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Echocardiography uses ultrasound waves which emit from a probe placed on the chest of the patient and travel through the body. The sound waves are harmless. Within the body, the bounce off of various body tissues and are reflected back towards the transducer with a different frequency of sound waves form that which was originally sent into the body. Various tissues can alter these sound waves differently, resulting in various different wave lengths of reflected sound waves. The echocardiogram machine receives and interprets these sound waves and makes a representing picture of the inside structures based upon the received sound waves. Furthermore, since the probe constantly emits ultrasound waves, it will receive a constant feed back of the heart structures as it changes during its contraction. This will enable the visualization of the heart muscles, valves and blood vessels in motion.


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Echocardiography can provide the following information:
  • Cardiac structures: The various components of the heart (muscle, valves, etc.) could be seen. Therefore a hole in a heart septal wall or deformity of a cardiac valve, etc could be identified.
  • The motion of the ventricular muscular walls can be seen (as ventricles pump blood out of them). Reduction in the capability of the ventricles to pump can therefore be evaluated.

For an echocardiogram movie clip, click here or on the image above.  In this image a 4-chamber view is demonstrated.  This shows the four chambers of the heart as seen in the still image above.  The cardiac function and the opening and closing motion of the mitral and tricuspid valves can be seen.
  • The flow of blood within the heart and blood vessels could also be seen in a feature termed color Doppler. This will represent the blood in usually two different colors: blue and red. The blue represents the blood which is heading away from the transducer and the red represents the blood which is flowing towards the transducer. This enables the visualization of abnormalities of blood flow such as leakage of blood through valves (regurgitation or insufficiency) since blood would be seen to leak back after the valve closes.
  • In addition the pressure difference between one part of the heart and the other could be determined since the ultrasound waves bouncing off blood would change its sound wave length depending upon the speed with which the blood flows (blood velocity). This is known as the Doppler phenomenon. Blood travels at higher velocities when there is a greater pressure difference between two parts of the heart. For example, if there is a narrowing of the pulmonary valve (pulmonary stenosis) the right ventricle will squeeze harder to push the blood through the smaller than normal pulmonary valve opening resulting in propelling the blood at a higher speed. This higher speed (velocity) of blood can then be measured by the Doppler equipment of the echocardiogram and an estimation of pressure gradient across the pulmonary valve can be calculated.
Limitations of echocardiography:
  • Ultrasound waves can not travel through air as well as it can through body tissue, therefore blood vessels within the lungs can not be seen such as parts of the pulmonary arteries and veins far away from the heart.
  • Doppler can measure the pressure difference between one part of the heart and the other, however, it is not capable of measuring the blood pressure at any given point within the heart as it is possible in the cardiac catheterization laboratory.

 

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