(Circulation. 2000;101:631.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department de Rhythmologie, Hôpital Cardiologique du Haut-Lévêque, Bordeaux-Pessac, France.
Correspondence to Dr Dipen C. Shah, Department de Rhythmologie, Hôpital Cardiologique du Haut-Lévêque, Ave de Magellan, 33604 Bordeaux-Pessac, France.
| Abstract |
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Methods and ResultsFive patients (3 men, 2 women; mean age, 48±16 years) were studied 24±15 years after surgical closure of an ostium secundum atrial septal defect for drug-resistant atrial tachycardia. Complete tachycardia mapping was performed in the right atrium with multipolar catheters and a 3-dimensional electroanatomic mapping system (Biosense), followed by linear radiofrequency ablation of the narrowest part of each complete loop. Six tachycardias with a typical flutter morphology, a cycle length of 262±40 ms, and a superior f-wave axis (-77±11°) were mapped, 4 with a Biosense map including 106±32 points. Five figure-8 tachycardias had a counterclockwise loop around the tricuspid valve sharing a common anterior channel with a clockwise loop around the lateral atriotomy scar. One tachycardia was thought to have 2 counterclockwise loops around the same obstacles. Radiofrequency delivery in the cavotricuspid isthmus in each case transformed the tachycardia without any pause in a different morphology tachycardia with an inferior P-wave axis (50±42°) and nearly the same cycle length (272±39 ms) but with the periatriotomy loop alone. This arrhythmia required ablation of a second isthmus: between the lower end of the atriotomy and the inferior vena cava in 4 and the superior tricuspid annulus in 1. After a follow-up of 19±6 months, there were no recurrences.
ConclusionsFigure-8 double-loop tachycardias mimicking the ECG pattern of a common atrial flutter occur in some patients after a surgical atriotomy. Ablation of 1 loop produces a sudden transformation to a new reentrant tachycardia formed of the remaining loop that requires ablation at a second isthmus.
Key Words: atrial flutter catheter ablation heart defects, congenital heart septal defects surgery
| Introduction |
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| Methods |
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Electrophysiological Study and
Ablation
Mapping and catheter ablation were performed with informed
consent after 4 to 6 hours of fasting and after all antiarrhythmic
drugs had been stopped for 48 hours. Femoral venous access was obtained
to introduce a 6F quadripolar diagnostic catheter, a 7F
quadripolar thermocouple equipped ablation catheter, and a duodecapolar
Halo catheter (Cordis-Webster) into the RA. Bipolar electrograms were
filtered between a band pass of 30 to 500 Hz and recorded at high
gains of 0.1 mV/cm at a paper speed of 100 mm/s. A programmable
stimulator (Cardiostimulateur Ela Medical) with a 2-ms output pulse
width and an amplitude 4 times the threshold was used.
Mapping Techniques
Sequential mapping of the cavotricuspid isthmus was performed
during supraventricular tachycardia by
recording activation at the ostium of the coronary
sinus, at the lateral edge of the cavotricuspid isthmus (7 oclock on
the tricuspid annulus in the left anterior oblique view), and in its
center (6 oclock on the annulus) relative to the surface ECG onset of
the flutter wavein lead II, III, or aVF. Activation in the
cavotricuspid isthmus was categorized as lateral to medial, medial to
lateral, or convergent/colliding.8
A duodecapolar Halo catheter was placed in 2 patients with its most distal bipole at 7 oclock on the tricuspid annulus and its most proximal bipole at 2 oclock in the left anterior oblique view. Gentle torquing of the catheter shaft in either direction produced movement of the electrode-bearing portion so that the lateral right atrial wall could be scanned.
Comprehensive 3-dimensional (3D) endocardial activation maps of the RA were generated in 5 patients (4 before and 4 after cavotricuspid isthmus ablation, including both before and after in 3 patients) with the Cordis-Biosense EP navigation system and Navistar mapping and reference catheters. The technique has been described in detail elsewhere.9 10 Automatically assigned activation times were manually verified and corrected when necessary, and a single activation was contextually assigned for fractionated and double-spike potentials on the basis of simultaneous tip unipolar signals and surrounding activation.11
Definitions
Local block was defined by a conduction delay between
contiguously located points of
30 ms produced by an activation detour
around the block. The complete reentrant circuit was considered to be
the spatially shortest route of unidirectional activation encompassing
the full range of mapped activation times (>90% of the cycle length
of the tachycardia) and returning to the site of earliest
activation. Bystander fronts encompassed a significantly smaller range
of activation timings and failed to return to the site of earliest
activation. Double-loop reentry was considered to exist when 2 loops,
each fulfilling the definition of a reentrant circuit, were
simultaneously documented; ie, another front also
demonstrated unidirectional activation spanning the full cycle length
with terminal activation returning to the site of earliest activation.
A figure-8 activation pattern was defined as a specific type of
double-loop reentry involving 2 simultaneously coexisting
loops rotating in opposite directions and sharing a common segment of
unidirectional activation. Atriotomy scars were located and defined by
contiguous low-voltage (<0.5 mV) double potentials commensurate with
the surgical incision in the anterior right atrial free wall. Their
position was confirmed by conventional or Biosense mapping in
sinus rhythm.
The mean P- or f-wave axis of each tachycardia was calculated on the basis of the maximum amplitude in the limb leads relative to the intervening truly isoelectric baseline in case of P-wave tachycardias or the plateau in case of the typical sawtooth morphology flutters.
Ablation
RF energy was delivered in the cavotricuspid isthmus and from
the inferior margin of the atriotomy scar down to the
inferior vena cava (IVC). In 1 case, RF applications were
delivered from the lower end of the scar as defined above to the
nearest segment of the tricuspid annulus. The ablation sites were
chosen on the basis of catheter stability as demonstrated
fluoroscopically and on the electroanatomic and conventional mapping
data. Sequential point-by-point ablation was performed with a catheter
equipped with a 4-mm-tip electrode thermocouple connected to a
Stockert-Cordis RF generator delivering a 550-kHz unmodulated sine wave
output between the tip electrode and a 575-cm2
back plate placed under the patients left shoulder. RF energy was
delivered in the temperature-controlled mode (60°C to 70°C) for 60
to 90 seconds. Sedation with intravenous Midazolam was used
as necessary. Successful ablation was defined as termination of the
tachycardia by RF application and noninducibility of any
organized atrial tachycardia. Isthmus block was verified
during pacing in sinus rhythm and defined as a detour of activation
around the cavotricuspid isthmus; similarly, complete block of the
atriotomy incision line was defined by a detour of activation around
the atriotomy and the contiguous great vessel (IVC or superior vena
cava [SVC]) or annulus.
| Results |
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Four RA 3D electroanatomic maps of 106±32 points were obtained during
different tachycardias in 4 patients
(Table
). In all cases, the
cavotricuspid isthmus was activated unidirectionally from
lateral to medial; the interatrial septum was activated
caudocranially while activation coursed anteriorly to the SVC in the
medial-to-lateral direction (counterclockwise) before descending down
the free wall anterior to the atriotomy scar to return to the
cavotricuspid isthmus. This descending front bifurcated into 2 toward
the inferior end of the atriotomy scar. One continued into
the cavotricuspid isthmus, whereas the other passed posteriorly through
the narrow isthmus formed by the scar and the IVC, ascended upward
along the posterior aspect of the RA free wall and the posterior
RA. This clockwise circuit was completed by
activation rejoining the descending corridor anterior to the atriotomy
scar both around the SVC and between it and the superior aspect of the
atriotomy scar (Figures 1
and 2
). In 1 of these cases, a clockwise loop
formed around the SVC and a contiguous atriotomy scar, along with a
counterclockwise loop around the tricuspid annulus.
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The 2 loops of activation spanning the full tachycardia
cycle length were recorded in 1 case with conventional mapping
only, with sequential isthmus mapping and with the Halo in position
around the tricuspid annulus. Counterclockwise activation around the
tricuspid annulus (including lateral-to-medial isthmus activation)
combined with bifurcating ascending and descending activation on the RA
free wall (Figure 2C
). Counterclockwise activation around the
tricuspid annulus alone could be documented in another patient with a
Halo catheter, the second loop being demonstrated by only a 3D
electroanatomic map.
Tachycardia Transformation by Ablation
RF applications were delivered in the cavotricuspid isthmus or at
its lateral part. After a mean of 7±6 RF applications, the flutter ECG
changed abruptly into a dominant positive or completely positive
deflection flutter in inferior leads II, III, aVF, and
V6 with an inferiorly directed mean
P-wave axis of 50±42°, a similar or identical cycle length
(transformed cycle length, 272±39 ms; change in cycle length, 13±11
ms; range, 0 to 30 ms), and no intervening pause (Figures 1B
and 2D
). Less marked changes were seen in other leads: from negative
to positive in aVR and aVL, isoelectric to positive in I, and various
morphological changes in chest leads.
One patient (patient 4) had a second tachycardia with a superior axis that was indistinguishable on the surface ECG from the presenting flutter except for its cycle length; sequential mapping of the isthmus also revealed lateral-to-medial activation. Ablation in the isthmus again produced a transformation to a different inferior-axis flutter (see below).
The transformed inferior-axis flutters were mapped with the
3D electroanatomic system in 4 cases (87±5 points), and 2 circuits
were documented with a Halo catheter complemented by sequential
mapping. Convergent bystander activation of the cavotricuspid isthmus
by colliding wave fronts from 2 directions was demonstrated in all
cases (Figure 1C
). Five of the inferior-axis
flutters were the result of a clockwise single-loop reentry circuit
around the atriotomy scar. The 3D electroanatomic mapping revealed
descending activation of the interatrial septum (Figure 1C
). The
sixth inferior-axis flutter in patient 4, however, was due
to counterclockwise activation around the atriotomy scar.
Ablation of the Second Loop
Successful ablation of all the inferior-axis flutter
morphologies was performed by delivering additional RF energy (12±15
applications) at a second isthmus in each patientin 4 formed by the
end of the atriotomy scar and the nearest great caval vein, the
IVCand in 1 patient between the lower end of the atriotomy scar and
the superior tricuspid annulus (patient 5).
Procedural Outcome
During sinus rhythm, complete cavotricuspid isthmus block
was verified in all patients, and block was achieved across the second
isthmus between the lower end of the atriotomy scar and the IVC or the
tricuspid annulus in 2 patients (Figure 2E
). Despite multiple
attempts, block could not be achieved in the isthmus between the lower
end of the atriotomy scar and the superior tricuspid annulus in 1
patient. Block in the second isthmus was not verified in the other 2
patients. After a follow-up of 19±6 months (without antiarrhythmic
drugs), there were no recurrences.
| Discussion |
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Circuit Characteristics
Double-loop figure-8 activation characteristically involved
counterclockwise activation around the tricuspid valve and clockwise
activation around the atriotomy, with activation from both loops
coalescing into a common pathway anterior to it. In 1 case, both loops
were counterclockwise, although other variations,
including clockwise loops and >2 loops, are also
possible.12
The simultaneous coexistence of both loops was proved by
comprehensive 3D mapping and transformation to a single-loop circuit
with appropriately targeted RF application. Entrainment mapping was not
systematically performed to avoid terminating or transforming the
tachycardia or inducing atrial fibrillation (which could be
considered a limitation). However, in view of the
30-ms change in
cycle length after transformation in 1 case, discordant postpacing
intervals in the 2 loops may also be possible. Transection of 1 loop
(peritricuspid) allowed unopposed atrial activation by the other loop
(periatriotomy) to be evident on the surface ECG. This novel mechanism
of transformation of a reentrant tachycardia ECG may also
be considered the gold standard test for a true figure-8 reentry
circuit in which the remaining loop is capable of independent stability
as opposed to a figure-8 activation pattern.5
Complete figure-8 circuits were first described by El Sherif et
al,5 who mapped ventricular
arrhythmias resulting from figure-8 activation patterns in the
surviving epicardium 3 to 5 days after ligation of the left anterior
descending artery in dogs. The 2 loops rotated around 2 separate arcs
of functional block with a common channel of slow conduction. These
lines of block were attributed to spatial inhomogeneities in
repolarization and anisotropic myocardial properties. A cryothermal
probe terminated the tachycardia only when applied to the
common channel. Similar figure-8 ventricular circuitbased
arcs of functional block have been mapped intraoperatively in patients
with ischemic heart disease.6 7 Figure
-8 atrial
circuits have also been epicardially mapped in a canine sterile
pericarditis model, again around lines of functional
block.13
The figure-8 circuits (as well as the variant double-loop circuit) described in this article differ because activation revolved in the form of 2 loops around anatomic and fixed obstacles: the atriotomy scar in the free RA wall and the tricuspid valve annulus. This permitted the dual-loop reentrant circuit to function stably as a symbiotic arrhythmia and as a single-loop arrhythmia (resulting from the parent arrhythmia) by sectioning of the other loop. This tachycardia transformation could be considered a variant of Mines test for verifying the reentrant nature of each the circuits constituent loops. The common channel between the 2 also did not behave like the slowest part of the circuit. The isthmuses themselves resulted from an atriotomy adjacent to multiple anatomical defectsthe IVC and tricuspid valvein the RA.
ECG Recognition
All patients presented with a typical-flutter ECG
pattern with no features distinguishing this type of dual-loop figure-8
reentry circuit from typical counterclockwise isthmus-dependent
flutter. All had undergone surgery for ostium secundum atrial septal
defect closure representing 30% of a consecutive cohort (5
of 15). Such reentry might also probably be seen after a similar
atriotomy for other forms of heart disease and in both atria. The small
or nonexistent change in flutter cycle length after transection of the
peritricuspid loop indicates the requirement of an appropriately long
and freely hanging (not extending to the IVC or tricuspid valve
annulus) atriotomy with or without a zone of slow conduction at its
periphery to permit matching activation times around the atriotomy and
tricuspid valve. After transection of 1 loop, the cycle length of the
remaining loop (and therefore of the tachycardia) changed
slightly in 4 of 6 instances, probably as a result of the loss of the
modulating effect of the ablated loop. Despite the
simultaneous coexistence of an additional circuit loop and
posterior RA activation that was significantly different from that in
typical flutter,10 the ECG was indistinguishable from that
of typical flutter, indicating that simultaneous
periatriotomy loop activation is not clearly evident on the surface ECG
and that similarly posterior RA activation in typical flutter may not
contribute to the surface ECG tracing. The role of the crista
terminalis in these arrhythmias is unclear, although in each
case the center of the RA free wall loop (the atriotomy) was in an
anatomic position that was clearly distinct (lateral and anterior) from
that expected of the crista terminalis. Additionally, activation in
this region during tachycardia was parallel to the long
axis of the crista terminalis, thus masking any marker double
potentials. Mapping in sinus rhythm confirmed the position and fixed
nature of the atriotomy line of block in 3 patients.
The double-loop mechanism was revealed on ECG only by transection of 1 loop. The ECG transformation was instantaneous and without an intervening pause, which might suggest termination followed by induction. The mapping of transformation of a superior-axis negative-deflection flutter (in inferior leads) to a positive-deflection flutter (inferior P-wave axis) with a periatriotomy reentry circuit indicates that the polarity change on the surface ECG is associated with altered septal activation from caudocranial to craniocaudal and possibly a similar change in left atrial activation. In all the above cases, ablation was begun in the cavotricuspid isthmus; however, if we had begun by ablating the IVC-atriotomy isthmus, in all likelihood no significant surface ECG changes would have occurred because the resulting change in atrial activation would be limited to only a part of the lateral and posterior RA, which appears to be silent on the ECG.
Ablation
The dual-loop reentry circuit required ablation at 2 distinct
isthmuses. Although theoretically ablation of the common corridor
between the atriotomy scar and the tricuspid annulus represents
a more parsimonious approach, catheter stability in this region is a
major problem. Moreover, ablation of this corridor would not be
expected to be effective in the event of a single-loop typical-flutter
circuit or a counterclockwise double-loop circuit; therefore, such an
ablation strategy would require prior recognition of a figure-8 circuit
by detailed intracardiac mapping.
Conclusions
A specific type of figure-8 reentry circuit involving
simultaneously the atriotomy scar and the tricuspid valve
can be encountered in postatrial septal defect surgical closure
patients with apparently typical atrial flutter. Ablation of the
cavotricuspid isthmus transects the peritricuspid loop and leaves a
single periatriotomy loop tachycardia, producing an
instantaneous change in the ECG pattern, which requires ablation in a
second isthmus.
Received April 26, 1999; revision received August 30, 1999; accepted September 15, 1999.
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