Increase in organization index predicts atrial fibrillation termination with flecainide post-ablation: spectral analysis of intracardiac electrograms.

Aims: The mechanism of the action of flecainide in the termination of human atrial fibrillation (AF) is not fully understood. We studied the acute effects of flecainide on AF electrograms in the time and frequency domain to identify factors associated with AF termination.

Methods And Results: Patients who were still in AF at the end of catheter ablation for AF were given intravenous flecainide. Dominant frequency (DF) and organization index (OI) were obtained by fast Fourier transform of electrograms from the coronary sinus catheter over 10 s in AF, before and after flecainide infusion. Mean AF cycle length (CL) was also calculated. Twenty-six patients were studied (16 paroxysmal AF and 10 persistent AF). Seven converted to sinus rhythm (SR) with flecainide. In all patients, mean CL increased from 211 +/- 44 to 321 +/- 85 ms (P < 0.001). Mean DF decreased from 5.2 +/- 1.03 to 3.6 +/- 1.04 Hz (P < 0.001). Mean OI was 0.33 +/- 0.13 before and 0.32 +/- 0.11 after flecainide (P = 0.90). Comparing patients who converted to SR with those who did not, OI post-flecainide was 0.41 +/- 0.12 vs. 0.29 +/- 0.10 (P = 0.013), and the relative change in OI was 29 +/- 33 vs. -3.9 +/- 27% (P = 0.016), respectively. No significant difference was noted in the change in CL and DF in the two groups.

Conclusion: Increase in OI, independent of changes to CL and DF, appears critical to AF termination with flecainide. Increase in OI holds promise as a sensitive predictor of AF termination.