T. Suga et al.

Table 1. The distance between the positions of the catheter tip
Patient
NumberLocationof theaccessory pathway

Before elimination ofthe accessory pathway
RAO
LAO

After elimination ofthe accessory pathway
RAO
LAO

1
Left antero-lateral
15.8 ± 1.4
16.1 ± 1.7
16.3 ± 1.2
16.3 ± 1.3
2
Left antero-lateral
15.8 ± 1.4
16.1 ± 0.8
16.3 ± 1.2
16.3 ± 1.6
3
Left postero-lateral
12.4 ± 1.2
10.1 ± 0.9
12.3 ± 1.2
11.3 ± 0.9
4Right lateral
12.8 ± 0.8
7.7 ± 0.8
12.0 ± 1.0
7.6 ± 1.0
5
Right antero-lateral
9.0 ± 1.2
11.1 ± 1.3
9.3 ± 1.6
11.3 ± 1.46
Left septal
13.5 ± 1.4
15.3 ± 1.2
12.8 ± 1.2
14.8 ± 1.0
Mean13.2 ± 2.5
12.7 ± 3.6
13.1 ± 2.7
12.9 ± 3.5
Data are expressed as mean ± SD in mm.
LAO, 45˚ left anterior oblique view; RAO, 30˚ right anterior oblique view.
There is no significant difference between values obtained before and after elimination of the accessory
pathway in either projection.

IIV1SHRA 3–4500

S500

S500

S500

S

HB 5–6
HB 3–4
HB 1–2
CS 7–8
CS 5–6
CS 3–4*CS 1–2
ABL 3–4
ABL 1–2
RVA 3–4

S500

S500

S

(RVA S – HRA S: 60 ms)

500

S500

S200 ms

Fig. 6. Surface electrocardiographic (ECG) tracings and intracardiac electrograms recorded during
radiofrequency (RF) catheter ablation of a concealed left lateral accessory pathway during sequential
ventriculo-high right atrium (HRA) pacing (VRA pacing). This figure demonstrates, from top to bottom,
ECG leads II and V1; intracardiac electrograms recorded from the HRA, proximal (HB5–6) and distal (HB1–2)
His-bundle region, proximal (CS7–8) and distal (CS1–2) coronary sinus (CS), proximal (ABL3–4) and distal(ABL1–2) bipoles of the ablation catheter, and right ventricular apex (RVA). The earliest retrograde atrial
activation prior to ablation is observed at the distal CS (CS1–2). The HRA is paced constantly at an interval of
60 ms following the constant right ventricular (RV) pacing with a drive cycle length of 500 ms before theapplication of RF current. In this situation, the 2 activation waves in the left atrium, one through the accessory
pathway during the RV pacing and the other from the right atrium resulting from the sequential VRA pacing,collided between CS3–4 and CS5–6. Note the change in the activation sequence of the atrium at CS1–2 within 5s of initiation of the RF energy application as indicated by the asterisk. This change exhibited by lengtheningof the ventriculo-atrial interval at CS1–2 during sequential VRA pacing, shows that the accessory pathway
conduction is eliminated by the RF current. The paper speed is 100 mm/s. S, stimulus artifact.

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A technique for avoiding catheter dislodgment

retrograde atrial activation pattern. After observing that the local atrial activation sequence
at CS1–2 indicated that there was a loss of VA
conduction over the accessory pathway 5 s after
RF current delivery had begun, and the RF
current was continued for 60 s. During the RF
application, the ablation catheter had a stable
position and no fusion beats occurred.
Other examples from a patient with a rightsided accessory pathway are shown in Fig. 7. In
this case, sequential VCS pacing was performed at a cycle length of 500 ms and with a VA
interval of 90 ms. The distal (TVA 1–2) andproximal (TVA3–4) bipoles of the quadripolar
catheter placed near the accessory pathway

reflected the activation of the atria through theaccessory pathway during the right ventriculobasal pacing. When a change in the local atrial
activation sequence in the TVA was observed at
7 s after initiation of RF current delivery, indicating loss of VA conduction over the accessory pathway, the RF application was continuedfor 60 s. During the RF application, the position of the ablation catheter was stable and nofusion beats occurred.

Complications
There were no complications, such as hemodynamic disturbance or serious arrhythmias

IIV1
HRA 3–4
HB 5–6
HB 3–4
HB 1–2
TVA 3–4*

TVA 1–2
ABL 3–4
ABL 1–2
CS 7–8
CS 5–6S

CS 3–4
RVB 3–4

S

500

500

S

S

500

500

SS

(RVB S–CS S: 90 ms)

500

500

SS

500

500

SS
200 msFig. 7. Surface electrocardiographic (ECG) tracings and intracardiac electrograms recorded during
radiofrequency (RF) catheter ablation of a concealed right lateral accessory pathway during ventriculocoronary sinus (VCS) pacing. This figure demonstrates, from top to bottom, ECG leads II and V 1 ;intracardiac electrograms recorded from the high right atrium (HRA), proximal (HB5–6) and distal (HB1–2)
His-bundle region, proximal (TVA3–4) and distal (TVA1–2) bipoles of the quadripolar catheter placed at thetricuspid valve annulus (TVA), proximal (ABL3–4) and distal (ABL1–2) bipoles of the ablation catheter,proximal (CS7–8) and distal (CS3–4) coronary sinus (CS), and right ventriculo-basal (RVB) region. The TVA
catheter was placed near the accessory pathway. The CS is constantly paced before the application of the RF
current at an interval of 90 ms after the constant RVB pacing stimulus with a drive cycle length of 500 ms.
Note the change in the activation sequence of the atrium at TVA1–2 within 7 s after initiating the RF
application, as indicated by the asterisk. This change shows that the accessory pathway conduction iseliminated by the RF current. The paper speed is 100 mm/s. S, stimulus artifact.

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during the procedure. No accidents involving
impedance rises while delivering energy
through the ablation catheter occurred during
the sequential VRA or VCS pacing.

Discussion

The main findings of this study
In the present study, we found that: i) the AV
dissociation after elimination of accessory
pathway conduction during the delivery of theRF energy when using RV pacing made thestability of ablation catheter worse; and ii)
sequential VRA or VCS pacing during the RF
application provided a useful method for maintaining a stable catheter position for catheter
ablation of accessory pathways.

The relationship between AV dissociationand the stability of the ablation catheter
In this study, the manner of AV annulus motion
was probably related to ventricular contraction
rather than the atrial contraction. In visuallycomparing the TVA motion during sequential
VA pacing with that during RV pacing on fluoroscopy, we could not find any significant difference in the degree of movement of the catheter on the TVA between these 2 pacing
methods. However, when a fusion beat during
RV pacing occurred, the distances observedwith the fusion beats were substantially longer
than those during sequential VA pacing. In
other words, the AV annulus motion during AV
dissociation occurring during the RV pacing
exhibited little change when no fusion beatsoccurred. On the other hand, when fusion beats
during RV pacing occurred, there was a strong
and abrupt movement of the catheter on theTVA. Occetta et al. (1990) reported that adequate ventricular diastolic filling was important
for the efficiency of the subsequent ventricularejection. Dritsas et al. (1993) reported that themagnitude of the beat-to-beat variability in thestroke volume during VVI pacing reflects therelative contribution of the atrium to LV filling.
Kuo et al. (1987) reported that left ventricularcompliance increased the dependence of cardiac output on atrial filling during late diastole. In
our case, ventricular filling was increased byatrial filling in order to maintain AV synchrony
with fusion beats. Furthermore, the fusion
beats in which the QRS complex on the electrocardiogram was narrower than that with RV
pacing, had a reduced ventricular activation
time. The ejection timing for each ventricle
with fusion beats was shorter than with RV pacing. Therefore RV pacing altered the ventricular contraction during fusion beats. We considered the cause of the ablation catheter dislodgment might be due to the change in themanner of AV annulus motion produced by thealteration in the ventricular contraction patternduring fusion beats.

The novel technique for maintaining
catheter position during RF application
Li et al. (1994) reported that entrainment oforthodromic tachycardia during RF application
was useful for maintaining catheter position foraccessory pathway ablation during atrioventricular reentrant tachycardia. Entrainment oforthodromic tachycardia with RV pacing prevents this abrupt slowing when the orthodromic
tachycardia is terminated. However, if the rateof the tachycardia is relatively fast, the patients
may experience discomfort due to worsening of
the hemodynamic status from the rapid RV
pacing at a rate faster than the tachycardia,
making it impossible to continue to ablate thepathway. By using sequential VA pacing, noneof the patients complained of any symptoms(data not shown). In this study, the rate of sequential VA pacing was not so fast, and we feltthat the sequential VA pacing did not affect thehemodynamic status.
RV pacing before the elimination of the accessory pathway conduction by the RF energy
delivery also prevents catheter dislodgment empirically. We believed this was due to the stability of the catheter from VA conduction occurring through the accessory pathway during theRV pacing. However, after elimination of accessory pathway conduction, we usually observed catheter dislodgment. This is because118

A technique for avoiding catheter dislodgment

the ventricular contraction pattern changes
from VA conduction due to RV pacing to AV
conduction in fusion beat when the sinus nodefunction recovers after the accessory pathway iseliminated. If retrograde AV nodal conduction
occurs during parahisian pacing, there should
be little chance of dislodgment since fusion
beats also should not occur (Buitleir andMorady, 1997). Clinically, in the case of retrograde conduction propagating through both
the AV node and accessory pathway, RV pacing during ablation of accessory pathways waseffective in preventing dislodgment of theablation catheter when no fusion beats occurred. On the other hand, in the case of retrograde
conduction propagating through the accessory
pathway alone, when fusion beats during RV
pacing occurred, there was a strong and abrupt
movement of the ablation catheter. As a result,elimination of the accessory pathway may
cause dislodgment of the catheter.

Sequential VRA or VCS pacing during RF
application
sequential VRA or VCS pacing which inhibits
the sinus node function during RF energy delivery is necessary in order to prevent catheter
dislodgment. We felt that sequential VRA andVCS pacings were good optional techniques.
During the sequential VRA or VCS pacing, dislodgment of the ablation catheter did not occur
when elimination of the accessory pathway
conduction occurred during the RF applicationin any of the patients. Fusion beats did not occur since the atrium was activated by the constant atrial pacing instead of propagation
through the accessory pathway from the RV
pacing following elimination of the accessory
pathway conduction. However, strictly speaking, the local activation pattern changed fromthat of conduction over the accessory pathway
to that of atrial pacing, and in a patient with aseptal accessory pathway this change was remarkable. We believed that using sequential
pacing was better than RV pacing alone, when
the accessory pathway was eliminated, because
it prevented fusion beats.
One of the problems with this technique wasthat the optimal RV-HRA or RV-CS pacing
interval was necessary to program for various
accessory pathway locations. The most optimal
pacing interval was programmed to the maximum interval at which the atrial wave front
propagating from the HRA or CS pacing site
did not hide the earliest activation of the left orright atrium through the accessory pathway.
Further, this pacing interval, which was programmed in order to minimize the local atrial
activation through the accessory pathway, minimized the change in the manner of AV annulus
motion when the atrium was activated by constant atrial pacing instead of through the accessory pathway from the RV pacing following theelimination of the accessory pathway conduction.

Conclusion
The AV dissociation after the elimination of theaccessory pathway conduction during RF energy delivery while using RV pacing worsened
the stability of the ablation catheter. During theRF application, sequential VA pacing was
better than RV pacing, because no fusion beatsoccurred. Furthermore, sequential VRA orVCS pacing during the RF application provides
a useful method for maintaining stable catheter
position for catheter ablation of accessory pathways. This technique may be especially usefulin patients with concealed accessory pathways
and no retrograde conduction over the AVnode.

119

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Received August 21, 2000; accepted September 11, 2000
Corresponding author: Dr. Toshimitsu Suga