From the Guidelines
The best TTE window to assess aortic stenosis with Doppler is the apical view, as it provides optimal alignment of the Doppler beam with blood flow through the aortic valve, allowing for the most accurate measurement of peak and mean transaortic gradients. This is supported by the 2020 ACC/AHA guideline for the management of patients with valvular heart disease, which emphasizes the importance of echocardiographic imaging in evaluating valve anatomy and motion, as well as the degree of valve obstruction 1.
When using the apical view, it is essential to position the ultrasound beam parallel to the direction of blood flow across the aortic valve to minimize angle-related errors in velocity measurements. If the apical window provides suboptimal images, alternative windows such as the right parasternal view or suprasternal notch may be used, though these typically require angle correction.
During the examination, it's crucial to perform multiple measurements and use the highest obtained velocity for calculations, as misalignment will underestimate the true gradient. The continuous wave Doppler should be used to measure the maximum velocity, which can then be converted to pressure gradient using the modified Bernoulli equation (ΔP = 4v²) 1. This approach provides the most reliable assessment of aortic stenosis severity, which is crucial for clinical decision-making regarding timing of intervention.
Some key considerations when assessing aortic stenosis with Doppler include:
- Measuring the maximum aortic velocity, mean pressure gradient, and valve area, as these are the key measurements for clinical decision-making 1
- Using the continuity equation to calculate valve area, and the Bernoulli equation to calculate mean pressure gradient 1
- Considering the degree of aortic valve calcification, as it is a strong predictor of clinical outcome, even when evaluated qualitatively by echocardiography 1
- Being aware of the potential for impaired coronary perfusion, particularly in patients with supravalvular aortic stenosis, and using TEE with Doppler or CMR to assess proximal coronary patency 1
From the Research
Assessment of Aortic Stenosis using TTE
To assess aortic stenosis with Doppler using a transthoracic echocardiogram (TTE), multiple windows should be utilized to align the Doppler beam with the flow direction of the stenotic jet 2. The choice of window can significantly impact the accuracy of the assessment.
Comparison of TTE Windows
- The right parasternal window (RPW) has been found to be useful in assessing aortic stenosis severity, especially in patients with an aortoseptal angle <119° in the parasternal long-axis view as measured by echocardiography 2.
- The apical window (AW) is also commonly used, but the RPW may provide a more accurate assessment of aortic stenosis severity in certain patients 2, 3.
- The use of the RPW in addition to the apical method can decrease the number of low-pressure gradient AS cases and increase the number of very severe AS cases 4.
Factors Influencing Window Choice
- The aortoseptal angle, measured by echocardiography or computed tomography, can influence the choice of window, with a more acute angle potentially requiring the use of the RPW 2, 3.
- Valve type and sinus of Valsalva diameter can also impact the choice of window, with certain types of valves or diameters potentially benefiting from the use of the RPW 2.
- The degree of calcification and the Doppler angle can also affect the accuracy of the assessment, with technical adjustments necessary to minimize the Doppler angle and avoid bulky calcification 3.
Diagnostic Significance of Non-Apical Methods
- The use of non-apical methods, such as the RPW, can provide additional diagnostic value in assessing aortic stenosis severity, particularly in cases where the apical method may underestimate the severity of the condition 4.
- The combination of apical and non-apical methods can help resolve the diagnosis of aortic stenosis in approximately 10% of cases 4.