Mapping of ganglionated plexi during electrophysiological study
Two approaches can be used for selective identification of GPs: (1)
high-frequency stimulation (HFS) and (2) electrogram analysis.
Although different groups have defined different settings for HFS
application, in our laboratory, HFS is delivered at a frequency of 20
Hz, amplitude 10 V, and pulse duration of 10ms, for 2-5 seconds, aiming
to test at least 100 HFS sites evenly distributed around the left
atrium, as previously described (20). HFS applications longer than 5
seconds may stimulate sympathetic fibers and mitigate the
parasympathetic response. HFS may cause two types of response: a vagal
response (VR), defined as a transient ventricular asystole
> 3sec, atrioventricular block (second or third-degree), or
an R-R interval prolongation by 50%, and a normal response
characterized by the absence of any effect or nonsignificant changes on
the PR or RR intervals. Theoretically, demonstration of a positive VR
differentiates GP sites. The response to HFS should be reproducible at
each site. In our laboratory, HFS-guided GP mapping strategy is used
only for specific research protocols purposes, the following part of the
review will discuss our favored electrogram-guided GP mapping strategy.
Lellouche et al (21) analyzed electrogram characteristics based on VRs
during radiofrequency application and demonstrated that the best single
predictor of VR during radiofrequency application was the number of
electrogram deflections at the ablation site. In our initial work, GP
sites were detected through a combination of fast Fourier transform
analysis of electrograms and HFS (22). In accordance with Lellouche’s
observations, radiofrequency application on the sites showing
fractionated electrogram pattern caused vagal response in all cases,
whereas there was no vagal response in normal atrial myocardium sites
during radiofrequency application. Because the better resolution
afforded by the usage of higher high‐pass filters allowed better
appreciation of electrogram fragmentation (23), in our subsequent work,
we used band‐pass filter settings of 200–500 Hz instead of conventional
band‐pass filter settings of 30–500 Hz during sinus rhythm and targeted
all fragmented electrograms in regions which are anatomically consistent
with GPs (24). Compared with previous combined approach, fragmented
electrogram-guided GP ablation decreased the procedure and fluoroscopy
times while maintaining success rates.