172 Extreme inter-atrial conduction slowing without Bachman's bundle block

Introduction A complete inter-atrial conduction block (CIACB) is defined as a surface ECG p wave duration 120 ms with a biphasic pattern in inferior leads. The main mechanism is thought to lie in complete Bachmann's bundle block responsible for a retrograde left atrium depolarization. Some patients may meet the p wave duration criterion for CIACB without a biphasic pattern in inferior leads. We hypothesized that some patients may present extreme inter-atrial conduction slowing without Bachman's bundle block. Methods Ten patients with p wave prolongation (p > 120 ms) were divided into two groups: five patients with a biphasic pattern in inferior leads (BP group), and five patients without a biphasic pattern in inferior leads (No-BP group). Conduction velocity from right to left atria was measured invasively using a 24-pole mapping catheter placed around the tricuspid annulus with distal dipoles positioned at the lateral wall of the left atrium (at 3 hours around the mitral annulus in LAO 45° view), and proximal dipoles at the lateral wall of the right atrium (at 9 hours around the tricuspid annulus in LAO 45° view). Results BP group had shorter p wave duration compared to No-BP group (140 ± 10 ms vs 170 ± 15 ms vs, p  Conclusions As opposed to patients with CIACB, patients with an extreme p wave prolongation (p > 150 ms) and no biphasic pattern may have a delayed conduction through the Bachmann's bundle without a complete block.