Are mean or peak pressures used to grade aortic stenosis severity?

From the Guidelines

When grading the severity of aortic stenosis by pressure gradient, the mean pressure gradient is the preferred measurement, with severe aortic stenosis typically defined as a mean gradient greater than 40 mmHg. This is based on the most recent and highest quality study available, which emphasizes the importance of the mean gradient in assessing the hemodynamic burden of the stenotic valve throughout the cardiac cycle 1.

Key Points to Consider

• The mean pressure gradient is calculated by averaging the instantaneous gradients over the ejection period, and it cannot be calculated from the mean velocity 1.
• Peak gradients are also recorded, but they represent only the maximum instantaneous pressure difference and can be more variable 1.
• Severe aortic stenosis is typically defined as a mean gradient greater than 40 mmHg, a peak gradient greater than 64 mmHg, or a valve area less than 1.0 cm² 1.
• Echocardiography is the standard method for measuring these gradients, and interpretation should always consider other parameters such as valve area and the patient's cardiac output 1.
• Low-flow states can lead to lower gradients despite severe stenosis, making a comprehensive assessment essential to avoid underestimating severity in patients with reduced left ventricular function 1.

Clinical Implications

• The definition of severe aortic stenosis is consistent among guidelines, with a mean gradient greater than 40 mmHg being a key criterion 1.
• The use of dobutamine stress echocardiography and/or noncontrast computed tomography (CT) aortic valve calcium scoring is recommended in patients with low-gradient AS presenting with reduced left ventricular ejection fraction (LVEF) ≤50% or paradoxical low-flow low-gradient AS 1.
• An integrative approach including echocardiographic, CT aortic valve calcium score, and clinical variables is recommended to assess the severity of paradoxical low-flow low-gradient AS 1.

From the Research

Grading Severity of Aortic Stenosis

When grading the severity of aortic stenosis by pressure gradient, the key consideration is whether to use mean pressures or max pressures. The evidence suggests that:

• Mean pressure gradients are an important measure of the severity of aortic stenosis 2
• The mean pressure gradient can be calculated using Doppler echocardiography, which has been shown to be reliable and accurate 2
• Peak pressure gradients are also used to assess the severity of aortic stenosis, with higher peak velocities indicating more severe stenosis 3
• The use of peak aortic jet velocity (Vmax) values ≥ 6 m/s is defined as "extremely" severe aortic stenosis in some studies 3

Key Findings

Some key findings related to the grading of aortic stenosis severity include:

• A high correlation between peak pressure gradients determined by Doppler technique and catheterization 2
• A high correlation between mean pressure gradients determined by Doppler echocardiography and catheterization 2
• The use of transcatheter aortic valve replacement (TAVR) in patients with severe aortic stenosis, including those with extremely severe stenosis 4, 3, 5
• The importance of considering the risks and benefits of TAVR in patients with severe aortic stenosis, including the risk of procedural complications and paravalvular leak 3, 5