[Identification of deep septal ventricular tachycardia substrates from epicardial breakthrough characteristics]

This study aimed to elucidate the relationship between the epicardial activation pattern and the site of origin of the ventricular tachycardia (VT) occurring from the interventricular septum, and to find epicardial breakthrough characteristics identifying VT substrates. Seven patients undergoing intraoperative mapping including right ventricular endocardial mapping were studied. Thirteen septal VTs, which were defined as VTs in which both right and left ventricular endocardial breakthroughs were on the septal aspect, were induced. The VT site of origin was identified from the site and timing of right and left septal endocardial breakthroughs. All VTs were classified into three groups according to the site of epicardial breakthrough: type A, epicardial breakthrough in the anterior interventricular area; type F, epicardial breakthrough in the right ventricular free wall; type P, epicardial breakthrough in the posterior interventricular area. All type F VTs had a right ventricular endocardial breakthrough in the anterior septum and preceded the left ventricular endocardial breakthrough, thereby indicating right anterior septal origin. In the types A and P, both the right and left endocardial breakthroughs were localized in consistent (anterior and posterior, respectively) halves of the septum, but their relative timing was inconstant. This result suggests that epicardial mapping, and even noninvasive methods like body surface mapping, can identify the site of origin of the septal VTs, especially when the epicardial breakthrough occurs in the right ventricular free wall.