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.
Highlights
Aortic stenosis (AS) is one of the most common and critical valve diseases in the world
Where LVOT-VTI is velocity-time integral in the left ventricular outflow tract, LVOT-CSA is the cross-sectional area of the left ventricular outflow tract, AV-VTI is velocity-time integral across the aortic valve, and aortic valve area (AVA) is the area of the stenotic aortic valve (Figure 1)
We summarize the hemodynamics of severe aortic stenosis (AS), global LV load, valvulo-arterial impedance (Zva), and accurate assessment of severity with dimensionless index (DI) in different clinical situations, which might aid in improving the prognosis of AS (Figure 1, Table 2)
Summary
Aortic stenosis (AS) is one of the most common and critical valve diseases in the world. In North America and Europe, aortic valve disease is primarily due to calcification or a congenital bicuspid valve. AS progresses with aging as calcium, thickening, inflammation, or scarring damages the valve, which restricts blood flow. The normal aortic valve area is between 3.0 and 4.0 cm. The pressure gradient across the aortic valve and aortic transvalvular flow is directly correlated to the aortic valve area. Patients with AS will have symptoms of heart failure when the aortic valve area is
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