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ADVANCED SYSTOLIC FUNCTION
Albert T. Cheung, M.D.
Department of Anesthesiology and Critical Care
University of Pennsylvania, Philadelphia, PA
Multiplane 2-dimensional TEE permits the entire left ventricle to be imaged throughout
the cardiac cycle. Direct imaging of the left ventricle throughout the cardiac cycle can be
used to provide information about left ventricular wall thickness, chamber size, and
contractile performance. TEE measurements of global systolic function are useful for
clinical decision making because they provide information pertaining to prognosis, the
risk of cardiac operations, the severity of valvular heart disease, the extent of coronary
artery disease, and the responses to vasoactive or other cardiovascular drug therapy. For
example, in the American Heart Association guidelines for the management of patients
with valvular heart disease, the decision for aortic valve replacement in patients with
chronic aortic regurgitation without symptoms of heart failure is contingent on measures
of left ventricular ejection fraction and left ventricular diameters (Figure 4, ACC/AHA
2006 Guidelines for the Management of Patients with Valvular Heart Disease).
GLOBAL LEFT VENTRICULAR SIZE AND SYSTOLIC FUNCTION
The normal left ventricle is a muscular organ of nearly uniform wall thickness
surrounding a cavity with a circular cross section. The cross sectional area of the left
ventricular cavity is greatest at the base and decreases toward the apex. Contraction of
myocardial fibers during systole causes an increase in left ventricular wall thickness and
a decrease in both the diameter and the length of the left ventricular chamber. The mitral
valve leaflets, chordae tendineae, papillary muscles, and left ventricular apex provide
anatomical landmarks for establishing the level of the cross-sectional imaging planes
during the 2-dimensional echocardiographic examination. The entire left ventricle can be
examined by TEE using the transgastric short-axis imaging planes at the level of the left
ventricular apex, mid-papillary muscles, and left ventricular base. Alternatively, the
entire left ventricle can also be examined using the TEE mid-esophageal long-axis
imaging planes at multiplane angles of 0-20° (4-chamber), 80-100° (2-chamber), and
120-160° (long-axis).
Chronic systolic pressure overload caused by hypertension or aortic stenosis produces
concentric left ventricular hypertrophy. In patients with compensated left ventricular
hypertrophy, left ventricular mass increases relative to the cavity volume. This change
can be most readily detected by TEE as an increase in left ventricular wall thickness. A
left ventricular end-diastolic posterior wall thickness greater than 1.1 cm suggests left
ventricular hypertrophy.
Chronic volume overload caused by congestive heart failure, aortic regurgitation, or
mitral regurgitation also causes left ventricular hypertrophy. In contrast to chronic
pressure overload, volume overload causes an increase in left ventricular cavity size
without an increase in ventricular wall thickness. An end-diastolic short-axis left
ventricular cavity diameter greater than 5.5 cm or cross-sectional area greater than 22
cm2 at the mid-papillary level suggests left ventricular dilation or eccentric hypertophy.
Left ventricular end diastolic and end systolic cavity volume can be measured from the
mid-esophageal left ventricular 4 chamber and 2 chamber views using Simpson’s rule.
This measurement is accomplished by tracing the left ventricular endocardial border up to
the mitral valve annulus and then using the calipers to measure the length of the left
ventricular cavity from the mitral valve annulus to the apex. The accuracy of TEE for
quantifying left ventricular volume is not as well established as with TTE.
Foreshortening of the left ventricular cavity occurs if the long-axis cross sectional
imaging plane is not directed through the true left ventricular apex and will cause
underestimation of the actual left ventricular cavity volume. Representative normal
echocardiographic values measured using Simpson’s rule are: LV end-diastolic volume
of 56-155 ml, LV end-systolic volume of 19-58 ml, and LV ejection fraction of > 55%.
Reference values for left ventricular dimensions measured by echocardiography have
recently been published in a consensus report from the American Society of
Echocardiography. In that report, dimensions are indexed by gender, height, and body
surface area. It is also important to note that the published reference dimensions were
obtained from transthoracic echocardiographic studies measuring left ventricular
dimensions at the mitral valve chordal level rather. TEE measurements often obtained at
the transgastric left ventricular mid-papillary muscle level may yield slightly smaller
dimensions.
From: J Am Soc Echocardiogr 2005;18:1440-1463.
From: J Am Soc Echocardiogr 2005;18:1440-1463.
Global indexes of left ventricular systolic function can be measured from the TEE images
based on the relative speed and change in end-diastolic and end-systolic left ventricular
cavity size. The transgastric left ventricular short axis end diastolic area (EDA) and end
systolic area (ESA) are often used for this purpose and are measured by manual
planimetry of the area bounded by the endocardium. The end systolic diameter (ESD) is
approximately 2.8 cm and the ESA is approximately 6.2 cm2 in normal adults.
1. Fractional shortening (FS) is the percent decrease in left ventricular cavity short axis
diameter from end diastole (LVIDed) to end systole (LVIDes) and can be measured from
the endocardial border or the midwall of the left ventricle.
FS = (LVIDed – LVIDes)/LVIDed x100 (Normal range = 14-45%)
2. Fractional area change (FAC) is the percent decrease in the left ventricular cavity
cross-sectional area from end-diastole to end-systole.
FAC (%) =
(EDA − ESA)
× 100
EDA
(Normal = 57%).
3. Mean velocity of circumferential fiber shortening (Vcf )
Vcf (circumference/second) =
EDD − ESD
× 100
EDD × LVET
where EDD = end-diastolic LV cavity diameter,
ESD = end-systolic LV cavity diameter, and
LVET = left ventricular ejection time (seconds).
4. Heart rate corrected mean velocity of circumferential fiber shortening (Vcfc)
Vcfc (circ/s) =
Vcf
R − R interval
(Normal ≥ 1.1 circ/s)
All of these indexes of global ventricular function are based on a single cross-section of
the left ventricle. The presence of ventricular asymmetry or dysynergy, especially when
abnormal regions are not within the plane of the image used to calculate the index may
render the index a poor indicator of global left ventricular function. Corrections to the
global left ventricular ejection fraction can be estimated based on the presence of akinetic
or dyskinetic regions outside of the imaging plane. For example, global left ventricular
ejection fraction estimated from the transgastric mid-ventricular short axis image should
be decreased by approximately 10% in the presence of an akinetic left ventricular apex.
Alternatively, a qualitative estimation of global ventricular function can be made based
on visual inspection. Global ventricular function is graded as being normal, mildly,
moderately, or severely impaired based on estimation of the left ventricular ejection
fraction. The advantages of visual assessment are that it is based on multiple views,
incorporates multiple parameters of left ventricular function, and can be performed
immediately without the need for off-line image analysis. Studies have demonstrated that
visual assessment of left ventricular function, despite its limitations, correlate well with
quantitative measurements and is a useful parameter for predicting cardiac risk and
morbidity. An echocardiographic left ventricular ejection fraction less than 30% is
consistent with severe left ventricular dysfunction based on clinical trials involving
patients with heart failure. Subjective estimation of global ventricular function or left
ventricular ejection fraction is dependent on the experience of the echocardiographer and
inter-observer variability may exist depending upon the parameters used to grade
ventricular function. The accuracy and consistency of subjective estimation of global
ventricular function can be improved by calibrating the estimation with established
methods of quantification.
One difficulty encountered with the assessment of left ventricular function is that
measures of systolic performance are dependent on the ventricular loading conditions at
the time of the study. An abnormally high systolic blood pressure increases left
ventricular afterload and decreases the FAC or Vcfc. A reduction in preload decreases
both left ventricular end diastolic and end systolic cavity size. For these reasons, it is
necessary to plot indexes such as the FAC or Vcfc against the systolic blood pressure or
left ventricular wall stress to obtain an afterload-independent assessment of ventricular
contractility. Left ventricular meridional wall stress (ESWS), an estimate of afterload
that incorporates measures of peak systolic blood pressure (SBP), left ventricular wall
thickness (H), and left ventricular end-systolic cavity diameter (ESD) can be estimated
with the following formula :
ESWS (x103 dynes/cm2) =
(0.334)(SBP)(ESD)
(H )(1+ H / ESD)
Estimating load-independent indexes of left ventricular contractile performance is tedious
to perform clinically, but has been used in clinical studies to demonstrate the increase in
left ventricular contractility in response to inotropic agents or the decrease in ventricular
contractility in response to volatile anesthetic agents. Despite the recognition that
performance measures such as ejection fraction are load-depend, echocardiographic
measures of global left ventricular function has proven prognostic value in the clinical
setting.
LEFT VENTRICULAR FUNCTION AND THE ECHO REPORT
The American Society of Echocardiography, European Society of Echocardiography,
American College of Cardiology, and the American Heart Association have published
guidelines with recommendations for definitions used in the reporting of cardiac imaging
studies (15-16). Attached is an example of a format that can be used for the reporting of
left ventricular size and function as assessed by the echocardiographic examination.
CONCLUSION
Echocardiographic measurements of left ventricular wall thickness, cavity size, and
segmental wall motion obtained by TEE can be used to assess global and regional left
ventricular function. The information provided by TEE is an important supplement to
hemodynamic and electrocardiographic measurements for the diagnosis of left ventricular
hypertrophy, cardiomyopathy, and the consequences of myocardial ischemia and
infarction. It is important to recognize that left ventricular volumes cannot be directly
measured from a single cross-sectional image. It is also important to recognize that left
ventricular systolic function is dynamic and changes in response to anesthetic agents,
vasoactive drug therapy, intravascular volume status, and arterial blood pressure.
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