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Back to Cardiac Imaging
Echocardiography
The echocardiogram is an ultrasound of the heart. Using standard
ultrasound techniques, two-dimensional slices of the heart can be
imaged. Ultrasonographic imaging of the heart is a noninvasive technique
that depends on the differing ability of the structures within the
heart to reflect ultrasound waves.
The standard echocardiogram is also known as a trans-thoracic
echocardiogram, or TTE. In this case, the echocardiography transducer
(or probe) is placed on the chest wall (or thorax) of the subject,
and images are taken through the chest wall.
Another method to perform an echocardiogram is to insert the
echocardiography transducer within the patient's esophagus, and
record pictures from there. This is known as
transesophageal echo,
or
TEE. The advantage of
TEE over
TTE are that better pictures can be produced, since there is less
tissue between the transducer and the structures that are being
imaged. Also, certain structures of the cardiovascular system are
not ammenable to adequate imaging via TTE, including the aorta,
the pulmonary artery, the valves of the heart, and the left and
right atria. These structures are usually well visualized on trans-esophageal
echocardiography.
In addition to creating two-dimensional pictures of the cardiovascular
system, the echocardiogram can also produce accurate assessment
of the direction of blood flow and the velocity of blood and cardiac
tissue at any arbitrary point. This allows assessment of cardiac
valve areas and function, any abnormal communications between the
left and right side of the heart, any leaking of blood through the
valves (valvular regurgitation), and calculation of the cardiac
output.
Echocardiography was the first medical application of ultrasound.
Types
M-mode echogardiography: A scan is produced on a paper
moving at constant speed to produce a single dimension image.
2-dimensional (real time) echocardiography: A 2-D fan
shaped image of a segment of the heart which may be frozen and hard
copied. Several views are possible, the commonest being: long axis,
short axis, 4-chamber, and subcostal.
Doppler (color flow) ultrasonography: This is good for
visualizing blood flow across valves and congenital abnormalities.
The blood flow is colorized.
Transesophageal echocardiography: A special device is
inserted into the esophagus that enables ultrasonographic visualization
of the heart and large vessels. Good for diagnosing aortic dissection,
vegetations on heart valves. For a more detailed discussion of transesophageal
echo, click here!
Stress echocardiography: Used to evaluate ventricular
function, ejection fraction and regional wall motion in response
to exercise.
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Indications
- Diagnosis of
heart failure (almost 10 times more accurate than the ECG)
and estimation of ventricular heart function.
- Diagnosis of congenital
heart disease
- Diagnosis of
endocarditis
and valve disease
- Diagnosis of pericardial effusions
- Diagnosis of mural thrombus
- Diagnosis of aortic aneurysms
- Diagnosis of
cardiomyopathy
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