CASE REPORTS
Case presentation
A 40 year-old woman who had undergone a left mastectomy and breast
reconstruction for breast cancer was admitted to our hospital because of
palpitations and dyspnea on exertion. A 12-lead electrocardiogram showed
atrial tachycardia (AT) with a positive notched P wave in leads I, II,
III, aVF, V1, and V2 (Figure 1A). A Holter electrogram
revealed incessant AT and transient atrial fibrillation (AF). A thoracic
echocardiogram indicated reduced contractility, with an ejection
fraction (EF) of 35%. A radiofrequency ablation for AT was performed
due to severe discomfort caused by palpitations after obtaining informed
consent. AT with a constant atrial activation sequence constantly
appeared, and the cycle length during tachycardia varied between 260 and
310 ms (Figure 1B). Activation mapping of the AT was performed in the
left atrium (LA) using a three-dimensional mapping system (NavX, St.
Jude Medical, St. Paul, Minnesota, USA). The earliest AT activation site
was observed at the bottom of the left inferior pulmonary vein (LIPV)
ostium (Figures 2A and 2B). Because AF and AT were identified prior to
the procedure, we attempted PV isolation using a 28-mm cryoballoon (CB)
(Arctic Front, Medtronic, Minneapolis, Minnesota, USA). First, CB
ablation of the left superior PV (LSPV) orifice and antrum resulted in
the termination of AT 51 seconds after the temperature measured at the
balloon’s base dropped below freezing (Figures 2C and 3A). Thereafter, a
single atrial extrastimulus with the same atrial activation sequence was
observed; however, AT was no longer induced. Subsequently, after the CB
ablation of the LIPV (Figure 3A), the atrial extrastimulus also
disappeared. In this case, CB ablation of the LSPV resulted in
termination and no induction of AT originating from the bottom of the
LIPV ostium. Hence, this study aimed to identify the mechanism of AT.
Discussion
AF is primarily initiated by
arrhythmogenic triggers originating from the PV. PV isolation is the
cornerstone of AF ablation, and PVI with CB ablation has been proven to
be non-inferior to radiofrequency ablation with regard to safety and
clinical outcomes.1 In this case, the AT was a focal
tachycardia originating from the LIPV ostium. Kistler et al.
demonstrated that in the vast majority of AT originating from the PVs,
the tachycardia focus originated from the ostium of the PV rather than
from further distal PVs, in contrast to AF.2 Wei et
al. showed that CB ablation was an effective and safe tool to treat AT
originating from the PVs.3 In this case, CB ablation
of the LSPV resulted in termination and no induction of the AT
originating from the bottom of the LIPV ostium. We hypothesized that the
mechanism of AT initiation and maintenance might be related to
ganglion plexus (GP)
hyperactivity near the vicinity of the PV-LA junction.
Previous studies have shown that
the intrinsic cardiac autonomic
nervous system (ANS), an epicardial neural system composed of GPs and a
complex network of interconnecting neurons, plays a crucial role in the
induction and maintenance of AF through both sympathetic and
parasympathetic nervous system stimulation.4 The GPs
act as an integration and interconnection system between the extrinsic
cardiac ANS nerves, originating from the central ANS and reaching the
heart through the mediastinum, and the rest of the intrinsic cardiac
ANS. The function of GPs is not only to modulate the autonomic interplay
between the extrinsic and intrinsic cardiac ANS, but also to
independently regulate cardiac electrical and mechanical functions
through the transduction of local signals. In LA, the major GPs are
located close to the PV-LA junction. GPs contain both sympathetic and
parasympathetic components. GPs activation creates intracellular calcium
overload and shortening of action potential duration, which in turn
results in early after depolarization and triggers firing in surrounding
atrial tissue or neighboring PVs, thereby causing initiation and
maintenance of AF.4 Vagal reactions manifesting as
bradycardia and hypotension have been reported as markers of GPs
modification during PVI.5 Vagal reactions during
CB-based PVI were reported to be frequent from 36 % to 50 %. PVI with
the 28-mm CB catheter is associated with a broad antral ablation area
that extends from the PV ostium toward the LA, thus increasing the
possibility of concomitant and extended GP ablation.6Yorgun et al. demonstrated that the patients with vagal response during
CB ablation had a lower incidence of AF recurrence, suggesting
modulation of the cardiac ANS through GP
modification.5 Other studies have suggested that
adding GP ablation to PV isolation may achieve better clinical outcomes
in patients with AF.7 These findings indicate that both
larger areas of transmural lesion formation and GP modification may
contribute to the efficacy of CB ablation. In this case, one minute
after CB ablation of the LSPV was completed, transient sinus arrest and
atrioventricular block due to the vagal response were also observed
(Figure 3B). Histological examination of the human heart has
demonstrated that the Marshall tract GP is located within the fat pad
anterior to the LSPV and LIPV, and the superior left GP is located on
the roof of the LA, medial to the LSPV.4 The
interruption of axons from these hyperactive GP to the LIPV by CB
ablation of the LSPV may have contributed to eliminating the initiation
and maintenance of this AT.
The present case highlighted termination and no induction of AT
originating from the LIPV and the vagal response was observed with CB
ablation of the LSPV. It could also be deduced that the mechanism of the
AT strongly involved the GPs hyperactivity.