Background: Short atrial fibrillation cycle lengths (AFCLs) and regular activation patterns are associated with drivers of atrial fibrillation, although the relation with underlying patterns of activation is incompletely understood. Previous studies used automated assessment of electrograms to determine fast and regular fibrillatory rates. Objective: We investigated the relation among AFCL, temporal variation in AFCL, and the occurrence of driver-like patterns of activation using high-density local activation time mapping. Methods: High-density epicardial mapping of the right atrium and left atrial ventricular groove including Bachmann's bundle was performed in 71 patients admitted for elective cardiac surgery. Recording sites with the shortest median AFCL or the smallest standard deviation of AFCL were identified. Patterns of activation included focal or rotational activation, smooth propagation, propagation with conduction block (CB), collision, and remnant activity. Results: There was a higher number of fibrillation waves with CB (81% [interquartile range (IQR) 76%–85%] vs 74% [68%–76%]; P < .001) and fractionated potentials (22% [12%–37%] vs 12% [9%–15%]; P < .001) at shortest median AFCL than at other recording sites. Smallest standard deviation sites harbored more smoothly propagating waves (33% [24%–54%] vs 17% [11%–25%]; P < .001) and a higher proportion of single potentials (76% [60%–89%] vs 59% [54%–65%]; P < .001). Both highly regular and fastest reactivated sites did not correspond to the origin of (repetitive) focal fibrillation waves. Conclusion: During extensive mapping, the fastest or most regularly activated areas are characterized by CB and smoothly propagating fibrillation waves instead of repetitive occurrence of focal or rotational activation patterns. This study rejects the concept of detecting drivers by identifying the fastest or most regularly activated recording sites.

Background: Dominant frequencies (DFs) or complex fractionated atrial electrograms (CFAEs), indicative of focal sources or rotational activation, are used to identify target sites for atrial fibrillation (AF) ablation in clinical studies, although the relationship among DF, CFAE, and activation patterns remains unclear. Objectives: This study sought to investigate the relationship between patterns of activation underlying DF and CFAE sites during AF. Methods: Epicardial high-resolution mapping of the right and left atrium including Bachmann's bundle was performed in 71 participants. We identified the highest dominant frequency (DF _max) and highest degree of CFAE (CFAE _max) with the use of existing clinical criteria and classified patterns of activation as focal or rotational activation and smooth propagation, conduction block (CB), collision and remnant activity, and fibrillation potentials as single, double, or fractionated potentials containing, respectively, 1, 2, or 3 or more negative deflections. Relationships among activation patterns, DF _max, and potential types were investigated. Results: DF _max were primarily located at the left atrioventricular groove and did not harbor focal activation (proportion focal waves: 0% [IQR: 0%-2%]). Compared with non-DF _max sites, DF _max were characterized by more frequent smooth propagation (22% [IQR: 7%-48%] vs 17% [IQR: 11%-24%]; P = 0.001), less frequent conduction block (69% [IQR: 51%-81%] vs 74% [IQR: 69%-78%]; P = 0.006), a higher proportion of single potentials (72% [IQR: 55%-84%] vs 6%1 [IQR: 55%-65%]; P = 0.003), and a lower proportion of fractionated potentials (4% [IQR: 1%-11%] vs 12% [IQR: 9%-15%]; P = 0.004). CFAE _max were mainly found at the pulmonary veins area, and only 1% [IQR: 0%-2%] of all CFAE _max contained focal activation. Compared with non-CFAE _max sites, CFAE _max sites were characterized by less frequent smooth propagation (1% [IQR: 0%-1%] vs 17% [IQR: 12%-24%]; P < 0.001) and more frequent remnant activity (20% [IQR: 12%-29%] vs 8% [IQR: 5%-10%]; P < 0.001), and harbored predominantly fractionated potentials (52% [IQR: 43%-66%] vs 12% [IQR: 9%-14%]; P < 0.001). Conclusions: Focal or rotational patterns of activation were not consistently detected at DF _max domains and CFAE _max sites. These findings do not support the concept of targeting DF _max or CFAE _max according to existing criteria for AF ablation.