1008-12 Electrophyslologic Characteristics of Manifest Endocardial Accessory Pathways Located in the Left Posteroseptal Space, as Defined by Radlofrequency Current Ablation

The aim of the study was to assess whether local electrogram (EG) analysis is predictive of the endocardial (ENDO) ventricular (V) insertion of accessory pathways (APs) located in the left postero-septal (L PS) space. In 22 (3.6%) out of 619 manifest APs, the successful (S) out of 14 (2–30) pulses was delivered at the ENDO ventricular aspect of the PS mitral annulus (28 sessions; 4.0  ±  1.3 h duration; 69  ±  38 min fluoroscopy time). Of local EGs retrospectively analyzed, 22 were recorded at Sand 49 at unsuccessful (U) ENDO sites in the L PS V, 75 at U risght (R) PS sites, 72 at U epicardial (EPI) sites, of which 52 from within the coronary sinus (CS) and 10 from the middle cardiac vein (MCV). An AP potential could be distinguished in 18/24 (81%) S sites, but also in 41/49 (84%) U sites. Local A-V (42  ±  12 ms vs 43  ±  11 ms) and Δ-V intervals (-5  ±  7 ms vs -2  ±  9 ms) as well as A/V ratio (0.15 vs 0.17) did not differ between Sand U sites. Intermittent conduction block was induced during 50% of pulses delivered from the R PS region and 30% of those delivered from both the CS and 3 the MCV. Compared to S sites. A-V was longer at R PS (53  ±  10 ms, p l 0.01), and CS (52  ±  ms, p l 0.01), but not at the MCV (43  ±  12 ms). At all these sites, Δ-V was similar to that at S sites (R PS, -2  ±  8 ms, CS -4  ±  8 ms. MCV, -8  ±  12 ms). Conclusions Geometrical complexity of PS APs is reflected in the set of L PS APs ablated at the ENDO aspect. In such set, AP potentials are frequently recorded at the R PS and L EPI site; also, Δ-V intervals at these sites similar to those at S sites, thus rendering mapping techniques for AP localization and ablation in this region difficult.