Aims: It is unclear how the amplitude of bipolar electrogram relates to the local conduction velocity (CV) in patients with atrial fibrillation (AF). For 50 AF patients (paroxysmal/persistent AF: 40/10 patients), contact bipolar voltage maps of the left atrium (LA) were constructed during sinus rhythm using EnSite version 6.0J in a point-by-point recording fashion. Patients were divided into Groups A (n = 16), B (n = 19), and C (n = 15) according to the level of the lowest electrogram amplitudes: <0.5, 0.5-0.75, and 0.75-1.0 mV, respectively. Low-voltage zone (LVZ) was defined separately for these groups as a bipolar electrogram amplitude of <0.5, 0.5-0.75, and 0.75-1.0 mV, respectively. The local CV through the LVZ and non-LVZ was calculated along the direction of local activation within each zone for all groups.
Methods and results: Low-voltage zone was consistently found at the septal, anterior, and posterior LA in all groups. In Group A, CV through the LVZ was significantly slower compared with the non-LVZ (0.8 +/- 0.5 vs. 1.4 +/- 0.6 m/s, P = 0.004), but those through the LVZ and non-LVZ were similar in Group B (1.2 +/- 0.5 vs. 1.3 +/- 0.5 m/s, P = 0.07) and Group C (1.5 +/- 0.5 vs. 1.4 +/- 0.6 m/s, P = 0.79). The percentage of points showing fractionated or double potentials in the LVZ was significantly more in Group A (76/293 points, 26%) than in Group B (11/185 points, 6%), and Group C (7/135 points, 5%) (P < 0.0001 and P < 0.0001, respectively).
Conclusion: There was a significant slowing of local conduction in the LVZ defined as <0.5 mV and was frequently associated with fractionated or double potentials in patients with AF.