Quantitative 2D

2D Echocardiographic evaluation of left ventricular function starts with the anatomical makeup of the left ventricle. Two factors, mass and volume, allows characterization of the left ventricular anatomy which indicates the pathological state of the left ventricle. In order to calculate mass and volume true short and long axis measurements must be obtained. Foreshortening of the left ventricle will yield incorrect values and mislead the therapy. Two models, the prolate ellipse model and the hemiellipse model are used, along with other models, to calculate the left ventricular mass and volume. Once global function has be defined, 2D echocardiography also allows for the assessment of regional function of the left ventricle.

The left ventricle wall is separated into the subendocardial, midwall, and subepicardial muscle fibers. Each section of fibers is arranged in different directions, such that, during contraction, each set of muscle fibers contributes to different aspects of the contraction process. When the left ventricle contracts it shortens the left ventricle's long axis, short axis, and lastly, a "wringing effect" whereby the base and the apex of the ventricle rotate around the long axis of the left ventricle.

If area and length are measured then the mass of the left ventricle can be calculated from the cylinder-hemiellipsoid method. Using the formula:

where Area is the area of the left ventricle in a LVSAX view (just below the mitral valve leaflet tips or high papillary view) and length is the base-to-apex length (Long Axis (LAX)) in a non-foreshortened LVLAX view, usually the 4 chamber view. The measurements are made in end-diastole.  The cavitary volume is calculated using the endocardial border.  The heart volume is calculated using the epicardial border.  The difference between the heart volume and cavitary volume is the myocardial volume. To calculate the myocardial mass, the myocardial volume is multiplied by the myocardial specific gravity, 1.04 g/ml.

Instead of area, circumference can be used to indicate the function of the heart.  Circumferential shortening, which uses circumference, can be calculated by the formula:

CS is Circumferential shortening, EDC is end-diastolic circumference, and ESC is end-systolic circumference.  The circumference is measured along the endocardial border.  While area and circumference can indicate the function of the left ventricle, area and circumference only measures ejection fraction in one plane.  Also, wall thickening, an indication of ventricular function, is not measured. 

Fractional shortening or change is the amount of change of the SAX of the left ventricle. Fractional shortening is usually measured utilizing M Mode. Fractional shortening is calculated using the left ventricular short axis in systole and diastole:

Normal values for fractional shortening are 30 percent. Fractional shortening is affected by preload, afterload, and contractility, similar to ejection fraction. If focal regional wall motion abnormalities are present that are not recognized by M Mode evaluation, then the Fractional shortening measurement will overestimate the myocardial function.

Fractional shortening of the midwall, instead of the endocardium can be calculated using M mode echocardiography. Fractional shortening of the midwall, FSmw is calculated using a modified two-shell cylindrical model. Constant LV mass during the cardiac cycle is assumed. The two-shell cylindrical model does not require that the inner and out wall thickening fractions be equal. FSmw is not dependent upon relative wall thickness, and, therefore, is useful in left ventricular hypertrophy.

Volume measurements look at multiple planes of ventricular function.  By viewing multiple planes, the volume measurements can be more accurate than FAC or FS.  The volume of a cardiac chamber can be measured by two methods:

• Method of Discs (MOD)
• Area-Length Method

From the measurement of volumes in systole and diastole, the ejection volume, ejection fraction, end-diastolic volume, end-systolic volume and others can be calculated.

To describe each disc or ellipse the left ventricular cavity long axis should be measured in two perpendicular views (LVLAX and 4CV). The diameters from each view can then be used to calculate the area of each disc (pi * a * b). Multiplying each disc by it's thickness yields a volume. The total volume of the discs is the left ventricular volume.

Ejection Fraction (EF) is the fraction of left ventricular volume that is ejected during systole.  The difference between the end-diastolic volume (EDV) and the end-systolic volume (ESV) is the stroke volume (SV).  The stoke volume is divided by the end-diastolic volume.  Ejection Fraction is preload, afterload, and contractility dependent.  The formula for Ejection Fraction is:

SV = EDV - ESV

EF = SV / EDV

Left ventricular volume calculations, although fairly accurate, tend to underestimate the left ventricular volume when compared to angiographic data. Foreshortening of the left ventricle, LV LAX measurement differences, and contrast filling intermyocardial interstices account for the underestimation of echocardiographic left ventricular volume measurements.