Global Left Ventricular Contractile Function
Measuring LV contractility is much more difficult. The fractional
area change (FAC) of the left ventricle can be measured by using the TG mid SAX or
any of the LAX cross sections (provided that the LAX cross sections include the apex
of the left ventricle) with the following formula:
(EDA − ESA)/EDA
where EDA is the cross-sectional area at end-diastole and ESA is the cross-sectional
area at end-systole. EDA and ESA are easily measured with the standard software
supplied with all ultrasonographs. In the absence of segmental dysfunction, FAC
is a reasonable approximation of LV ejection fraction, but the ejection fraction
is clearly load dependent and should be viewed cautiously as an index of ventricular
function. However, the LV ejection fraction is an excellent predictor of survival
in patients with coronary artery disease and is widely used in the perioperative
assessment of high-risk patients. Load-independent measures of LV contractility
are possible with TEE but are too complex for clinical practice.[56]
Figure 33-11
Normal pulmonary venous flow pattern. Pulsed-wave Doppler
measurement of normal blood flow velocities in the left upper pulmonary vein (LUPV)
is shown. At the top of the figure is a still-frame image of the two-dimensional
cross section used to position the Doppler sample volume (the round
white sphere). On the bottom two thirds of the figure is the display
in white of the instantaneous blood flow velocities (vertical axis) versus time (horizontal
axis) occurring in that sample volume. The electrocardiogram provides timing, and
the bold horizontal line is the baseline (zero flow)
for the flow velocities. Flow velocities above the red line
are positive (i.e., toward the transducer) to a maximum of 69 cm/sec. Flow below
the red line is negative (i.e., away from the transducer)
to a maximum of -32 cm/sec. In this patient with normal left atrial pressure, systolic
predominance of flow is evident; that is, more flow enters the atrium during the
period of ventricular systole than during ventricular diastole as evidenced by the
greater peak and average flow velocities during systole than during diastole. LA,
left atrium. (From Cahalan MK: Intraoperative Transesophageal Echocardiography.
An Interactive Text and Atlas. New York, Churchill Livingstone, 1997.)
Figure 33-12
High left atrial pressure produces diastolic predominance
in the pulmonary venous flow pattern. Pulsed-wave Doppler measurement of blood flow
velocities in the left upper pulmonary vein (LUPV) in a patient with abnormally high
left atrial pressure is shown. At the top of the figure is a still-frame image of
the two-dimensional cross section used to position the Doppler sample volume (the
round white sphere). On the bottom two thirds of
the figure is the display in white of the instantaneous blood flow velocities (vertical
axis) versus time (horizontal axis) occurring in that sample volume. The electrocardiogram
provides timing, and the bold horizontal line is
the baseline (zero flow) for the flow velocities. Flow velocities above the red
line are positive (i.e., toward the transducer) to a maximum of 80 cm/sec.
Flow below the red line is negative (i.e., away
from the transducer) to a maximum of -44 cm/sec. In this patient with abnormally
high left atrial pressure, diastolic predominance of flow is evident; that is, more
flow enters the atrium during the period of ventricular diastole than during ventricular
systole as evidenced by the greater peak and average flow velocities during diastole
than during systole. The negative flow velocities are due to atrial contraction
pushing blood back into the pulmonary vein. LA, left atrium. (From Cahalan
MK: Intraoperative Transesophageal Echocardiography. An Interactive Text and Atlas.
New York, Churchill Livingstone, 1997.)
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