What severity of aortic stenosis is indicated by a dimensionless velocity ratio (left ventricular outflow tract velocity-time integral ÷ aortic velocity-time integral) of 0.42?

Dimensionless Ratio of 0.42 Represents Mild-to-Moderate Aortic Stenosis

A dimensionless velocity ratio (also called velocity ratio or dimensionless index) of 0.42 indicates mild-to-moderate aortic stenosis, well above the threshold for severe disease. This value suggests the effective aortic valve area is approximately 42% of the patient's normal left ventricular outflow tract area, which is substantially larger than what defines severe stenosis.

Understanding the Dimensionless Index

The dimensionless index is calculated as:

• LVOT velocity ÷ Aortic valve velocity (or LVOT VTI ÷ AV VTI)

This ratio approaches 1.0 in normal valves, with progressively smaller numbers indicating worsening stenosis 1.

Severity Classification

According to the 2020 ACC/AHA Guidelines and the 2017 EACVI/ASE Focused Update, the critical threshold for severe aortic stenosis is:

• Dimensionless ratio ≤0.25 = Severe AS 2, 1

This cutoff corresponds to a valve area that is 25% or less of the patient's normal expected valve area and is a validated predictor of symptom onset and adverse outcomes 2.

Your Patient's Value of 0.42

With a ratio of 0.42, this patient has:

• Nearly twice the dimensionless index of the severe AS threshold
• An effective valve area approximately 42% of their normal LVOT area
• No evidence of severe stenosis by this parameter

Clinical Context and Integration

The dimensionless index has several advantages 1:

• Independent of body size (already normalized to the patient's LVOT)
• Eliminates measurement errors from LVOT diameter calculation
• Particularly useful when other AS parameters are discordant

However, do not rely on dimensionless index alone. The primary parameters for AS severity grading remain 2, 1:

1. Peak aortic jet velocity (severe if ≥4.0 m/s)
2. Mean pressure gradient (severe if ≥40 mmHg)
3. Aortic valve area (severe if <1.0 cm²)

Important Caveats

When dimensionless index appears discordant with other parameters:

• Verify LVOT velocity measurement quality (should be laminar flow without spectral dispersion) 1
• Confirm aortic jet velocity was obtained from multiple windows using dedicated continuous-wave Doppler 1
• Consider measurement errors in LVOT diameter if calculated AVA seems inconsistent 3
• Evaluate for low-flow states (stroke volume index <35 mL/m²) that may affect gradient-based parameters 1

In low-gradient AS with preserved ejection fraction, a dimensionless index <0.25 has proven particularly valuable for risk stratification, identifying patients at higher mortality risk who benefit from intervention 4, 5. Your patient's value of 0.42 places them well outside this high-risk category.

Prognostic Implications

Research demonstrates that dimensionless index provides independent prognostic information 6, 7:

• Values <0.25 associate with significantly increased mortality and cardiovascular events
• The parameter performs especially well in patients with reduced ejection fraction or low-flow states 7, 5
• A value of 0.42 suggests favorable hemodynamics from a prognostic standpoint

Bottom line: This dimensionless ratio of 0.42 does not meet criteria for severe aortic stenosis and likely represents mild-to-moderate disease, assuming other echocardiographic parameters are concordant.