused by reduced cardiac output
M-mode:
  • Used to assess systolic leaflet separation
  • <12 mm cusp separation indicates significant obstruction
  • Method is not very accurate in determining the severity of the stenosis
  • Thickened leaflets cause multiple echoes to be displayed in diastole
  • Decreased leaflet separation and multiple echoes filling the space between the aortic root and valve opening
  • LV ejection time evaluated using the length of time the AV is open
  • The presence of early systolic closure of the aortic valve indicates the stenosis is subvalvular (not valvular)
  • LVH noted on LV m-mode due to pressure overload
  • Post stenotic aortic root dilatation due to eccentric flow through stenosis
2D and Doppler Evaluation:
  • 2D evaluation: short and long axis images used to identify the number of cusps, describe cusp mobility, thickness, and calcification
  • Doppler: used to identify the location of the stenosis – subvalvular, valvular or supravalvular
  • PLAX
    • Delineates the restricted opening of the tips of the aortic leaflets and systolic doming
    • LVOT diameter measurement performed at mid systole, inner to inner dimension
  • PSAX - at the level of the aortic valve
    • Demonstrates the true orifice of the stenotic valve
    • Area can be traced, ****planimetry is not very accurate because heavily calcified leaflets cause bright echoes with poorly defined borders making measurement difficult
  • AP 5/AP 3
    • Align the Doppler cursor parallel (0 degree angle) to the flow through the LVOT/AV; more than a 20 degree incident angle can cause a significant change in calculated flow velocity
    • LVOT
      • PW Doppler evaluation of the performed at same location as LVOT diameter measured
      • 2-3mm sample volume
      • Should produce a waveform with a spectral window
      • Increase sweep speed to perform velocity time integral (VTI) measurement by tracing the outer edge of the waveform
      • The peak pressure gradient (PPG) and mean pressure gradient (MPG) are also provided from the tracing
    • Aortic Valve
      • CW Doppler used due to high velocity and sampling depth
      • NO spectral window displayed
      • Increase wall filter and decrease Doppler gain
      • Increase sweep speed to 100mm/s to perform VTI measurement, PPG and MPG by tracing the outer edge of the waveform
      • Differences in cardiac output will cause variations in the velocity and the pressure gradient across a stenotic aortic valve
      • The continuity equation corrects for differences in left ventricular function, stroke volume and cardiac output
  • Pedoff probe applied at the apical, right parasternal and suprasternal windows
  • Different views used with an assumed 0 degree angle of insonation
  • The acoustic window used for the peak velocity and pressure measurements should be recorded so the method remains constant on sequential studies
  • The aortic peak systolic velocity should always be recorded from the same acoustic window as the previous exams
  • Average normal aortic valve area is 3 - 4cm²
  • Increasing velocities and pressure gradients are noted with increasing severity of stenosis
  • Velocity and PPG alone cannot diagnose stenosis due to variations in cardiac output, you must know the valve area
  • Velocity Ratio and VTI Ratio are methods used to reduce errors in AVA calculation due to inaccurate measurement of the LVOT diameter
  • Severe regurgitation can falsely elevate the peak velocity and pressure gradients but the AVA and velocity ratios should still be accurate
  • PPG is not an accurate method of assessing aortic stenosis in patients with severe aortic insufficiency; left ventricle becomes hypercontractile due to the continuous reprocessing of the same blood; PPG will be higher than the actual gradient related to the stenotic valve
  • MPG can be used to assess valvular gradient in aortic stenosis patients who also have significant aortic insufficiency
  • MPG calculated on Doppler best correlates with the mean pressure gradient obtained during heart catheterization

 

  • Continuity Equation
    • Used to calculate the AVA
    • Corrects for differences in left ventricular function, stroke volume and cardiac output
      • on serial exams
    • Requires careful 2D measurement of LVOT diameter and accurate cursor placement for recording of velocity measurements
    • Numerous factors can cause incorrect calculation of the AVA
    • Cannot be used to assess a transcatheter aortic valve replacement (relies on pressure gradients and the velocity ratio to assess stenosis)
  • Incorrect LVOT Measurement:
    • Because the LVOT diameter is squared for the calculation of CSA, it is the greatest potential source of measurement error in the continuity equation
    • Calcification of the aortic annulus can extend to the base of the anterior mitral leaflet causing inaccurate LVOT diameter measurements A ‘sigmoid septum’ can cause the underestimation of the LVOT diameter
    • If the PLAX view is poor, the diameter can be overestimated = larger AVA or the diameter can be underestimated = smaller AVA
    • When the calculated AVA changes on serial exams, look for differences in the components incorporated in the equation
    • LVOT size rarely changes over time in adults with stable hemodynamic conditions

  • Other causes of incorrect results for calculating aortic valve area using the continuity equation:
    • Poor Doppler cursor alignment with flow through the LVOT or AV
    • Doppler cursor placement too close to LVOT
      • records higher velocity that is used in continuity equation
      • underestimates stenosis
      • overestimates AVA or larger AVA
      • can explain an AVA that indicates moderate stenosis but AV velocity and peak pressure gradients indicate severe stenosis
    • Doppler cursor placement too far from LVOT
      • records lower velocity that is used in continuity equation
      • overestimated stenosis
      • underestimated or smaller AVA
      • can explain an AVA that indicates severe stenosis but AV velocity and peak pressure gradients indicate moderate stenosis
    • Heavy calcification on the leaflets can lead to underestimation of stenosis due to degraded Doppler signal and inability to locate the highest velocity
    • Mistaking mitral regurgitation jet for aortic flow
      • Both MR and AV velocities are demonstrated on the under side of the baseline
      • MR jets are longer in duration that the AV flow
      • MR jets peak later than the tracing from the AV (difference in acceleration times)
      • MR peak velocity is higher than the peak velocity across the AV
    • Sub-aortic or supra-aortic stenosis
    • Using aortic tracing following a PVC
      • The PVC will produce an early contraction with a lower velocity waveform
      • The waveform after the PVC will demonstrate a higher velocity waveform that compensates for the previous premature contraction
    • Atrial fibrillation
      • Flow velocity should be averaged across 5or more beats in AS patients with atrial fibrillation
      • When there is a long R-R interval, the PSV measurement is higher on the next beat
      • When there is a short R-R interval, the PSV measurement is lower on the next beat
    • Systolic BP is elevated
      • Hypertension can affect the peak velocity/mean gradient across the valve
      • Systolic BP should be recorded on each exam
      • The optimal evaluation of aortic stenosis should be performed when the patient’s blood pressure is normal

 

Secondary Findings:
  • Left ventricular hypertrophy with left heart pressure overload
  • Increased LV mass
  • Dilated aortic root
  • Turbulence distal to the valve
  • Can be associated with CVA/Stroke due to decreased flow to brain and embolus potential from atherosclerotic disease on cusps
  • Aortic regurgitation – most patients have mild to moderate regurgitation
  • Mitral regurgitation - MR severity does not affect evaluation of AS severity
  • Mitral stenosis - can result in low cardiac output and low flow volume, low gradient AS
  • Dilated aortic root
  • Systemic HTN


 


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