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Aortic Valve
In this chapter we will be primarily interested in the identification of catastrophic, gross valve failure or dysfunction that is severe enough to impact patient hemodynamics. This is the primary goal of the focused cardiac ultrasound (FoCUS) assessment and heavily relies on 2D ultrasound technology. A comprehensive evaluation of the valves involves color flow doppler (CFD), pulsed wave doppler (PWD) and continuous wave doppler (CWD) which are out of the scope of FoCUS but that we will briefly touch base. It is through these other techniques that we can have a better and more precise assessment of the different degrees of valve dysfunction.
Aortic Valve Anatomy and Function Recap
The aortic valve has 3 cusps: left coronary, right coronary and the non-coronary cusp. The valve opens and closes due to changes in pressure between the ventricle and the aorta. On systole, the intraventricular pressure rises above the aortic pressure causing the aortic valve to open and blood moves forward into the aorta. Once the pressure of the left ventricle is lower than that of the aorta, the aortic valve closes.
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Aortic valve with normal function. 1, The clip above was taken from the aortic root in a living, beating pig heart. 2, still image of the aortic valve at maximal leaflet displacement. 3, still image of the aortic valve on diastole. Notice the very tight coaptation points which prevents flow from moving back into the ventricle. Clips modified from Valguru with permission.
As you can appreciate, the aortic valve cusps move in 3 dimensions as they open up towards the aortic root. This makes the evaluation under ultrasound challenging since we are only able to observe two dimensional sections. A comprehensive evaluation of the valve entails an analysis of the flows (with pulsed and continuous wave doppler) on multiple cardiac windows that go above and beyond the scope of the focused cardiac exam but will be mentioned in this section. Luckily for us our job is to determine extremes: Is the aortic valve stenotic or insufficient enough that I can detect it with ultrasound?
Aortic Valve Stenosis
Aortic stenosis is very common in the elderly population. When it is present, it complicates hemodynamic management of patients with septic shock.
On ultrasound we typically observe a hyperechoic and heavily calcified valve with significant reduction of movement. The diagrams display the movement of the valve on systole without and with stenosis as they would be seen on the parasternal long axis view.
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Normal valve vs aortic valve stenosis schematic in systole. In 1 we observe normal displacement of the aortic valve cusps. In 2, we see heavily calcified cusps with severe severe flow restriction.
Parasternal Long Axis
We can appreciate the restriction of movement of the aortic valve when seen on the parasternal long axis.
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Aortic valve stenosis on the parasternal long axis view. 1, normal movement of the aortic valve without restriction. 2, heavily calcified (hyperechoic) aortic valve leaflets with restriction to flow on systole.
The following ultrasound exams also show a heavily calcified valve with restriction of movement.
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Aortic valve stenosis on the parasternal long axis view. Both clips 1 and 2 show decreased valve movement. We can also observe and hyperechoic (white) valvular apparatus due to the extensive calcium deposits.
Parasternal Short Axis - Beyond FoCUSed
The following clips below show the normal appearance of the aortic valve on the short axis view. This is not part of the views required for FoCUS and to get this view we start with the short axis mid pap and tilt the probe towards the patient's head. The other clips show restricted movement. Additionally we can observe heavy calcification at the commissures.
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Aortic valve stenosis on parasternal short axis view. 1, Normal aortic valve motion and function. Notice that the three cusps open without restriction of movement. 2, Severe aortic valve stenosis. On this clip we appreciate severe restriction of movement in all three leaflets although they do not appear heavily calcified. 3, Severe aortic stenosis with severe restriction of all leaflets with heavy calcification. This clip is obtained by zooming on the aortic valve while in the parasternal short axis view. In this clip the leaflets appear fused with each other. 4, Severe aortic stenosis with heavily calcified leaflets.
Bioprosthetic Aortic Valve-Beyond the scope of FoCUs
The following clips display a patient with a bioprosthetic aortic valve. It is difficult to appreciate the function of the valve on 2D alone since bioprosthetic and mechanical valves typically cause a lot of acoustic shadowing within the valve. A more detailed assessment is beyond the scope of FoCUS and thus hard to tell if they have a malfunction. Clips 1 and 2 display a bioprosthetic aortic valve.
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Grading AV Stenosis Severity - Beyond the scope of FoCUS
While beyond the scope of FoCUS we have a great appreciation of the severity of AS based on the use of pulsed wave doppler (PWD) and continuous wave doppler (CWD). On the 5 chamber view we can assess all flow through the aortic valve with the use of CWD and flow through the LVOT with PWD.
All of the following features indicate severe aortic stenosis: A maximum aortic velocity >4m/s (indicated with the circle in red) or a pressure gradient >40mmHg (which is the area traced on the CWD waveform in green). We can also use a dimensionless index (DI) which is the ratio of LVOT VTI / AV VTI for severity of AS assessment. A ratio lower than 0.25 indicates severe AS. In the example below, the DI=24/72 or 0.33
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AV VTI
LVOT VTI
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Aortic valve stenosis with Doppler interrogation. 1, Aortic valve velocity time integral (AV VTI) across the aortic valve on the 5 chamber view. 2, Left ventricular outflow tract velocity time integral (LVOT VT).
Aortic Regurgitation
Severe acute aortic regurgitation is life-threatening as the LV has had no time to adapt to the volume it suddenly sees. This leads to fulminant pulmonary edema. Surgical intervention may be required when present.
The schematics show a simplified view of the normal behavior of the aortic valve on diastole and what can be seen on prolapse.
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Aortic Regurgitation schematic representation. 1, normal tricuspid valve coaptation. 2, prolapse of a leaflet indicating severe regurgitation.
The following clips show a normal aortic valve vs a prolapsed aortic valve. More specifically, the non coronary cusp is the one that has been compromised. The other images below show thickened (concerning for endocarditits) and prolapsed non coronary leaflet.
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NCC
RCC
Aortic valve prolapse. All clips with the exception of 4 were taken from the parasternal long axis view. 1, Normal coaptation of the AV; 2, Prolapse of the Non-coronary cusp (NCC). RCC, right coronary cusp; 3. Thickened AV and prolapse of the NCC; 4. Prolapse of the NCC as seen in the 5 chamber view. Clips 3 and 4 are courtesy of NephroPOCUS.com.
Grading AV Regurgitation - Beyond the scope of FoCUS
While beyond the scope of FoCUS, color flow doppler can give us a great depiction of the valve function.
On the following clips the Nyquist limit has been set high to account for the high velocities. We can observe that on diastole there is a significant amount of flow traveling down the LVOT to the LV. In these images we do not have a prolapsed valve yet by appearance alone it would seem that the degree of AI is severe. In this case we compare the amount of area the regurgitant jet produces over the total LVOT and an amount >65% is considered severe. In the following images the jet occupies the LVOT entirely.
For completeness we can also observe that there is restriction of flow on systole on the long axis view with heavily calcified valves. It is very likely this patient also has a significant amount of aortic stenosis.
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We can also use CWD to our advantage to determine the severity of AI on the 5 chamber view.
The still image depicts a CWD taken over the 5 chamber view. It displays all velocities that the scan line can measure over time display on the x axis. Pressure half time is the amount the peak pressure to go down by half or the decrease in peak velocity depicted here as the line traced in green. A bigger number indicates that the Aorta and LV don't equilibrate at all while a low number, that it does so fast so it correlates with the severity of AI. This is because the LV fills up quickly with blood. A PHT greater less than 200 ms is considered severe (not the case in the clip)
References
1. Baumgartner H and all. Echocardiographic assessment of valve stenosis: EAE/ASE recommendation for clinical practice. European Journal of Echocardiography (2009) 10,1-25.
2. Via G, Hussain A, Wells M, Reardon R, ElBarbary M, Noble VE, Tsung JW, Neskovic AN, Price S, Oren-Grinberg A, Liteplo A, Cordioli R, Naqvi N, Rola P, Poelaert J, Guliĉ TG, Sloth E, Labovitz A, Kimura B, Breitkreutz R, Masani N, Bowra J, Talmor D, Guarracino F, Goudie A, Xiaoting W, Chawla R, Galderisi M, Blaivas M, Petrovic T, Storti E, Neri L, Melniker L; International Liaison Committee on Focused Cardiac UltraSound (ILC-FoCUS); International Conference on Focused Cardiac UltraSound (IC-FoCUS). International evidence-based recommendations for focused cardiac ultrasound. J Am Soc Echocardiogr. 2014 Jul;27(7):683.e1-683.e33. doi: 10.1016/j.echo.2014.05.001. PMID: 24951446.