Most ventricular tachyarrhythmias result from re-entrant phenomena. The normal progress of electrical impulses may be obstructed by an area of abnormal
(commonly ischemic) myocardium exhibiting unidirectional block (Binah a.n..d, R.os.e..n 1992). The impulse travels round this zone and returns through an area of slow conduction, at which time repolarization has occurred and a sustained re-entrant rhythm can occur. If a single circuit with ordered re-entry is established, ventricular tachycardia results; if multiple circuits (random re-entry) are involved, ventricular fibrillation occurs ( Fig.;.. . . .2).
Fig. 2 The diagram shows a Purkinje fiber bundle dividing into two branches which are attached to ventricular muscle. The area at 1 (green shading) shows a zone of slow conduction and unidirectional block. The wave of depolarization travels normally down fiber 2 but cannot traverse fiber 1. The wave is conducted back up fiber 1 in a retrograde fashion, and may cause a circular or re-entrant rhythm if the proximal part of the loop is not refractory. (Reproduced from Bina.d §D.d R2se.D (1992.) )
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