479 Role of Bachmann's bundle during chronic atrial fibrillation in patients with mitral valve disease

Introduction Animal studies have shown that bachmann's bundle (BB) is essential for development of mukiple reentrant circuits perpetuating atrial fibrillation (AF). Mapping of BB in humans has sofar not been performed. In this study, high density epicardial mapping of BB was performed to study conduction characteristics of fibrillation waves across BB during chronic AF in humans. Methods Epicardial mapping studies of BB were performed in pts (n=10, age 58-4-3 yrs) with chronic AF during cardiac surgery for mitral valve disease with a template containing 60 unipolar electrodes (interelectrode distance 1.5 mm). Ten seconds of AF were recorded from the middle (MBB), right (RBB) and left site of BB (LBB). Isochronal maps were off-line constructed. For each mapping site, AF cycle length (ACFL), conduction velocity (CV) and the incidence of conduction block (CV< 7.5 cm/s) was determined. Fibrillation potentials were classified according to the degree of fractionation. Results 3988-4-2039 fibrillation potentials and 197-4-56 fibrillation maps/pt were analysed. In most pts, mukiple waves separated by arcs of conduction block were observed. In 3 pts, only single waves propagating at high CV were present. There were no preferential conduction directions. Electrophysiological variables are summarized in Table 1. CV was slower and conduction block occurred more frequently at MBB compared to RBB and LBB (CV: MBB:29+18cm/s vs RBB:46+30cm/s, LLB: 52+20cm/s, p<0.02, conduction block: MBB:20+10% vs RBB:5+3%, LLB:7+2%, p<0.01).