Aortic stenosis assessment
From Echocardiography in ICU
Acquired degenerative valvular calcification is by far the most frequent cause of aortic stenosis. It is frequent in older patients and results from progressive calcification and restriction of the aortic cusps. Other etiologies include congenital aortic stenosis and rheumatic disease.
Aortic stenosis is suspected on two-dimensional images in patients with calcified and/or restricted aortic cusps. Valve calcifications appear as "echo bright" reflectivity of the cusps.Parasternal long axis. There is calcification of the aortic annulus and cusps. Parasternal long axis view, zoom on aortic valve. There is severe calcifications of the aortic valve which almost does not open. Parasternal short axis, level of the aortic valve. The aortic annulus and cusps are very calcified, only a small aortic orifice remains.
When limitation of valve opening is diagnosed, Doppler evaluation is mandatory to quantitate the stenosis.
Please go to the images library to see more examples of aortic stenosis.
- Mean and maximum gradient
Stenosis of the aortic valve creates an obstacle to aortic ejection, thus a gradient of pressure between the left ventricle and the aorta. This gradient of pressure can be measured, using Bernouilli law, by measurement of the maximum velocity across the aortic valve with continuous Doppler. In aortic stenosis, trans-aortic velocity is 3 to 5 m/s.
Quantification of the degree of aortic stenosis is realized with continuous Doppler
To obtain an accurate measurement, it is crucial to optimize the alignment of the Doppler beam with the jet. The views which allow the best alignement are apical 5 and 3 chamber views. You can use color Doppler to adjust the alignement of the Doppler beam with the maximum flow velocity (aliasing flow).
To obtain the maximum gradient, use "caliper" to determine the maximum velocity of the regurgitant jet. The echo machine will give you the maximum gradient, derived from Bernouilli law.
To obtain the mean gradient, use "trace" to trace the envelope of the aortic outflow. The machine will calculate the area under the curve and will give you the mean gradient across the aortic valve.
- Continuity equation
With the continuity equation you will be able to calculate the aortic valve area. The principle of the continuity equation is that the amount of flow before the valve (left ventricular outflow) equals the amount of flow across the valve:
- Assessment of stenosis severity
|Severity||Jet velocity (m/s)||Mean gradient (mmHg)||Area (cm2)|
- Doppler alignement
The severity of the aortic stenosis will be underestimated if the Doppler beam is not aligned with the jet. It is important to check the location of the Doppler beam on 2D images and with color Doppler.
- Accuracy of measurements
Three different measurements are used for the calculation of aortic valve area: LVOT diameter, LVOT VTI and aortic VTI. When approximations or errors are made for any of these measurements, there is a high risk of miscalculation and wrong evaluation of the valve area. If you don't have good parasternal image quality to measure the LVOT diameter, it will be more accurate to rely on the determination of mean and maximum gradients.
- Underestimation of stenosis
In patients with low EF, there is a risk of underestimation of the severity of the aortic stenosis. Indeed, the left ventricle is not able to generate enough pressure to create a high gradient between LV and aorta. When you suspect aortic stenosis on 2D criteria, in a patient with low EF, it is important to ask for reference echocardiography by experienced cardiologists.
- Overestimation of stenosis
In patients with high output state (hemorrhagic shock, initial phase of septic shock), a gradient may exist across the aortic valve. It can be secondary only to the high cardiac output, with minor or none real aortic stenosis. In these patients, the 2D aspect of the aortic valve is important, as well as the reevaluation of possible stenosis after hemodynamic stabilization.
- Concentric hypertrophy: result of chronic high afterload
- Post-stenotic aortic dilatation: turbulent aortic flow after the stenosis
- Elevation RVSP
- Associated diseases: it is important to look for other valvulopathies or dilated aortic root, since their association may change the patient's management and outcomes
ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart DiseaseA Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease) Developed in Collaboration With the Society of Cardiovascular Anesthesiologists Endorsed by the Society for Cardiovascular Angiography and Interventions and the Society of Thoracic Surgeons . Journal of the American College of Cardiology , Volume 48 , Issue 3 , Pages e1 - e148