From the Guidelines
Normal aortic valve measurements on transthoracic echocardiogram include a peak velocity less than 2.0 m/s, a mean pressure gradient less than 7 mmHg is not well defined in recent literature, and a valve area greater than 1.0 cm² is considered non-severe stenosis. These parameters reflect normal hemodynamics across the aortic valve during left ventricular ejection. The peak velocity represents the maximum blood flow speed through the valve, while the mean pressure gradient indicates the average pressure difference between the left ventricle and aorta during systole. Valve area is calculated using the continuity equation and represents the opening size of the valve during peak systole.
Key Parameters
- Peak velocity: less than 2.0 m/s is not well defined, but a peak velocity greater than 4 m/s is consistent with severe aortic stenosis 1
- Mean pressure gradient: a mean gradient of greater than 40 mmHg is consistent with severe aortic stenosis 1
- Valve area: an AVA of less than 1.0 cm² is consistent with severe aortic stenosis 1 These values are important baseline measurements when assessing for aortic stenosis, which is characterized by increased velocities, elevated pressure gradients, and reduced valve areas. Measurements may vary slightly based on patient factors such as age, body size, and cardiac output. When interpreting these values, it's essential to consider the patient's clinical context and other echocardiographic findings to ensure accurate assessment of aortic valve function. According to the most recent guidelines, the assessment of aortic stenosis severity should be based on multiple parameters, including peak jet velocity, mean transvalvular pressure gradient, and valve area by continuity equation 1.
From the Research
Normal Aortic Valve Parameters
The following are normal parameters for the aortic valve as measured by transthoracic echocardiogram (TTE):
- Peak velocities:
- The normal peak aortic valve velocity is not explicitly stated in the provided studies, but a velocity of < 2.0 m/s is generally considered normal 2.
- A peak velocity of ≥ 3 m/sec is associated with severe aortic stenosis, with corresponding mean pressure gradient and aortic valve area values of 22 mmHg and 1.15 cm², respectively 3.
- Mean pressure gradients:
- A mean pressure gradient of < 20 mmHg is generally considered normal.
- A mean pressure gradient of ≥ 22 mmHg is associated with severe aortic stenosis, with a corresponding peak velocity of ≥ 3 m/sec 3.
- Valve areas:
- The normal aortic valve area is approximately 2.5-3.5 cm², but this can vary depending on the individual and the measurement technique used.
- An aortic valve area of ≤ 1.0 cm² is generally considered indicative of severe aortic stenosis 4.
- The aortic valve area can be indexed to body surface area, with a normal indexed valve area of approximately 1.5-2.5 cm²/m².
Factors Affecting Aortic Valve Parameters
Several factors can affect aortic valve parameters, including:
- Sex: Women tend to have smaller left ventricular outflow tract diameters and aortic valve areas, as well as higher peak velocities and mean gradients, compared to men 2.
- Age: Older individuals tend to have lower left ventricular outflow tract diameters and aortic valve areas, as well as higher peak velocities and mean gradients, compared to younger individuals 2.
- Race: There may be racial differences in aortic valve parameters, with Asians tend to have lower left ventricular outflow tract diameters and aortic valve areas compared to whites and blacks 2.
- Flow rate: The flow rate across the aortic valve can affect the measurement of valve area and mean pressure gradient, with lower flow rates potentially leading to underestimation of valve area and overestimation of mean pressure gradient 4.