M-Mode Echocardiographic Measurements
M-Mode Echocardiography has good temporal resolution. Hence measurements of the left ventricle are often taken with M-Mode. End diastolic and end systolic volumes are estimated from these measurements. the stroke volume and ejection fraction are also calculated from these measurements. Usually M-Mode cursor is guided by a two dimensional image in the parasternal long axis view (seen as inset above). The position of the cursor corresponds to the M-Mode cut. The cut is at the chordal level for left ventricular measurements. The following measurements are marked out in the M-Mode tracing:
LVPWs: Left ventricular posterior wall, systolic
LVIDs: Left ventricular internal diameter, systolic
IVSs: Interventricular septum, systolic
LVPWd: Left ventricular posterior wall, diastolic
LVIDd: Left ventricular internal diameter, diastolic
IVSd: Interventricular septum, diastolic
From these measured values, other estimates are calculated by the computerized algorithm of the echocardiograph:
EDV: End diastolic volume.
IVS / LVPW: Ratio of thickness of IVS and LVPW in diastole. In asymmetric septal hypertrophy due to hypertrophic cardiomyopathy, this ratio is increased. It is reduced in septal thinning due to anterior wall myocardial infarction.
IVS %: Percentage systolic thickening of the interventricular septum. Systolic thickening is reduced in scars of myocardial infarction as well as in hypertrophic cardiomyopathy.
FS: Fractional shortening.
ESV: End systolic volume.
EF: Ejection fraction – the most important and popular measure of left ventricular systolic function. It is the ratio of stroke volume to end diastolic volume, expressed as percentage.
LVPW %: Systolic thickening of the left ventricular posterior wall – reduced in scarring due to myocardial infarction.
M-Mode measurements of the right ventricle (RV) are seldom taken as this view cuts only through the right ventricular outflow tract and does not assess the major part of the right ventricle. Calculation of ejection fraction of the right ventricle is difficult due to its complex shape.
Ideally the M-Mode tracing has to be timed with simultaneous ECG. But this is often not done as it is cumbersome to connect ECG leads in a busy echocardiography laboratory. If an ECG is attached, correct timing of end systole and end diastole is possible.
M-Mode measurements have an inherent limitation in that it is one dimensional. Better methods of assessing left ventricular function would be two dimensional or preferably three dimensional in modern echocardiographs. But it is often restricted to the research scenario, again due to constraints of time.