(Circulation. 2000;101:772.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Hôpital Cardiologique du Haut-Lévêque, Bordeaux-Pessac, France.
Correspondence to Docteur Pierre Jaïs, Hôpital Cardiologique du Haut-Lévêque, Avenue de Magellan, 33604 Bordeaux-Pessac, France.
| Abstract |
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Methods and ResultsCavotricuspid ablation was performed with a conventional (n=26) or an irrigated-tip catheter (n=24). RF was applied for 60 minutes with a temperature-controlled mode: 65°C to 70°C up to 70 W with a conventional catheter or 50°C up to 50 W (with a 17-mL/min saline flow rate) with the irrigated-tip catheter. The end point was the achievement of bidirectional isthmus block, and a crossover was performed after 21 unsuccessful applications. Procedural ablation parameters as well as number of applications, x-ray exposure, procedure duration, impedance rise, and clot formation were compared for each group. A coronary angiogram was performed before and after each ablation for the first 30 patients. Complete bidirectional isthmus block was achieved for all patients. Four patients crossed over from conventional to irrigated-tip catheters. The number of applications, procedure duration, and x-ray exposure were significantly higher with the conventional than with the irrigated-tip catheter: 13±10 versus 5±3 pulses, 53±41 versus 27±16 minutes, and 18±14 versus 9±6 minutes, respectively. No significant side effects occurred, and the coronary angiograms of the first 30 patients after ablation were unchanged.
ConclusionsIrrigated-tip catheters were found to be more effective than and as safe as conventional catheters for flutter ablation, facilitating the rapid achievement of bidirectional isthmus block.
Key Words: catheter ablation atrial flutter catheters
| Introduction |
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| Methods |
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The patients were randomly assigned to ablation with a conventional 4-mm-tip thermocouple catheter (Cordis Webster D curve) or an irrigated 3.5- or 5-mm-tip thermocouple catheter (Cordis Webster Thermocool D curve). The protocol was approved by the hospital ethics committee. Informed consent was obtained from all patients.
Electrophysiological Study and
Ablation
Patients were studied in the postabsorptive state under light
sedation (midazolam 2 to 5 mg) and/or analgesia (nalbuphine 10
to 20 mg), if required. Two catheters were inserted from the right
femoral vein for pacing (Xtrem Medicorp, Viking Bard) and ablation,
respectively. Ablation of the cavotricuspid isthmus was performed
during flutter in 29 patients and during low lateral right atrial
pacing in 21. For patients in flutter, right atrial mapping was
performed to demonstrate counterclockwise activation around the
tricuspid annulus and through the isthmus with local electrograms
centered on the flutter plateau. Electrograms were recorded with a
PPG Midas polygraph using high-gain amplification (0.1 mV/cm) and a 30-
to 500-Hz bandpass. The linear lesion was made sequentially with
coalescent point-by-point ablation lesions (without moving the catheter
during RF delivery) from the tricuspid annulus to the
inferior vena cava. An SR0 long sheath (Daig) was used in
case of difficulty in reaching the ventricular side of the
cavotricuspid isthmus. To minimize the risk of AV block,
coronary artery damage, or perforation, ablation was not
performed in the septal isthmus or inside the ostium of the
coronary sinus.17
RF energy (550-Hz unmodulated sine-wave output up to 70 W) was delivered through a Cordis Stockert generator with a temperature setting of 65°C to 70°C for 60 seconds at each point with a conventional ablation catheter. The irrigated-tip catheter was used according to a protocol found to be safe in patients in whom isthmus block could not be achieved with conventional RF energy.14 This consisted of temperature-controlled RF delivery with a power limit of 50 W and a target temperature of 50°C applied for 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.
The power and temperature achieved, as well as impedance, were noted at
20 seconds during the RF application for all patients. After every 3
applications or after an impedance rise (defined as an elevation of
25
), the ablation catheter was removed to note the presence of
clot or char on the ablation electrode. No procedural anticoagulation
was used.
The end point was flutter termination and bidirectional isthmus block
demonstrated by activation mapping during pacing from the low lateral
right atrium and proximal coronary sinus adjacent to the
ablation line5 11 12 in addition to a complete line of
block defined by on-site recording of widely separated local
parallel double potentials all along the line.14 18 The
double potential included a first component resulting from local
activation on the upstream flank of the line, and the second was the
latest component of right atrial activation propagating around the
tricuspid annulus to the opposite flank of the line. Conduction time
from the pacing artifact to the atrial electrogram at the His bundle,
at the coronary sinus ostium, and to the second component were
measured at the end of the procedure
(Figure
) and similarly during
coronary sinus pacing. If >21 RF applications were
unsuccessful,14 the patient crossed over from one group to
the other.
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A coronary angiogram was systematically performed before and after the isthmus ablation to rule out any asymptomatic coronary damage related to the ablation procedure. At least 2 orthogonal views, usually the 30° right anterior oblique and 60° left anterior oblique views, were performed. After unchanged coronary angiograms in 30 patients (including 20 treated by irrigated-tip catheter), coronary angiography was no longer performed, but the surface ECG, physical examination, and stress test were used to assess coronary status.
Postablation Care
Subcutaneous low-molecular-weight heparin (2500 IU) was usually
administered once or twice a day if left ventricular
function was impaired. Twenty-four-hour Holter recording was
performed on day 1 to 3 after ablation, combined with in-hospital
telemetry. Twelve-lead ECGs and physical examinations were performed
every day to ensure that no side effects, including silent 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.
Comparative Analysis and Statistical Methods
The following variables were assessed. The pain related to
RF delivery was quantified by the patient between 0 (no pain) and 3
(very painful). The number of applications (lasting
20 seconds)
required for successful achievement of the end point, procedure
duration, x-ray exposure, impedance rise, and presence of clot on the
ablation electrode were compared for the 2 groups. Procedure duration
was timed from the placement of the introducer sheaths to the removal
of all catheters from the heart. Fluoroscopy duration was timed from an
automatic fluoroscopy counter during the procedure. For all RF
applications, the estimated total energy required was calculated by
multiplying the delivered power at 20 minutes by the duration of RF
delivery. The number of applications, procedure duration, and x-ray
exposure were analyzed on an intention-to-treat basis.
Continuous variables were expressed as mean value±SD and compared
by a Mann-Whitney test. The
2 test was used
for qualitative variables. Statistical significance was selected at
P<0.05.
| Results |
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Efficacy of Flutter Ablation
The end point was achieved for all patients with irrigated-tip
catheters and for 22 (85%) with a conventional catheter
(P=NS). After 21 unsuccessful conventional RF applications,
4 patients crossed over and were treated successfully with 1 to 11
additional irrigated-tip catheter applications. Procedural
parameters are reported in Table 2
and showed significant differences:
13±10 conventional RF applications were required to achieve the
complete isthmus block, compared with 5±3 applications in the
irrigated-tip group (P=0.0003). The mean procedure duration
and x-ray exposure time in the conventional group (53±41 and 18±14
minutes, respectively, versus 27±16 [P<0.0008] and 9±6
[P=0.01] minutes) were approximately twice those in the
irrigated-tip group. During ablation, the pain score, 2±1, was similar
in the 2 groups. Analgesia was required for 7 patients in the
conventional group and 5 in the irrigated-tip group. An SR0 Daig sheath
was used for 3 patients in each group. The
electrophysiological consequences of the
cavotricuspid ablation are shown in Table 3
.
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In the group of 24 patients treated with the irrigated-tip catheter,
the mean power achieved was significantly higher (43±3 W) than with
the conventional catheter (34±14 W). There were very limited
variations of the delivered power with the irrigated-tip catheter from
one application to another and from one patient to another as opposed
to with the conventional catheter, as reflected by differences in SD.
However, despite a higher mean delivered power, the estimated total
delivered energy was significantly lower with the irrigated-tip
catheters (Table 2
).
Follow-Up
With a mean follow-up of 5±2 months, all patients but 1 were free
of recurrence of flutter. A new ablation procedure was
successfully performed in 1 patient treated 2 days earlier with a
conventional catheter.
Safety of Flutter Ablation
During ablation, charring on the conventional ablation electrode
tip was observed in 20 patients, whereas this was never seen with the
irrigated-tip catheter (P<0.01), including 4 crossover
patients in whom 18 instances of catheter-tip char were noted with the
conventional catheter. Six instances of impedance rise were observed
during RF delivery through the conventional catheter and 1 with the
irrigated-tip catheter.
No significant side effects related to RF ablation occurred. However, 1 false femoral aneurysm, which required surgical treatment, developed at the arterial puncture site for a coronary angiogram in a patient in the conventional catheter group. There was no change in the coronary angiogram performed after ablation whichever catheter was used, even in the 5 patients with coronary artery disease (including the right coronary artery in 4). There was no evidence of coronary damage on clinical examination, surface ECG, or stress test for all patients. The transthoracic echocardiography performed after each ablation did not show any significant pericardial effusion.
| Discussion |
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Initially, RF catheter ablation was used to treat focal targets like Wolff-Parkinson-White syndrome and AV nodal reentrant tachycardia or focal atrial tachycardias. The initial 2-mm-tip catheters provided very limited success with RF energy.19 Increasing the ablation electrode size to 4 mm and using steerable catheters was found to produce excellent results in a large majority of patients,20 representing a major advance in the treatment of those arrhythmias.21 22 For the past few years, there has been a shift from focal to linear catheterbased ablation to cure arrhythmias related to reentrant circuits with large critical isthmuses. The most common example is the type 1 flutter, but this is also true for left atrial flutter or multiple reentrant wavelet atrial fibrillation. There is no available catheter for creating long linear lesions with 1 application. Therefore, putative linear lesions are made of adjacent and hopefully coalescent sequential applications.
Different flutter ablation protocols have been reported in the literature, using progressive pullback of the catheter along the isthmus or sequential point-by-point applications of various durations.23 24 25 In studies that used bidirectional isthmus block as end point, the procedure duration and x-ray exposure reported were usually long. With mainly conventional 4-mm-tip catheters, they ranged from 76 to 197 minutes and 20 to 41 minutes, respectively. In 12 patients treated with an 8-mm-tip catheter, Iesaka et al26 reported a procedure duration of 59±8 minutes and an x-ray exposure time of 26±11 minutes, indicating a slightly better efficiency of these large electrodes. This exposure to x-ray is believed to carry an excess risk of fatal malignancy that is difficult to accept for the treatment of benign arrhythmias.27 In the conventional arm of our study, the procedure duration of 53 minutes is in the lower part of the range, as is the x-ray exposure time of 23 minutes. The significant reduction of procedure and x-ray exposure times observed in patients treated by the irrigated-tip catheters is remarkable. To the best of our knowledge, this is the first time flutter ablation has been performed with <10 minutes of x-ray exposure.
Saline irrigation of the ablation electrode maintains a low electrode-tissue interface temperature, which prevents impedance rise and allows greater RF power delivery, resulting in larger and deeper lesions, thus increasing the likelihood of achieving a continuous and transmural linear lesion. With a conventional catheter, the temperature-controlled mode reduces the occurrence of impedance rise compared with no temperature monitoring, but if the local convective cooling of the electrode is low, the elevation of the electrode temperature dramatically reduces the delivered power and therefore the size of the lesions. The irrigation of the ablation electrode dissociates the delivered power from the local convective cooling. Therefore, a nearly constant and stable amount of power can be delivered effectively for each application (in any location). Moreover, the very limited electrode temperature attained (42°C) prevents any clot or char formation. This point is useful for right-sided ablation by protecting the pulmonary circulation from embolism and is crucial for left-sided ablations.
The major concern with this kind of catheter was considered to be the
risk of tamponade and coronary damage related to deeper lesions
or "pops" as shown during ablation for the
Wolff-Parkinson-White syndrome, but with different physical
parameters used during ablation. The protocol used in this
series has been shown to be safe in patients with resistant
flutters.14 This is probably because the power was limited
to 50 W, with a mean delivered power of
40 W (a frequently reached
power with conventional catheter), in fact resulting in a lower total
estimated delivered energy. It is also important to note that great
care was taken to stay away from the septal isthmus and the
coronary sinus because in this region, the proximity of the AV
conduction system and thin-walled coronary veins increases the
risk of damage to these structures.
Limitations
It is possible that some patients would have had a successful
outcome with additional applications with the conventional catheter
without requiring a crossover. However, this is of limited consequence
for the study, because only 4 patients crossed over.
Conclusions
The primary use of irrigated-tip catheters allows safe, efficient,
and rapid ablation of the cavotricuspid isthmus for the treatment of
common flutter.
Received April 29, 1999; revision received September 14, 1999; accepted September 23, 1999.
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