What is the clinical significance of the dimensionless index in aortic (Aortic Valve) valve stenosis?

From the Guidelines

The dimensionless index (DI) is a crucial echocardiographic parameter for assessing aortic valve stenosis severity, particularly in patients with low-flow states or inconsistent measurements from other parameters, as it remains relatively stable across different hemodynamic conditions, according to the most recent guidelines 1. The clinical significance of the DI lies in its ability to help overcome technical limitations of other measurements, such as pressure gradients or valve area calculations, which can be affected by flow rate.

• The DI represents the ratio of the left ventricular outflow tract velocity to the aortic valve velocity, with a value less than 0.25 indicating severe aortic stenosis.
• Unlike other parameters, the DI doesn't require measurement of the left ventricular outflow tract diameter, eliminating a common source of error in valve area calculations.
• When integrated with other echocardiographic and clinical findings, the DI helps clinicians make more accurate decisions regarding the timing of intervention for aortic valve stenosis, as recommended by recent guidelines 1. The DI is especially valuable in challenging scenarios such as low-flow, low-gradient aortic stenosis or in patients with reduced ejection fraction where other parameters might underestimate stenosis severity, and its use is supported by recent studies and guidelines 1. Therefore, the DI should be used as a key parameter in the assessment of aortic valve stenosis severity, particularly in complex cases, to guide clinical decision-making and improve patient outcomes, as emphasized by the latest clinical guidelines 1.

From the Research

Clinical Significance of Dimensionless Index in Aortic Valve Stenosis

The dimensionless index (DI) is a significant parameter in assessing the severity of aortic valve stenosis (AS) and its prognostic implications. Key findings from various studies include:

• The DI is a reliable marker of AS severity, with clear prognostic implications 2.
• A DI <0.25 is associated with an excess risk of events after diagnosis, and this cutoff should be used for AS severity assessment and therapeutic decisions 2.
• The DI is useful in identifying patients with low-flow low-gradient severe AS who are at higher risk of mortality and may benefit from aortic valve replacement 3, 4.
• The combined use of DI and transvalvular flow rate (Q) can improve risk stratification and clinical decision-making in patients with severe AS 5.
• Decreased DI is associated with increased mortality and decreased event-free survival in patients with aortic valve disease 6.

Prognostic Value of Dimensionless Index

The prognostic value of DI has been consistently demonstrated across various studies, including:

• A study of 488 patients with preserved ejection fraction and no or minimal subjective symptoms, which found that DI <0.25 was associated with an increased risk of events 2.
• A study of 755 patients with low-gradient severe AS and preserved left ventricular ejection fraction, which found that DI <0.25 was associated with a considerable increased risk of death 4.
• A large cohort study of 9393 patients with aortic valve disease, which found that decreasing DI was associated with significantly decreased survival and event-free survival 6.

Clinical Applications of Dimensionless Index

The DI has several clinical applications, including:

• Risk stratification of patients with severe AS 2, 5.
• Identification of patients with low-flow low-gradient severe AS who may benefit from aortic valve replacement 3, 4.
• Assessment of prognosis in patients with aortic valve disease 6.
• Integration into the assessment of patients with AS to improve clinical decision-making 3, 5, 6.