Role of M Mode Technique in Today's Echocardiography
Highlights
- The original stand-alone M-mode instruments recorded at a sampling rate of2000 per second. Even with the 2D-guided M-mode recording oftoday, the sampling rate is still at least 1000 samples per second. (View Highlight)
- the middiastolic reopening of the mitral valve in the M-mode recording in Figure 1 represents volumetric blood flow rather than velocity. (View Highlight)
- Normally, mitral valve closure begins with atrial relaxation and then is completed with LV contraction. This process is usually smooth and uninterrupted. The corresponding pressure between the left atrium and the left ventricle is characterized by a gradual increase in left atrial pressure after atrial contraction, which in turn produces a gradual increase in LV pressure (View Highlight)
- When there is an elevated LV end-diastolic pressure as a result of the left atrium contracting against a stiff or already fully dilated left ventricle, there is a rapid increase in the LV pressure to a point that it exceeds the left atrial pressure earlier than is normal.8 This earlier reversal in the pressures causes the peak of the mitral valve A-wave to be earlier. Then there is a more prolonged closure of the mitral valve before ventricular contraction with a frequent interruption or plateau caused by equalization of the pressures. This interruption is called a ‘‘B-bump,’’ (View Highlight)
- In current discussions of diastolic function and LV pressure, the
M-mode mitral valve ‘‘B-bump’’ is almost never mentioned. It is not a strictly quantitative assessment; however, it almost never occurs unless the LVend-diastolic pressure is more than 20 mm Hg. (View Highlight)
- A ‘‘B-bump’’ is not a normal finding and should not occur if the LV diastolic pressure is normal and the mitral flow is truly normal. This M-mode finding can also be useful in differentiating patients who have a mitral Doppler E/A ratio less than 1 because of abnormal LV relaxation from those in whom the abnormal ratio is caused by low LV filling pressures (View Highlight)