Procedural steps of electrogram-guided ganglionated plexus mapping
and ablation
After creation of 3D mapping of both atria, fragmented bipolar
endocardial atrial electrograms are evaluated for number of deflections
at filter settings of 200–500 Hz by using the ablation catheter. This
setting is available in WorkMate™ Claris™ system (St Jude Medical,
Abbott, St. Paul, MN, USA). In Prucka Cardiolab system (GE Healthcare,
Wauwatosa, WI), 100–500 Hz can be selected as default setting (18). The
EGMs demonstrating greater or equal to 3 deflections in regions which
are anatomically consistent with GP sites are tagged as ablation targets
(Figure 3). Although both atria are included in the analysis, ablation
is started at the left atrium. After all GP targets have been identified
in the left atrium, we deliver radiofrequency ablation of targeted areas
in the following order: the superior left atrial GP; the posterolateral
(inferior) left atrial GP; the
Marshall tract GP (MTGP) on the endocardial aspect of the vein of
Marshall; the superior right atrial GP; and the posterior (inferior)
right atrial GP (Figure 3). If the heart rate after left atrial GP
ablation reaches the pre-ablation atropine response test, we do not
perform additional ablation in the right atrium. Otherwise, we perform
empirical ablation around the posteroseptal wall of the superior vena
cava for the superior right atrial GP site (Video 1). We have recently
demonstrated that different GP sites demonstrate different
neuromodulation characteristics during radiofrequency application (25).
While ablation around the left-sided GPs causes a VR (Video 2 and 3),
ablation of the superior right atrial GP increases heart rate acutely
without any VR (Video 4). Furthermore, we demonstrated that right side
first strategy may cause an attenuation of VR ablation around the
left-sided GPs (26), and hence our preference for starting from the left
sided GPs. Ablation of the inferior right atrial GP is not related to a
significant VR regardless of ablation strategy.
In the human heart, the superior right atrial GP supplies epicardial
nerves to the sinoatrial nodal neural network, and it is likely that
ablation around this area first affects endocardial and myocardial
postganglionated nerve fibers before affecting epicardial ganglia which
likely causes an increase in heart rate by blocking parasympathetic
innervation of the sinoatrial node without vagal discharge effect (27).
In patients with atrioventricular block,
the posteromedial left atrial GP
should also be targeted because postganglionated nerves from the
posteromedial left atrial GP extend towards the interatrial septum and
presumably supply the atrioventricular nodal region (28). We have
recently demonstrated that ablation around the posteromedial left atrial
GP resulted in 1:1 atrioventricular conduction in 13 (76.4%) of 17
patients with persistent second-degree atrioventricular block (Video 5)
(17). However, we may need to extended ablation to other GP sites if
desired atrioventricular response is not achieved after ablation around
the posteromedial left atrial GP (Video 6).
We have recently compared the acute procedural characteristics and
clinical success rates with fragmented-guided GP ablation in patients
with vagally mediated bradyarrhythmias performed by first-time operators
and those of a single high-volume operator center with an international
multicenter registry from 16 sites (29). The proctor (TA) reviewed the
electrograms and 3D maps in real time and opined on the suitability of
ablation sites in all cases who were done by virtual proctoring.
Although the procedure time was longer in the first-time GP ablation
group, acute procedural success was achieved in all cases without any
major adverse events. At a mean follow-up of 8.0 ± 3 months, none had
recurrent syncope.