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Supraventricular tachycardia (SVT) is a cardiac arrhythmia arising from improper electrical activity of the heart. It is a type of tachycardia (rapid heart rhythm) originating at or above the atrioventricular node. It can be contrasted with the potentially more dangerous ventricular tachycardias—rapid rhythms that originate ''within'' the ventricular tissue. Although "SVT" can be due to any supraventricular cause, the term usually refers to a specific example, paroxysmal supraventricular tachycardia (PSVT), two common types being atrioventricular reciprocating tachycardia and AV nodal reentrant tachycardia. In the older population atrial fibrillation becomes a common type of supraventricular arrhythmias—though it is typically considered separately. In general, SVT is caused by one of two mechanisms: re-entry and automaticity. Re-entry (such as AV nodal reentrant tachycardia and atrioventricular reciprocating tachycardia) often presents with an almost immediate increase in heart rate. Someone experiencing this type of PSVT may feel the heart rate accelerate from 60 to 200 beats per minute or more. Typically, when it reverts to normal, this is also sudden. The main pumping chamber, the ventricle, is protected (to a certain extent) against excessively high rates arising from the supraventricular areas by a 'gating mechanism' at the atrioventricular node, which allows only a proportion of the fast impulses to pass through to the ventricles. In Wolff-Parkinson-White Syndrome, a 'bypass tract' avoids this node and its protection and the fast rate may be directly transmitted to the ventricles. This situation has characteristic findings on ECG. In 'automaticity' types of SVT (atrial tachycardia, junctional ectopic tachycardia), there is more typically a gradual increase and decrease in the heart rate. These are due to an area in the heart that generates its own electrical signal. ==Types== The following types of supraventricular tachycardias are more precisely classified by their specific site of origin. While each belongs to the broad classification of SVT, the specific term/diagnosis is preferred when possible: Sinoatrial origin: * Sinoatrial nodal reentrant tachycardia (SNRT) Atrial origin: *Ectopic (unifocal) atrial tachycardia (EAT) *Multifocal atrial tachycardia (MAT) *Atrial fibrillation with rapid ventricular response *Atrial flutter with rapid ventricular response :(Without rapid ventricular response, fibrillation and flutter are usually not classified as SVT) Atrioventricular origin (junctional tachycardia): *AV nodal reentrant tachycardia (AVNRT) or junctional reciprocating tachycardia (JRT) * *Permanent (or persistent) junctional reciprocating tachycardia (PJRT), a form of JRT that occurs predominantly in infants and children but can occasionally occur in adults *AV reciprocating tachycardia (AVRT) – visible or concealed (including Wolff-Parkinson-White syndrome) *Junctional ectopic tachycardia (JET) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Supraventricular tachycardia」の詳細全文を読む スポンサード リンク
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