An unusually fast but regular beating of the HEART occurring for periods that may last several hours or days. In most people with this abnormality the heart rate is between 140 and 180 beats a minute; rarely, the rate may rise as high as 250–300 beats. The condition occurs when abnormal electrical impulses that arise in the upper chambers (atria) of the heart override the normal control centre – the sinoatrial node – for the heartbeat. Symptoms usually include breathlessness, palpitations, pain in the chest and fainting. An ELECTROCARDIOGRAM (ECG) is taken to help make the diagnosis. An acute episode can sometimes be stopped by VALSAVA’S MANOEUVRE or by drinking cold water. Anti-arrhythmic drugs (see ARRHYTHMIA) such as adenosine and digoxin are used to treat recurrent attacks. Occasionally, a severe attack may need to be treated with an electric shock to the heart: this is known as DEFIBRILLATION.... supraventricular tachycardia
A regular heart rate of 100 or more beats a minute, caused by increased electrical activity in the SINOATRIAL NODE (see also HEART). This level of tachycardia is normal during and just after exercise, and may also be caused by stress or anxiety. If tachycardia persists when the person is resting, it may be due to underlying disease such as thyrotoxicosis (see under THYROID GLAND, DISEASES OF) and investigation is advisable.... sinus tachycardia
A serious cardiac arrhythmia in which each heartbeat is initiated from electrical activity in the ventricles rather than from the sinoatrial node in the right atrium.
It is caused by an abnormally fast heart-rate due to serious heart disease, such as myocardial infarction or cardiomyopathy.
It may last for a few seconds or for several days.
Diagnosis is confirmed by ECG.
Emergency treatment is with defibrillation and an antiarrhythmic drug.... ventricular tachycardia
(AVNRT) *re-entry tachycardia arising from the presence of an abnormal electrical connection between atria and ventricles situated within the *atrioventricular node.... atrioventricular nodal re-entry tachycardia
(AVRT) *re-entry tachycardia arising from the presence of an abnormal electrical connection between atria and ventricles situated outside the *atrioventricular node. See accessory pathway.... atrioventricular reciprocating tachycardia
a rapid heart rate due to a self-sustaining circulation of electrical impulses from the atria to the ventricles and back again. This re-entry circuit requires the presence of an abnormal second electrical conduction pathway in addition to the usual atrioventricular nodal connection route. The abnormal pathway may be located within the *atrioventricular node (causing *atrioventricular nodal re-entry tachycardia) or it may be an *accessory pathway situated outside the atrioventricular node (causing *atrioventricular reciprocating tachycardia). Medication is often effective and *radiofrequency ablation is usually curative.... re-entry tachycardia
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