Show me the POCUS
Mitral Valve
Like with the 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.
Mitral Valve Anatomy and Function Recap
The mitral valve is a bicuspid structure that allows directional flow of blood. Both the posterior and the anterior mitral valve leaflets are divided into eight segments with a thickness ranging between 1 to 5mm. On diastole, the mitral valve opens on the early filling stage when the left atrial pressure is greater than that of the left ventricle allowing it to fill with blood. Most of the blood flows during this initial phase of left ventricular relaxation. Atrial contraction contributes up to 25% of the cardiac output before the onset of systole. On systole, the pressure generated by the LV moves the scallops back to their closed position. The chordae tendinea prevent the valve from prolapsing into the atrium. The mitral annulus is the fibrous ring that supports the mitral valve leaflets and changes its shape throughout the cardiac cycle.
Mitral valve. On the left, its bileaflet structure with their corresponding scallops as seen from the left atrium. On the right we appreciate a 3D cine of the MV viewed from the left ventricle. Notice the movement of anterior mitral valve on early and late diastole as the anterior mitral valve appears to flicker. Also notice the shape of the MV annulus on systole and diastole. Images courtesy of Innotata and Kjetil Lenes.
Mitral Valve Stenosis
The most common cause of mitral valve stenosis is rheumatic heart disease. The typical immobility of the valve tips creates a typical hokey stick configuration.
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.
Normal valve function on diastole
Mitral valve stenosis
2D Views
We can appreciate the restriction of movement of the anterior leaflet of the mitral valve in a hockey stick configuration on diastole when seen on the parasternal long axis and apical 4 chamber views. Compare the normal findings with that of a patient with MS.
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Mitral valve stenosis. Clips 1 and 3, normal MV movement. Clips 2 and 4, a heavily calcified, thickened mitral valve with restriction of movement.
Diagnosis of the severity of mitral valve stenosis requires Doppler measurements and is beyond the scope for focused cardiac ultrasound (FoCUS). On the apical 5 chamber view, continuous wave doppler on the mitral valve will measure all velocities across that scan line and we are interrogating diastole. The following are examples of level 1 recommendations for measuring the severity of MS.
As we can imagine we would typically expect large fast flows into the LV. We can measure pressure half time which is the time the max pressure takes to half (this is a load dependent measure). A high number means that the pressure never equilibrates between the LA and LV. A low number implies that the equilibration of pressures happens fast. We estimate MV area by the formula MV area= 220/PHT. In the case below the pressure half time appears traced by the white dots seen on the screen with a MV area of 220/228 or <1cm square area or severe MS. Also by tracing the CWD envelope we can also calculate the mean pressure gradient and a value >10mmHg is considered severe.
Flow
Spectral Doppler analysis of the Mitral Valve on the Apical 5 chamber view with the CWD at the level of the MV tips. Here we are deriving pressure half time to estimate the degree of mitral valve stenosis. See text for details.
Mitral Valve Stenosis Severity Assessment- Beyond FoCUS
Mitral valve regurgitation. Clips 1 and 3 show a normal MV. Clips 2 and 4 show mitral valve prolapse.
Mitral valve (MV) regurgitation is common valvular dysfunction consisting the backward flow from the LV into the LA. The MV is a three dimensional structure consisting of two leaflets and it is the failure to have seal between them that lead to regurgitation. Schematically we represent these in the diagrams shown with arrows in red depicting flow of blood.
It is important to keep these in mind since they represent what you are likely to see on 2D ultrasound. Structural changes that can be identified include:
1. MV prolapse: bulging of the MV into the LA
2. Flail leaflet: failure of leaflet coaption typically as a consequence of ruptured chordae or papillary muscle.
3. Mitral annular calcification
Normal valve function
on systole. Notice coaptation points
MV prolapse
Flail Mitral Valve
Functional MV regurgitation
Lets start looking Normal MV movement compared to a clips of the MV with a prolapsed valve:
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The following clips display a normal MV vs a flair posterior leaflet. You can also observe the chordea tendineae
Mitral valve regurgitation. Apical 4 chamber view for both clips. Normal vs prolapsed posterior mitral valve leaflet.
MV Regurgitation - Beyond the scope of FoCUS
While beyond the scope of FoCUS, color flow doppler (CFD) and a detailed Doppler analysis can give us a more precise estimation of the different degrees of mitral valve regurgitation.
For illustration purposes we will slightly skim through CFD since it is easy to see the color changes and leave more advanced CWD and PWD out of this review. We can very roughly estimate the degree of severity of MR based on the jet regurgitant area compared to that of the LA area.
The following clips show severe MR. The first show an eccentric jet from a prolapsed anterior mitral valve leaflet causing posterior directing jet. This is the coanda effect seen on CFD. The second clip with central directed jet also appears from a prolapsed MV.
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Mitral valve regurgitation with the use of Color Flow Doppler. Clips 1 and 2 are on the parasternal long axis. Clips one shows coanda effect as the flow wraps around the left atrium. Clip 2 shows a large central jet that is directed posteriorly. Prolapse of the anterior mitral valve is seen here as well. Clips 3 and 4 with severe mitral valve regurgitation features. All clips above have a high Nyquist limit.
Systolic Anterior Motion of the MV
Systolic Anterior Motion describes the dynamic movement of the MVd during systole anteriorly towards the left ventricular outflow tract (LVOT) causing obstruction. It is recognized as a consequence of any setting that alters the complex dynamic anatomy of the LV. It typically arises after MV repair as the disruption of the dynamic function of the MV annulus and its leaflets. Excessive anterior or posterior leaflet tissue can predispose to SAM drawing the MV anteriorly towards the LVOT. There are other causes of SAM including diabetes, following dobutamine stress echo, post myocardial infarction and following general anesthesia in patients without cardiac pathology. Occurrence of SAM under GA is rare.
The following clips compare normal anatomy to patients who have SAM. We can appreciate significant amount of LVH on the second clip with a pattern of hypertrophic cardiomyopathy with a very thickened interventricular septum. Note the motion of the MV on systole.
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SAM. Clips 1 and 3 are normal views. Clips 2 and 4 with evidence of SAM. Notice the motion of the anterior mitral valve as the heart goes into systole.
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. Ibrahim M, Rao C, Ashrafian H, Chaudhry U, Darzi A, Athanasiou T. Modern management of systolic anterior motion of the mitral valve. Eur J Cardiothorac Surg. 2012 Jun;41(6):1260-70. doi: 10.1093/ejcts/ezr232. Epub 2012 Jan 18. PMID: 22290892.