M-Mode echocardiogram in LV dysfunction: M-mode echocardiogram in left ventricular dysfunction showing reduced contractile excursions of the interventricular septum (IVS) and left ventricular posterior wall (LVPW). The vertical axis shows the distance from the transducer and horizontal axis is time. Left ventricular internal diameter in diastole (LVIDd) is increased to 6.3 cm (upper limit of normal is 5.5cm). The ejection fraction (EF) is also reduced to 35%. Ejection fraction of 35% is the cutoff for most studies on left ventricular dysfunction. It is also the threshold for implantation of an ICD (implantable cardioverter defibrillator). LVIDs: left ventricular internal diameter in systole; LVPWd: left ventricular posterior wall in diastole; IVSd: interventricular septum in diastole; EDV: end diastolic volume; IVS/LVPW: ratio of septal to posterior wall thickness; ESV: end systolic volume; FS: fractional shortening. Here the end diastolic volume and end systolic volume are elevated as the left ventricle is dilated and not contracting well. For the same reason, fractional shortening is also reduced.
The inset above shows the 2-D echo picture while the tracing below is the M-mode. The sweep speed of M-mode is shown as 75 mm/second. RV: right ventricle. The method for estimating ejection fraction with M-mode echo is useful when there is global left ventricular dysfunction. If there is regional wall motion abnormality, the assessment by M-mode may be inaccurate. In such situations, area-length method or Simpson’s method using 2-D echocardiography will be more useful in assessing left ventricular function. 3-D (3 dimensional) echocardiography if available, will give a better assessment of left ventricular function.