A B C D E F G H I J K L M N O P R S T U V W

ECHOCARDIOGRAPHY-NONINVASIVE HEART INVESTIGATIONS

Electrocardiogram (ECG)

The heart has an electrical system, rather like that of a car engine. It makes sure that the four chambers of the heart beat in a regular and synchronised way. Each heartbeat starts with a burst of electric current. This begins in the atria (the smaller and upper chambers of the heart) and spreads to the muscles in the ventricles (the larger and stronger chambers) through the electrical conducting system. The ECG is a recording of this electrical activity taken whilst you are resting. It can show up many different types of problem. These might be in the conducting system or in the heart muscle itself. It is very helpful for picking up a heart attack. It also shows up lesser degrees of damage where there is not enough blood getting to the heart muscle. It is also good for picking up problems of heart rhythm. The routine is to attach self-adhesive pads to the skin of the arms, legs and chest. Most equipment can do the recording in less than a minute.

Exercise (Stress) test

The electrocardiogram recorded while you are at rest is a simple test and may not provide enough information for a definite diagnosis. Sometimes it makes more sense to see how the heart behaves when the heart is challenged. This is most easily done using exercise. Wires are attached, as above. The equipment, however, is more complex. Your ECG is recorded whilst you walk on a treadmill or pedal an exercise bicycle. The exercise starts slowly. On a treadmill, the speed and slope are increased every 3 minutes, so that gradually increasing amounts of stress are applied. The blood pressure, the rhythm of the heart and your symptoms are also recorded during and after the exercise. The ECG may show an abnormality which was not present when you were at rest. This is often the case with angina due to coronary heart disease (see leaflet 9.1). The test is also used to measure the heart's reserve strength after having had a heart attack.

Ambulatory “Holter” Electrocardiogram

This type of recording may be useful for picking up the cause of some types of "palpitation", a dizzy turn or a blackout. Such a symptom may be produced when there is a only a very brief change of rhythm. Some very fleeting changes of rhythm can also occur without you being aware of it. They may not be picked up during the brief recording of an ordinary ECG, taken while at rest. The Holter recording is made on a small recorder (like a Walkman) over a 24 or 48-hour period. Recording wires attached to the skin of your chest are connected to the recorder, which you carry on a belt or a shoulder strap. The recording continues both during usual daytime activity and at night whilst asleep. When you return the recorder, the tracing is then analysed by a computer. Your doctor then has a clear picture of any changes which occurred during that 24 or 48-hour period. You may be asked to make a note of any symptom you had during that 24 hours: the doctor can then link it to any change in the ECG.

Event and Loop ECG Recordings

When a palpitation, dizzy turn or blackout does not occur very often (perhaps once a week or so), small solid-state recorders can be used. These can either be worn like wrist watches or carried in the pocket. You can also place them on the skin when you have an attack, and switch them on with a button. Recordings can be relayed to a hospital over a telephone line, and the memory then wiped dean with a second button to allow more recordings to be done. This is called an event ECG. If the attacks are too brief to allow you to make the recording, a loop ECG can be recorded. These are similar recorders but they can be programmed to record for several days (as long as the batteries last). They only retain the last 10-20 minutes recording in the memory. After an attack, this can be ‘frozen’ in the memory by pressing a button.

Echocardiograms

Echocardiography uses very high frequency sound to produce pictures of the heart. These ultrasound waves cannot be heard or felt. The ultrasound impulse is generated by an instrument called a transducer, which is placed on the chest. Good contact with the skin is ensured by using a jelly. Ultrasound impulses are reflected back from the different parts of the heart, like echoes The transducer picks up the echoes and they are then converted into electrical impulses. These impulses are changed into an image, similar to a radar picture, which is displayed on a television screen. The pictures can be recorded on video tapes and photographed, so that a permanent records can be kept. A similar method, called Doppler, uses a beam of ultrasound impulses in a slightly different way. These are directed towards the blood which flows through the heart. As the blood flows, the impulses are reflected back. The motion of the blood alters the frequency of the ultrasound. The equipment allows one to measure the speed and direction of blood flow. Narrowed valves will tend to make the blood flow faster. Leaking valves can be seen because the blood flows in the wrong direction. The pictures can demonstrate these problems and can show how severe they are. Echocardiography is a good test when inborn heart defects are suspected. It can be used in adults and children. Holes in the heart may be seen, as well as the blood flowing though them. Narrowed and leaking valves can be seen as with adults. Sometimes the blood-vessels are wrongly connected to the heart and this also may be picked up. Even the heart of a baby in the womb can be imaged. This allows a diagnosis to be made before birth. There are a few problems though. Good ultrasound scans can be difficult to produce in some people. Under sedation, an ultrasound probe can be passed down the gullet (oesophagus). This provides more accurate close-up pictures from the back of the heart. This is called trans-oesophageal echocardiography (TOE). Echocardiography is not very good at showing up the coronary arteries which supply the blood to the muscles of the heart. This is a shame because coronary artery disease is so common. Unfortunately most of the coronary arteries are too small to be examined by this technique. However, defective pumping of the heart caused by the blocked coronary arteries can be seen. Pumping abnormalities, not seen at rest, may also be shown up by doing exercise during echocardiography.

Heart Isotope Scans

These scans are done in nuclear medicine departments. Images of the heart and of the blood inside the heart can be made with very tiny amounts of radioactive isotopes. These are injected into the blood circulation through a vein in the arm. The radiation dose is no greater than with a chest x-ray. Myocardial perfusion scans use isotopes which are carried in the blood into the heart muscle. Here, they release "gamma rays" which can be photographed using a "gamma camera". Several views of the heart are required and each takes several minutes to record. If heart muscle is under-supplied with blood (for example due to narrowed or blocked coronary arteries), fewer gamma rays are released. This can be seen on the photograph. The pictures are processed by a computer, and are usually taken, during exercise or, if the patient cannot exercise very much, by "stressing" the heart with drugs. They are then repeated a few hours later, at rest. This test can be used as an alternative to the exercise ECG and useful for patient whose exercise capability is limited. MUGA scans show up the blood inside the heart, rather than the heart muscle itself. They are produced in a similar way to perfusion scans. They are good for finding out how well the heart is pumping. They can also show up abnormal blood flow as happens with holes-in-the-heart. Computers are also required to process the pictures.

Computerised Tomography (CT) Scanning

This is a computerised x-ray technique. It is widely used in medicine but has a limited use in cardiology. This is because several seconds are required to take a picture. Because the heart is moving the images may be blurred. Also some structures such as the coronary arteries are too small to be seen very well. Nevertheless, CT scans can be useful in some situations such as in (very rare) tumours involving the heart or disease of the pericardium.

Magnetic Resistance Imaging (MRI)

This technique uses a large electro-magnet to give pictures of the structure and function of the heart and of the blood flow. It is very useful for taking pictures of congenital heart abnormalities, especially when the abnormality is complex. It is also It is possible to image the larger coronary arteries but the pictures are not yet good enough to replace cardiac catheterisation. It can be used as an alternative to CT scanning in some situations. It is not used as a routine in adult heart conditions, but may prove more valuable in the future for providing information not available with other methods.