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

Abstract

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. 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). BP group had shorter p wave duration compared to No-BP group (140 ± 10 ms vs 170 ± 15 ms vs, p < 0.05). As expected, BP patients had a retrograde left atrium depolarization confirming a complete Bachmann's bundle conduction block. In contrast, wave front collisions were recorded at the lateral wall of the left atrium (distant dipoles 1–2) in all five No-BP patients. However, No-BP patients had slower inter-atrial conduction velocity compared to BP patients (0.71 ± 0.22 m/s vs 1.10 ± 0.20 m/s, p < 0.05). We therefore may infer that an extreme inter-atrial conduction slowing may give some time for the atrial electrical activity to travel through the Bachman's bundle. 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.