From the Guidelines
The dimensionless index (DI) is a crucial echocardiographic parameter for assessing aortic stenosis severity, providing complementary information to traditional parameters and helping clinicians make more accurate assessments, particularly in challenging clinical scenarios. 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 1. The clinical significance of the DI lies in its independence from flow conditions, making it particularly useful in low-flow states where other parameters may underestimate stenosis severity.
Key Points
- The DI is especially valuable in patients with reduced ejection fraction, obesity, or poor acoustic windows, as it remains accurate in patients with inconsistent findings between valve area and gradient measurements.
- The DI provides a more accurate assessment of aortic stenosis severity compared to traditional parameters, such as aortic valve area or mean gradient, which may be limited by measurement errors or flow conditions.
- The use of the DI is supported by recent guidelines, including the 2023 ACC/AHA and ESC/EACTS guidelines for the management of valvular heart diseases, which emphasize the importance of an integrative approach to assessing aortic stenosis severity 1.
- The DI is a valuable tool in clinical practice, allowing clinicians to make more informed decisions about patient management, including the timing of aortic valve replacement (AVR) and the selection of patients for transcatheter AVR (TAVR) or surgical AVR (SAVR).
Clinical Implications
- The DI should be used in conjunction with other echocardiographic parameters, such as valve area and mean gradient, to provide a comprehensive assessment of aortic stenosis severity.
- Clinicians should be aware of the limitations of traditional parameters and consider the use of the DI in patients with challenging clinical scenarios, such as low-flow states or inconsistent findings between valve area and gradient measurements.
- The DI may be particularly useful in patients with paradoxical low-flow low-gradient AS, where the use of dobutamine stress echocardiography and/or noncontrast computed tomography (CT) aortic valve calcium scoring is recommended 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 stenosis (AS) and its prognostic implications. Studies have shown that a lower DI is associated with increased mortality and decreased event-free survival in patients with AS 2, 3, 4, 5.
Prognostic Implications of Dimensionless Index
- A DI <0.25 is associated with an excess risk of events after diagnosis, including death or need for aortic valve replacement 2.
- Patients with low-gradient severe AS and preserved left ventricular ejection fraction, who have a DI <0.25, exhibit a considerable increased risk of death compared to those with DI ≥0.25 3.
- Decreasing DI is associated with significantly decreased survival and event-free survival, which remains highly significant on multivariate analysis 4.
Combined Value of Dimensionless Index and Other Parameters
- The combined use of DI and transvalvular flow rate (Q) can provide a more accurate assessment of AS severity and prognostic value 5.
- The valvulo-arterial impedance (Zva) and DI can be useful parameters in risk stratifying patients with severe AS, especially in those with low-flow low-gradient AS and preserved left ventricular ejection fraction 6.
Clinical Application of Dimensionless Index
- The DI is a simple and reliable marker of AS severity, which can be easily obtained and integrated into the assessment of patients with AS 2, 4.
- The DI can be used to identify a subgroup of patients at higher risk of mortality who may derive benefit from aortic valve replacement, especially in those with low-flow low-gradient AS and preserved left ventricular ejection fraction 3, 6.