Electrogram fractionation: the relationship between spatiotemporal variation of tissue excitation and electrode spatial resolution.

BACKGROUND: Fractionated electrograms are used by some as targets for ablation in atrial and ventricular arrhythmias. Fractionation has been demonstrated to result when there is repetitive or asynchronous activation of separate groups of cells within the recording region of a mapping electrode(s). METHODS AND RESULTS: Using a computer model, we generated tissue activation patterns with increasing spatiotemporal variation and calculated virtual electrograms from electrodes with decreasing resolution. We then quantified electrogram fractionation. In addition, we recorded unipolar electrograms during atrial fibrillation in 20 patients undergoing atrial fibrillation ablation. From these we constructed bipolar electrograms with increasing interelectrode spacing and quantified fractionation. During modeling of spatiotemporal variation, fractionation varied directly with electrode length, diameter, height, and interelectrode spacing. When resolution was held constant, fractionation increased with increasing spatiotemporal variation. In the absence of spatial variation, fractionation was independent of resolution and proportional to excitation frequency. In patients with atrial fibrillation, fractionation increased as interelectrode spacing increased. CONCLUSIONS: We created a model for distinguishing the roles of spatial and temporal electric variation and electrode resolution in producing electrogram fractionation. Spatial resolution affects fractionation attributable to spatiotemporal variation but not temporal variation alone. Electrogram fractionation was directly proportional to spatiotemporal variation and inversely proportional to spatial resolution. Spatial resolution limits the ability to distinguish high-frequency excitation from overcounting. In patients with atrial fibrillation, complex fractionated atrial electrogram detection varies with spatial resolution. Electrode resolution must therefore be considered when interpreting and comparing studies of fractionation.

The impact of pharmacologic sympathetic and parasympathetic blockade on atrial electrogram characteristics in patients with atrial fibrillation.

BACKGROUND: Ablation of atrial autonomic inputs exerts antifibrillatory effects. However, because ablation destroys both myocardium and nerve cells, the effect of autonomic withdrawal alone remains unclear. We therefore examined the effects of pharmacologic autonomic blockade (PAB) on frequency and fractionation in patients with atrial fibrillation (AF). METHODS: Esmolol and atropine were administered and electrograms were recorded simultaneously from both atria and the coronary sinus. In 17 patients, AF was recorded for 5 minutes and dominant frequency (DF) and continuous activity (CA) were compared before and during PAB. RESULTS: Examination of the pooled data (537 sites, 17 patients) revealed a statistically significant decrease in mean DF (5.61­5.43Hz, P < 0.001) during PAB. Site-by-site analysis showed that 67% of sites slowed (0.45 ± 0.59 Hz), whereas 32% accelerated (0.49 ± 0.59Hz). Fractionation was reduced: median CA decreased from 31% to 26% (P < 0.001). In patient-by-patient analysis, mean DF/median CA decreased in 13 of 17 patients and increased in four. The spatial heterogeneity of DF decreased in nine of 17 patients (spatial coefficient of variation of DF at "nondriver sites" decreased by a mean of 2%). CONCLUSION: PAB decreases DF and CA in the majority of sites. Given the complexity of interactions between atrial cells during AF, the effects of PAB on DF and fractionation are more heterogeneous than the effects of PAB on isolated cells.

The temporal variability of dominant frequency and complex fractionated atrial electrograms constrains the validity of sequential mapping in human atrial fibrillation.

BACKGROUND: It has been proposed that sequential mapping of dominant frequency (DF) and complex fractionated atrial electrograms (CFAE) can identify target sites for ablation of atrial fibrillation (AF). These mapping strategies are valid only if DF and CFAE are temporally stable on the timescale of the mapping procedure. We postulate that DF and CFAE are temporally variable; consequently, sequential mapping can be misleading. OBJECTIVE: To make prolonged spatially stable multielectrode recordings to assess the temporal stability of DF and CFAE. METHODS: We recorded electrical activity for 5 minutes with the use of a 64-electrode basket catheter placed in the left atrium of 18 patients presenting for AF ablation. DF and CFAE were determined off-line, and their temporal variability was quantified. Maps created from simultaneous versus sequentially acquired data were compared. RESULTS: DF was temporally variable: the average temporal coefficient of variation was 22.7% +/- 5.4%. DF sites were transient, meeting criteria for only 22.1 seconds out of 5 minutes. Similarly, CFAEs were transient (average duration of CFAE 8.8 +/- 11.3 seconds). DF and CFAE sequential maps failed to identify 93.0% +/- 12.4% and 35.9% +/- 14.9% of DF and CFAE sites, respectively. CONCLUSION: Because of temporal variability, sequential DF and CFAE maps do not accurately reflect the spatial distribution of excitation frequency during any given sampling interval. The spatial distribution of DF and CFAE sites on maps created with sequential point acquisition depends upon the time at which each site is sampled.