High-frequency stimulation
Animal experiments demonstrated that electrical stimulation of left
atrial sites areas caused 2 types of response in different parts of the
LA: a vagal response (VR), defined as a significant prolongation of the
PR and/or RR intervals, and a normal response characterized by the
absence of any effect or nonsignificant changes on the PR or RR
intervals (55). Theoretically, demonstration of a positive VR
differentiates autonomic innervation sites than normal atrial
myocardium. Because each epicardiac ganglia contains both
parasympathetic and sympathetic neural elements, response to HFS may
change according to duration of application. While shorter applications
stimulate parasympathetic fibers, if HFS is delivered more than 2–5
seconds, sympathetic fibers may be stimulated, which may subsequently
mitigate the parasympathetic response (55, 59).
According to the sites exhibiting a VR to HFS and fractionated
electrogram characteristics during AF, 5 major epicardiac GPs were
identified by Nakagawa et al (55): 1) the right anterior GP ; 2)the right inferior GP ; 3) the left superior GP ; 4)the left inferior GP ; and 5) the Marshall ligament GP .
Figure 5 demonstrates the
anatomical distribution of these 5 GPs (55). Interestingly, in spite of
using a quite similar HFS protocol, Kim et al (60) found a more
scattered distribution although the VR sites were located mainly on the
posterior wall of the LA. We believe that one reason for this
discrepancy may be that HFS may stimulate not only epicardial ganglia
but also nerves that extend from epicardial ganglia towards the atrial
regions. Indeed, despite its strong theoretical background, a HFS-based
strategy has not demonstrated an advantage over empirical anatomic
ablation in patients with AF as well as VVS (61, 62).