(Circulation. 1998;98:2296-2300.)
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports |
Absence of Junctional Rhythm During Successful Slow-Pathway Ablation in Patients With Atrioventricular Nodal Reentrant Tachycardia
From the Division of Cardiology, Department of Medicine, National Yang-Ming University, School of Medicine, and Veterans General Hospital-Taipei, Taiwan.
Correspondence to Shih-Ann Chen, MD, Division of Cardiology, Veterans General Hospital-Taipei, 201 Sec 2, Shih-Pai Rd, Taipei, Taiwan. E-mail sachen{at}vghtpe.gov.tw
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Abstract |
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Background—The presence of junctional rhythm has been considered to be a sensitive marker of successful slow-pathway ablation. However, in rare cases, junctional rhythm was absent despite multiple radiofrequency applications delivered over a large area in the Koch's triangle, and successful ablation was achieved in the absence of a junctional rhythm.
Methods and Results—This study included 353 patients with AV nodal reentrant tachycardia (143 men and 210 women; mean age, 50±17 years) who underwent catheter ablation of the slow pathway. Combined anatomic and electrogram approaches were used to guide ablation. Inducibility of AV nodal reentrant tachycardia was assessed after each application of radiofrequency energy. Successful sites were located in the posterior area in 18 (90%) of 20 patients without junctional rhythm during slow-pathway ablation compared with 200 (60%) of 333 patients with junctional rhythm (P<0.001). The fast-slow form of tachycardia was more common in patients without than in those with junctional rhythm (30% versus 3%; P=0.001). At the successful ablation sites, patients with junctional rhythm had a higher incidence of a multicomponent or slow-pathway potential (51% versus 10%; P<0.001), a longer duration of the atrial electrogram (64±8 versus 50±9 ms; P=0.04), and a smaller atrial/ventricular electrogram amplitude ratio (0.29±0.18 versus 0.65±0.27; P<0.001) than those without junctional rhythm. Mean temperatures at successful sites (56±6°C versus 58±9°C; P=0.57) and incidence of transient AV block (2% versus 0%; P=0.86) were similar between patients with and without junctional rhythms. By multivariate analysis, location of ablation sites, atrial/ventricular electrogram amplitude ratio, absence of a multicomponent or slow-pathway potential, and occurrence of the fast-slow form of tachycardia were independent predictors of the absence of a junctional rhythm during successful slow-pathway ablation.
Conclusions—In some rare cases, successful slow-pathway ablation is possible in the absence of a junctional rhythm.
Key Words: atrioventricular node • catheter ablation • tachyarrhythmias
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Introduction |
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Selective radiofrequency catheter ablation of the slow AV nodal pathway has been established as a first-line curative treatment modality in patients with symptomatic AV nodal reentrant tachycardia. Many investigators have used several different methods to perform successful ablation of the slow pathway.1 2 3 4 5 6 7 The presence of a junctional rhythm during slow-pathway ablation has been indisputably considered to be the most sensitive but nonspecific marker of successful ablation.8 9 10 11 However, the absence of junctional rhythm during successful slow-pathway ablation has not been well described. The purposes of the present study were to investigate electrophysiological characteristics in patients with and those without junctional rhythm and to determine the variables related to the absence of junctional rhythm during successful slow-pathway ablation.
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Methods |
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Patient Population
The present study included 353 consecutive patients with AV nodal reentrant tachycardia. These patients underwent successful radiofrequency catheter ablation of the slow pathway between January 1995 and June 1997. Patients who received ablation of the retrograde slow pathway under ventricular pacing were excluded because it was difficult to observe junctional rhythm while radiofrequency energy was delivered during ventricular pacing. There were 143 men and 210 women included in the present study, and their mean age was 50±17 years (range, 15 to 80 years).
Electrophysiological Test
Informed consent was obtained from all patients, and they were
studied in the postabsorptive, nonsedated state after written informed
consent had been obtained. Details of the
electrophysiological study have been
described previously.12 13 Intracardiac
electrograms were filtered at 30 to 500 Hz and
simultaneously displayed with surface ECG leads I, II, and
V1 on a multichannel oscilloscope (Electronics
for Medicine, VR-13, MIDAS 2500, or ART Prucka recording
system) and were recorded at a paper speed of 100 to 150 mm/s.
The baseline electrophysiological study was
performed after antiarrhythmic drugs had been discontinued for 
5
half-lives; this included determination of the effective refractory
periods of the right atrium, the AV node (fast and slow pathways in the
antegrade and retrograde directions), and the right ventricle. If
tachycardia was not induced in the baseline state,
isoproterenol (at graded doses from 1 to 4 µg/min IV) or atropine
(0.01 to 0.02 mg/kg IV) was infused to facilitate its induction. AV
nodal reentrant tachycardia was diagnosed by previously
described criteria; intra-atrial reentrant tachycardia and
tachycardia incorporating a midseptal or paraseptal
accessory pathway were excluded.14 15 16
Mapping/Ablation and Junctional Rhythm
The method used for mapping and ablation has been described
previously.12 13 The right atrial septum adjacent
to the septal leaflet of the tricuspid valve, extending from the ostium
of the coronary sinus (posterior) to the recording site
at the His bundle area (anterior), was divided into posterior, medial,
and anterior regions. To determine the possible anatomic site of the
slow pathway, the mapping and ablation catheter tip was initially
positioned in the posterior area, then the medial and finally the
anterior areas, if necessary. The presumed ablation site was considered
optimal if bipolar electrograms obtained from the distal electrodes
showed an atrial/ventricular electrogram amplitude ratio of
0.1 to 0.5, with a multicomponent or a putative slow-pathway
potential.1 3 7 Radiofrequency energy was applied
for 20 seconds after a target site was identified. If AV nodal
reentrant tachycardia could not be eliminated after
delivery of radiofrequency energy to the optimal sites, areas with
different electrogram characteristics were chosen for ablation. The
electrode catheter used for ablation had a thermistor embedded in the
deflectable 4-mm-tip electrode (7F, EP Technologies, Inc).
Radiofrequency energy was delivered from a generator (EPT-1000, EP
Technologies, Inc), which supplied continuous, unmodulated sine-wave
output at 500 kHz. Power, impedance, and temperature were measured,
displayed, and stored during each application of radiofrequency energy
via an interface with a microcomputer (NEC DX33–486). The maximum
preset temperature was 70°C in every patient. Radiofrequency energy
was terminated immediately in the event of impedance rise, displacement
of the catheter, an increase in PR interval, or occurrence of AV
conduction block.
Junctional rhythm was identified on the basis of an intracardiac electrogram with a low-to-high atrial activation sequence and shorter, irregular cycle length.8 10 11 17 Once junctional rhythm during ablation for 20 seconds was noted, radiofrequency energy was applied again for 60 seconds under high right atrial overdrive pacing. If no junctional rhythm was observed, radiofrequency energy was aborted at 20 seconds, then programmed stimulation was performed to test inducibility of AV nodal reentrant tachycardia. If tachycardia was inducible, application of radiofrequency energy was tried again after the ablation catheter was repositioned. If tachycardia was not inducible, radiofrequency energy was applied for 60 seconds despite the absence of junctional rhythm.
Ablation-Site Electrogram
In the present study, local atrial electrograms at
successful ablation sites were divided into 2 forms, a single-component
or a multicomponent atrial electrogram
(Figure
). A multicomponent atrial
electrogram was defined as one with several small deflections on the
focal atrial electrogram.
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Postablation Follow-Up
A complete electrophysiological
study was performed 20 to 30 minutes after the ablation procedure to
determine the immediate effects of radiofrequency ablation. As
described previously,12 13 all patients were
observed in the coronary care unit and were monitored by ECG
for 24 hours. After discharge from hospital, patients returned to our
outpatient clinic 1 week, 1 month, 2 month and subsequently every 3
months after ablation. Ambulatory ECG monitoring or cardiac-event
recording was performed in patients who experienced palpitation
or tachycardia.
Analysis of Different Parameters
Data on ablation-site locations (including posterior, medial,
and anterior areas), ablation-site electrograms (including amplitude of
atrial and ventricular electrograms,
atrial/ventricular electrogram amplitude ratio, atrial
electrogram duration, and presence of a multicomponent atrial
electrogram), forms of tachycardia (slow-fast, fast-slow,
or both), mean and maximum temperatures of successful ablation sites,
number of radiofrequency applications, and antegrade conduction
impairment (AV block or impairment) were obtained for
analysis.
Statistical Analysis
All parametric data are expressed as mean±SD.
Comparisons of parametric data were analyzed by a
2-tailed Student's t test. The 
2
test with Yates' correction or Fisher's exact test was used to
compare nonparametric data in different groups.
Univariate and multivariate
analyses with a stepwise logistic regression model were
performed to analyze variables that could predict the
absence of junctional rhythm. A P value < 0.05 was
considered statistically significant.
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Results |
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Patient Characteristics
Among the 353 patients with AV nodal reentrant tachycardia who underwent successful slow-pathway ablation, 333 (94.3%) had junctional rhythm during the successful radiofrequency pulses, but 20 (5.7%) did not. Three forms of tachycardia were found, including slow-fast (319 patients, 90%), fast-slow (16 patients, 5%), and both forms of tachycardia (18 patients, 5%). In patients without junctional rhythm during successful pulses, the fast-slow form of tachycardia was more common than in those with junctional rhythm (30% versus 3%; P=0.001), and the slow-fast form of tachycardia was more common in patients with than in those without junctional rhythm (92% versus 65%; P=0.001) (Table
).
In addition, 13 (4%) of 319 patients with slow-fast AV nodal reentrant
tachycardia and 6 (37%) of 16 patients with fast-slow AV
nodal reentrant tachycardia did not have junctional rhythm.
There was no occurrence of permanent AV block after successful
ablation.
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Locations and Electrograms of Successful Sites
More patients without junctional rhythm had successful ablation
sites in the posterior area than those with junctional rhythm (90%
versus 60%; P<0.001) (Table
). The amplitudes of atrial
electrograms were similar between patients with and without junctional
rhythms during successful slow-pathway ablation (0.19±0.11 versus
0.30±0.20 mV; P=0.10) (Table). However, in patients with
junctional rhythm, the amplitudes of ventricular
electrograms were significantly larger than in those without junctional
rhythm (0.77±0.27 versus 0.50±0.28 mV; P=0.02).
Furthermore, the atrial/ventricular electrogram amplitude
ratios were significantly larger in patients without junctional rhythm
than in those with junctional rhythm (0.65±0.27 versus 0.29±0.18;
P<0.001). The duration of the atrial electrogram was
significantly longer at the successful ablation sites in patients with
junctional rhythm than in those without junctional rhythm (64±8 versus
50±9 ms; P=0.04). At the successful ablation sites, a
multicomponent atrial electrogram was more common in patients with than
in those without junctional rhythm (51% versus 10%;
P<0.001).
Other Parameters
Mean (56±6°C versus 58±9°C; P=0.57) and maximum
(66±8°C versus 69±5°C; P=0.40) target-site
temperatures during successful slow-pathway ablation were similar
between patients with and without junctional rhythms (Table). The mean
number of radiofrequency pulses used for successful slow-pathway
ablation was significantly greater in patients without junctional
rhythm than in those with junctional rhythm (10±5 versus 5±3;
P=0.01). During or after radiofrequency ablation, the
incidences of transient AV block (2% versus 0%; P=0.86)
and AV nodal function impairment (1% versus 0%; P=0.91)
were similar between patients with and without junctional rhythms
(Table).
Predictors of Absence of Junctional Rhythm
By multivariate analysis, location of
ablation site (P=0.01; OR, 7.83; 95% CI, 1.52 to 40.51),
atrial/ventricular electrogram amplitude ratio
(P<0.001; OR, 18.80; 95% CI, 4.87 to 72.60), absence of a
multicomponent or putative slow-pathway potential (P=0.002;
OR, 19.13; 95% CI, 3.07 to 119.30), and tachycardia form
(fast-slow form) (P=0.01; OR, 9.12; 95% CI, 1.94 to 42.86)
were independent predictors of the absence of junctional rhythm during
successful slow-pathway ablation.
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Discussion |
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Major Findings
The major findings of the present study are as follows: (1) successful ablation sites in patients without junctional rhythm during slow-pathway ablation were located mostly in the posterior area; (2) atrial/ventricular electrogram amplitude ratios were significantly larger in patients without junctional rhythm than in those with junctional rhythm; (3) a multicomponent or a putative slow-pathway potential was rarely seen in patients without junctional rhythm; and (4) absence of junctional rhythm was more frequently noted in patients with the fast-slow form of AV nodal reentrant tachycardia.
Possible Mechanism of Absence of Junctional Rhythm With
Successful Ablation
In the present study, successful ablation sites were located
in the posterior and medial areas in almost all patients; however,
successful sites were located mostly in the posterior area, far from
the His bundle, in patients without junctional rhythm. Furthermore, the
atrial/ventricular electrogram amplitude ratio at
successful ablation sites was significantly larger in patients without
than in those with junctional rhythm. These findings suggest that
successful ablation sites were closer to the atrial aspect of posterior
AV junctional tissue in patients without junctional rhythm. This area
of posterior input into the AV node is very complex, and the atrial
electrograms may differ at different points along the pathway.
Therefore, the different atrial electrograms seen when this area is
mapped in patients with or without junctional rhythm may
represent different target sites along this pathway. The other
possibility is that the slow AV nodal pathways in these patients
without junctional rhythm may be different from those in patients with
junctional rhythm. This hypothesis could explain why junctional rhythm
was so difficult to induce in some patients.
Furthermore, the present study showed that the form of tachycardia was significantly different between patients with and without junctional rhythms. In patients without junctional rhythm during slow-pathway ablation, the incidence of the fast-slow form of tachycardia was higher than in those with junctional rhythm. Previous study18 has also shown that most of the retrograde slow pathways are in the lower anatomic location of Koch's triangle, which is different from the antegrade slow pathways. Thus, ablation of the retrograde slow pathway had a lower incidence of junctional rhythm because the successful ablation sites were far from the His bundle area.
A multicomponent atrial electrogram, which is characterized by a sequence of multiple small deflections, is produced by nonuniformly anisotropic tissue.19 In nonuniformly anisotropic tissue, defined by Spach and Josephson,19 conduction through atrial and ventricular myocardium is much slower and characteristically produces a prolonged, multiphasic extracellular electrogram. In animal studies,20 21 22 the atrial myocardium adjacent to the ostium of the coronary sinus, which served as the posterior input into the AV node, was associated with fractionated electrograms or double atrial electrograms similar to slow-pathway potentials. In human studies, Niebauer et al23 found that slow-pathway potential or multicomponent atrial electrograms were recorded at many locations around the tricuspid annulus in the right atrium, and the prevalence was significantly higher at the posterior septum than at other right atrial sites. However, a multicomponent atrial electrogram was present only in 10% of our patients without junctional rhythm, and successful sites were located mostly in the posterior area. Thus, the tissue characteristics of these slow pathways may be different from those in patients without junctional rhythm.
Relation Between Junctional Rhythm and Ablation-Site
Electrogram
Although Jackman et al1 found a discrete
slow-pathway potential at nearly all successful ablation sites, there
have been several conflicting reports discussing the different
prevalences and definitions of these
potentials.3 7 9 24 25 26 Haissaguerre et
al3 reported that during ablation of the slow
pathway with discrete slow potentials used as a guide, 78% of 64
patients developed junctional rhythms. Kelly et
al9 demonstrated several independent predictors
of successful ablation, including the occurrence of junctional rhythm
(93%) during ablation and the presence of a discrete slow-pathway
potential (81%) in the successful ablation site. In the present
study, a multicomponent atrial electrogram was present in 49% of
successful ablation sites (172 patients), and the prevalence of a
multicomponent atrial electrogram was significantly higher in patients
with than in those without junctional rhythm. These reports suggest
that junctional rhythm occurs frequently in the presence of a
multicomponent atrial electrogram or slow-pathway potentials.
Several studies7 9 25 reported that a longer duration of atrial electrograms was seen at the successful ablation site in patients with AV nodal reentrant tachycardia. In the present study, the duration of atrial electrograms was significantly longer in patients with junctional rhythm than in those without junctional rhythm during successful slow-pathway ablation. The duration of atrial electrograms would be longer in the presence of a multicomponent atrial electrogram. Therefore, the duration of atrial electrograms was significantly longer in patients with junctional rhythm because they had a higher incidence of multicomponent atrial electrograms.
Study Limitations
This was a retrospective study, and therefore we could not study
several variables that would have furthered our understanding of
the electrophysiological mechanism in
patients with or without junctional rhythms during slow-pathway
ablation. However, a prospective study would have been difficult to
perform because the incidence of absence of junctional rhythm was very
low. Therefore, we looked for different characteristics in these 2
groups of patients with the hope that our results would prove
instructive in the future. The number of radiofrequency pulses was
smaller in patients with junctional rhythm than in those without
junctional rhythm. This finding may be related to several factors,
including the fact that easy induction of junctional rhythm results in
early ablation success. On the other hand, the use of a greater number
of pulses produces more severe tissue edema, after which more pulses
are required to perform successful ablation.
Clinical Implications
The major clinical implication in the present study is that in
rare cases, successful slow-pathway ablation can be achieved in the
absence of junctional rhythm with unusual atrial electrograms. We were
able to deliver radiofrequency energy for a longer duration, although
we could not induce a junctional rhythm or standard atrial electrograms
during ablation after systematic mapping. This could decrease procedure
and fluoroscopic times.
Conclusions
Patients without junctional rhythm during successful slow-pathway
ablation predominantly had posterior locations of the ablation site,
larger atrial/ventricular electrogram amplitude ratio,
shorter duration of the atrial electrogram, and a lower incidence of a
multicomponent or slow-pathway potential than patients with junctional
rhythm. Thus, in some rare patients with AV nodal reentrant
tachycardia, successful slow-pathway ablation is possible
in the absence of junctional rhythm during radiofrequency
applications.
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Acknowledgments |
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This study was supported in part by grants from the National Science Council (NSC-87-2314-B-010-058, 87-2314-B-010-059, NSC-87-2314-075-070; 87-2314-B-075-071) and Tzou's Foundation (VGH-33, VGHYM 86-S4-30, and VGHYM 86-S4-31), Taipei, Taiwan.
Received March 3, 1998; revision received July 21, 1998; accepted July 22, 1998.
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