(Circulation. 1997;96:2505-2508.)
© 1997 American Heart Association, Inc.
Articles |
From Service de Rhythmologie, Hôpital Cardiologique du Haut-Lévêque, Bordeaux-Pessac, France.
Correspondence to Dr Dipen C. Shah, Service du Professeur J. Clementy, Hôpital Cardiologique du Haut-Lévêque, Avenue de Magellan, 33604 Bordeaux-Pessac, France.
| Abstract |
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Methods and Results Twenty-one patients (18 men and 3 women, age, 54±10 years) with a recurrence of typical atrial flutter 6±7 months after an apparently successful catheter ablation in the IVC-TA isthmus prospectively underwent electrophysiologically targeted reablation during flutter. Sites with narrow electrograms or fractionated electrograms interposed between adjacent sites with double potentials considered to represent gaps were ablated without movement of the catheter. Mapping showed that 18 of 21 patients had a single gap. Successful ablation required a single application in 14 patients and, in the group as a whole, a median of one application (mean, 2±2; range, 1 to 11) with resultant bidirectional block in 13 of 16. A single narrow electrogram (duration, 48±6 ms; amplitude, 0.1±0.05 mV) was noted at the successful site in 11, whereas a fractionated electrogram (97±32 ms, 0.05±0.04 mV, P<.05) was noted in 9. There were four additional recurrences during a follow-up at 7±5 months; three were similarly ablated with a median of one pulse.
Conclusions Transmural ablation lesions in the isthmus can be recognized during flutter by double potentials separated by an isoelectric interval. Postablation recurrent flutter is usually due to a single discrete recovered gap; this is represented by a single or a fractionated potential spanning the isoelectric interval of adjacent double potentials, which can be selectively targeted to minimize repeat ablation.
Key Words: atrial flutter catheter ablation
| Introduction |
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9%.3 Although
published experience on reablation is limited, repeat complete linear
ablation within the above anatomic limits is commonly performed. This
practice may not be necessary if the remnant of recovered conducting
tissue could be identified and selectively ablated. In this study, we
evaluate the relative extent of this conducting tissue and describe a
simplified electrophysiologically directed
strategy of RF catheter reablation in a consecutive prospectively
enrolled cohort of patients with recurrence of common atrial
flutter after previous apparently successful IVC-TA isthmus
ablation. | Methods |
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Index Ablation
Based on the technique initially described,1 we
previously reported electrophysiologically
and anatomically directed ablation in the IVC-TA isthmus with the aim
of creating a linear lesion using sequential point-by-point RF
application directed at sites in the isthmus with atrial electrograms
centered on the surface ECG flutter wave plateau.5
Consistent targeting of sites with this timing while
withdrawing the catheter from the RV to the IVC edge ensures a linear
lesion perpendicular to the wave front independent of fluoroscopic
orientation. In all 21 cases, the target site during the index ablation
was the IVC-TA isthmus, with ablation directed during flutter at
electrograms in the center of the surface ECG flutter wave plateau in
19 of 21 patients. Two patients underwent anatomic ablation: 1 during
flutter and another during atrial fibrillation. Noninducibility of
typical atrial flutter was demonstrated as an end point of successful
ablation in all cases by programmed or incremental right atrial
stimulation. Isthmus conduction was assessed in 9 cases: bidirectional
isthmus conduction block was found in 7 and unidirectional block in
2.6 7
Present Ablation
All antiarrhythmic medications were stopped 3 or 4 days before
the present ablation procedure. The ablation was performed with the
patient under light sedation (2 to 4 mg midazolam IV) and after 4 to 6
hours of fasting. Informed consent was obtained in all cases. Standard
quadripolar catheters (Bard Inc) with 5- to 10-mm interelectrode
spacing were introduced through the femoral veins for stimulation and
for verification of isthmus conduction block. In 2 cases, a
duodecapolar Halo catheter (Cordis-Webster Inc) was used for the latter
purpose. Bipolar electrograms were filtered with a bandpass setting of
30 to 500 Hz and amplified at high gains (0.1 mV/cm) on a PPG Midas
polygraph and recorded at paper speeds of 100 mm/s. RF
application as well as rove mapping were performed with a 4-mm
thermocouple-equippedtip electrode, quadripolar catheter
(Cordis-Webster Inc) with 2-5-2mm interelectrode spacing. A
Stockert-Cordis RF generator was used to apply closed-loop
temperature-controlled RF current (as a 550-kHz unmodulated sine wave)
in unipolar mode between the catheter tip electrode and an indifferent
525-cm2 electrode placed under the patient's back.
Individual applications were nominally of 90 seconds' duration but
were interrupted earlier in case of an impedance rise. The target
temperature was set between 60° and 70°C. Isthmus conduction was
assessed by comparing activation times between two sites low down in
the lateral right atrial free wall during coronary sinus ostium
pacing as well as between the His bundlerecording position
and the coronary sinus ostium during low lateral right atrial
pacing.6 A programmable stimulator (Cardiostimulateur
Orthorythmique) with a 2-ms output pulse width and four-times-threshold
amplitude was used. Procedural success was defined as interruption of
flutter with noninducibility during high rate incremental atrial pacing
from two right atrial sites, the region of the ostium of the
coronary sinus and the low lateral right atrium, as well as
evidence of at least counterclockwise isthmus block.
Electrophysiological Study and Ablation
Strategy
All patients underwent RF ablation during sustained typical
atrial flutter during the procedure (1 patient required rapid atrial
stimulation for induction). The IVC-TA was carefully "scanned" in
each case during flutter, with the ablation catheter being
progressively withdrawn from the RV margin of the isthmus to its
junction with the IVC during continuous recording from the
distal bipole. On the basis of earlier data,8 9 10 we
hypothesized that previously ablated atrial tissue within this region
could be identified by relatively widely separated double potentials
(with an isoelectric interval) centered around an imaginary midpoint of
the surface ECG flutter wave plateau best seen in leads II, III, and
aVF. This allowed exclusion of double potentials from the region of the
ostium of the coronary sinus, where such potentials may be
found in the absence of previous ablation attempts but coincide with
the end of the plateau. Clockwise or counterclockwise torquing of the
catheter recording double potentials allowed registration of
large-amplitude sharp and single atrial electrograms flanking either
side of the center of the surface ECG flutter wave plateau. This zone
of previous ablation was traced from the RV margin to the
inferior vena cava, and we considered gaps within the
initial ablation line to be indicated by sites with (i) a single
electrogram centered on or (ii) a fractionated or "triple"
potential straddling the center of the surface ECG flutter wave
plateau. During continuing atrial flutter, RF energy was applied at
such sites in the above order of preference without moving the catheter
(ie, if both types of potentials were encountered, the narrow
higher-amplitude single potential was preferentially targeted).
Continuous variables are presented as mean±SD values, and
comparisons were made using Student's t test.
| Results |
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Activation Mapping in the Isthmus
During typical atrial flutter (cycle length, 237±30 ms), the
region of the previous ablation was in all cases easily located by the
presence of widely separated double potentials in the appropriate
anatomic context with a characteristic convergent configuration. The
configuration varied according to the position of the gap, with
narrower interspike intervals at one edge indicating gap proximity to
this border (RV edge interspike intervals, 67±19 ms; IVC edge, 94±25
ms). Withdrawal mapping demonstrated that this zone of double
potentials occupied all the isthmus except a single discrete gap in 18
patients (Figure
). There were 2 gaps in 2
patients and 1 large gap in 1 patient who had a small zone of double
potentials and a larger zone of single potentials, suggesting only
minor damage to the isthmus as a result of the initial ablation.
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Ablation Results
Atrial flutter was successfully ablated and definitively
interrupted by 1 application in 14 patients, 2 applications in 2
patients, 3 applications in 4 patients, and 11 applications in the
patient with a large gap, for a median of 1 and a mean of 2±2 RF
applications (range, 1 to 11). Atrial flutter was terminated 12±10
seconds after application of RF energy. Bidirectional block was
confirmed after flutter interruption in 13 patients, whereas 3 others
were noted to have only counterclockwise isthmus block, which remained
unchanged despite additional (1.6±0.9; range, 1 to 3; median, 1)
applications. Isthmus conduction was not assessed in 5 patientsin 2
because of sustained atrial arrhythmias induced by atrial burst
pacing. The procedure and fluoroscopic durations were 56±30 and 19±13
minutes, respectively. There were no significant side effects. For 11
of the patients, the electrogram at the successful site was a narrow
single potential (48±6 ms); for 9 others, it was a fractionated/triple
potential (97±32 ms). In 1 patient, a narrow double potential without
an isoelectric interval was observed. The fractionated atrial
electrograms had a lower amplitude than the single ones (0.05±0.04
versus 0.1±0.05 mV, P<.05). There was no specific location
of the gaps along the isthmus. For sites with single electrograms, the
time to interruption of flutter was longer than that for sites with
fractionated electrograms (15.5±10 versus 7±7 seconds,
P<.05).
After a follow-up of 7±5 months, 4 patients had a recurrence of typical flutter; 3 of these 4 had had previous unidirectional counterclockwise block, and 1 had had bidirectional counterclockwise block. Three were successfully reablated (median, 1 pulse; mean, 2±2; range, 1 to 4); 2 of these patients were ablated at discrete similar sites, and 1 at the same site as the previous ablation. This patient with previously documented complete bidirectional block was successfully reablated at the identical site, requiring 4 applications, because of rapid recovery of isthmus conduction after each of the first 3 transiently successful applications. One patient refused repeat ablation.
| Discussion |
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Activation in the IVC-TA isthmus during common atrial flutter is unidirectional and proceeds from the lateral to the medial right atrium.11 12 Thus, a transmural lesion in this region with spared tissue on both sides will result in the activation wave front detouring around both sides of the lesion. A bipole (such as used clinically with 4-mm-tip ablation catheters) when placed astride the lesion will therefore record sequential nonsimultaneous activation from both the upstream and downstream aspects of the lesion in the form of double potentials. Movement of the bipole toward the healthy margins on either side will result in recording of a single short duration potential, the position of which is indicated by the atrioventricular ratio and a different relation to the surface ECG flutter wave. By extension, with a large lesion almost spanning the isthmus and a relatively small zone of spared tissue (the "gap"), the activation wave front during recurrent flutter would be expected to pass through the remaining conducting isthmus tissue (gap) and activate the downstream flank of the lesion antidromically. Double potentials with progressively increasing isoelectric interpotential intervals were accordingly recorded as the bipole was gradually withdrawn toward either edge but with fractionated or narrow single electrograms on the gap occupying the isoelectric interval of adjacent double potentials. The significance of single versus fractionated electrograms on the gap is unclear, but single, short-duration electrograms may indicate a rapidly and homogeneously conducting tissue, whereas fractionation indicates a more tenuous, slowly conducting tissue gap, as suggested by the shorter time to flutter interruption and lower amplitude in our study. Alternatively, the two morphologies (in cases in which both were noted) could be a function of the distance between the recording bipole and the actual gap tissue.
The most important proof of the accurate location of the gap in the lesion line/zone was successful ablation of flutter with a single punctiform RF application in most patients. It is important to emphasize that we could fill in the "gaps" with relative ease because of the similar technique used for the previous index ablation and, notably, because of the previous effort to trace a relatively straight line. This strategy therefore may not be as efficacious for previous wide and irregularly targeted ablation lesions. This is supported by the requirement of 11 applications for 1 of our patients in whom mapping demonstrated a large gap of healthy potentials, thus necessitating practically a new ablation line. Of course, such an assessment is valid only when activation through the IVC-TA isthmus is strictly unidirectional, as occurs during typical atrial flutter and presumably during inverse clockwise flutter.
Our results can also be applied to facilitate first-time ablation of typical atrial flutter to search for remnant gaps in the newly created line after previous applications of RF energy failed to terminate flutter. In a broader sense, this cohort also represents a near-perfect paradigm of an incomplete (discontinuous) linear ablation lesion that can be completed by specifically targeted "point" lesions.
Additional Recurrences
Additional recurrences occurred despite the targeting of
localized gaps; they were due to inaccurate ablation and/or a difficult
anatomy, with both resulting in a transient conduction block.
Of the 4 patients with a recurrence, 3 were noted to have a
unidirectional counterclockwise isthmus block. Additional
recurrences may also reflect stereotypical limitations of the
similar anatomic and technical milieu at successive ablations.
Successful additional reablation with stable bidirectional isthmus
block was, however, accomplished with the same strategy (again, with a
median of 1 application).
Conclusions
Most postablation recurrent typical flutters are due to a discrete
gap in the ablation line permitting conduction through the isthmus.
Both the transmural ablation lesion and the "gap" can be
identified by on-site electrograms, permitting ablation in the majority
with a single RF application and a relatively short procedure.
| Selected Abbreviations and Acronyms |
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Received June 12, 1997; revision received August 4, 1997; accepted August 7, 1997.
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