From the Hôpital Cardiologique du Haut-Lévêque,
Bordeaux-Pessac, France.
Correspondence to Pierre Jaïs, MD, Hôpital Cardiologique du Haut-Lévêque, Avenue de Magellan, 33604 Bordeaux-Pessac, France.
Abstract
Background—Catheter ablation of
typical right atrial flutter is now widely performed. The best end
point has been demonstrated to be bidirectional isthmus block. We
investigated the use of irrigated-tip catheters in a small subset of
patients who failed isthmus ablation with conventional radiofrequency
(RF) ablation.
Methods and Results—Of 170 patients referred for ablation of
common atrial flutter, conventional ablation of the cavotricuspid
isthmus with >21 applications failed to create a bidirectional block
in 13 (7.6%). An irrigated-tip catheter ablation was performed on
identified gaps in the ablation line according to a protocol found to
be safe in animals: a moderate flow rate of 17 mL/min and
temperature-controlled (target, 50°C) RF delivery with a power limit
of 50 W. Bidirectional isthmus block was achieved in 12 patients by use
of a mean delivered power of 40±6 W with a single application in 6
patients and 2 to 6 applications in the other 6. No side effects
occurred during or after the procedure.
Conclusions—Irrigated-tip catheter ablation is safe and effective
for achieving cavotricuspid isthmus block when conventional RF energy
has failed.
Right atrial flutter is a macroreentrant
tachycardia propagating counterclockwise or, less commonly,
clockwise in the right atrium (RA). Its circuit has now been
extensively mapped.1 2 3 Catheter ablation using
radiofrequency (RF) energy targeting the cavotricuspid isthmus is very
effective.4 5 6 7 Bidirectional isthmus conduction
block is the best end point to reduce as much as possible the
recurrence rate after
ablation.2 8 9 Nevertheless, it cannot be
achieved with conventional RF technology in a small subset of
patients.5 Experimental studies have shown that
deeper and wider lesions can be performed safely in the atrial
myocardium with irrigated-tip
catheters.10 We investigated the safety and
efficacy of irrigated-tip catheters in a consecutive series of patients
referred for ablation of typical atrial flutter in whom isthmus block
could not be achieved with conventional RF energy.
Methods
Between April 1997 and May 1998, 170 patients underwent typical
flutter ablation at our institution. Patients with recurrent flutter or
those who had had a failed ablation at other centers were excluded.
Catheter ablation failed to create isthmus block in 13 patients: 1
woman and 12 men, 33 to 71 years old (mean, 56±10 years) who had been
suffering from atrial flutter for 20±20 months. A mean number of
2.5±1 antiarrhythmic drugs, including amiodarone in 8, were
tried unsuccessfully. Seven patients had structural heart disease:
surgically closed atrial septal defect (n=1), dilated
cardiomyopathy (n=1), ischemic heart
disease (n=2), and hypertrophic cardiomyopathy
(n=3) (Table
Conventional RF Ablation
An incomplete line was identified by the presence of gaps defined as
isolated or fractionated potentials centered on the isoelectric
interval of adjacent double potentials as previously
described.11 In the present study group,
failure of conventional RF ablation was defined as the inability to
achieve isthmus block after >21 RF applications, which is the mean
number +2 SD of RF applications required for successful conventional RF
ablation in our patients.
Irrigated-Tip Catheter Ablation
Postablation Care
Results
Efficacy
Bidirectional isthmus block was associated with conduction times from
the low lateral RA pacing stimulus to the atrial electrogram at the His
bundle of 113 ms, to the proximal coronary sinus of 140 ms, and
to DP2 of 156 ms, as well as a craniocaudal low lateral RA activation
sequence during coronary sinus pacing. A line of double
potentials with a mean DP1-DP2 interval of 123±25 ms was observed
during low lateral RA pacing (Table
In patient 3, the procedure failed to interrupt the reinduced flutter
despite 22 irrigated-tip catheter RF applications with a mean delivered
power of 40±5 W, including repeating the ablation line 3 times. The
postpacing interval during entrainment from the isthmus was within 10
ms of the cycle length, and the cycle length increased during ablation
in the isthmus from 260 to 320 ms without change in morphology and
isthmus activation sequence, demonstrating participation in the
circuit. For safety reasons, no attempt was made to exceed the power
limit of 50 W, and the flutter was converted to sinus rhythm by
overdrive pacing.
Safety
Discussion
The present study indicates that bidirectional block can be
successfully achieved with an irrigated-tip catheter in patients in
whom conventional RF applications have failed.
Among 170 consecutive patients referred for cavotricuspid isthmus
ablation, the incidence of resistant cases was 7.6%,
comparable to that of other series.5 Because the
long-term success of flutter ablation is clearly linked to the creation
of bidirectional isthmus block, this has now become the usual end point
for flutter ablation.2 8 9 The exact reason for
resistance to conventional RF is unclear; it may be due to thicker than
usual isthmus myocardium (as probably in patient 3) or to a
site topography associated with an entrapped catheter preventing
convective cooling by local blood flow and resulting in limited
delivered power as low as 5 W (Table
Saline irrigation is a double-edged sword: by elimination of impedance
rise, the autolimiting effect on delivered RF energy is lost, exposing
the patients to a higher risk of tamponade or coronary injury
due to very large lesions or popping.14 As
demonstrated in animals,10 the risk is minimized
by use of a relatively low power limit of 50 W, in the range of what is
currently used in conventional RF ablation. Despite contradictory data
in the literature,13 15 16 a
temperature-controlled mode of RF delivery was used, in combination
with a moderate flow rate, to preserve the relation between tip
temperature and tissue temperature and therefore decrease the risk of
popping; the mean achieved power was clearly under the upper limit
chosen, which supports this hypothesis. Eight-millimeter-tip electrode
catheters may also achieve similar results for resistant
flutter.17
Limitations
Conclusions
Received March 24, 1998;
revision received June 29, 1998;
accepted July 1, 1998.
References
© 1998 American Heart Association, Inc.
Brief Rapid Communication
Successful Irrigated-Tip Catheter Ablation of Atrial Flutter Resistant to Conventional Radiofrequency Ablation
Key Words: atrial flutter • catheter ablation
).
View this table:
[in a new window]
Table 1. Clinical and Procedural
Data
The method of RF ablation has been described
elsewhere.6 RA mapping was performed to
demonstrate activation around the tricuspid annulus and through the
isthmus: lateromedial for counterclockwise flutter with isthmus
electrograms centered on the flutter plateau or mediolateral for
clockwise flutter. Electrograms were recorded with a PPG Midas
polygraph using high-gain amplification (0.1 mV/cm) and a 30/500-Hz
band pass. The linear lesion was made sequentially (with point-by-point
ablation) from the tricuspid annulus to the inferior vena
cava with a quadripolar 4-mm-tip electrode catheter with temperature
control (Cordis-Webster, Medtronic Inc). RF energy (550-kHz unmodulated
sine wave output up to 70 W) was delivered through a Cordis-Stockert
generator with a temperature setting of 70°C for 60 to 90 seconds at
each point without moving the catheter. The end point was interruption
of flutter and bidirectional isthmus block demonstrated by activation
mapping during pacing from the low lateral RA and proximal
coronary sinus adjacent to the ablation
line,2 8 9 in addition to a complete line of
block defined by on-site recording of widely separated local
double potentials (Figure 1). The first
component (DP1) resulted from local activation produced by the upstream
flank of the line, and the second potential (DP2) was the latest
component of RA activation propagating around the tricuspid annulus to
the opposite flank of the line.
View larger version (26K):
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Figure 1. Changes in RA and local activation resulting from
complete isthmus block. Halo catheter (20 poles) is placed in RA with
distal tip (1–2) near isthmus ablation line and proximal (19–20)
bipole at high septum. Roving catheter (site) is on ablation line
recording double potentials with isoelectric interval during
low lateral RA (LLRA) pacing on left and coronary sinus (CS)
pacing on right. After ablation, a complete bidirectional isthmus block
is achieved, as demonstrated by distal-to-proximal activation of Halo
during LLRA pacing and proximal-to-distal during coronary sinus
pacing. In both cases, widely separated double potentials are
recorded on ablation line. First component results from local
activation at upstream flank of line, and second component is latest
component of RA activation propagating around tricuspid annulus to
opposite flank of line. In both panels, second potential on line (DP2)
is later than latest bipole recorded on Halo catheter:
Stimulus-DP2=170 ms during LLRA pacing (left) and 180 ms during
coronary sinus pacing (right), while distal bipole of Halo is
activated 155 ms after pacing artifact. S indicates pacing
stimulus; V, ventricular activation.
The irrigated-tip catheter (Cordin Webster, Medtronic Inc) was
used for ablation during the same session by targeting previously
identified resistant gap(s) (during flutter or low lateral RA
pacing) (Figure 2). RF was delivered
according to a protocol found to be safe in experimental
studies.10 This consisted of
temperature-controlled RF delivery (a power limit of 50 W with a target
temperature of 50°C) for 30 to 60 seconds at each point. Normal
saline (0.9%) was infused through the irrigated-tip catheter with a
Gemini Imed pump (battery powered to avoid 50-Hz line noise) at
a rate of 17 mL/min during RF delivery. Between applications, a flow
rate of 3 mL/min was used to maintain patency. For each application,
the achieved power and temperature as well as impedance were noted at
20 seconds. The 12-lead ECG was carefully scrutinized during and after
each application as well as at the end of the procedure to monitor ST
changes. Procedural success was defined as the achievement of stable
bidirectional isthmus block. When the irrigated-tip catheter was
withdrawn, the tip was carefully examined to note the presence of clot
or char. No procedural anticoagulation was used.
View larger version (15K):
[in a new window]
Figure 2. Efficacy of irrigated-tip ablation at a
resistant gap site. Top, Ablation site is shown during low
lateral RA pacing (S) before (Pre) and after (Post) ablation with a
standard catheter (Stand catheter). Delivered power in
temperature-control mode (70°C) was between 10 and 15 W, with no
change in timing and amplitude of local fractionated electrogram
(arrows) representing gap in line near inferior
vena cava edge. Bottom, Irrigated-tip catheter (Irr catheter) delivered
40 to 45 W at exact same site, transforming fractionated electrograms
into 2 widely separated double potentials. First component
represents activation upstream of ablation line, and second
component 230 ms after pacing stimulus is related to activation front
propagating around tricuspid annulus and then reaching opposite flank
of line. Note also concomitant prolongation of stimulus to QRS
interval. S indicates pacing stimulus. Paper speed, 100 mm/s;
amplification, 0.1 mV/cm.
Subcutaneous low-molecular-weight heparin (2500 IU) was usually
administered once or twice a day if left ventricular
function was impaired. In case of a prior thromboembolic event and/or
history of atrial fibrillation, subcutaneous heparin was preferred
(partial thromboplastin time=twice the control value). Twenty-four-hour
Holter recording was performed on day 1 to 3 after ablation
combined with 5 days of in-hospital telemetry. Twelve-lead ECGs and
physical examinations were performed every day to be sure that no side
effects, including myocardial ischemia, occurred.
Transthoracic echocardiography and an
exercise stress test were performed 3 to 5 days after the procedure.
Patients were discharged on day 5 without antiarrhythmic drugs.
Follow-up examination was performed by the referring physician, and
information regarding any cardiovascular events was
obtained by telephone.
At the end of the failed ablation procedure with conventional RF,
9 patients were in sinus rhythm and 4 (patients 2, 3, 11, and 12) in
persistent flutter (counterclockwise, n=3, and clockwise, n=1). With
the irrigated-tip catheter, the flutter was interrupted within 30
seconds during the first application in patients 2 and 11, the second
application in patient 12, and the ninth application in patient 3.
However, it was reinducible in patient 3. Bidirectional isthmus block
was achieved in 12 patients (all except patient 3) with a median of 1
and a mean of 2.5±1.9 RF applications. The mean delivered power was
40±6 versus 14±6 W with conventional RF energy. Six patients required
a single application, and 6 required 2 to 6 RF applications (Table
). In
patients successfully ablated with a single RF application, the site of
ablation was a previously identified gap exactly where multiple
attempts failed (Figure 2). The resistant gaps were located in
the ventricular third of the isthmus in 6 patients, in the
middle of the isthmus in 5, and near the inferior vena cava
edge in 2. The mean procedure duration and fluoroscopic time
(conventional and irrigated ablation) were 185±54 and 76±38
minutes. ).
One audible pop was noted, but no impedance rise was observed.
There were no significant side effects during or after the procedure as
assessed by clinical evaluation and serial 12-lead ECG. After ablation,
a stress test was obtained for all but 2 patients who were in cardiac
failure. There was no clinical or electrical evidence of
ischemia, although in patient 2, a 4-mm ST-segment depression
was observed, related to hypertrophic
cardiomyopathy. After a mean follow-up of 5±3
months, no recurrence of flutter was observed, including in
patient 3. No patient developed clinical or ECG signs of
ischemic disease. ). Saline irrigation of the
ablation electrode maintains a low electrode-tissue interface
temperature and thus prevents impedance rise,12
allowing greater RF power delivery and thus producing larger and deeper
lesions.13 This is certainly the mechanism of
success particularly in patients cured with a single application,
because an identical site was targeted with both RF modalities.
The small number of patients included in our series is an
important limitation; however, they were selected from a large patient
base. The repetition of lines at a more septal or lateral level might
have been effective with conventional RF. This was not evaluated in
this study but could be attempted before the use of an irrigated-tip
catheter is envisaged. We did not systematically perform a
coronary angiogram after the procedure as suggested in some
studies using higher RF power, but we assessed coronary status
by clinical and stress test evaluation and did not observe
coronary side effects. However, the long-term follow-up of
irrigated-tip lesions is unknown.
In a small subset of patients, complete cavotricuspid isthmus
block cannot be achieved with conventional RF energy. Irrigated-tip
catheters capable of delivering a higher amount of energy on sites
resistant to conventional ablation RF allow this end point to
be reached. The protocol used in this study with temperature control
mode, low flow rates, and a power limit of 50 W appeared to be safe.
Nevertheless, irrigated-tip catheters should be considered as backup
therapy for resistant cases until a larger series with longer
follow-up is available.
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