Rheumatic mitral regurgitation
Mitral valve is the commonest valve involved in rheumatic heart disease. Mitral regurgitation occurs in the early phase of acute rheumatic fever itself. In fact it is almost an invariable association of rheumatic carditis. In very early stages of rheumatic carditis, the mitral regurgitation can be clinically silent, but demonstrable by Doppler echocardiography. Some studies have shown that Doppler echocardiographic detection of mitral regurgitation in the acute phase of rheumatic carditis predates clinical detection by up to two weeks. Many of the cases of mitral regurgitation due to rheumatic carditis resolve later on or decrease in severity on follow up. Even though the carditis in rheumatic fever is a pancarditis, the predominant involvement is that of the endocardium in the form of valvular involvement. Hence the mechanism of mitral regurgitation in the acute phase is mainly valvular and seldom due to left ventricular dilatation due to myocarditis and left ventricular failure. But significant mitral regurgitation itself can set up a vicious cycle because left ventricular dilatation caused by mitral regurgitation can further increase the mitral regurgitation by the dilatation of the mitral annulus which decreases the coaptation of the mitral leaflets in systole.
Clinically chronic rheumatic mitral regurgitation is associated with a left ventricular forceful apical impulse, cardiomegaly, soft first heart sound, left ventricular third heart sound and an apical pan systolic murmur which is conducted to the axilla. The conduction to axilla differentiates the murmur from the murmur of papillary muscle dysfunction and mitral regurgitation, which is usually conducted to the base of the heart. Sometimes late systolic pulsation of the left parasternal region due to the expansion of the left atrium may also be felt.
The electrocardiogram may show PR interval prolongation in the acute phase of rheumatic mitral regurgitation with carditis. In chronic rheumatic mitral regurgitation of significant severity, ECG shows left atrial and left ventricular enlargement.
The chest x-ray shows cardiomegaly and left atrial enlargement in severe rheumatic mitral regurgitation. Pulmonary congestion and features pulmonary hypertension may occur in late stages. Pulmonary congestion and cardiac failure can also occur in the acute phase if the rheumatic carditis if fulminant.
Echocardiography shows thickening of the mitral leaflets with tethering of the posterior mitral leaflet with restriction of movement. But frank reversal of movement (paradoxical anterior movement of posterior leaflet in diastole) as in mitral stenosis does not occur in isolated rheumatic mitral stenosis. Immobility of the posterior leaflet is the hall mark of rheumatic mitral regurgitation which differentiates it from non rheumatic mitral regurgitation on echocardiography. Systolic separation of the mitral leaflets can be seen sometimes. Dilated left atrium and left ventricle gives a suggestion that the mitral regurgitation is significant. Doppler echocardiography is needed to confirm mitral regurgitation and quantify it. The intensity of the spectral tracing and depth to which the jet is located by pulsed Doppler is an indication of severity of mitral regurgitation. By colour Doppler, the area of the jet in relation to the left atrium determines the severity. The depth to which the jet reaches in the left atrium is also an important determinant of severity.
Unlike the mitral valve in non-rheumatic mitral regurgitation, the heavily scarred mitral valve in rheumatic mitral regurgitation may not be always suitable for a conservative mitral valve repair procedure. Very often they end up in mitral valve replacement if severe enough to produce symptoms or impairment of left ventricular function.
RHD, MR on colour Doppler echo
Colour Doppler echocardiogram in RHD, MR
Colour Doppler echocardiogram in rheumatic heart disease (RHD), mitral regurgitation (MR). The mosaic coloured MR jet is outlined in the left atrium (LA). Ao: aorta; LV: left ventricle; RV: right ventricle. The left frame shows the apical five chamber view in diastole, while the right frame shows the apical four chamber view in systole. The apical five chamber view also shows an aortic regurgitation jet which merges with the jet of mitral stenosis in the left ventricle. Mitral leaflets appear thickened, though the finer morphological details of the mitral and aortic valves are not clear in these colour flow mapping images. MR severity can be assessed by comparing the MR jet area with that of the left atrium as well as by observing the extend of penetration of the jet into the left atrium. The larger the comparitive jet area and more distant the penetration of the jet, higher the severity of the mitral regurgitation. A disadvantage for comparing the area of the jet with that of the left atrium is in the presence of a grossly dilated left atrium. Similarly, the depth of jet penetration may vary depending on the eccentricity of the jet. This is also applicable to jet area, with eccentric jet appearing smaller in area.
Colour Doppler echocardiogram in RHD, MR – annotated
Grading severity of mitral regurgitation by color Doppler echocardiography
There are various ways to assess the severity of mitral regurgitation by color Doppler echocardiography. One method is to measure the mitral regurgitation jet area in the apical four chamber view and compare it with the area of the left atrium. The ratio of the maximum mitral regurgitation jet area by color Doppler to the area of the left atrium is calculated.
The grading of severity of mitral regurgitation by color Doppler is as follows:
Grade 1 (mild): Mitral regurgitation jet area / left atrium area ratio ?20%
Grade 2 (moderate): Mitral regurgitation jet area / left atrium area ratio 20 – 40%
Grade 3 (severe): Mitral regurgitation jet area / left atrium area ratio >40%
When the left atrium is grossly dilated, the ratio may be erroneously low even in severe mitral regurgitation and this is a limitation of this method.
Another method is by looking at the extend of the jet into the left atrium. A jet reaching upto the pulmonary veins is graded as severe.
Proximal Isovelocity Surface Area (PISA) method for estimation of mitral regurgitation
Proximal Isovelocity Surface Area (PISA) method is based on the continuity equation. When a flow passes through a narrow orifice, as it approaches the narrowest region, there is a flow convergence and flow acceleration. PISA is the surface area of the hemisphere at the aliasing region of the flow convergence. PISA increases as the flow increases and also with lower aliasing velocity. To reduce errors in measurement, smaller aliasing velocity has to be set, to get higher PISA measurement with lower chance for errors.
Regurgitant flow rate can be calculated as:
2 Pi r2 x V aliasing
Radius is measured from the orifice to point of colour change. If the flow convergence is not a true hemisphere, the angle subtended by the flow convergence at the orifice has to be measured and divided by 180 to get a correction factor. Good correlation between angiographic estimates of regurgitant flow and PISA based estimates have been reported.
Limitations of PISA method:
Dynamic changes in orifice
Non optimal flow convergence
Vena contracta
Vena contracta is the narrowest part of the regurgitant jet. Roughly, vena contracta diameter between 3 – 6 mm can be taken as moderate mitral regurgitation; below 3 mm can be considered mild and more than 6 mm as severe.
Colour M-mode will identify whether the mitral regurgitation is pansystolic or not.