The echocardiogram is an ultrasound of the heart. Using standard ultrasound techniques, two-dimensional slices of the heart can be imaged. The latest ultrasound systems now employ 3D real-time imaging.
In addition to creating two-dimensional pictures of the cardiovascular system, the echocardiogram can also produce accurate assessment of the velocity of blood and cardiac tissue at any arbitrary point using pulsed or continuous wave doppler ultrasound. 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 as well as the ejection fraction.
Echocardiography was the first medical application of ultrasound. Echocardiography was also the first application of intravenous contrast-enhanced ultrasound. This technique injects gas-filled microbubbles into the venous system to improve tissue and blood delineation. Contrast is also currently being evaluated for its effectiveness in evaluating myocardial perfusion. It can also be used with Doppler ultrasound to improve flow-related measurements.
Echocardiography is usually performed by cardiologists or cardiac sonographers.
Transthoracic echocardiogram
The standard echocardiogram is also known as a transthoracic 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. This is a non-invasive, highly accurate and quick assessment of the overall health of the heart. A cardiologist can quickly assess a patient’s heart valves and degree of heart muscle contraction (an indicator of the ejection fraction). The images are displayed on a video screen, and are recorded either by videotape (analog) or by digital techniques.
An echocardiogram can be used to evaluate all four chambers of the heart. It can determine strength of the heart, the condition of the heart valves, the lining of the heart (the pericardium), and the aorta. It can be used to detect a heart attack, enlargement or hypertrophy of the heart, infiltration of the heart with an abnormal substance. Weakness of the heart, cardiac tumors, and a variety of other findings can be diagnosed with an echocardiogram.
The TTE is commonly used to help diagnose endocarditis. Diagnostic findings by the Echocardiogram include definitive evidence of vegetation or thrombus on valves or other endocardiac structures, abscesses, or disruption of a prosthetic heart valve.
The TTE is highly accurate for identifying vegetations, but the accuracy can be reduced in up to 20% of adults because of obesity, chronic obstructive pulmonary disease, chest-wall deformities, or otherwise technically difficult patients. TTE in adults is also of limited use for the structures at the back of the heart like left atrium and the left atrial appendage. Transesophageal echocardiography, if available, may be more accurate than TTE because it excludes the variables previously mentioned and allows closer visualization of common sites for vegetations and other abnormalities. Transesophageal echocardiography also affords better visualization of prosthetic heart valves.
Transesophageal echocardiogram
This is an alternative way to perform an echocardiogram. A specialized probe containing an ultrasound transducer at its tip is passed into the patient’s esophagus. This allows image and Doppler evaluation which can be recorded. This is known as a transesophageal echocardiogram, or TEE (TOE in the United Kingdom). The advantage of TEE over TTE are usually clearer images, especially of structures that are difficult to view transthoracicly–from through the chest wall. The explaination for this is the heart rests directly upon the esophagus leaving only millimeters in distance that the ultrasound beam has to travel. This reduces the attenuation of the ultrasound signal engendering a stronger return signal, ultimately enhancing image and Doppler quality. Comparatively, transthoracic ultrasound must first traverse skin, fat, ribs and lungs before reflecting off the heart and back to the probe before an image can be created. All these structures, and the distance the beam must travel, attenuate the ultrasound signal, degrading image and Doppler quality.
In adults, several structures can be evaluated and imaged better with the TEE, including the aorta, pulmonary artery, valves of the heart, both atria, atrial septum, left atrial appendage, and coronary arteries. While TTE can be performed quickly, easily and without pain for the patient, TEE requires a fasting patient, a team of medical personel, takes longer to perform, is uncomfortable for the patient and has significant risks associated with the procedure (esophageal perforation–1 in 10,000, and adverse reactions to the medication).
Before inserting the probe conscious sedation is induced with the patient to ease the discomfort of the individual and to decrease the gag reflex, thus making the ultrasound probe easier to pass into the esophagus. Conscious sedation is a light sedation usually using the medications midazolam (a benzodiazepine with sedating, amnesiac qualities) and fentanyl (an opioid 100 times stronger than morphine). Sometimes a local anesthetic spray is used for the back of the throat such a xylocaine and/or a jelly/lubricant anesthetic for the esophagus. Children are anesthetized. Unlike the TTE, the TEE is considered an invasive procedure.
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