Electrocardiography Health Dictionary

ARRHYTHMIA is a variation in the normal rhythm of the heartbeat. Management of the condition requires accurate diagnosis of the type, and ELECTROCARDIOGRAPHY is vital in this process (see HEART, DISEASES OF). Drug treatment is usually part of the management, and antiarrhythmic drugs can be divided clinically into those that act on supraventricular arrhythmias, those that act on both supraventricular and ventricular arrythmias, and those that act on ventricular arrythmias. Respective examples are VERAPAMIL, DISOPYRAMIDE and LIDOCAINE. This large group of drugs can also be classi?ed according to their effects on the electrical reactions of active myocardial cells. The many drugs available are described in the British National Formulary.... antiarrhythmic drugs

A record of the variations in electric potential which occur in the HEART as it contracts and relaxes. Any muscle in use produces an electric current, but when an individual is at rest, the main muscular current in the body is that produced by the heart. This can be recorded by connecting the outside of the body by electrodes with an instrument known as an electrocardiograph. The patient is connected to the electrocardiograph by leads from either the arms and legs or di?erent points on the chest. The normal electrocardiogram of each heartbeat shows one wave corresponding to the activity of the atria and four waves corresponding to the phases of each ventricular beat. Various readily recognisable changes are seen in cases in which the heart is acting in an abnormal manner, or in which one or other side of the heart is enlarged. This record therefore forms a useful aid in many cases of heart disease (see HEART, DISEASES OF). The main applications of the electrocardiogram are in the diagnosis of myocardial infarction and of cardiac ARRHYTHMIA.

Electrocardiography

A method of recording the electrical activity of the heart muscles. Electrodes from a recording machine (electrocardiograph) are placed on the skin of the chest wall, arms and legs. The record of the electrical changes is called an ECG (electrocardiogram). The number of electrodes used depends on the complexity of the heart disorder being monitored. The procedure can be done in hospital, doctors’ surgeries and the patient’s home, and should not cause any discomfort.

In certain circumstances – for example, where a person has had bouts of chest pain – an exercise ECG may be performed under medical supervision. The patient walks on a treadmill while the ECG is recorded continuously.... electrocardiogram (ecg)

A sleep apnoea is conventionally de?ned as the cessation of breathing for ten seconds or more. Apnoeas, which affect around 5 per cent of adults and are markedly more common in men, may occur as frequently as 400 times per night. They can be due to a failure of the physiological drive to breathe (central sleep apnoeas) but much more often are due to a transient obstruction of the airway between the level of the soft PALATE and the LARYNX (obstructive sleep apnoeas) when the airway dilator muscles over-relax. Any factor such as alcohol or sedative drugs that accentuates this, or that makes the airway narrower (such as obesity or large TONSILS), will tend to cause sleep apnoeas.

Vigorous respiratory movements are made to overcome the obstruction during each apnoea. These are associated with snoring and snorting noises. The apnoea ends with a mini-arousal from sleep. As a result, sleep becomes fragmented and sleep deprivation, manifested as sleepiness during the day, is common. This may result in accidents – for instance, at work or while driving – and sleep apnoea is also linked with an increased risk of STROKE, heart attacks and HYPERTENSION.

The diagnosis of sleep apnoea has recently been facilitated by linking specially designed software with ELECTROCARDIOGRAPHY performed during sleep, with minimal disturbance of the subject.

Initial treatment is directed at correcting the cause (e.g. obesity), but if the apnoeas persist or are severe a nasal mask and pump which introduces air under slight pressure into the upper airway (continuous positive airway pressure, CPAP) is almost invariably e?ective.... sleep apnoeas

In ambulatory

(electrocardiography), a wearable device called a Holter monitor is used to record the electrical activity of the heart by means of electrodes attached to the chest. The monitor is usually worn for 24 hours or longer and detects intermittent arrhythmias (abnormal heart rates and rhythms). The wearer can press a button on the monitor to mark the recording whenever symptoms occur. The recording can later be analysed to see if the periods of arrhythmia coincide with the symptoms.... ambulatory ecg

The abbreviation for electrocardiography, a method of recording the electrical activity of the heart muscle.An is useful for diagnosing heart disorders, many of which produce deviations from normal electrical patterns.

Electrodes connected to a recording machine are placed on the chest, wrists, and ankles.

The machine displays the electrical activity of the heart on a screen or as a printed trace.... ecg

The use of electrocardiography (see ECG) to assess the function of the heart when it is put under the stress of exercise.

Exercise is usually carried out when coronary artery disease is suspected.

It involves raising the heart rate by exercising, usually on a treadmill with an adjustable gradient or an exercise bicycle, and recording the heart’s electrical activity for analysis.... exercise ecg

A wearable device used in ambulatory electrocardiography (ECG) to record the heart’s electrical activity

continuously for 24 hours or longer.

The monitor records by means of electrodes attached to the chest and allows the detection of intermittent arrhythmias.... holter monitor

(ECG) n. a tracing of the electrical activity of the heart recorded by *electrocardiography (see illustration). It aids in the diagnosis of heart disease, which may produce characteristic changes in the ECG. See QRS complex; Q–T interval; S–T segment.... electrocardiogram

n. a cathode-ray tube designed to display electronically a wave form corresponding to the electrical data fed into it. Oscilloscopes are used to provide a continuous record of many different measurements, such as the activity of the heart and brain. See electrocardiography; electroencephalography.... oscilloscope

a familial condition affecting the heart, characterized by unexplained thickening (hypertrophy) of the wall of the left ventricle. In many cases this is an incidental finding and patients have a good outcome. However, more severely affected patients may suffer chest pain, tachyarrhythmia (see arrhythmia), heart failure, and sudden death. In some cases there is focal thickening of muscle around the left ventricular outflow tract (asymmetric septal hypertrophy, ASH), and this can result in restriction of blood flow to the body (hypertrophic obstructive cardiomyopathy, HOCM). The diagnosis is made by electrocardiography, echocardiography, and cardiac *magnetic resonance imaging. Usually drug treatment is sufficient to control symptoms, but some patients require cardiac *catheterization or surgical treatment. Those deemed at highest risk of sudden death may require an *implantable cardiovertor defibrillator.... hypertrophic cardiomyopathy

n. see levodopa.

lead1 n. a soft bluish-grey metallic element that forms several poisonous compounds. Acute lead poisoning, which may follow inhalation of lead fumes or dust, causes abdominal pains, vomiting, and diarrhoea, with paralysis and convulsions and sometimes *encephalitis. In chronic poisoning a characteristic bluish marking of the gums (‘lead line’) is seen and the peripheral nerves are affected; there is also anaemia. Treatment is with *edetate. The use of lead in paints is now strictly controlled. Symbol: Pb.

lead2 n. 1. a portion of an electrocardiographic record that is obtained from a single electrode or a combination of electrodes placed on a particular part of the body (see electrocardiogram; electrocardiography). In the conventional ECG, 12 leads are recorded. Each lead represents the electrical activity of the heart as ‘viewed’ from a different position on the body surface and may help to localize myocardial damage. 2. a flexible steerable insulated wire introduced into the heart under X-ray control to allow electrical stimulation of the heart for the purpose of pacing (see pacemaker).... l-dopa

(in *electrocardiography) the superimposition of an R wave (ventricular *depolarization) on the T wave (ventricular *repolarization) of the preceding heartbeat. It may trigger ventricular fibrillation. See QRS complex; Q–T interval; S–T segment.... r on t phenomenon

an investigation to seek evidence of cardiac *ischaemia. The heart is stressed by exercise or by the administration of an intravenous drug that increases heart rate (i.e. mimicked exercise). Ischaemia may then be detected by electrocardiography (stress ECG or exercise ECG), *echocardiography (showing the development of impaired function in areas of heart muscle that are ischaemic), *myocardial perfusion scan, or cardiac MRI.... stress test