Dimensionless index (DI) is the ratio of the velocity-time integral of the left ventricular outflow tract (LVOT-VTI) to that of the aortic valve jet (AV VTI)1-2.
Dimensionless index (DI) = LVOT VTI / AV VTI
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Usage
Dimensionless index is a classic marker of severity in aortic stenosis that does not rely on calculating the cross-sectional size of the left ventricular outflow tract (LVOT)4. It represents the size of the valvular effective area as a proportion of the LVOT's cross sectional area1. Unlike aortic valve area (AVA), DI does not require the computation of LVOT cross-sectional area, which is a main source of inaccurate evaluation and underestimation of AVA2.
Measurement
It is expressed as the ratio of the sub-valvular velocity time integral acquired by pulsed-wave Doppler (LVOT-VTI) divided by the maximum velocity time integral obtained by continuous-wave Doppler across the aortic valve (AV-VTI). Alternatively, the ratio of the LVOT peak velocity to the AV jet peak velocity can be deployed1.
Interpretation
The following values are used:
mild aortic stenosis: >0.50
moderate aortic stenosis: 0.25-0.50
severe aortic stenosis: <0.25 3
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