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Valvulo-Arterial Impedance and Dimensionless Index for Risk Stratifying Patients With Severe Aortic Stenosis
Yogamaya Mantha1, Shutaro Futami2, Shohei Moriyama2
1Division of Cardiovascular Medicine, University of Texas Health Sciences, San Antonio, TX, United States.
Insights
Valvulo-arterial impedance (Zva) and dimensionless index (DI) offer better assessment of global left ventricular load in aortic stenosis. These parameters aid in risk stratification and clinical decisions for severe aortic stenosis patients.
Area of Science:
- Cardiology
- Echocardiography
- Hemodynamics
Background:
- Aortic stenosis (AS) increases left ventricular (LV) afterload, reduces compliance, and raises workload.
- LV faces dual loads: valvular and arterial, necessitating global burden assessment beyond traditional metrics like transvalvular gradient and aortic valve area (AVA).
- Accurate stenosis severity assessment is crucial, especially in low-flow, low-gradient (LF-LG) severe AS with preserved LV ejection fraction.
Purpose of the Study:
- To elucidate the role of valvulo-arterial impedance (Zva) and dimensionless index (DI) in assessing global LV hemodynamic load in AS.
- To correlate Zva and DI with standard AS severity indexes, LV geometry, and function.
- To demonstrate the utility of Zva and DI in improving risk stratification and clinical decision-making for severe AS patients.
Main Methods:
- Calculation of valvulo-arterial impedance (Zva) to estimate global LV hemodynamic load.
- Calculation of dimensionless index (DI) using LVOT-VTI and AV-VTI, avoiding LVOT area calculation.
- Correlation analysis of Zva and DI with established AS severity metrics and LV parameters.
Main Results:
- Zva provides an estimate of the combined valvular and vascular loads on the LV.
- DI offers a reliable measure of stenosis severity, particularly useful in LF-LG AS by avoiding LVOT area measurement.
- DI calculation in routine echocardiography may identify high-risk patients with LG severe AS and preserved LVEF who could benefit from aortic valve replacement.
Conclusions:
- Zva and DI are valuable parameters for assessing global LV afterload and stenosis severity in aortic stenosis.
- These indices improve risk stratification and clinical decision-making, especially in complex cases like LF-LG severe AS with preserved LVEF.
- Routine use of DI in echocardiography can enhance the identification of patients who may benefit from aortic valve replacement.
Abstract:
The hemodynamic effects of aortic stenosis (AS) consist of increased left ventricular (LV) afterload, reduced myocardial compliance, and increased myocardial workload. The LV in AS patients faces a double load: valvular and arterial loads. As such, the presence of symptoms and occurrence of adverse events in AS should better correlate with calculating the global burden faced by the LV in addition to the transvalvular gradient and aortic valve area (AVA). The valvulo-arterial impedance (Zva) is a useful parameter providing an estimate of the global LV hemodynamic load that results from the summation of the valvular and vascular loads. In addition to calculating the global LV afterload, it is paramount to estimate the stenosis severity accurately. In clinical practice, the management of low-flow low-gradient (LF-LG) severe AS with preserved LV ejection fraction requires careful confirmation of stenosis severity. In addition to the Zva, the dimensionless index (DI) is a very useful parameter to express the size of the effective valvular area as a proportion of the cross-section area of the left ventricular outlet tract velocity-time integral (LVOT-VTI) to that of the aortic valve jet (dimensionless velocity ratio). The DI is calculated by a ratio of the sub-valvular velocity obtained by pulsed-wave Doppler (LVOT-VTI) divided by the maximum velocity obtained by continuous-wave Doppler across the aortic valve (AV-VTI). In contrast to AVA measurement, the DI does not require the calculation of LVOT cross-sectional area, a major cause of erroneous assessment and underestimation of AVA. Hence, among patients with LG severe AS and preserved LV ejection fraction, calculation of DI in routine echocardiographic practice may be useful to identify a subgroup of patients at higher risk of mortality who may derive benefit from aortic valve replacement. This article aims to elucidate the Zva and DI in different clinical situations, correlate with the standard indexes of AS severity, LV geometry, and function, and thus prove to improve risk stratification and clinical decision making in patients with severe AS.
