Financial support:
The Section of Arrhythmia is supported by an endowment from Medtronic
Japan and Abbott Japan. KH chairs the Section, and KF and KK belong to
the Section. The authors report no relationships relevant to the
contents of this study.
Conflict of interest: All authors declare no conflicts of
interest for this article.
Short title: Catheter ablation of postoperative atrial
tachycardia
Total word count: 2204 words
Data Availability
Statement : The data
underlying this article will be shared upon reasonable request to the
corresponding author.
ABSTRACT
Atrial tachycardia (AT) in the right atrium often occurs following
open-heart surgery. Catheter ablation for these AT is challenging and
can lead to unintended conduction block. We performed late-gadolinium
enhancement magnetic resonance imaging (LGE-MRI) prior to catheter
ablation and predicted wavefront propagation during SR as well as the
slow conduction zone during tachycardia. LGE-MRI may assist predicting
the conduction disturbance and reducing the risk of unexpected sinus
exit block.
INTRODUCTION
Atrial tachycardia (AT) in the right atrium (RA) often occurs following
open-heart surgery and is difficult to treat. Although 3D mapping
systems have improved treatment rates of AT, catheter ablation (CA) can
lead to unintended conduction
block.111Markowitz, S. M., Choi, D.Y., Daian, F. et al. ”Regional isolation in
the right atrium with disruption of intra‐atrial conduction after
catheter ablation of atrial tachycardia. Journal of Cardiovascular
Electrophysiology 2019;30(10): 1773-1785. Early detection of fibrosis
in RA is hence important. Recently, late-gadolinium enhancement magnetic
resonance imaging (LGE-MRI) has been proposed as a useful tool for
visualization of left atrial fibrosis.
222Oakes, R. S., Badger, T.J., Kholmovski, E.G. et al. Detection and
quantification of left atrial structural remodeling using delayed
enhancement MRI in patients with atrial fibrillation.” Circulation
2009;119(13): 1758-1767.
In this report we describe a successful ablation of postoperative AT in
the RA where LGE-MRI accurately predicted the conduction disturbance.
CASE REPORT
A 53-year-old male was referred to our hospital with dyspnea, and
12-lead electrocardiograms indicated AT. He had undergone surgery at the
age of 9 years for tetralogy of Fallot. At the age of 49 years, he
underwent tricuspid and mitral valvuloplasty, as well as pulmonary
artery replacement for severe tricuspid, mitral, and pulmonary valve
regurgitation, using a superior transseptal approach. On this occasion,
the patient was diagnosed with tachycardia-induced cardiomyopathy
because his heart function dramatically improved after electrical
cardioversion of the AT.
To prevent AT recurrence, CA was conducted. LGE-MRI was performed prior
to CA and showed linear or patchy late-gadolinium enhancements (LGEs) in
the RA (Figure 1 A and B). The long linear LGE reached from the RA free
wall to the septum, and an LGE gap was partly visible near the sinus
node (SN) (Figure 1 A and B, black arrows: long linear LGE, and white
arrows: visual LGE gap). Furthermore, five patchy LGEs were found around
the linear LGE: between the linear LGE and the inferior vena cava (Area
A), below the SN (Area B), and around the posterior septum (Areas C, D,
and E) (Figure 1 A and B). Based on the LGE-MRI, we speculated the wave
front propagation during sinus rhythm (SR) and tachycardia circuits
(Figure 2). The SN was surrounded by the long linear LGE and patchy LGEs
(Areas B and D), where radio frequency (RF) application potentially
risked isolation of the SN (Figure 2 A and D). On the other hand, the
atrioventricular node (AVN) was activated by two pathways through the
low lateral RA (Area A) and the posterior RA (Area C, E). Therefore, we
considered that RF application at the low lateral RA (Area A) could be
performed without compromising safety.
Concerning the possible AT circuit, in addition to cavotricuspid
isthmus-dependent atrial flutter, the following two macro re-entrant ATs
associated with the long linear LGE were considered: (1) incisional AT1,
which turns around at the visual LGE gaps (Figure 2 B and E) and (2)
incisional AT2, which turns around at the septum edge of the long linear
LGE (Figure 2 C and F). If the conduction velocity was decreased in Area
A, it was considered a possible ablation target, as both incisional AT 1
and 2.
An automated high-resolution mapping system (Rhythmia, Boston
Scientific, Marlborough, Massachusetts) clearly demonstrated wide double
potentials at the linear LGE reaching from the RA free wall to the
septum during SR. This indicated conduction block along the linear LGE
(Figure 3 A and C). The activation from the SN propagated posteriorly or
caudally behind the linear LGE. Subsequently, these two activations
turned around both edges of the linear LGE and collided at the tricuspid
valve site of the low lateral RA. Notably, a slightly fragmented atrial
voltage was found at the patchy LGE (Area A), and its conduction
velocity was extremely slow compared to the other patchy LGEs.
Therefore, the AVN was mainly activated by a posteriorly propagated
pathway rather than a caudally propagated pathway.
Clinical AT (Cycle length: 476ms) was easily induced by burst pacing,
and the rhythmic system demonstrated that the activation propagated
clockwise around the long linear LGE (Figure 3 B and D). The
fractionated potentials could be recorded at the patchy LGE (Area A),
where the single RF application could terminate the AT without
prolongation of the PR interval. At the end of the procedure, no AT was
induced. The patient has been free from AT recurrence for six months
after CA.
DISCUSSION
Our case report demonstrated the usefulness of LGE-MRI to assess
conduction delay or block during SR and tachycardia in postoperative
patients. To the best of our knowledge, there has been no previous
report of the relationship between LGE-MRI and conduction disturbances
in postoperative RA.
AT in the RA after open-heart surgery is difficult to diagnose and treat
because of the effects of scar tissue associated with surgery and
pre-existing functional conduction block specific to the RA. In
addition, CA has a potential risk of unintended localized conduction
block in the RA. Furthermore, in some cases, isolation of the lateral RA
may result in complete sinus exit block requiring pacemaker
implantation.1 Although this might be prevented if
wavefront propagation during SR was assessed in advance, in many cases
the RF application is performed during tachycardia. Therefore, it is
beneficial to assess fibrosis distribution of the RA prior to the
procedure.
Recently, LGE-MRI has been proposed as a method to assess atrial
fibrosis.2 Cardiac fibrosis leads to conduction delay
and local conduction block, which promote functional re-entry.333Spach, M. S. and P. C. Dolber. ”Relating extracellular potentials and
their derivatives to anisotropic propagation at a microscopic level in
human cardiac muscle. Evidence for electrical uncoupling of
side-to-side fiber connections with increasing age.” Circulation
Research 1986;58(3): 356-371. It has been reported that increased
left atrial LGE is associated with lower local conduction
velocity.444 Fukumoto, K., Habibi, M., Ipek,
E.G. et al. Association of left atrial local conduction velocity with
late gadolinium enhancement on cardiac magnetic resonance in patients
with atrial fibrillation. Circulation: Arrhythmia and
Electrophysiology 2016;9(3): e002897. In the our case, LGE-MRI was
performed in the RA. This showed a correlation between the LGE sites and
conduction delay or block in high-resolution mapping. Comparing the
LGE-MRI and electro-anatomical mapping, the conduction velocities were
slower in Areas A and D than in Area B, despite similar patchy LGE
sites. This discrepancy may be caused by the direction of wavefront
propagation. Animal studies have shown that longitudinal conduction
velocities are 2 to 10 times faster than transversal velocities in the
RA, owing to a uniform longitudinal arrangement of muscle fibers and
non-uniform distribution of connexins to the interstitial
collagen.555 Gonzalez, M. D., Erga, K.S.,
Rivera, J. et al. Rate‐dependent block in the sinus venosa of the
swine heart during transverse right atrial activation: Correlation
between electrophysiologic and anatomic findings. Journal of
Cardiovascular Electrophysiology 2005;16(2): 193-200. This suggests
that, although fibrosis causes conduction delay, transversal fibrosis
causes a more pronounced conduction delay and may form the basis of the
re-entry circuit.
Linear LGE appeared to have a visual gap in the superior right appendage
on LGE-MRI; however, no conduction across the line during both SR and AT
could be detected. A previous report showed that the visual gap length
in the PV ablation line on LGE-MRI was associated with AF recurrence
after PV isolation, and the threshold for the highest specificity was a
gap length of 4.3 mm.666 Linhart, M., Alarcon,
F., Borras, R. et al. Delayed gadolinium enhancement magnetic
resonance imaging detected anatomic gap length in wide circumferential
pulmonary vein ablation lesions is associated with recurrence of
atrial fibrillation. Circulation: Arrhythmia and Electrophysiology
2018;11(12): e006659. In our case, the gap length on LGE-MRI was 2.7
mm. Therefore, we should have speculated that these small visual gaps
might demonstrate a conduction block.
CONCLUSIONS
By using the LGE-MRI prior to CA, wavefront propagation during SR as
well as the slow conduction zone during tachycardia could be assessed.
After CA of postoperative AT, this may assist in reducing the risk of
unexpected sinus exit block and it may negate the need for pacemaker
implantation.
ACKNOWLEDGMENTS
We would like to thank Editage
(www.editage.com) for English
language editing.
FIGURE LEGEND