1 Characterization of Fractionated Atrial Electrograms Critical for Maintenance of AF:

2 Background- Whether ablation of complex fractionated atrial electrograms (CFAE) modifies AF by eliminating drivers or atrial de-bulking remains unknown. This randomised study aimed to determine the effect of ablating different CFAE morphologies compared to normal electrograms (i.e. de-bulking normal tissue) on the cycle length of persistent AF (AFCL). Methods and Results- After pulmonary vein isolation left and right atrial CFAE were targeted, until termination of AF or abolition of CFAE prior to DC cardioversion. 10s electrograms were classified according to a validated scale, with Grade 1 being most fractionated and grade 5 normal. Patients were randomised to have CFAE grades eliminated sequentially, from grade 1 to 5 (group 1) or grade 5 to 1 (group 2). An increase in AFCL (mean of left and right atrial appendage) 5 ms following a lesion was regarded as significant. 968 CFAE were targeted in 20 patients. AFCL increased after targeting 51 ± 35