Mitral stenosis assessment
From Echocardiography in ICU
The most frequent etiology of MS is rheumatic disease, which prevalence is low in developped countries.
Rheumatic mitral valve disease causes thickening and shortening of the leaflets and chordae, fusion of the commissures with "doming" of the leaflets in diastole. These damages restric the valve opening and create mitral stenosis.
MS is an obstacle to LV diastolic filling, leading to elevation of left atrium pressure and left atrium dilatation. The upstream effect on the right heart is elevation of right ventricle after-load and pulmonary hypertension.
Positive diagnosis of mitral stenosis (MS)
There is thickening and fusion of the mitral valve commissural edges and chordae, which will result in a "doming" appearance of the mitral valve opening. Stiffening and calcification of the mitral apparatus is variable, and results in further narrowing of the mitral orifice.
The anterior leaflet has been described as opening in a "hockey stick" appearance in parasternal long axis view.
This results in reduction of the mitral orifice area into a funnel shape, as you can see in this parasternal short axis view at the level of the mitral valve.
Color Doppler across the stenotic mitral valve may be of poor quality, due to the leaflets calcifications reflecting the ultrasounds. When the valve is not calcified, you will see a very narrow, funnel-shaped forward jet through the mitral valve, with acceleration and spreading after the valve. It is important to look for associated MR.
Grading MS severity: continuous Doppler
The main tool to assess MS severity is continuous Doppler across the mitral valve, which will determine the pressure gradient between LV and LA. Pressure gradient is dependent on both pre-load (volume status) and filling time (heart rate).
The transmitral gradient is recorded from apical approach, using continuous wave Doppler across the mitral valve, aligned as parallel as possible with the anticipated mitral inflow. If necessary, color Doppler can be used to locate the direction of the flow.
The mean gradient is calculated by electronic planimetry of the spectral profile (use trace).
In patients with atrial fibrillation, the duration of diastole, i.e. LV filling time, varies widely between cardiac cycles. It is important to measure the mean gradient in at least 5 cardiac cycles and to average them.
|Mean gradient (mmHg)||< 5||5-10||> 10|
|Surface (cm2)||> 2||1-2||< 1|
The surface of the mitral valve can be measured on 2D images, rarely on parasternal short axis images, more often by TEE.
Consequences on left atrium (LA)
Chronic elevation of LA pressure results in LA dilatation. LA dilatation and fibrotic remodeling lead to higher risk of atrial fibrillation.
The dilatation and decreased contractility of LA and left atrium appendage enhance propensity to thrombus formation.
Consequences on right heart and pulmonary vasculature
Long-standing mitral stenosis and high right ventricle after-load results in reversible, then irreversible increased pulmonary vasculature resistance and secondary pulmonary hypertension.
It is important to assess right ventricle pressures in all patients with MS to evaluate its consequences on the right ventricle.
Tricuspid regurgitation is frequent in patients with MS, due to the high right ventricle after-load and/or to rheumatic disease of the tricuspid valve.