Effects of baseline P-wave duration and choice of atrial septal pacing site on shortening atrial activation time during pacing.

BACKGROUND Atrial septal pacing (ASP) has been shown to shorten P-wave duration (PWD) and reduce recurrence of atrial fibrillation (AF) in patients with bradyarrhythmias. However, variability of interatrial connections and atrial conduction properties may explain ASP's modest clinical benefit. The aim of this study was to assess the effect of ASP site on the duration of the paced P wave. METHODS AND RESULTS Atrial septal pacing at high atrial septum (HAS), posterior septum behind the fossa ovalis (PSFO), and coronary sinus ostium (CSo) was performed in 69 patients admitted for electrophysiological study (52 ± 16 years, 41 men). Twelve-lead electrocardiogram was recorded at baseline and during pacing, signal-averaged for analysis of PWD and P-wave shortening achieved by ASP (ΔPWD = paced PWD-baseline PWD). Baseline PWD was 128 ± 15 ms. The shortest PWD during pacing was achieved at CSo (112 ± 15 ms) followed by HAS (122 ± 14 ms, P< 0.001 vs. CSo) and PSFO (124 ± 21 ms, P< 0.001 vs. CSo). P wave was shortened during pacing in patients with baseline PWD of > 120 ms (n= 50), whereas those with PWD of ≤ 120 ms showed PWD lengthening (n= 19) when paced at HAS (8 ± 17 vs. -12 ± 15 ms, P< 0.001), PSFO (15 ± 17 vs. -12 ± 26 ms, P< 0.001) and CSo (6 ± 16 vs. -25 ± 18 ms, P< 0.001). CONCLUSION Pacing at CSo is associated with the shortest PWD. P-wave shortening is greatest in patients with baseline PWD of > 120 ms regardless of the pacing site. The results may have implications on the selection of candidates for ASP and the placement of the atrial septal lead, and warrant further evaluation in cases of permanent pacing in patients with paroxysmal AF.