In patients with a structural heart disease, in particular, postinfarct patients, ventricular tachycardias (VT) are mostly related to the presence of a ventricular scar in which surviving myocytes are surrounded by a certain amount of fibrous tissue, which favors slow conduction. Because slow conduction is one of the electrophysiological characteristics of such scars, it explains why macro-reentry is the underlying mechanisms of most scar-related VTs. The so-called protected isthmus of the reentrant circuit is the critical element for the maintenance of these VTs and, therefore, the target for ablation. Identifying such a protected isthmus may be performed by a conventional electrophysiological approach either based on VT entrainment techniques or by an electroanatomical activation mapping during VT using a 3-dimensional (3D) mapping system. In greater than 90 of postinfarct mappable VTs, complete activation maps during VT demonstrate an endocardial macro-reentrant circuit, usually with 2 loops rotating around a protected isthmus bounded by 2 approximately parallel conduction barriers, which consist of either a line of double potentials, a scar area, or the mitral annulus.
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