SAR405 Introduction Catheter ablation of accessory pathways

Introduction Catheter ablation of accessory pathways (APs) can be challenging depending on the location of the AP. Anteroseptal APs are rare but associated with lower success rates and higher incidence of atrioventricular (AV) block [1,2]. Data regarding the electrocardiographic and electrophysiological characteristics as well as the safety and efficacy of catheter ablation of anteroseptal APs through the aortic cusps are limited [3–18]. We describe two cases of para-Hisian APs successfully ablated from the aortic cusps along with a detailed review of the current literature.
Cases
Discussion We presented the electocardiographic and electrophysiological characteristics of two patients with para-Hisian APs successfully ablated from the RCC near the RCC–NCC junction and the NCC, respectively. A comprehensive literature search of relevant studies published in MEDLINE up to November 2015 was additionally conducted. Sixteen case studies [3–18] comprising 36 patients with septal APs successfully ablated through the aortic cusps were included in this analysis. In most of these cases, a right-sided approach was initially undertaken and had been unsuccessful highlighting the importance of recognizing the presence of an aortic cusp pathway when present. As shown in Table 1, the majority of APs were located at the NCC (66.6%) and the RCC (19.4%), and less commonly at the left coronary cusp (LCC) (5.5%), at the RCC–NCC commissure (5.5%), and at the LCC–NCC commissure (2.7%). The delta waves were usually positive in lateral (I, aVL) and inferior leads (II, III, aVF), while varied in lead V1 (positive, isoelectric, negative). The polarity of the delta wave in lead V1 was not site specific. Although NCC APs (n=4) (posterior location) displayed more commonly positive delta waves in lead V1, there were also NCC APs (n=2) exhibiting negative delta waves. RCC APs (anterior location) displayed negative delta waves in lead V1. For APs located in the NCC, the delta wave in lead III was less positive than that in lead II. The transition zone was usually in lead V3 (less commonly in leads V2 and V4). Both para-Hisian AP cases described in our study displayed positive delta waves in leads I, aVL, II, aVF, and V1. In case 1, the delta wave in lead III was less positive than that in lead II, while in case 2 the delta wave in lead III was negative. As shown in Table 1, RF SAR405 delivered with irrigated and non-irrigated tip catheters was most commonly used. Cryoablation was used in few cases (2 out 36). The incidence of AV block was very low (1 out of 36 cases, 2.7%). No other complications were reported. The data regarding the efficacy and safety of the conventional right-sided catheter ablation approach of anteroseptal APs are controversial. There are studies demonstrating excellent long-term outcomes without any damage of the AV node [21,22], while other studies report lower success rates and higher incidence of AV block [1,2,23]. In the largest case series up to now, Xu et al. compared the safety, efficacy, and long-term outcome of the two different ablation approaches for para-Hisian APs [3]. RF energy delivered at the NCC had a higher success rate (11/12 vs. 5/12) and a lower complication rate (0/12 vs. 4/12) compared with the right anteroseptal approach. From an electrophysiological point of view, it is essential to understand the importance of the central position of the aortic valve and its relationship with adjacent structures. The aortic valve is directly related with both atria, the interatrial septum, the right ventricular outflow tract, the aortomitral continuity, the pulmonary valve, and the conduction system [20,24]. The RCC lies immediately posterior to the relatively thick posterior wall of the right ventricular outflow tract. The LCC is also related to the posterior wall of the right ventricular outflow tract, but more posteriorly continuous with the anterior leaflet of the mitral valve as the aortomitral continuity. The NCC is located more posterior in relation to other cusps and forms the superior margin of the interatrial septum. As the conduction system penetrates to the left, it becomes located at the base of the interleaflet triangle between the NCC and the RCC [24]. The latter possibly explains that the majority of septal APs were successfully ablated at the NCC, RCC, or RCC–NCC junction (33 out of 36 APs). These APs are possibly electrically active connections between the ventricular myocardium (just below and extending above the aortic cusps) and atrial myocardium (adjacent interatrial septum). The mechanical block of the AP seen in case 1 supports this notion. Myocardial sleeves have been demonstrated to extend beyond the plane of attachment of the semilunar valves into the aorta. In autopsied hearts, myocardial extensions were noted above the RCC in 55%, LCC in 24%, non-coronary/posterior cusp in 0.66%, intercuspally in 49% (2.2±1.1mm), and in the cusps in 2.2% of cases [25]. Yamada et al. suggested that the NCC exhibits direct musculature connection with the His-bundle region and the mid-interatrial septum in the left atrium [26]. In animal studies, RF catheter ablation within the NCC has been shown to create lesions at the left atrial septum located between the floor of the fossa ovalis and the mitral annulus. These findings are strongly indicating the close anatomical proximity of the NCC with the interatrial septum [27].