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package (Fig. 9). It is important to ensure that it is actually the aortic envelope that is traced, as a mitral or tricuspid regurgitant jet may mimic an aortic stenotic envelope (Fig. 10).

calculation of aortic valve area

The calculation of aortic valve area (AVA) is based on the continuity equation (Fig. 11). This equation relates the flow proximal to the stenosis and flow through the valve.

Are&vrrr x VIvrfr = AVA x V

^VOT LVOT max

Where the AVA is the aortic valve area and V is the max maximal velocity obtained by CW Doppler. VLVOT is the velocity in the LVOT obtained by pulse wave Doppler usually in the apical five-chamber view. AreaLVOT is the area of the LVOT and is calculated by multiplying n by the square of the radius of the LVOT. The equation thus becomes:

AVA = n(radius of LVOT)2 x VLVOT/Vmax

Therefore, the AVA can be easily calculated using velocities. Alternatively, the velocity time integral (VTI) can also be used instead of velocities to obtain the AVA.

assessment of stenosis severity

The normal aortic valve orifice area in adults ranges from 2 to 4 cm2. In general terms, severe stenosis is not seen with an AVA of more than 1.0 cm2. According to American College of Cardiology/American Heart Association guidelines, severe aortic stenosis is seen when the AVA is less than 1 cm2 (Table 2). Transvalvular gradients should not be ignored when assessing severity of aortic stenosis. Overall, when the mean transvalvular gradient exceeds 50 mmHg, severe stenosis is usually present.

Alternative methods of assessing aortic stenosis severity exist (Table 3). The Doppler Velocity index or Dimensionless index is a measure of the ratio of the LVOT velocity to the AV velocity using CW Doppler

Fig. 8. (A) Continuous-wave (CW) Doppler of maximum velocity assessment of peak velocities in aortic stenosis.

across stenotic aortic valve. (B) Optimal Doppler alignment for

Fig. 8. (A) Continuous-wave (CW) Doppler of maximum velocity assessment of peak velocities in aortic stenosis.

across the aortic valve (Fig. 12). It is normally higher than 0.28 but decreases with significant aortic stenosis. An index of less than 0.25 generally correlates with severe aortic stenosis. VTI may be used instead of velocities. In addition, because peak transvalvular gradients are linearly correlated with mean gradients, a peak gradient greater than 4.5 m/s is also indicative of severe stenosis.

across stenotic aortic valve. (B) Optimal Doppler alignment for

Therefore, a combination of methods may be used to assess aortic stenosis severity. Nonetheless, symptoms are the major guide to therapeutic decisions, and no single measurement is used to guide referral for surgical intervention. Thus, echocardiographic measurements of severe stenosis in conjunction with the wider clinical picture are the benchmarks for referral for aortic valve replacement.