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In previous articles in this series we looked at the various types of medical equipment and then covered the items that you will find in every physician’s bag or office. Then we started looking at the various types of medical monitors that you are likely to encounter. The older analog devices have been almost completely replaced by digital ones. The development of digital signal processing (DSP) technology caused a rapid evolution of multiparameter medical monitors. They are more accurate, require less maintenance and can provide more sophisticated readouts than the original analog instruments.
In this article we’ll take a closer look at a medical monitoring device that just about everyone will have encountered – the electrocardiograph (ECG) monitor. The display or printout that the machine produces is called an electrocardiogram. Most doctor’s offices have an ECG, but its more complex partner, the echocardiograph, is most often encountered in hospitals. It is used to produce two or three-dimensional images of the heart. Both types of monitor have become essential to diagnosing and monitoring patients, particularly those with heart conditions.
Electrocardiograph (ECG)
Electrical impulses in the heart originate in the sinoatrial node and travel to the heart muscle. The impulses stimulate the heart’s muscle fibres to contract and drive blood out of the heart, a process known as systole. The electrical waves can be measured at electrodes placed at specific points on the skin. Electrodes on different sides of the heart measure the activity of different parts of the heart muscle.
An ECG displays the voltage between pairs of these electrodes. They measure muscle activity from different directions, allowing the ECG to display the overall rhythm of the heart and highlight weaknesses in different parts of the heart muscle. It is the best way to measure and diagnose abnormal rhythms of the heart, particularly abnormal rhythms caused by:
- Damage to the conductive tissue that carries electrical signals.
- Electrolyte imbalances (which can lead to heart, muscle and neurological problems).
- Damage to the heart muscle.
The images below show a typical ECG machine, the electrodes attached to a patient, and the output (the electrocardiogram) from the ECG monitor. Large clinics often have a specialist who scrutinizes and interprets the output from the monitor, highlighting anomalies for the physician’s benefit.
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Not all areas of the heart are covered by the ECG. It cannot reliably measure the pumping ability of the heart, for which nuclear medicine and ultrasound-based (echocardiography) tests are used. In nuclear medicine imaging, radiopharmaceuticals are taken internally, generally intravenously or orally. External detectors (gamma ray cameras) capture and form images from the radiation emitted by the radiopharmaceuticals. We’ll return to this technique later in the series.
Echocardiograph
An echocardigraph uses ultrasound techniques to image two-dimensional slices of the heart. The latest ultrasound systems can display 3D real-time images. Ultrasonic (ultra high frequency) sound waves are directed at the heart and the reflections are detected and interpreted by a computer program in much the same way that SONAR can detect and produce images of objects that are underwater. Similar machines are used to monitor the development of the fetus during pregnancy and to examine other internal organs, such as the liver, kidneys and spleen. Echocardiography is noninvasive and it has no known risks or side effects. A special transducer is placed on the chest or lowered into the oesophagus. Several transducers, placed around the abdomen, are used when accurate 3D images are required.
Echocardiography is one of the most widely used diagnostic tests for heart disease. It can show the size and shape of the heart, its pumping capacity and the location and extent of any damage to its tissues. It is especially useful for assessing diseases of the heart valves. By assessing the motion of the heart wall, echocardiography can help detect the presence and assess the severity of coronary artery disease, as well as help determine whether any chest pain is related to heart disease. Echocardiography can also help detect hypertrophic cardiomyopathy, a condition where there is abnormal thickening of the heart muscles. It has often been linked to the death of young athletes.
An echocardiograph can also produce accurate assessment of the velocity of blood and cardiac tissue at any point using continuous wave or pulsed 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, and calculation of the effectiveness and regularity of the heart.
The images below show a typical echocardiograph machine, transducers/sensors placed on a patient’s chest and an electrocardiogram. The image is displayed directly on a computer display. It is usually possible to record the whole session and to produce printouts of any areas of interest. More complex computer programs will find and highlight areas that may indicate an abnormality.
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Things To Come
In the next article in this series we’ll look at the, generally behind the scenes, medical laboratory equipment that automates or helps analyze blood, cerebrospinal fluid, bodily waste products and gene information. Many physicians routinely call for a battery of such tests prior to seeing a patient for routine examinations. They can also ask for more complex laboratory tests if they are trying to diagnose a problem. Unlike the monitoring equipment we’ve described so far, many of these tests can take many days to produce accurate results, or the samples may have to be sent to a specialized laboratory for analysis.
Related Articles: Part 1 – Basics | Part 2 – Starter Kit A | Part 3 – Starter Kit B | Part 4 – Starter Kit C. | Part 5 – Medical Monitors
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