Peak Transvalvular velocity
Peak gradient (in m/sec) is converted to mmHg using the modified Bernoulli equation
- >4m/sec = severe
- May be reduced if LVEF% is reduced (therefore not the best index of severity)
- 5% inaccuracy if the beam aligned at more than a 15 degree tangent to the stenotic jet. Poor alignment gives a more rounded shape to the doppler spectrum and readings become exponentially less reliable as alignment worsens beyond 20 degrees.
Mean Pressure gradient
- >40mmHg = severe
Aortic valve area
Calculated by using the continuity equation with the aim to calculate AV CSA.
LVOT diameter and VTI should be measured in mid systole 0.5-1cm proximal to the AV away from the flow convergence zone proximal to the AV (use colour and PWD to identify this).
If possible the "double envelope" technique can be used with CWD.
AVA by continuity equation is less affected by loading conditions and is therefore a good assessment of severity unlike peak velocity and pressure gradients.
AV VTI measurements are acquired in the deep TG view at 0 degrees or 90-120 degrees, wherever beam alignment is best.
- <1cm = severe, <0.8cm = critical
- Note: the valve area may be larger in mixed AS / AR but features still be consistent with severe AS.
Dimensionless Index (doppler velocity index)
- Represents the ratio of the LVOT VTI to the AV VTI or the LVOT peak velocity to the AV peak velocity.
- DSI <0.25 = severe AS
- Can be rapidly measured if the double envelope technique is feasible.
- Normal LVOT VTI = 15-20cm