(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.
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
(AV bundle, bundle of His) a bundle of modified heart muscle fibres (Purkinje fibres) passing from the *atrioventricular node forward to the septum between the ventricles, where it divides into right and left bundles, one for each ventricle. The fibres transmit contraction waves from the atria, via the AV node, to the ventricles.... atrioventricular bundle
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