Echocardiography

Watching the heart in action

Echocardiography (or sonography) is currently the most important and common method for diagnosis of a congenital heart defect. It is a non-invasive ultrasonic examination that provides the doctor with accurate ultrasound images and audio recordings of the patient’s heart. Thus, the examining doctor can:

• display in detail the heart walls, its chambers and valves to assess their size and structure, and to identify potential abnormal changes;
• assess the pumping capability of the heart—ie, the strength of the heart muscle;
• assess the speed and direction of blood flow and the blood pressure at specific locations inside the heart;
• investigate the cause of an abnormal heart murmur; and
• check whether there is fluid around the heart or ascertain whether the covering of the heart (pericardium) is inflamed.

Because of the detailed display of the heart’s structure and function, echocardiography allows nearly all heart malformations to be detected.

The refined technique of the so-called colour Doppler echocardiography (or Doppler colour flow imaging), which is a standard means to investigate congenital heart defects, adds to the diagnostic power of echocardiography. It leads to an improved visualisation of the blood flow in the heart and vessels and helps to identify potential leaks or other malformations in the heart valves. It uses different colours to represent the speeds, directions or potential turbulences of the blood. For example, red is assigned to blood flowing towards the transducer, whereas blue is assigned to blood flowing away from the transducer. Varying shades of these colours represent the speed (velocity) of the blood flow: the brighter the colour, the higher the velocity.

Additionally, an audio signal is produced so that the doctor can hear the blood flowing through the vessels and the opening and closing of the valves. The valves’ function and heart pressure can be established through the visualisation of this audio signal on a graph.

What happens during an echocardiographic examination?

Because this technique uses inaudible sound waves and no radiation, it is completely painless and risk free.

The most common examination is the transthoracic echocardiography (TTE). During this non-invasive procedure, recordings are obtained from through the patient’s chest. The doctor moves a probe (transducer), which has a special gel on the top to enable the ultrasound signal to penetrate the chest wall, over specific regions on the patient’s chest, neck and abdomen, with slight pressure. This probe sends high-frequency sound waves into the patient’s chest, where they rebound from the walls and valves of the heart. Their echo bounces back to the probe, where it is received and interpreted. The speed and intensity of the reflected sound waves provide information about the heart tissue. This information is then transformed into a two-dimensional grey-scale image of the heart that can be viewed on the monitor. The heart’s movements are displayed in real time. By slightly turning the transducer to different angles, the doctor is able to obtain different views of the heart.

Echocardiography is usually done in combination with an ECG, and both procedures are undertaken simultaneously. Its results are displayed at the bottom of the monitor at the same time that the echocardiogram is recorded, so that the electrical activity of the heart can be assigned to specific heart movements.

An echocardiographic examination usually takes between 30 and 60 minutes. You can ask your doctor to turn the monitor toward you if you are interested in looking at your own heart in action. You probably need some explanations by your doctor to recognise the different parts of your heart. The images obtained during the procedure can be recorded and saved in the patient’s file to be reviewed later or compared with future recordings.

Because a wide range of mild to severe congenital heart defects exist, and because each defect has its individual disease pattern, a specially trained doctor who has experience in this field needs to undertake the echocardiography. This doctor might need to consult other experts, since some disorders are very rare and complex.
Because of the excellent quality of its images, the ECG is in many cases better than cardiac catheterisation; thus this invasive and much more complex and time consuming procedure is often unnecessary.

Special forms of echocardiography

Contrast echocardiography

Sometimes, the images obtained by standard echocardiography are not sufficient. In this case, the doctor will inject the patient with a contrast agent—a special solution that allows the doctor to see the inside of the heart more clearly. The solution is injected into the patient’s vein through an intravenous line.

Normally, this goes without any complications because the contrast solution that is used is very safe. However, in rare cases, some mild side-effects or adverse reactions to the contrast media can occur. Those most frequently reported include:

• Mild and transient local discomfort at the injection site
• Heat sensation
• Headache
• Backache
• Dizziness
• Nausea
• Palpitations—unpleasant sensation of an abnormally rapid, strong or irregular heart beat
• Urticaria (also known as hives or nettle rash)—a skin condition that is mainly caused by an allergic reaction. It is characterised by itchy red swelling of varying size that can appear on any part of the skin and that usually last a few hours before disappearing completely.
• Hypotension—abnormally low blood pressure that can occur because of vasodilatation (widening of the blood vessels). Very rarely, it can progress to hypotensive shock and anaphylactic reactions.

Every contrast agent has its own profile of potential side-effects. Your doctor will discuss with you whether or why a contrast echocardiography is needed and inform you about potential side-effects that you might experience.

Contrast echocardiography is often done in combination with stress echocardiography.

Transoesophageal echocardiography (TOE)

Sometimes, the usual transthoracic echocardiogram does not provide all the images that the examining doctor needs, possibly because the chest wall and lung tissue do not transmit the sound waves very well so they are considerably attenuated.

In this case, the doctor might recommend a transoesophageal echocardiogram. By contrast with the regular transthoracic echocardiogram, this refined examination is a minimally invasive procedure, during which images are taken from inside the chest. For this procedure, a special tube with a miniature ultrasound transducer on its end is gently and slowly passed down the patient’s throat and into the oesophagus until it is situated right behind the heart. From this position, very clear and high-quality moving images of the heart and its structures can be obtained since hardly any attenuating tissue is in the way of the emitted sound waves. Thus, interference can be kept to a minimum.

Transoesophageal echocardiography is often used for the assessment of congenital heart defects. Serious heart conditions in particular can be accurately assessed by this method. It is the best method to investigate the heart valves and look for valvular disorders or abnormal changes (such as infective endocarditis). Furthermore, it is also the method of choice for checking the aorta for any dissection or other complications.

Similar to transthoracic echocardiography, transoesophageal echocardiography is always combined with a simultaneous ECG recording. Blood pressure is also monitored during the examination.

The recording of a transoesophageal echocardiogram usually takes about 20 minutes. If the patient wishes, he or she can be sedated during the procedure. Depending on the individual case, possible options range from mild sedation to general anaesthesia.

Because transoesophageal echocardiography is a minimally invasive procedure, it is not quite as safe and unproblematic as the non-invasive methods. Thus, some things have to be considered before this examination is done. The patient should not eat for at least 4–6 hours before the test. Other contraindications ruling out the possibility of transoesophageal echocardiography include:

• Patients having an unstable cervical spine (ie, the neck section of your spine)
• Any history of previous oesophageal surgery
• Any form of oesophageal disease such as oesophagitis
• Presence of upper gastrointestinal bleeding or recent upper gastrointestinal surgery. The upper gastrointestinal area is very sensitive and should not be unnecessarily touched or irritated in case damage occurs
• Non-compliant patients or patients unable to cooperate (eg, small children without sedation, mentally retarded patients)

Should you require transoesophageal echocardiography, your doctor will discuss the procedure with you. Tell your doctor if one or more of these contraindications apply to you, or if you are uncertain, since they greatly increase the risk of adverse events.

The findings of the examination are correlated with those of the transthoracic echocardiography. Despite its obvious benefit, transoesophageal echocardiography is to be viewed as a complementary procedure to transthoracic echocardiography. Since both methods have their own assets and drawbacks, neither can be regarded as being better than the other.

Stress echocardiography

Some conditions are only detectable under physical strain—ie, when the heart is forced to beat harder or faster. Stress echocardiography is used to look for such defects, since it can show how well the heart is able to deal with increased activity. In this procedure, an echocardiogram recorded at rest is compared with one taken straight after physical exertion.

The recording procedures for this test are the same as those in a regular echocardiographic examination are. After an echocardiogram has been taken of the heart at rest, the patient will be asked to exercise on a treadmill or on a stationary bike. If a patient is not physically able to exercise because of a medical condition, he or she can be given a drug called dobutamin. This drug increases the heart rate, thus simulating stress.

After the heart rate has been increased by physical activity or medication, the patient has to lie down immediately so that a second set of images can be recorded while the heart is still beating harder and faster. During this second examination, the doctor is able to observe the heart under conditions in which it needs more blood and oxygen to function. Additionally, the doctor can observe the recovery process of the heart. Areas that do not receive enough blood, and therefore oxygen, can be clearly identified.

As in the other tests described above, the heart’s electrical activity (with an ECG) and blood pressure are monitored during a stress echocardiography. The findings of the tests are then compared.

Recording a stress echocardiogram usually takes about 1–2 hours. You should not eat or drink for at least 3 hours before the test, since it might affect your exercise capacity. Because normal ultrasound is used, the procedure carries low risk for most conditions. Adverse events that might occur are mainly typical signs of overexertion and related to the physical exercise that is done during the test. These side-effects include chest pain or chest tightness, pain in the left arm or shoulder, and shortness of breath or dizziness. In rare cases, some of these symptoms might indicate a heart attack. If you experience any such feelings, immediately tell your doctor who will  be able to asses the pain you are having by studying your heart tracing. If necessary, the test will terminated and further measures can be taken. In some disorders, such as aortic aneurysm, severe valve stenosis, carditis or severe arrhythmias, a stress echocardiogram should not be done since it can be dangerous to challenge the heart. If you are unsure, talk to your doctor about your individual case.

Stress echocardiography is most commonly used for the detection of coronary artery disease—an acquired heart disease that mainly affects elderly people—because it can reliably identify narrowed or blocked vessels. However, it is also important for the diagnosis and observation of congenital heart defects, since these are often associated with reduced or hampered blood flow and restricted oxygen supply of different areas. Furthermore, a comparison of the examination results from different times will allow the progress of an already known congenital heart defect to be monitored.

Recent developments in echocardiography—tissue Doppler echocardiography and three-dimensional echocardiography

To date, the standard method that is routinely used for the diagnosis and assessment of congenital heart defects is two-dimensional echocardiography. This technique has proven to be an invaluable diagnostic method providing high-quality images of the heart and its vessels. Nowadays, the diagnosis and treatment of congenital heart defects are unthinkable without echocardiography.

The technique has become more refined and further developed over recent years. One of the most substantial new developments is tissue Doppler echocardiography. Tissue Doppler imaging can quantify myocardial velocities and is therefore able to measure regional function of different parts of the heart muscle. Thus, myocardial function can be described very accurately, and this method can add useful information to a standard echocardiographic exam, especially in patients with ischaemia or those with congenital heart defects. Recent studies have shown that some conditions can be detected earlier with tissue Doppler echocardiography than with standard echocardiography.

Another interesting technique is three-dimensional echocardiography. This new technology allows for a real-time three-dimensional visualisation of the heart, thus providing true-to-life images. Over the past few years, studies have been confirming the value of this new method and have especially praised its use for the detection and assessment of congenital heart defects.

Three-dimensional echocardiography is without doubt a highly promising imaging method. However, this technique is still far from being well established, and its value for the detection of congenital heart defects still needs to be confirmed. For example, the resolution of the three-dimensional images cannot yet be compared with that of conventional two-dimensional echocardiography, since it is not sufficiently high. Moreover, no standards have yet been established for the recording and assessment of the three-dimensional images. These standards have to be set to assure unambiguous and comparable results. Equally, reference values for both research and care have to be defined.

How three-dimensional echocardiography will develop further remains to be seen. If expectations are met, this new technique will substantially add to the diagnostic methods used in the field of congenital heart defects.