br Discussion The site of the successful ablation was
Discussion The site of the successful ablation was the earliest site where a TSP was recorded during tachycardia. The TSP preceded each His bundle deflection by 15ms during tachycardia, but was inverted during atrial pacing. Moreover, the TSP–His deflection interval remained unchanged at different pacing RGDfK lengths, suggesting that the TSP was derived from the conducting system. In addition, both the RBB and LBB were activated in a proximal-to-distal direction during tachycardia. Activation of the HPS started at the distal portion of the His bundle; the His bundle was activated in a retrograde manner, whereas both the RBB and LBB were activated in an antegrade manner. Because the LCC where the TSP was recorded was not connected to either the His bundle or the LAF, the tissue conducting the TSP was presumed to be directly connected to the distal portion of the His bundle (Fig. 4A). The clinical tachycardia was associated with a narrow QRS configuration, since the activation pattern of the ventricle was the same as the junctional rhythm or atrial pacing rhythm. The HV shortening can be explained by the activation pattern of the HPS, with the timing of the antegrade conduction of the ventricular conduction system being offset by the retrograde conduction of the His bundle. We hypothesize that the source of the TSP could be a conducting tissue such as a Purkinje fiber, in the subaortic region. This hypothesis is supported by the findings of Kurosawa et al.  who reported that a “dead-end-tract” – a remnant of the AV non-branching conducting system – was observed beneath the aortic root. Under normal circumstances, this branch disappears at maturity; however, sex hormones may persist as a remnant of the conducting tissue extending from the distal portion of the His bundle. Two studies [6,7] have described this remnant tract as an “aortic ring.” If this remnant conducting tissue is present in the extended myocardium of the left coronary cusp, it could become an arrhythmogenic focus. Anatomically, at the level of the ASV, the myocardium of the LV comes in direct contact with the aorta, thus facilitating the ablation of ventricular arrhythmias in the ASV. A focal activation from this remnant of the subaortic conducting tissue could activate the distal portion of the His bundle, resulting in retrograde activation of the His bundle and antegrade activation of the ventricular conducting system (Fig. 4A). Some cases of focal Purkinje VT, a less common form of HPS-related VT, have been reported [2–4]. Focal Purkinje VT is considered to be due to abnormal automaticity or triggered activity in the damaged HPS, arising from both the LBB and RBB. RF catheter ablation is normally attempted at the earliest site during tachycardia; however if, the VT originates in a proximal portion of the conduction system, a bundle branch block or AV block may occur. In the present case, the tachycardia was treated by RF ablation at the earliest site. As the clinical tachycardia originated in the LCC, anatomically separated from the specialized conducting system, the tachycardia could be eliminated without impairing the conducting system.
Conflict of interest