br Catheter ablation A reentry circuit

Catheter ablation A reentry circuit is supported by complex anatomy and a thick and/or damaged myocardium; thus, high-energy RF application is usually required to create the conduction block line through the critical isthmus of the reentry circuit in patients after ToF repair. A large-tip (8mm) ablation catheter (50–60W) or an open irrigation catheter (30–50W) can create larger or deeper RF lesions than those created by a standard 4-mm-tip ablation catheter [20,21]. Catheter stability may be improved by using a steerable sheath [22]. As described above, four discrete anatomical isthmuses that often support VT have been identified. Among them, the most common is the type 1 isthmus, which is located between the superior aspect of the TA and an unexcitable scar and/or patch in the free wall of the RVOT. Therefore, in previous studies, first ablation was usually performed on the type 1 isthmus as follows. If the induced VT was hemodynamically stable and entrainment pacing showed the type 1 isthmus to be in the reentry circuit, a line of RF lesions was placed to transect this isthmus. During ablation, the ck2 inhibitor length of VT is generally prolonged, and VT is then terminated. If VT is not stable for mapping, but pace mapping or brief entrainment mapping indicates that the type 1 isthmus is an essential part of the reentry circuit, a line of RF lesions is placed across the type 1 isthmus during sinus rhythm. Successful creation of the linear conduction block through the isthmus would be confirmed by (1) the absence of local capture during pacing along the line, (2) double potentials during basic rhythm (or pacing) along the line, and/or (3) demonstration of the conduction block through the isthmus during pacing from above or below the line. However, because of RV hypertrophy and a relatively longer length of the isthmus, creation of a complete line conduction block through the type 1 isthmus may be challenging in some patients [23] (Fig. 3). On the other hand, type 2–4 isthmuses are shorter and usually consist of damaged low-voltage myocardium [24,25], which suggests Renaturation creation of a conduction block in these isthmuses (types 2–4) is much easier than that in type 1 isthmuses. In addition, if ablation to the type 1 isthmus is unsuccessful, an incomplete conduction block through the isthmus may facilitate VT recurrence. Therefore, before RF application to the type 1 isthmus, we carefully analyze the presence or absence of type 2–4 isthmuses and examine the possibility of whether ablation to these isthmuses (types 2–4) could interrupt the reentrant circuit of VT. Moore et al. recently described the characterization of the anatomy and histology of VT isthmuses in patients after surgical repair of ToF [24]. In the 27 autopsied hearts, the length and wall thickness of each anatomical isthmus were measured. In that study, the region between the RVOT ventriculotomy site and TA was classified as the type 1A isthmus and that between the RVOT ventriculotomy site and VSD patch was defined as the type 1B isthmus. In patients aged ≥5 years at death, type 1A and type 1B isthmuses were present in 88%, type 2 isthmus in 25%, type 3 isthmus in 94%, and type 4 isthmus in 13%. Type 1A isthmus had the greatest dimensions (mean length, 3.9±1.08; thickness, 1.5±0.3cm), type 1B isthmus had intermediate dimensions (mean length, 2.4±0.8; thickness, 1.1±0.4cm), and type 2, type 3, and type 4 isthmuses had the smallest dimensions (mean length, 1.5±0.5, 1.4±0.8, and 0.6±0.4cm, respectively; thickness, 0.5±0.2, 0.6±0.2, and 0.3±0.04cm, respectively). This study demonstrated that type 1A isthmus was frequently present, but creation of linear transmural RF lesions through the isthmus would be technically difficult even when using irrigation and/or large-tip ablation catheters.
Case presentation To date, we have treated 12 patients with macroreentrant VT after ToF repair. The following are some example cases of our treatment experience [26].