

Introduction 

There is a large variablility of how measurements are imaged, measeaured, recorded and interpreted. The guidelines attempt to standardize how images are performed, where measurements are made, what part of the cycle measurements are performed, and to provide cutoffs for mild, moderate, and severe disease so reports between labs can become standardized and useful in following patients. 

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.


Foreshortening 

Foreshortening is the incorrect measurement of the left ventricular axis, usually the long axis, due to improper sector scan of the left ventricle. The sector scan, instead of cutting across the true long axis of the left ventricle, cuts an acute angled sector scan that will yield a shorter axis than the true axis length. The apex of the left ventricle should remain stationary throughout the cardiac cycle in the TTE (apical) views. If the apex of the left ventricle appears to move towards the base of the heart then the sector scan is foreshortened. The apex of the left ventricle is relatively immobile throughout the cardiac cycle. If a foreshortened view is obtained, change the angle and/or location of the probe to obtain a nonforeshortened view. 



Normal View 
Foreshortened View 


Left Ventricular Contraction 

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.




Circumferential (SAX) Contraction 
Longitudinal (LAX) Contraction 
Axial (Wringing) Contraction 


Image Axis of LV 

The midwall fibers are run circumferentially around the left ventricle's short axis. During the contraction process the midwall fibers contribute to the shortening of the short axis of the left ventricle. The major portion of the stroke volume comes from the shortening of the short axis of the left ventricle.
The subendocardial and subepicardial fibers are oriented longitudinally. The longitudinally oriented fibers cause the shortening of the apextobase or long axis of the left ventricle. Note that it is the base, not the apex, of the heart that is displaced towards the apex of the heart. The apex is relatively immobile during the contraction of the heart.
The third contribution to the stroke volume is the apicaltobase twisting or wringing effect. The apex of the left ventricle will turn counter clockwise with respect to the base of the heart. The twisting or wringing effect is most due to the contractile state of the myocardium and the counter opposed spiral arrangement of the cardiac musculature.




Electrocardiogram and Mechanical EndSystole and EndDiastole Events 


When measuring enddiastolic and endsystolic parameters, use the ECG. The onset of systole occurs at the peak of the QRS complex and the end of systole occurs at the end of the T wave (when the ventricle is repolarized). Enddiastole occurs just prior to the initiation of the QRS complex. It is very difficult to be consistent in measuring cardiac timing events by looping thru the mechanical movements. Using the electrical events of the cardiac cycle will make the measurements more consistent. 

Mass 

Cylinderhemiellipsoid
Method 

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

V = 5/6 * Area * Length

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 basetoapex length (Long Axis (LAX)) in a nonforeshortened LVLAX view, usually the 4 chamber view. The measurements are made in enddiastole. 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.


Area 

Fractional Area Change (FAC) 

2D Echocardiography can measure areas, circumferences and lengths from the caliper and tracing function on the echocardiographic machine. Various formulas can be used to calculate areas, volume, ejection fraction, fractional shortening, etc. Area can be measured using the echocardiographic tracing function. The tracing function will yield a circumference and an area. The area and circumference can be measured in systole and diastole to give an indication of the function of the heart. The fractional area of change (FAC) of the heart is calculated by dividing the difference between the diastolic and systolic areas by the diastolic area.
Normally, the EDA is approximately 14 cm2 and the ESA is approximately 6cm2 for a FAC of 60%. The FAC is load dependent. Also the SAX view may be truncated if it is not at perpendicular to the long axis. Remote disease not viewable in the SAX may cause you to overestimate the FAC of the LV.



Fractional Area Change (FAC) 


Circumferential Shortening 

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:



Circumferential Shortening (CS) 


CS is Circumferential shortening, EDC is enddiastolic
circumference, and ESC is endsystolic 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 (FS) 

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:



Fractional Shortening Image 


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 twoshell cylindrical model. Constant LV mass during the cardiac cycle is assumed. The twoshell 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 

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)
 AreaLength Method
From the measurement of volumes in systole and diastole,
the ejection volume, ejection fraction, enddiastolic
volume, endsystolic volume and others can be calculated.


Method of Discs (MOD) 

The method of discs (MOD) can be applied by using a Biplane method or a single plane method. The method of discs divides up the volume being measured into multiple discs and calculates the volume of each disc then adds the volumes together to yield a volume. This is more accurate than utilizing the assumptions of shape used by the MMode method. 

Biplane Method 

In the biplane method, two orthogonal (90 degrees from each other)
planes of the left ventricle are used, usually the 2 chamber
view and the 4 chamber view. The longest axis of the
two planes is used for the axis length. The left ventricular
cavity is divided into usually 20 discs. The area of each of the discs are calculated then an integral of the disc area to calculate the volume of the left ventricle is performed. The ventricle is divided into discs and the volume calculation
is performed. By using the biplane method, significant
anatomical variations of the two planes will be included
in the calculation, resulting in a more accurate value for
left ventricular volume. 




Method
of Discs (MOD) Formula 
Volume
by Method of Discs (MOD) 
Volume
by Method of DIscs (MOD) 4 chamber view 


To describe each disc or ellipse the left
ventricular cavity long axis should be measured in two
perpendicular views (2CV 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.


Acoustic Quantification
(AQ) 

Acoustic quantification is a special
method to detect the endocardial border in an echocardiographic
scan. Once the border has been optimally detected,
the volume of the left ventricle (or other chamber) can
be calculated in real time. The patient's ejection
fraction, enddiastolic volume, endsystolic volume and
cardiac output can be performed beattobeat. This
advanced method has many uses but it is technically difficult
to do and has a significant error rate if not properly performed. 

To perform AQ the LVLAX is imaged
in 2D mode. The endomyocardial borders will need
to be visible by manipulating the LGC and TGC gain controls.
An regionofinterest (ROI) is drawn. The area of
interest must include the whole LVLAX view and the endocardial
movement. If the endocardial moves beyond the regionofinterest
(ROI) then that portion of the LVLAX will not be included
in the calculations. Reproducibility determines
the quality of the scan. If multiple successive cardiac
cycles yield values which are close to each other (accuracy)
then the scan is considered to be of high quality.
However, if successive values are not accurate then the
scan is considered to be of low quality. The MOD
calculation is used for AQ and carries all of the inherent
errors in the MOD method. AQ can calculate the following
values:
 FAC (Fractional Area Change)
 dA/dt (Area Change versus Time Change)
 EDA (End Diastolic Area)
 EDV (End Diastolic Volume)
 dV/dt (Volume Change versus Time Change)
 EF (Ejection Fraction)
 PEF (Peak Ejection Rate)
 PRFR (Peak Rapid Filling Rate)
 Atrial Filling Fraction (AFF)




SAX/LAX Method 

Tortoledo et al developed a formula
that uses the LAX and the SAX of the left ventricle to calculate
the enddiastolic left ventricular volume. The formula
is: 
EDV
= (SAX * LAX * 3.42)  6.44 


LV Volume by SAX & LAX 
LAX 
SAX 


AreaLength Method 

The arealength method
uses the LAX of the left ventricle and the
endocardial area of the left ventricle.
A formula, given below, has been developed
to calculate the volume of the left ventricle.

As above, Acoustic Quantification (AQ)
can utilize the AreaLength Method.
Again, geometric errors can occur since
the AreaLength method assumes a geometric
ellipsoid and the left ventricle may not
match that assumption.




AreaLength Formula 
AreaLength Method 


Ejection Fraction (EF) 

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

SV = EDV  ESV 
EF = SV / EDV 

To calculate an ejection fraction, the volume of the left ventricle can be calculated utilizing the Teicholz or spherical formulas and measuring the left ventricular enddiastolic and endsystolic diameters. The Teicholz formula is accurate for non dilated hearts. For dilated, spherical hearts the spherical formula is more accurate. 



Teicholz Formula 
Spherical Formula 


The ejection fraction does not equal fractional area change (FAC). Ejection fraction is a volume change calculation whereas, fractional area change is an area change calculation. The table below shows how ejection fraction and fractional area change relate in a normal heart. Also, the three animations show the central area displacement for different fractional area changes. 

FAC 
Ejection Fraction 
60% 
75% 
50% 
66% 
40% 
54% 
30% 
42% 
20% 
29% 
10% 
15% 




FAC and Ejection Fraction Relationship 
60 % FAC 
40 % FAC 
20 % FAC 



Left Ventricle 

Measurements of the left ventricle should be made at enddiastole or endsystole so calulations of ventricular performance can be performed. Chamber sizes should be indexed to BSA to allow comparisons between patients of different sizes. 

Linear measurements of the left ventricle should be done in the parasternal long axis so the walls are perpendicular to the ultrasound beam and be measured immediately below the mitral valve leaflet tips. MMode can be used but avoid an oblique angle of interrogation so 2D may be preferred for measurements. 

Teicholz and Quinonnes methods for volume measurements rely on assumptions and are no longer used. Volume measurements that rely on linear measurements have assumptions that do not apply in many disease states. When useing the left ventricle long axis length, the longest length is used in imaged in two different views (apical two and four chamber views). A linear line at the base of the mitral valve represents the base of the heart. If the endocardial border is poorly visualized, contrast agents should be used, recognizing that contranst enhanced imaging results in a larger left ventricular cavity measurement than 2D measurements.
The recommended method of volume measurements by 2D is the biplane method of disks (MOD). If the apex is not visible then the arealength method is the next best calculation, recognizing that assumptions of shape are inherent in the calculation. 3D calculations do not have shape assumptions and are the most accurate when compared to CMR as long as endocardial borders are accurately detected. 

Method 
Images 
Advantages 
Disadvantages 
MMode 

Reproducible
High Temporal Resolution 
Single Dimmension
Beam Orientation 
2D 

Perpendicular measurement 
Single Dimmension
Lower Frame Rate

Biplane MOD 

Less Geometric Assumptions 
Apex Foreshortened (frequently)
Endocardial Dropout
Miss outofplane shape distortion 
Area Length 

More geometric Assumptions 
Apex Foreshortened (frequently)
Geometric Assumptions 
Contrast Enhanced 

Good Endocardial Borders 
Basal Shadowing
Same geometric assumptions of method used 
3D 

No geometric assumption
Most accurate 
Low temporal resolution
Image quality dependent 
Strain 

Angle Independent
Prognostic 
Vendor Dependent 


Normal Values for Left Ventricular Size and Function by Gender 
Parameter 
Male (±2SD) 
Female (±2SD) 
Dimmensions 


LVIDs (mm) 
50.2 ± 4.1 (42.058.4) 
45.0 ± 3.6 (37.852.2) 
LVIDd (mm) 
32.4 ± 3.7 (25.039.8) 
28.2 ± 3.3 (21.634.8) 
Biplane MOD 


LVEDV (mls) 
106 ± 22 (62105) 
76 ± 15 (46106) 
LVESV (mls) 
41 ± 10 (2161) 
28 ± 7 (1442) 
LVSV (mls) 
55 ± 12 
48 ± 8 



LVEDV (mls/m2) 
54 ± 10 (3474) 
45 ± 8 (2961) 
LVESV (mls/m2) 
21 ± 5 (1131) 
16 ± 4 (824) 
LVSV (mls/m2) 
33 ± 5 
29 ± 4 



LVEF(%) 
62 ± 5 (5272) 
64 ± 5 (5474) 

*LVEF = (LVEDV  LVESV)/LVEDV 

Conclusions 

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. 

