A circling excitation represents a basal form of the disturbance of the excitation line at the heart. While a normal heart action comes each excitation to activation of the ventricle musculature to expiring, since it then only more by is, thus heavily or not at all excitable fabric surrounded. Also within the Purkinje fibers the excitation can spread in both directions and expires immediately, if two impulses meet. Now for example if an anatomical or functional obstacle is present itself in a bundle of a up-branching Purkinje fiber, before the transition is here completely blocked, a dangerous provisional stage can occur: a unidirectional block.

The damaged area slowed down thereby depresses an excitation, to it sometime opposite the following thus heavily or not at all excitable, is. This excitation can go through the damaged area now however in the opposite direction, since it reaches it at one time, where it is possibly no more Now behind this antidromen (in the opposite direction running) excitation if the staying is shorter than the circular path, the excitation is not no more deleted within the circle and can go through it permanently. One speaks of a circling excitation.

The danger thereby exists in a reentry ("„reentry "“) of the excitation wave into the surrounding fabric, if these no more is. An excitation can be formed, which converses as it were. This represents the cause more heavily, with the danger of flickering accompanying tachycardiac rhythm disturbances.

A condition

As a condition is considered after the equation

 =  * speed, 

whereby the is proportionally the wavelength Lamda, the proportionally the potential duration, the transmission rate dependent on the number of sodium channels that the circular path must be longer than the of the potentially circling excitation due to it. This is favoured with degraded and decreased transmission rate.

for Reentry phenomena

• particularly the area around the AV-range
• accessory AV-Leitungsbahn (Wolff Parkinson White syndrome)
• acutely ischemic zones
• Edge zones of all Infarkte

Effect of antiarrhythmics on circling excitation

Class Ia antiarrhythmics:

• Extension of the absolute
• stronger reduction of the transmission rate

By increase of the probability of a decreased wavelength Lamda with preventive continuous gift it comes to the increased probability of small Reentrykreise (upto max. four myocardium cells extent) - proarrhytmisch.

Class Ib antiarrhythmics:

• hardly change to reduction of the absolute
• weak reduction of the transmission rate

Preferential decrease of the transmission rate in partially depolarisierten fabrics opposite healthy fabric (prototype Lidocain). A circling excitation can be broken through in such a way in the place unidirectional block by its transfer into a bi-directional block, without retarding at the healthy fabric the excitation line considerably - small proarrhytmisch.

Class IC antiarrhythmics:

• hardly extension of the absolute
• strong reduction of the transmission rate

By strong increase of the probability of a decreased wavelength Lamda with preventive continuous gift is increased the probability of small Reentrykreise at the strongest - strongly proarrhytmisch (see CAST study - Cardiac Arrhythmia Suppression Trial).

Class iii-antiarrhythmics:

• clear extension of the absolute
• insignificant change of the transmission rate

By increased it comes inevitably to larger wavelengths. Lambda can become more largely, even more largely than finally the diameter of the heart - small proarrythmisch.

Literature

• Hans Peter shoemaker, Hans Joachim Trappe: Electrocardiogram course for Isabel. Thieme, Stuttgart 2005, ISBN 3131272848
• Klaus Aktories, Ulrich Franz Hofmann, Wolfgang Forth: General and special pharmacology and toxicology. Urban & Fischer with Elsevier, November 2004, ISBN 3437425218

See also

Electrocardiogram

Antiarrhythmic

Articles in category "Circling excitation"

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