| AS jet velocity (m/s) | |
|---|---|
| Direct measurement | |
| Cutoff for Severe: | 4.0 |
| Concept: | Velocity increases as stenosis severity increases. |
| Advantages: | Direct measurement of velocity. Strongest predictor of clinical outcome. |
| Disadvantages: | Correct measurement requires parallel alignment of ultrasound beam. Flow dependent. |
| Mean gradient (mmHg) | |
| ΔP ∑4v2 / Ν | |
| Cutoff for Severe: | 40* or 50** |
| Concept: | Pressure gradient calculated from velocity using the Bernoulli equation. |
| Advantages: | Mean gradient is averaged from the velocity curve. Units comparable to invasive measurements. |
| Disadvantages: | Accurate pressure gradients depend on accurate velocity data. Flow dependent. |
| Continuity equation valve area (cm2) | |
| AVA = (CSALVOT × VTILVOT)/VTIAV | |
| Cutoff for Severe: | 1.0 |
| Concept: | Volume flow proximal to and in the stenotic orifice is equal. |
| Advantages: | Measures effective orifice area. Feasible in nearly all patients. Relatively flow independent. |
| Disadvantages: | Requires LVOT diameter and flow velocity data, along with aortic velocity. Measurement error more likely. |
| Simplified continuity equation (cm2) | |
| AVA = (CSALVOT × VLVOT)/VAV | |
| Cutoff for Severe: | 1.0 |
| Concept: | The ratio of LVOT to aortic velocity is similar to the ratio of VTIs with native aortic valve stenosis. |
| Advantages: | Uses more easily measured velocities instead of VTIs. |
| Disadvantages: | Less accurate if shape of velocity curves is atypical. |
| Velocity ratio | |
| VR = VLVOT / VAV | |
| Cutoff for Severe: | 0.25 |
| Concept: | Effective aortic valve area expressed as a proportion of the LVOT area. |
| Advantages: | Doppler-only method. No need to measure LVOT size, less variability than continuity equation. |
| Disadvantages: | Limited longitudinal data. Ignores LVOT size variability beyond patient size dependence. |
VR, Velocity Ratio; LVOT, LV outflow tract; ΔP, mean transvalvular systolic pressure gradient; AVA, continuity-equation-derived aortic valve area.
*AHA/ACC Guidelines, **ESC Guidelines