BACKGROUND: trial fibrillation (AF) causes electrical remodeling of the atrium that plays an important role in increasing atrial vulnerability and the perpetuation of AF. The regional variation and heterogeneities of AF-induced electrical remodeling in patients with AF remain unclear. The purpose of present study was to test the hypothesis that regional heterogeneity of the atrial electrical properties including sinus node dysfunction is more apparent in patients with chronic AF than in patients with paroxysmal AF. METHODS: The study group consisted of chronic AF (CAF, n=19), paroxysmal AF (PAF, n=19) and control group (CON, n=13). Monophasic action potential duration 90% (MAPD90) and atrial effective refractory period (AERP) were measured at 9 different sites in the right atrium using MAP catheter. Dispersion of MAPD90 and AERP were calculated from the difference between the maximum and minimum value at 9 sites, respectively. Intra-atrial conduction time (IACT) was calculated from the distance between the earliest activation and the latest one of the electrograms by 20-pole steerable catheter with 2-mm interelectrode distance which was positioned along the tricuspid annulus anterior to the crista terminalis. To evaluate sinus node function, post shock sinus node recovery time (PSRT) was measured. A rate corrected PSRT (PSRTc) was calculated from the difference between PSRT and basic sinus cycle length. RESULTS: MAPD90 significantly shortened in patients with CAF (227.0+/-32.6 ms) compared with PAF (246.8+/-38.3 ms, p<0.05) and CON (239.1+/-39.3 ms, p<0.05), but AERP was not significantly different among 3 groups. The regional changes and dispersion of MAPD90 and AERP in patients with CAF did not differ from those of PAF and CON. IACT was prolonged in CAF group (73.8+/-22.5 ms) compared with PAF (58.2+/-8.0 ms, p<0.05) and CON groups (51.6+/-12.3 ms, p<0.05). IACT in CAF group (73.8+/-22.5 ms) was significantly prolonged compared with CON groups (51.6+/-12.3 ms, p<0.05) and was longer than that of PAF groups (58.2+/-8.0 ms) without statistical significance. PSRTc was longer in CAF group (758.3+/-525.8 ms) than in PAF group (209.5+/-125.0 ms, p<0.05). CONCLUSION: Electrical changes defined as shortened MAPD90, prolonged IACT and PSRTc were more apparent in patients with CAF compared with PAF. However, these were neither accompanied by the regional variations nor dispersion of refractoriness of the atrium. These findings suggest that regional heterogeneities of electrical properties are not related to the chronicity of atrial fibrillation.