: A rapid heart rate, usually defined as greater than 100 beats per minute. The tachycardias include sinus tachycardia, paroxysmal atrial tachycardia (PAT), and ventricular tachycardia. Sinus tachycardia is due to rapid firing of a normal structure called the sinoatrial (sinus) node which is the natural pacemaker of the heart. Sinus tachycardia occurs in response to exercise, exertion, excitement, pain, fever, excessive thyroid hormone, low blood oxygen (hypoxia), stimulant drugs (such as caffeine and amphetamines), etc. Paroxysmal atrial tachycardia (PAT) consists of bouts of rapid, regular heart beating originating in the atrium (upper chamber of the heart). Often due to abnormalities in the AV node "relay station" that lead to rapid firing of electrical impulses from the atrium which bypass the AV node under certain conditions. These conditions include alcohol excess, stress, caffeine, overactive thyroid or excessive thyroid hormone intake, and certain drugs. PAT is an example of an arrhythmia where the abnormality is in the electrical system of the heart, while the heart muscle and valves may be normal. Ventricular tachycardia is an abnormal heart rhythm that is rapid, regular and originates from an area of the ventricle, the lower chamber of the heart. Ventricular tachycardias are most commonly associated with heart attacks or scarring of the heart muscle from previous heart attacks and are life threatening.
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Rapid beating of the heart, conventionally applied to rates over 90 beats/min. SYN: polycardia, tachyrhythmia, tachysystole. [tachy- + G. kardia, heart]
- atrial t. paroxysmal t. originating in an ectopic focus in the atrium. SYN: auricular t..
- atrial chaotic t. multifocal origin of t. within the atrium; often confused with atrial fibrillation during physical examination. SYN: multifocal atrial t..
- atrioventricular junctional t. t. originating in the AV junction. SYN: AV junctional t., nodal t..
- auricular t. SYN: atrial t..
- AV junctional t. SYN: atrioventricular junctional t..
- bidirectional ventricular t. ventricular t. in which the QRS complexes in the electrocardiogram are alternately mainly positive and mainly negative; many such cases may represent ventricular t. with alternating forms of aberrant ventricular conduction.
- Coumel t. a persistent junctional reciprocating t. that usually uses a slowly conducting posteroseptal pathway for the retrograde journey.
- double t. the simultaneous t. of two ectopic pacemakers, e.g., atrial and junctional t..
- ectopic t. a t. originating in a focus other than the sinus node, e.g., atrial, AV junctional, or ventricular t..
- t. en salves short runs of paroxysmal t. of the Gallavardin type. Cf.:Gallavardin phenomenon. [Fr. t. in salvos]
- essential t. obsolete term for persistent rapid action of the heart due to no discoverable organic lesion.
- t. exophthalmica rapid heart action occurring as one of the symptoms of exophthalmic goiter.
- fetal t. a fetal heart rate of 160 or more beats/min.
- junctional t. supraventricular t. arising from the atrioventricular junction (formerly called nodal t.).
- multifocal atrial t. (MAT) SYN: atrial chaotic t..
- nodal t. SYN: atrioventricular junctional t..
- orthostatic t. increased heart rate on assuming the erect posture.
- paroxysmal t. recurrent attacks of t., usually with abrupt onset and often also abrupt termination, originating from an ectopic focus which may be atrial, AV junctional, or ventricular.
- reflex t. increased heart rate in response to some stimulus conveyed through the cardiac nerves.
- sinus t. t. originating in the sinus node.
- supraventricular t. rapid heart rate due to a pacemaker anywhere above the ventricular level, i.e., sinus node, atrium, atrioventricular junction. The QRS complexes are always narrow unless there is rate-related aberrancy or preexisting intraventricular conduction delay.
- ventricular t. paroxysmal t. originating in an ectopic focus in the ventricle. SEE ALSO: torsade de pointes.

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tachy·car·dia .tak-i-'kärd-ē-ə n relatively rapid heart action whether physiological (as after exercise) or pathological see JUNCTIONAL TACHYCARDIA, PAROXYSMAL TACHYCARDIA, SINUS TACHYCARDIA, VENTRICULAR TACHYCARDIA compare BRADYCARDIA

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an increase in the heart rate above normal. Sinus tachycardia may occur normally with exercise or excitement or it may be due to illness, such as fever. arrhythmia may also produce tachycardia (ectopic tachycardia). See ventricular tachycardia, supraventricular tachycardia.

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tachy·car·dia (tak″ĭ-kahrґde-ə) [tachy- + cardia] excessive rapidity in the action of the heart; the term is usually applied to a heart rate above 100 beats per minute in an adult and is often qualified by the locus of origin as well as by whether it is paroxysmal or nonparoxysmal.

Medical dictionary. 2011.

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