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2004
The Changing Left Ventricle

2003
Aortic Valve Disease: New Dimensions in Evaluation and Management

2002
Heart Failure: Echo's Role in and Emerging Health Crisis

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Chest Pain in Children & Adults: The Role of Echo

2000
Mitral Regurgitation: New Concept

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The Falling Left Ventricle: Diastolic & Systolic Function

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Diastolic and Systolic Function

Changing the Outcome of CAD

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2001 Chest Pain
2002 Heart Failure



The Atrioventricular Valves
Mitral Stenosis
Fig. 1

In mitral stenosis, fusion of the commissures between the mitral valve leaflets causes obstruction to left ventricular inflow. The leaflets also become infiltrated with fibrous tissue, which produces shrinkage, thickening and immobility, particularly at the tips of the leaflets (Fig. 1). Over a longer period, the fibrotic tissue may calcify and eventually the valve becomes a funnel- shaped structure that impedes blood flow as much by its rigidity as by actual stenosis of the orifice.

Chronic elevation of left atrial pressure in mitral stenosis usually causes the chamber to dilate, although the extent to which this occurs depends additionally on atrial wall stiffness. Elevated filling pressure also results in pulmonary venous hypertension, and hence a rise in pulmonary artery pressure. If severe, this leads eventually to right ventricular hypertrophy and the development of tricuspid regurgitation.

Fig. 2

The pathological changes in the valve apparatus produce dramatic alterations to the echocardiographic images (Fig. 2). On the M-mode recording, thickening of the leaflets and reduction in their mobility can be appreciated. Commissural fusion alters the motion of the posterior leaflet; instead of moving in the opposite direction to that of the anterior, it is pulled forward when the valve opens at the beginning of diastole. In the normal valve, rapid early diastolic filling of the left ventricle means that the valve can partially close in mid-diastole, and it then reopens during atrial systole.

This sequence produces the characteristic "M" shape of the recording, with the down slope of the "M" designated as the "E-F slope". With mitral stenosis, however rapid filling is not possible, so the valve leaflets have to remain as widely separated as they can throughout diastole, and the "M" disappears. Another reason for a different pattern of leaflet motion is that atrial fibrillation is frequently present, and this eliminates the late diastolic reopening.

Fig. 3

These changes are also apparent on two-dimensional recordings. (Fig. 3) shows commissural fusion causing the valve leaflets to assume a dome shape in diastole, with the anterior leaflet forming a characteristic "elbow" due to its tethering to the posterior leaflet. The hallmark of rheumatic mitral valve disease is the restriction of motion of the anterior mitral valve leaflet tip. Abrupt halting of the early diastolic opening motion coincides with the opening snap evident on auscultation.

Fig. 4

Echocardiography is a very sensitive method for detecting mitral stenosis and simple inspection of the recordings
(Fig. 4)
can often differentiate between mild and very severe stenosis. Quantification of severity has, however, proved more difficult by M-mode. Early attempts measured the "E-F slope", which indicates the difference between early and mid-diastolic leaflet position, but these proved unsatisfactory because the E-F slope is influenced by factors such as stroke output and ventricular stiffness.

Traditional approaches for the calculation of mitral valve area involve cardiac catheterization. The value of cardiac catheterization methods for assessing a patient with mitral stenosis is questionable; the end-diastolic valve gradient is influenced by heart rate, stroke volume, and the presence of mitral aortic regurgitation, which also invalidate estimation of valve orifice area by the "Gorlin" formula.

Fig. 5

Two-dimensional echocardiography is able to visualize the mitral orifice directly in diastole, thus providing information previously available only to the surgeon. Using the parasternal short-axis view, it is possible to differentiate between various orifice shapes that are indistinguishable by M-mode (Fig. 5).

Fig. 6

Planimetry of a still-frame image (Fig. 6) allows the mitral valve orifice area to be measured. Great care is needed to ensure that the image selected is accurate. If the scan plane transects the valve obliquely, above or below the region of maximum constriction, the orifice will appear too large; if the wrong part of the cardiac cycle is used, it will appear too small. Other technical difficulties arise from limitations of lateral resolution of the instrument, and from multiple reverberations produced by valve calcification. In spite of these problems, in the hands of an experienced operator two-dimensional echocardiography has proved the best method available for preoperative estimation of mitral valve area. Thoughtful clinical uses of the two-dimensional echocardiographic data will obviate the need for cardiac catheterization in most patients.

In the setting of previous mitral valve commissurotomy, however, caution should be exercised. Such direct planimetric methods have not been shown to be as reliable in this setting.

Doppler echocardiographic methods have also been shown to be useful for estimation of mitral valve area using the pressure half-time method and for the estimation of mean mitral gradient. Such methods are particularly useful in a patient with previous commissurotomy and also serve to double-check the direct planimetric approaches.

Fig. 7

Of course, with significant mitral stenosis, the left atrium will dilate. Such dilatation can be observed in any view of the left atrium (Fig. 7). Estimation of left atrial size using echocardiography is very important. The normal left atrial size is below 4 cm in adults and dilates with chronic mitral stenosis, insufficiency, or atrial fibrillation. Patients with severe left atrial dilatation are usually very difficult to convert to normal sinus rhythm with cardioversion. The echocardiogram helps to select patients in which cardioversion might or might not be successful

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