**3.1 Echocardiographic caveats in estimating AS severity**

Typically Doppler echocardiographic assessment is operator dependent. Optimal alignment of the continuous wave Doppler beam with the direction of the aortic flow jet is crucial to accurately quantify aortic valve gradient, aortic valve area and thereby severity of AS. The apical window detects peak velocity in 40% of cases where as the right parasternal window picks up peak velocity in 50% of cases [23]. A multiwindow approach is recommended which includes apical, right parasternal, suprasternal and right supraclavicular windows.

The most common technical pitfall that may lead to an erroneous diagnosis of lowflow state and overestimation of AS severity is underestimation of the left ventricular outflow tract (LVOT) diameter. The effective AVA is determined by the continuity equation method (**Figure 7**), which is based on the principle that the flow across the left ventricular outflow tract should be equal to the flow across the aortic valve. Since the LVOT diameter is squared in the equation, an underestimation of the LVOT diameter may lead to underestimation of valve area and thus the false conclusion that the patient has LFLG severe AS when, in fact, the patient has normal flow and/or moderate AS.

The 2009 European Association of Echocardiography/American Society of Echocardiography guidelines suggest measuring the diameter and velocity 5–10 mm below the aortic annulus. However, recent studies suggest measuring the LVOT diameter inner-edge-to-inner-edge from the base of the right coronary cusp anteriorly to the commissure posteriorly [24, 25]. From a practical standpoint, an easy way to measure the LVOT diameter is to assess the pulse wave Doppler signal from the distal to proximal LVOT in the apical view. The LVOT velocity time integral is then measured just below the point where aliasing is seen, when the flow signals are smooth with sharp borders. The LVOT diameter is ideally measured at this point in the parasternal long axis view (**Figure 8**).
