Abdurrahman Eksik, M.D., Ahmet Akyol, M.D.,
Tugrul Norgaz , M.D., Izzet Erdinler, M.D
Siyami Ersek Thoracic and Cardiovascular Surgery Center, Cardiology
Department, Istanbul-Turkey.
Address for
correspondence: Abdurrahman Eksik, Address for correspondence:
Abdurrahman Eksik, M.D., Eminbey caddesi, G-3 sokak,Kerimzade sitesi, A
blok D:12 Acıbadem,Kadıköy, Istanbul, Turkey. E-mail: abeksik@yahoo.com
Abstract
Background: Radiofrequency (RF) catheter ablation is the
procedure of choice for the potential cure of atrioventricular nodal
reentrant tachycardia (AVNRT) with high success rates. We hypothesed
that as a result of the close proximity of Koch’s triangle and low
inter-atrial septal fibers, the RF ablation applied at this region may
result in prolongation of inter-atrial conduction time (IACT).
Methods: RF ablation of AVNRT was performed by conventional
technique. IACT was measured before and 20 minutes after RF ablation
during sinus rhythm. Number of ablations given and duration of ablation
were noted.
Results: The study group was consisted of 48 patients (36 [75%]
female, 12 [25%] male, mean age 43.4 ± 14. 5 years). RF ablation
was successful in all patients. Mean RF time was 4. 0 ± 3. 3
minutes and mean number of RF was 11. 9 ± 9, 8. The mean IACT
was 70.1 ± 9.0 ms before ablation and 84.9 ± 12.7 ms
after ablation, which demonstrated a significant prolongation
(p<0.001). The prolongation of IACT was very well correlated with
the number of (r=0.897, p<0.001) and duration of RF (r=0.779;
p<0.001).
Conclusions: RF ablation of AVNRT results in prolongation of IACT.
The degree of prolongation is associated with the duration and number
of RF ablations given. The relationship between this conduction delay
and late arrhythmogenesis need to be evaluated.
Key words: RF ablation; AVNRT; inter-atrial conduction time
List of abbreviations used in the manuscript: RF (radiofrequency),
AVNRT (atrioventricular nodal reentrant tachycardia), IACT
(inter-atrial conduction time), SP (slow pathway), EPS
(electrophysiologic study).
Introduction
Radiofrequency
(RF) catheter ablation is the procedure of choice for the potential
cure of atrioventricular nodal reentrant tachycardia (AVNRT) with high
success rates. Slow pathway (SP) ablation is the best method for the
treatment of AVNRT. It has been shown that successful atrial flutter
ablation was associated with an altered sequence of left atrial
activation
1. But, no studies
have evaluated the effect of RF ablation of AVNRT on inter-atrial
conduction. We hypothesed that as a result of the close proximity of
Koch’s triangle and low inter-atrial septal fibers, the RF ablation
applied at this region may result in prolongation of inter-atrial
conduction time (IACT). For this purpose, we evaluated the effect of RF
ablation on IACT before and after ablation of SP, during sinus rhythm.
Materials and Methods
Patients
The study
group was consisted of 48 consecutive patients with common type AVNRT
who had inducible AVNRT with dual or multiple atrioventricular node
(AVN) physiology in the atrial extra-stimulations and who had undergone
SP ablation between April 2004 and March 2005. Exclusion criteria were
presence of clinically significant valvular, congenital or ischemic
heart disease, any type of cardiomyopathy, and heart failure and
patients with dilatated atria. After informed consent was obtained, the
electrophysiologic study (EPS) was performed in the fasting state
without any sedative medications. Antiarrhythmic drugs were
discontinued for at least 5 half-lives before the ablation.
Transthoracic echocardiography was performed in all patients to
determine the presence of exclusion criteria.
Catheters and Electrogram Recordings
Three 5F
quadripolar electrode catheters were introduced via the femoral vein,
and were positioned against the high right atrium (HRA), the His bundle
region, and the right ventricular apex (RVA) under fluoroscopic
guidance. One 7F decapolar catheter (inter-electrode distance: 2mm) was
introduced into the coronary sinus via the femoral vein. Patients’ data
were analyzed on a paper recording at 200 mm/s (Model VR-13, Biomedical
Systems, USA), and data were stored for analysis on optical disks using
a computer-recording system and were analyzed on screen (Cardio Lab
System, Marquette, MI,USA).
Basic Study and Diagnosis
Single
extra-stimulation and incremental pacing were performed at the HRA and
RVA sites for the basic electrophysiological evaluation. Prolongation
of the atria-His (AH) interval of not less than 50 ms in response to
the shortening of the coupling interval of the premature atrial
stimulus by 10 ms was defined as the ‘jump-up’ phenomenon of the AH
interval.
2 When the single
atrial stimulus could not induce the AH jump-up, a
double-atrial-extra-stimulus protocol was performed to achieve shorter
premature coupling intervals.
3
AVNRT was diagnosed in accordance with the following criteria: (1) the
jump-up phenomenon of the AH interval after single or double atrial
stimulus, (2) induction of narrow QRS regular tachycardia without the
participation of an accessory pathway, and (3) simultaneous activation
of the atrium and ventricle during tachycardia.
4
The second criterion was confirmed by single-ventricle scanning
(ventricular pacing during His refractoriness in order to observe
retrograde atrial activation) during tachycardia and sinus rhythm
to exclude orthodromic AV reciprocal tachycardia involving an accessory
pathway. When tachycardia could not be induced in the basic state,
atropine was infused intravenously at a dose 1 mg to increase the basic
sinus rate by 20-50%, and the same stimulation protocol was repeated.
Inter-atrial Conduction Time Measurement
The 5F
quadripolar electrode catheter was positioned at HRA during sinus
rhythm where the earliest RA activation was achieved. Right to
left IACT’s were measured from earliest right atrial activation to the
distal coronary sinus. Left to right IACT’s were measured from distal
coronary sinus pacing to earliest right atrial activation.
Measurements were done before ablation and 20 minutes after ablation.
In order to be sure for the exact position of catheter during
measurements before and after ablation, we stored the image of catheter
position before ablation and used this image to guide the position of
the catheter for measurement after ablation. In order to exclude
the autonomic effects produced by RF energy after the procedure IACT
measurement was repeated following atropine.
SP Ablation
After the
basic EPS, a 7F quadripolar steerable ablation catheter with 4 mm-tip
and 2.5 mm interelectrode spacing (Marinr, Medtronic, USA) was
introduced through the femoral vein. The catheter tip was initially
positioned along the tricuspid annulus anterior to the ostium of the
CS. In the lowest one-third of the area between the recording site at
the His bundle and the ostium of the coronary sinus, the optimal
ablation site was determined under guidance of the SP potential as
described by Jackman et al
5
with an A/V ratio of 0.1 to 0.5. Radiofrequency energy was delivered
with a temperature controlled ablation unit (Atakr RF Ablation system,
Medtronic) at 60°C during sinus rhythm. If a junctional beat was
recognized within 10s, the energy delivery was continued for 1 min, and
was terminated immediately in the cases showing impedance rise or any
signs of AH block. After each ablation procedure, the pacing protocol
was repeated to evaluate the inducibility of AVNRT. When AVNRT was
still inducible, the ablation catheter was repositioned to a more
superior region along the tricuspid annulus and the ablation procedure
was continued. The ablation procedure was considered to be successful
when AVNRT could not be induced 20 min after the last delivery of
radiofrequency energy. In the post-ablation study, atropine was infused
only when it had been needed for AVNRT induction in the basic state
before the ablation. Single atrial echo beat or jump-up of the AH
interval was allowed to remain.
Statistical analysis
All conduction
times were given in milliseconds and expressed as mean ±
Standard deviation. Statistical analyses of data were performed using
Student’s t test for paired data. Spearman’s correlation analyses were
used to evaluate correlation between parameters. All analyses were
performed by using SPSS 10.0 computer programme.A p value of < 0.05
was considered as statistically significant.
Results
The study
group was consisted of 48 patients (36 [75 %] female, 12 [25 %] male,
mean age 43. 4 ± 14 and 5 years). RF ablation was successful in
all patients. We observed no major complications. Mean RF time was 4. 0
± 3.3 minutes and mean number of RF was 11. 9 ± 9.8
including very short RF’s to confirm nodal beat formation. Tachycardia
was initiated by atrial extra stimulus in 43 patients and by atropine
infusion in 5 patients.
Post ablation
cycle length was 685.8 ± 81.0 ms. The sinus P wave morphology on
12-lead surface ECG was unchanged after ablation. The mean IACT was
70.1 ± 9. 0 ms before ablation and 84.9 ± 12.7 ms
after ablation, which demonstrated a significant prolongation
(p<0.001). Sample intracardiac ECG tracings and fluoroscopic figures
showing the position of catheters are presented in
Figures 1-5.
Figure 1: Left anterior
oblique radiograph of catheters position during measurements
Click here to enlarge
Figure 2: Right to left interatrial
conduction time(IACT) before ablation. Earliest right atrial activation
to the distal coronary sinus was measured as 60 msec.
Click here to enlarge
Figure 3: Right to left interatrial
conduction time(IACT) after ablation. Earliest right atrial activation
to the distal coronary sinus was measured as 92 msec.
Figure
4: Left to right interatrial conduction time(IACT) before
ablation. Left to right IACT’s were measured from distal coronary sinus
pacing to earliest right atrial activation was measured as 120 msec.
Figure
5: Left to right interatrial conduction time (IACT) after
ablation. Left to right IACT’s were measured from distal coronary sinus
pacing to earliest right atrial activation was measured as 119 msec.
Figure 6: Association of IACT
(Interatrial conduction time) prolongation (in miliseconds) and number
of RF (radiofrequency) ablation
Figure 7: Association of IACT
(Interatrial conduction time) prolongation (in miliseconds) and
duration of RF (radiofrequency) ablation.
Left to right
interatrial conduction time during pacing of distal coronary sinus was
unchanged before and after ablation. The prolongation of IACT was very
well correlated with the number of RF (r=0.897, p<0.001) and
duration of RF (r=0,779; p<0. 0 01) (
Figure
6-7). After ablation no IACT change was observed in repeated
measurements in which atropine was given (the mean IACT was
84,9±12.7 ms after ablation and 83.4 ± 10.1 ms
after atropine, p=0.884).
Discussion
The
atrioventricular (AV) junction is a complex anatomic structure located
within an area called Koch’s triangle
6,7. Koch’s triangle is bounded anteriorly
and superiorly by the tendon of Todaro, posteriorly by the coronary
sinus, and inferiorly by the annulus fibrosus of the tricuspid ring.
The base of the triangle is marked by the ostium of the coronary sinus.
SP conduction is registered near the ostium of the coronary sinus.
In adults, the
compact AV node is relatively uniform in size, with a length of 5 to 7
mm and a width of 2 to 5 mm
8.
A greater variability in the size of Koch’s triangle was observed in
the intraoperative and postmortem studies
9,10. Fluoroscopic measurement with
coronary sinus angiography also found a marked variation in the
triangle’s dimensions
11. In
the right oblique (RAO) view, the distance between the His potential
recording site and the floor of coronary sinus ostium was 25.9 + 7.9
mm. Marked differences in the arrangement of the superficial atrial
muscle fibers in the area of the triangle of Koch have been reported
in normal hearts
12.
Systematic anatomic investigation of the AV node in patients with AVNRT
is lacking
13.
In the RAO
view, the posteromedial tricuspid annulus between the level of the
coronary sinus ostium and the His potential recording site was divided
anatomically into posterior, median, and anterior zones. Energy was
delivered along the tricuspid annulus, starting at the most posterior
site, the floor of the coronary sinus ostium, and progressing to the
most anterior site, just inferior to the His potential recording site.
The inducibility of the AVNRT was assessed after each likely successful
application. If the tachycardia was still inducible after two
radiofrequency energy applications within each of the anatomic zones,
the process was repeated. With this approach, the SP was successfully
ablated in 188 (97%) of 193 patients
14.
Activation of
the left atrium (LA) is complicated. Three routes of intra-atrial
conduction are possible: (a) superiorly through Bachman’s bundle, (b)
through the mid-atrial septum at the fossa ovalis, and (c) at the
region of the central fibrous trigone at the apex of triangle of Koch.
Activation of the left atrium over Bachman’s bundle can be
observed in 50% - 70% of patients
15.
During sinus rhythm, two wave fronts depolarize the left atrium: one
antero-lateral emerging from the Bachman’s bundle and the anterior
aspect of the fossa ovalis, and one posterior proceeding from the low
inter atrial septum
16,17.
But, Bachman’s bundle can not be
differentiated from the circular fibers of the anterior wall or it is
not prominent in some subjects
18.
As a result, the impulse does not
move properly across the anterior wall from right to left atrium.
Besides, Bachman’s bundle is not the only pathway connecting right and
left atriums
18,19.
Although Bachmann’s bundle appeared to be the
predominant inter-atrial connection, technical limitations may have
reduced
the accuracy of mapping in the posteroseptal LA and the region of the
right inferior pulmonary vein ostium
20.
Markides et al.
have described characteristic preferential activation patterns in the
human LA. They have showed that, posterior inter-atrial connections, as
described in recent studies of human atrial anatomy, were found to be
at least as important as Bachmann’s bundle in right-to-left interatrial
conduction during SR
21.
As a result, Markides et al. have shown that
there are indeed multiple connections capable of right-to-left atrial
conduction and that posterior communications play a major role, in
contrast to left-to-right conduction. They also reported that the
earliest endocardial breakthrough during sinus rhythm (SR) occurred
more frequently in the septal (63%, principally posteroseptal) than
anterosuperior (37%) LA and varied little with isoproterenol or high
right atrial pacing rate
21.
Findings of
our
study suggest that, multiple RF ablations at the low interatrial septum
cause prolongation of IACT by affecting the posterior inter-atrial
fibers. Our observation that right to left IACT prolonged after
ablation but the left to right IACT remained constant supports the
proposal of Markides et al. This can be explained by the newly
understood importance of the posterior inter-atrial fibers in the
activation of left atrium and the close proximity between low
inter-atrial septum and Koch’s triangle.
Clinical Implications
The present
results may have clinical implications regarding atrial
arrhythmogenesis. In this study; postablation inter-atrial conduction
time increased significantly following RF ablation of the low
inter-atrial septum. The role of this augmented conduction delay in the
occurrence of late atrial arrhythmias needs to be evaluated in
prospective studies.
Study Limitations
The major
technical difficulty encountered in the present study was the inability
to achieve extensive mapping of the anterior and antero-septal aspects
of the mitral annulus. For ethical reasons, the authors did not
consider trans-septal or retrograde arterial approach in this study.
Furthermore, left atrial activation was mostly represented by coronary
sinus electrograms that provided information on the region of the left
atrium adjacent to the mitral annulus. Given the complexity of septal
activation pattern, simultaneous multisite mapping techniques
(non-contact mapping of the CARTO system) are required for more
accurate study of the interatrial electrical connections
22.
Conclusion
RF ablation of
AVNRT results in prolongation of IACT. The degree of prolongation is
associated with the duration and number of RF ablations given. The
relationship between this conduction delay and late arrhythmogenesis
need to be evaluated.
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