Monday, 4 July 2016

What's the best probe position to assess aortic stenosis severity?

When you're assessing aortic stenosis using echo, it's essential to make an accurate assessment of stenosis severity. One of the key indicators of severity is the peak flow velocity through the aortic valve (Vmax), as measured using continuous wave (CW) Doppler. Severe aortic stenosis is indicated by a peak velocity >4.0m/s. But where is the best probe position to measure this from?

CW measurement of aortic valve Vmax from the apical echo window

During transthoracic echo, CW Doppler measurements of aortic valve flow are most commonly made from the apical window, as in the image above. But is this always the best place to make this measurement?

In a 2015 paper by Thaden and colleagues, transthoracic echo studies were performed in 100 patients with severe aortic stenosis. The authors used CW Doppler to measure aortic valve Vmax from several different imaging windows during each patient's echo:
  • Apical window
  • Suprasternal notch
  • Right supraclavicular window
  • Right parasternal window
The authors then looked at where the highest value of Vmax was obtained. They found that the right parasternal window was the one where the highest Vmax was most often obtained (50% of cases), followed by the apical window (39% of cases).

The authors also found that if only the apical window was used, then in 23% of cases the Vmax was significantly underestimated (i.e. patients with severe aortic stenosis were misclassified as having moderate or even mild stenosis).

The take-home message from this study is that the sole use of the apical echo window to measure Vmax commonly leads to underestimation of the severity of aortic stenosis, and therefore that the echo assessment of aortic stenosis should include the use of multiple imaging windows (and in particular the routine use of the right parasternal window) to measure Vmax.

If you'd like to read the original paper, it can be accessed here:

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