Electrophysiological determinants of atrial fibrillation in sinus node dysfunction despite atrial pacing.

Abstract

The effectiveness of atrial pacing in reducing the incidence of atrial fibrillation in patients with sinus node dysfunction is incomplete, and the correlation between electrophysiological atrial properties and the effect of permanent atrial pacing has been poorly investigated. Accordingly, the aim of the present study was to correlate electrophysiological data, in terms of atrial refractoriness, conduction parameters, and propensity to atrial fibrillation induction, and the likelihood of atrial fibrillation after DDD device implantation. The authors reviewed electrophysiological data of 41 patients with sinus node dysfunction (mean age 70 +/- 8 years, who were investigated free of anti-arrhythmic treatments before pacemaker implantation. At a drive cycle length of 600 ms, effective and functional refractory periods, S1-A1 and S2-A2 latency, A1 and A2 width, and latent vulnerability index (effective refractory period [ERP] A2), were measured. Atrial fibrillation induction was tested with up to three extrastimuli in 34 patients. Induction of sustained atrial fibrillation (> 1 min) was considered as the end-point. P-wave duration on the surface ECG in lead II/V1 was also measured. Minimal atrial rate was programmed between 60 and 75 bpm (mean: 64 +/- 4 bpm). After implantation, the patients were followed-up for 28 +/- 17 months, and ECG-documented occurrence of atrial fibrillation was determined. Electrophysiological characteristics of patients with (n = 12) or without (n = 29) paroxysmal atrial fibrillation before implantation were similar. When comparing patients with (n = 11) or without (n = 30) post-pacing atrial fibrillation occurrence, no differences were found in age, underlying heart disease, left atrial size, minimal pacing rate, and follow-up duration. Additionally, between the two former groups, there was no significant difference in terms of effective refractory periods (233 +/- 47 ms vs 239 +/- 25 ms), functional refractory periods (280 +/- 48 ms vs 272 +/- 21 ms), S1-A1 (44 +/- 20 ms vs 37 +/- 13 ms) and S2-A2 latency (77 +/- 28 ms vs 66 +/- 22 ms), and A1 duration (60 +/- 23 ms vs 53 +/- 16 ms). In contrast, in patients with post-pacing atrial fibrillation occurrence, the P wave was more prolonged (116 +/- 22 ms vs 98 +/- 13 ms; P < 0.01), A2 was longer (116 +/- 41 ms vs 87 +/- 27 ms; P < 0.01), effective refractory periods/A2 was lower (2.1 +/- 0.4 cm vs 3.1 +/- 1.4 cm; P < 0.05), and rate of atrial fibrillation induction was higher (8/11 patients vs 8/23 patients; P < 0.05). Electrophysiological characteristics of patients free of post-pacing atrial fibrillation with associated (n = 6) or unassociated (n = 24) paroxysmal atrial fibrillation history before implantation were quite similar. In patients with post-pacing atrial fibrillation with associated (n = 6) or unassociated atrial fibrillation history (n = 5) before implantation, effective refractory periods was statistically different (207 +/- 23 ms vs 264 +/- 46 ms; P < 0.05). Values of effective refractory periods < 220 ms were significantly more frequent in patients with post-pacing atrial fibrillation than in patients without (4/11 patients vs 2/30 patients; P < 0.05). When comparing patients with post-pacing atrial fibrillation with effective refractory periods > or = 220 ms (n = 7) and < 220 ms (n = 4), A2 duration was remarkably prolonged (145 +/- 42 ms vs 90 +/- 11 ms; P < 0.05) in those with effective refractory periods > or = 220 ms. By contrast, between the two groups, effective refractory periods/A2 were identical (2.08 +/- 0.6 cm vs 2.15 +/- 0.3 cm; P = n.s.). Prolonged atrial refractoriness, lesser degrees of conduction disturbance and a lower rate of atrial fibrillation induction seem to be predictive of stable sinus rhythm. In contrast, patients with persistence of atrial fibrillation despite pacing have a more abnormal and inhomogeneous atrial substrate, as well as a higher rate of atrial fibrillation induction. Prolonged P wave, shortened refractoriness, or remarkably abnormal conduction disturbances in the presence of prolonged refractoriness limit the effectiveness of standard atrial pacing in atrial fibrillation prevention. Identification of predictive criteria of failure of single-site atrial pacing may be used to consider dual-site atrial pacing in such patients with sinus node dysfunction.