(Circulation. 1995;92:77-81.)
© 1995 American Heart Association, Inc.
Articles |
Atrial Electrogram Characteristics in Patients With and Without Atrioventricular Nodal Reentrant Tachycardia
From the Department of Internal Medicine, Division of Cardiology, the University of Michigan Medical Center, Ann Arbor.
Correspondence to Fred Morady, MD, University of Michigan Medical Center, 1500 E Medical Center Dr, B1F245, Ann Arbor, MI 48109-0022.
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Abstract |
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Background Multicomponent atrial electrograms and "slow pathway potentials" are helpful in identifying target sites for radiofrequency catheter ablation of the slow pathway in patients with atrioventricular (AV) nodal reentrant tachycardia. The purpose of this study was to compare the atrial electrograms recorded at various locations in the right atrium in patients with and without AV nodal reentrant tachycardia to assess the specificity of multicomponent atrial electrograms and possible slow pathway potentials both for the posteroseptal right atrium and for patients with AV nodal reentrant tachycardia.
Methods and Results In 25 patients with AV nodal reentrant
tachycardia and 23 control patients without AV nodal reentrant
tachycardia or dual AV nodal physiology, atrial electrograms with an AV
ratio of 
1:2 were recorded at the posteroseptal right atrium near the
coronary sinus ostium and in the right atrium near the posterior,
lateral, and anterior aspects of the tricuspid annulus. Attempts were
made to identify broad, multicomponent, and double atrial electrograms.
There were no significant differences between the patients with and
without AV nodal reentrant tachycardia in the mean number of
deflections in the atrial electrograms or in the mean duration of the
atrial electrograms recorded at any of the atrial sites. In all
patients, the number of atrial electrogram deflections and the atrial
electrogram duration were significantly greater at the posteroseptal
position than at the other three atrial sites. The prevalence of
potentials with the appearance of slow pathway potentials in the
posterior septum was similar in patients with and without AV nodal
reentrant tachycardia (68% and 70%, respectively). The prevalence of
these potentials was 6% to 25% at the other three atrial sites
(P<.005 compared with the posterior septum).
Conclusions The atrial electrogram characteristics that have been found to be useful in identifying effective posteroseptal slow pathway ablation sites in patients with AV nodal reentrant tachycardia are equally prevalent in patients without AV nodal reentrant tachycardia or dual AV nodal physiology. Atrial electrograms in the posteroseptal area are broader and contain more deflections than at other areas in the right atrium, possibly because of conduction properties of the posterior transitional zone that are independent of the presence of AV nodal reentrant tachycardia.
Key Words: atrioventricular node • tachycardia • potentials • electrocardiology • reentry
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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Multicomponent atrial electrograms and potentials referred to as "slow pathway potentials" or "slow potentials" have been found to be helpful in identifying target sites for radiofrequency catheter ablation of the slow pathway in patients with atrioventricular (AV) nodal reentrant tachycardia.1 2 3 4 5 Target sites for ablation of the slow pathway are often located in the posteroseptal right atrium near the ostium of the coronary sinus, in the region of the posterior atrionodal inputs to the AV node.6 7 8 Therefore, the features of the atrial electrogram at slow pathway target sites may reflect characteristics specific to the posterior atrionodal fibers. The purpose of this study was to compare quantitatively the atrial electrograms recorded at various locations in the right atrium in patients with and without AV nodal reentrant tachycardia to assess the specificity of multicomponent atrial electrograms and slow pathway potentials both for the posteroseptal right atrium and for patients with AV nodal reentrant tachycardia.
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Methods |
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Patient Characteristics
The subjects of this study were 48 patients who underwent a radiofrequency ablation procedure at the University of Michigan Medical Center. Twenty-five patients had AV nodal reentrant tachycardia, and 23 patients who had an accessory AV connection acted as a control group. None of the patients in the control group had inducible AV nodal reentrant tachycardia or echo beats, evidence of dual AV nodal physiology, or slow pathway conduction. Dual AV nodal physiology was identified by an increment of 50 ms or more in the A2H2 interval in response to a decrement of 10 ms in the A1A2 interval during programmed atrial stimulation with a single atrial extrastimulus.9 An AH interval of 240 ms or more during atrial overdrive pacing to the point of AV nodal Wenckebach block or an A2H2 interval of 240 ms or more during programmed atrial stimulation with a single atrial extrastimulus was considered evidence of slow pathway conduction.
The
AV nodal conduction properties and refractory periods for both
groups of patients are described in Table 1
. In the
control group, AV nodal properties were measured after accessory AV
connection ablation. Because ablative lesions in the right atrium might
alter the characteristics of the atrial electrogram, patients with
right-sided or posteroseptal accessory AV connections were not included
in the study. There were 24 men and 24 women, and their mean age was
40±18 years (±SD). None of the patients had structural heart
disease.
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Electrophysiological Testing and Catheter Ablation
The
electrophysiology procedures were performed after informed
consent was obtained and after all antiarrhythmic medications had been
withheld for at least five half-lives. Three quadripolar electrode
catheters were inserted into a femoral vein and positioned in the right
atrium, across the tricuspid valve to record the His bundle
electrogram, and in the right ventricle. Leads V1,
I, II, and III and the intracardiac electrograms were displayed on an
oscilloscope and recorded on paper with a Mingograph-7 recorder
(Siemens-Elema). Programmed stimulation was performed with a
programmable stimulator (Bloom). Tachycardia mechanisms were determined
using standard electrophysiological criteria.9
In patients with AV nodal reentrant tachycardia, radiofrequency ablation of the slow pathway was performed using a combined electrogram mapping and anatomic approach.5 In patients with an accessory AV connection, radiofrequency ablation of the accessory AV connection was performed as previously described.10
Study Protocol
The study protocol was performed before
ablation of the slow
pathway in patients with AV nodal reentrant tachycardia and after
ablation of the accessory AV connection in the control group. Bipolar
atrial electrograms were recorded at four sites in the right atrium
using a 7F catheter with a 4-mm distal electrode, 2-mm interelectrode
spacing, and a deflectable tip (Mansfield). These sites consisted of
the posterior septum near the ostium of the coronary sinus and sites
near the posterior, lateral, and anterior tricuspid annulus as
visualized fluoroscopically in the 60° left anterior oblique view. At
all sites and in all patients, electrograms were sought that had an AV
ratio of 1:2 or less, which were broad and multicomponent and contained
a potential similar in appearance to what has been referred to in prior
studies as slow pathway potentials or slow
potentials.1 2
In patients with AV nodal reentrant tachycardia, the electrogram
recorded before ablation at the effective slow pathway target site was
used as the posteroseptal site. The bipolar electrograms were filtered
at a band pass of 50 to 500 Hz and recorded at a gain setting of 80
mm/mV and a paper speed of 100 mm/s.
Analysis of Atrial Electrograms
Atrial electrograms were
analyzed in blinded fashion. The number
of atrial electrogram deflections that had an amplitude of at least 1
mm and an upstroke of at least 45° were counted (Fig 1).
The atrial electrogram duration was measured
manually to the nearest millimeter (equivalent to 10 ms) from the
beginning of the first deflection to the end of the last contiguous
deflection (Fig 1). The presence or absence of a possible slow
pathway
potential was noted, with slow pathway potentials being defined as
discrete potentials occurring in the terminal portion of the atrial
electrogram or separated by an isoelectric segment (Fig
2).1 2 The intraobserver
reproducibility in
determining the number of deflections, electrogram duration, and
presence of a slow pathway potential was 95%, 90%, and 94%,
respectively. The corresponding values for interobserver
reproducibility were 85%, 80%, and 88%. Differences in opinion
regarding the presence of slow pathway potentials were resolved by
consensus.
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Data Analysis
Values are expressed as mean±SD.
Electrogram characteristics at
sites recorded within patients were compared by ANOVA with repeated
measures. Comparisons were made between patients with and without AV
nodal reentrant tachycardia by ANOVA. Post hoc comparisons between
groups were made using the Sheffé means test. When there were no
differences between patients with and without AV nodal reentrant
tachycardia, the data were pooled for comparisons between right atrial
sites. The prevalence of slow pathway potentials was compared by
2 analysis. Probability values less than .05
were considered significant.
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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Number of Deflections
There were no significant differences between the patients with and without AV nodal reentrant tachycardia in the mean number of deflections in the atrial electrograms recorded at any of the atrial sites. In patients both with and without AV nodal reentrant tachycardia, the mean number of atrial electrogram deflections was significantly greater at the posteroseptal position than at the other three atrial sites. There were no significant differences between the other sites in the number of atrial electrogram deflections (see Table 2
).
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Atrial Electrogram Duration
There were no significant
differences between the patients with
and without AV nodal reentrant tachycardia in the mean duration of the
atrial electrograms recorded at any of the atrial sites. In patients
both with and without AV nodal reentrant tachycardia, the mean atrial
electrogram duration was significantly greater at the posteroseptal
position than at the other three atrial sites and was significantly
greater near the posterior aspect of the tricuspid annulus than near
its anterior aspect (see Table 3).
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Slow Pathway Potentials
A potential consistent with a slow
pathway potential was
identified in the posterior septum in 68% of patients with AV nodal
reentrant tachycardia and in 70% of patients without AV nodal
reentrant tachycardia (Fig 3); these prevalences did not
differ significantly. The mean duration of these potentials in patients
with and without AV nodal reentrant tachycardia did not differ
significantly (21±8 and 18±6 ms, respectively) (see Table
4).
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At sites near the posterior, lateral, and anterior
tricuspid annulus,
the prevalence of potentials identical in appearance to the slow
pathway potentials recorded in the posterior septum ranged from 4% to
16% in patients with AV nodal reentrant tachycardia and from 7% to
35% in patients without AV nodal reentrant tachycardia (Fig 4).
At no site was there a significant difference
between the patients with and without AV nodal reentrant tachycardia.
The prevalence of potentials consistent with a slow pathway potential
was significantly higher in the posterior septum than at the anterior
free wall of the tricuspid annulus (P<.05).
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The mean
interval between the two components of the atrial electrogram
in patients who had a potential consistent with a slow pathway
potential was 31±9 ms in patients with AV nodal reentrant tachycardia
and 28±8 ms in the control patients; these intervals did not differ
significantly. The onset of the apparent slow pathway potentials
consistently occurred after the onset of the atrial electrogram
recorded in the proximal coronary sinus regardless of where along the
tricuspid annulus they were recorded (Figs 2 through
4
).
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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Main Findings
The results of this study demonstrate that the features of the atrial electrogram that are helpful in identifying effective posteroseptal right atrial target sites for ablation of the slow AV nodal pathway are not specific to patients with AV nodal reentrant tachycardia. Multicomponent atrial electrograms and possible slow pathway potentials present at posteroseptal target sites that were effective in eliminating AV nodal reentrant tachycardia were found to be equally prevalent in the posteroseptal right atrium in patients with and without AV nodal reentrant tachycardia. The characteristics of the target site electrogram were dependent on the position of the recording site relative to the tricuspid annulus regardless of whether or not the patient had AV nodal reentrant tachycardia. Atrial electrograms recorded at the posteroseptal right atrium had a longer duration and more components than right atrial sites near the posterior, lateral, and anterior aspects of the tricuspid annulus and more often contained a potential consistent in appearance with a slow pathway potential.
Multicomponent Atrial Electrograms
In prior studies, low- or
high-frequency potentials attached to or
discrete from the atrial electrogram recorded in the mid or posterior
right atrial septum and distinct from the His bundle electrogram have
been variously referred to as double atrial electrograms,6
slow potentials,2 or slow pathway
potentials.1 3 Several studies have demonstrated that
these potentials are prevalent in the posterior septum near the ostium
of the coronary sinus in patients with AV nodal reentrant
tachycardia,1 2 6 8 in
individuals without AV nodal
reentrant tachycardia,2 and in porcine and canine
hearts.7 8
The results of the present study confirm the fact that the potentials in question are not specific to individuals who have AV nodal reentrant tachycardia and extend the findings of the prior studies to demonstrate that these potentials also may be found at right atrial sites remote from the posterior septum. Of note is that the potentials recorded at the posterior septum and at various locations around the tricuspid annulus in this study were similar in duration and timing to the slow pathway potentials reported in a prior study.1
Although a prior study of isolated porcine hearts demonstrated that slow potentials arise from transitional cells,8 our results indicate that this need not be the case in humans. In the present study, potentials identical to slow potentials recorded in the posterior septum were also recorded at sites in the right atrium, where transitional cells would not be expected to be found. This would be consistent with the results of postmortem examinations and histological studies in explanted hearts of transplant recipients that have demonstrated that there are no anatomic features in or adjacent to the AV node that distinguish patients who have AV nodal reentrant tachycardia or dual AV nodal physiology from others.11 12 13 14 Therefore, slow potentials or double atrial electrograms also may arise from some other mechanism. One possible explanation is that they result from asynchronous or sequential activation at the recording site due to anisotropy or slow conduction.15
Limitations
A limitation of this study is that data were
obtained from
only four right atrial sites near the tricuspid annulus. The recording
sites were confined to areas near the tricuspid annulus in order to
maintain an AV electrogram ratio less than 1:2, similar to the AV
electrogram ratio recorded at slow pathway ablation sites. Therefore,
although unlikely, the possibility that some difference between the
atrial electrograms of patients with and without AV nodal reentrant
tachycardia may exist at atrial sites other than those sampled in this
study cannot be ruled out.
A second limitation of this study is that identification of possible slow pathway potentials was based solely on morphological criteria, and no pacing maneuvers were performed to validate their presence. However, although prior studies have used pacing techniques to validate slow pathway potentials,1 2 the specificity of these pacing techniques for slow pathway potentials has not been established.
Conclusions and Implications
The atrial electrogram
characteristics that have been found to be
useful in identifying effective posteroseptal slow pathway ablation
sites in patients with AV nodal reentrant tachycardia are equally
prevalent in patients without AV nodal reentrant tachycardia or dual AV
nodal physiology. This suggests that the multicomponent or double
atrial electrogram may be a characteristic of the posterior
transitional zone independent of the presence or absence of AV nodal
reentrant tachycardia.
A second conclusion of this study is that although the electrogram features that are helpful in guiding slow pathway ablation are more prevalent in the posteroseptal right atrium than in other areas of the right atrium, these features, including broad, multicomponent electrograms and potentials consistent with slow pathway potentials, also may be recorded at atrial sites remote from the region near the coronary sinus ostium, where effective ablation sites are located. This implies that an approach to slow pathway ablation that depends only on mapping of the atrial electrogram would be highly inefficient and that the electrogram mapping approach must be combined with an anatomic approach to be effective.
Received November 28, 1994; accepted January 3, 1995.
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