1. The jet width/left ventricular outflow tract (LVOT) width ratio method: Perry et al. [4] compared the ratio of AR jet width to LVOT width in a parasternal long-axis view to angiography. A jet width/LVOT width <25% is specific for mild AR, whereas a jet width/LVOT width ratio >65% is specific for severe AR (Figure 6.2). This works best when the regurgitant orifice is relatively round in shape. When it is elliptical, as in bicuspid aortic valves, this ratio can lead to underestimation of AR severity [5]. The short-axis view is helpful in identifying such cases.

2. Vena contracta: It is defined as the narrowest central flow region of a jet. In AR, it can be measured in a parasternal long-axis or short-axis view in a color Doppler mode (Figure 6.3). Tribouilloy et al. [6] demonstrated that a vena contracta width of ≥6 mm correlates well with severe AR, having a sensitivity of 95% and a specificity of 90%, conversely, a vena contracta width <3 mm is specific for mild AR in a study with 79 patients. The advantages of this method are simple, quantitative, and good at identifying mild to severe AR. The limitation is not useful in multiple jets.

3. Proximal isovelocity surface area method: Compared with MR, it is less common to identify a clear proximal flow convergence in AR. However, when it is present, the Nyquist velocity should be shifted toward the direction of the jet to produce a clearly visible, round proximal isovelocity surface area (PISA) region that is as large as possible. The surface area of the PISA region is 2πr2, where r is the radius from the alias line to the orifice. Peak regurgitant flow (RF) is obtained by multiplying this value by the aliasing velocity (Va), which convert to formula is RF = (2πr2 × Va). The effective regurgitant orifice area (EROA) is the peak regurgitant flow divided by the peak velocity (PVar) obtained by continuous wave Doppler, The formula is ROA = (2πr2 × Va)/PVar. How to calculate this in a case is shown in Figure 6.4. The EROA < 0.1 cm2 is defined as mild, ≥0.3 cm2 as severe regurgitation. The PISA method has been shown to work in AR but is less accurate in eccentric jets or aortic root dilation [7].

4. Quantitative Doppler flow measurements: AR volume and fraction can be calculated by comparing flow at the aortic level with that at the mitral valve level [8]. The stroke volume is generally obtained by area of left ventricular out tract (LVOT area = πr2) times the velocity time integral (VTI) of pulsed Doppler LVOT flow. The mitral stroke volume is measured in similar fashion but is more prone to error because of difficulty in accurately measuring the mitral annulus. Measuring mitral stroke volume, the pulsed Doppler sample volume should be placed at the level of mitral annulus.
The AR volume is the difference between stroke volume of the mitral valve and forward stroke volume of the aortic valve. The cut points for AR severity measured by regurgitant volume are <30 mL/beat defined as mild, ≥60 mL/beat as severe. The regurgitant fraction is regurgitant volume divided by stroke volume of aortic valve, these cut points for AR severity are <30% defined as mild, ≥50% as severe. According to the formula-regurgitant volume (RV) = EROA × VTIAR, effective regurgitant orifice area (EROA) can be calculated by dividing the regurgitant volume (RV) by VTIAR jet obtained from continuous wave Doppler (VTIAR). The equation is EROA = RV/VTIAR, these cut points are <0.1 cm2 for mild, and ≥0.3 cm2

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