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.