A) General considerations valid for all prostheses

• Doppler signals from blood flow velocities should be recorded with the sound beam as parallel as possible to the velocity. Angles to the flow lead to an underestimation of velocities and hence pressure gradients (cosine in the Doppler equation):
  • 10° angle: underestimation of the velocity by 1.5% and of the pressure drop by 3%
  • 20° angle: underestimation of the velocity by 6% and of the pressure drop by 12%
  • 30° angle: underestimation of the velocity by 13% and of the pressure drop by 26%
  • Therefore, angles > 20° are generally not acceptable for precise measurements
• Of note: flow is three-dimensional! The main flow may therefore be angled considerably with respect to the visualized 2D plane.
• A sharply defined boundary at the upper edge of the gray scale display of the Doppler spectrogram (‘envelope’) is important. This envelope indicates that signals with the highest velocities have been recorded.
• The exact location of the beam through mechanical prostheses is irrelevant for clinical purposes. While in some prostheses the velocity in the central part is higher than in the outer part, the overall pressure difference across the valve does not depend on it as different orifices also have different pressure recovery/energy loss. The same holds true for the mitral valve after percutaneous repair by MitraClip.

B) PHV in aortic positions

B1) systolic gradients

• Consider measuring velocities using the right parasternal or suprasternal in addition to the more common apical approach.
• Velocity V₁ needs be considered: in cases where it exceeds 1m/s it cannot be neglected and must be subtracted from V₂ (Bernoulli equation).
• For comparison over time (serial exams): use the systolic mean gradient as it more reliably represents flow. The flow column is not homogenous, hence the peak velocity (and peak gradient) can easily be missed.
• Pressure recovery should be taken into account: In small sized sino-tubular junctions (STJ) of the ascending aorta, the pressure recovery is high and hence the pressure gradient smaller. On the other hand, in large sized STJ and ascending aortas, the pressure recovery is small.

• In patients with a STJ or supracoronary graft diameter < 3.0 cm, the calculation of the energy loss index (ELI) becomes relevant and the valve area has to be corrected according to the following equation (from Voelker W et al, Pressure recovery in aortic stenosis: an in vitro study in a pulsatile flow model. JACC 1992; 1585-93)
  • (1) ELI=[(AVA×AA)/(AA−AVA)]/BSA, where AA is Area at the STJ, AVA is the aortic valve area calculated by the continuity equation, AA the aortic area at the level of the STJ and BSA the body surface area according to Dubois

B2) diastolic gradients

• Distinguish between trans- and paravalvular regurgitation. The simultaneous use of two planes (3D probe) can be of additional help
• The intensity of the continuous wave (CW) spectrum in both trans- and paravalvular aortic regurgitation does not necessarily reflect the regurgitation severity - The pressure half time of the diastolic CW spectrum only reflects the severity of aortic insufficiency if the LVEPD is not elevated (i.e. in compensated aortic regurgitation).

C) PHV / annuloplasty rings in mitral positions

C1) diastolic gradients

• The mean diastolic gradient largely depends on hemodynamic parameters such as heart rate, blood pressure and haemoglobin levels. Mean gradients can only be used for comparison over time (serial measurements) if all these parameters are known as well.
• For serial measurements: use the systolic mean gradient as it more reliably represents flow. The flow column is not homogenous, hence the peak velocity (and peak gradient) can easily be missed.
• An increase in mean diastolic gradient with unchanged pressure half time is likely due to increase in flow (anaemia, increased heart rate, increase in mitral regurgitation) and not to due to obstruction.
• Velocity V1 must be considered: in cases where it exceeds 1m/s it can not be neglected and needs to be substracted from V2 (the Bernoulli equation).

C2) systolic gradients

• Distinguish between trans- and paravalvular regurgitation. The simultaneous use of two planes (3D probe) or the use of 3D colour-Doppler during 3D TEE can be particularly helpful.
• The intensity of the CW-spectrum in both trans- and paravalvular mitral regurgitation does not necessarily reflect the regurgitation severity. Correct beam alignment plays an important role, and this cannot always be achieved.
• The shape of the velocity curve in mitral regurgitation (peak velocity decreases rapidly in late systole) indicates a significant v-wave.
• In mechanical prostheses, a paravalvular regurgitant jet can be completely extinguished by the shadow of the PHV. In this case, assessment of the left atrium in parasternal short-axis view can give clues for relevant regurgitation. For a more detailed review of the echocardiographic assessment of PHV please refer to the current guidelines