© 2004 by European Society of Cardiology
A comparison of open irrigated and non-irrigated tip catheter ablation for pulmonary vein isolation
Department of Cardiology, Westmead Hospital and Westmead Private Hospital Westmead, NSW 2145, Australia
Manuscript submitted 8 July 2003. Accepted after revision 14 March 2004.
*Corresponding author. Tel.: +61-2-9845-6795; fax: +61-2-9845-8323. E-mail address: stuartpt{at}yahoo.com (S.P. Thomas).
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Abstract |
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AIMS: The relative efficacy and safety of open irrigated tip catheters compared with conventional non-irrigated catheters for pulmonary vein isolation (PVI) is unknown.
METHODS: Forty-eight patients undergoing PVI using an open irrigated tip ablation catheter (Group 1) were compared with a group of 31 historical controls (Group 2). The control group underwent similar procedures using a standard, 4 mm tip, temperature controlled ablation catheter. Electrical mapping with a circular catheter was used to guide segmental radiofrequency ablation at the vein ostia.
RESULTS: At follow-up (3.5±3.5 months) after a single procedure 35/48 (73%) patients in Group 1 and 14/31 (45%) in Group 2 were in sinus rhythm (p=0.03). Antiarrhythmic drug use was lower among those in Group 1 maintained in sinus rhythm (9/35 (26%) vs 8/14 (57%), p=0.002). Recurrent atrial fibrillation was more common in Group 2 (28/31 (90%) vs 28/48 (58%) p=0.004). Serious complications were uncommon in both groups.
CONCLUSIONS: Compared with an historical control group, pulmonary vein isolation using open irrigated tip catheters was superior to ablation with conventional 4 mm tip catheters. Patients undergoing ablation with an irrigated tip catheter were less likely to experience symptomatic recurrences of atrial fibrillation or require further therapy for post-procedural arrhythmias.
Key Words: atrial fibrillation, radiofrequency ablation, pulmonary vein isolation, pulmonary veins, irrigated tip, cooled tip
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Introduction |
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Atrial fibrillation is the most common clinically important cardiac arrhythmia [1]
. It is frequently precipitated by ectopic activity originating in the pulmonary veins [2,3]. Recent reports demonstrated that atrial fibrillation may be cured by electrical isolation of the pulmonary veins using guided application of radiofequency energy via transvenous catheters [4–8]. Unfortunately, the procedure is frequently unsuccessful in the mid- to long-term.
Recurrence of atrial fibrillation is almost always associated with restoration of conduction into one or more pulmonary veins. Ablation with conventional catheters results in unpredictable power delivery because of variations in endocardial contact and local blood flow. Irrigated catheters produce larger deeper lesions than conventional 4 mm tip ablation catheters [9]. Previous studies have demonstrated the safety and efficacy of open irrigated tip catheters for the treatment of atrial flutter, accessory atrioventricular connections resistant to ablation using conventional catheters, and ventricular tachycardia [10–12]. Recently Macle et al. [13] described their experience with this device for pulmonary vein isolation. In the present study, we compare our own experience using an open irrigated tip catheter with a group of historical controls treated using conventional 4 mm tip non-irrigated temperature controlled ablation catheters.
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Methods |
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Patient selection
Consecutive patients with severely symptomatic atrial fibrillation treated by pulmonary vein isolation were included in the study. Symptoms were considered severe when they interrupted normal activities. Forty-eight patients treated using an open irrigated tip catheter were compared with the last 31 patients treated using conventional catheters. All subjects had experienced recurrence of atrial fibrillation on antiarrhythmic medications or had contraindications to antiarrhythmic drugs.
Procedure
A transoesophageal echocardiogram was performed prior to each procedure to exclude left atrial thrombus. Electrical cardioversion was attempted prior to the procedure in patients presenting in atrial fibrillation. Ablation was performed in atrial fibrillation if the arrhythmia was permanent. In this group cardioversion was again attempted later during the procedure. Pulmonary vein isolation was performed via two transseptal punctures. Two long sheaths (Preface, Cordis-Webster) were used to introduce a circular decapolar mapping catheter (Lasso, Cordis-Webster) and an ablation catheter: an irrigated tip ablation catheter (Thermocool, Cordis-Webster) or a 4 mm tip temperature controlled non-irrigated catheter (Cordis-Webster or Boston Scientific, Blazer). The radiofrequency generator limits were set at 50 °C and 30–35 W and rarely at 40 W for both devices. The duration of radiofrequency energy delivery was 60 s. A 5 mm decapolar catheter was positioned in the coronary sinus for mapping and atrial pacing. Atrial pacing from the distal coronary sinus was used to expose left sided vein potentials.
The circumferential mapping catheter was placed in a stable position in the proximal vein. The ostium was identified using the ablation catheter by carefully withdrawing the catheter from the vein until it suddenly displaced into the atrium. The ostium was further defined by selective contrast venography of each vein prior to ablation. Pulmonary vein potentials were identified as previously described [4,5,14]. Stimulation within the left atrial appendage was used when required to distinguish far field atrial appendage signals from those of the left superior pulmonary vein [14]. Ablation was performed at the vein ostia. Lesions were placed either just outside the ostium or within 2 mm of the ostium (Fig. 1). Two radiographic views were used to evaluate each vein before and after radiofrequency ablation. Heparin was administered at an initial dose of 100 IU/kg, 25 IU/kg after the first hour and then 10 IU/kg/h.
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Post-procedural care and identification of endpoints
After the procedure, patients remaining in sinus rhythm were discharged on no antiarrhythmic medications. All patients had symptomatic atrial fibrillation that had been difficult to manage prior to the procedure. Report of intermittent symptoms was investigated using Holter monitoring or ambulatory event monitoring. Repeat procedures were offered to consenting patients experiencing recurrence of AF after the first or second procedure. The measured outcome variables were freedom from atrial fibrillation or flutter, rhythm at last follow-up, use of antiarrhythmic drugs, need for repeat procedures and procedural complications.
Statistical analysis
Continuous variables were expressed as mean ± standard deviations. Comparisons between groups were performed using the Student's t test, chi2 test or the Mann Whitney U test as appropriate. A multivariate analysis was used to determine the effect of baseline variables on rhythm outcomes. The limit of statistical significance was p<0.05.
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Results |
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Patient population
A total of 79 patients consisting of 48 men (80%) and 31 women (age: 55±12 years) were included in the study. Patients had failed treatment with 2.1±1.4 antiarrhythmic drugs including amiodarone in most cases. Atrial fibrillation was paroxysmal in 69%. In the remainder it was persistent or permanent. The mean duration of atrial fibrillation was 6.6±6.7 years. The majority of patients had structurally normal hearts (50/79, 63%). Seventeen (22%) had hypertension. The baseline variables were similar in the two treatment groups (Table 1).
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Procedure
Left atrial thrombus was not detected in any patients at pre-procedural transoesophageal echocardiography. Cardioversion was required to restore sinus rhythm in 28 patients. Pre-procedural cardioversion was not successful in 10 patients. Pulmonary vein potentials were identified and targeted in 244 veins (79%). The distribution of these veins is described in detail in Table 2. More pulmonary veins were targeted in patients of Group 1.
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Pulmonary vein isolation was successfully achieved in 98% (239/244) of targeted veins. Sinus rhythm was restored during the procedure in all but two patients. Patients in Group 1 had more radiofrequency energy applications (37±18) than those in Group 2 (25±16, p=0.006). However, the number of lesions required for each case was not a predictor of successful outcomes (sinus rhythm at follow-up, p=0.2; Fig. 2). Procedural success was independent of the number of veins targeted (p=0.43).
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Complications
There were no deaths. Serious complications occurred in two patients. One patient from Group 2 experienced tamponade requiring thoracotomy. The other serious complication was a transient neurological episode in a patient from Group 1. Pulmonary vein stenosis was assessed radiographically after electrical isolation of each vein. Severe pulmonary vein stenosis (>70%) did not occur. Moderate pulmonary vein stenosis (50–70%) occurred in six veins (2.5% of targeted veins), including two from Group 1 and four from Group 2. Mild pulmonary vein stenosis (20–50%) was more common in both groups. Mild pulmonary vein stenosis was detected in 14 veins from Group 1 patients (9%) and eight Group 2 patients (10%). No patients experienced symptomatic pulmonary vein stenosis. There were no non-cerebral thromboembolic events. The frequency of complications was similar in the two treatment groups (p=NS).
Rhythm outcomes
After 3.5±3.5 months 35/48 (73%) patients in Group 1 (open irrigated tip) and 14/31 (45%) in Group 2 (non-irrigated tip) were in sinus rhythm (p=0.02). Patients in Group 1 maintained in sinus rhythm were less likely to be taking antiarrhythmic medications than those in Group 2 (9/35 (26%) vs 8/14 (57%), p=0.002). Recurrence of symptomatic atrial fibrillation occurred in 28/48 (58%) Group 1 and 28/31 (90%) Group 2 (p=0.002) patients. A repeat procedure was performed in 12/48 (25%) Group 1 and 22/31 (71%) Group 2 (p<0.001) patients.
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Discussion |
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Pulmonary vein isolation is a successful strategy for selected patients with atrial fibrillation. However, several groups have now reported a significant failure rate and frequent need for repeat procedures [6
,7,15,16]. Failure is usually associated with a recurrence of conduction into the pulmonary veins [17]. Furthermore, re-isolation of the veins often leads to success at a second or subsequent procedures. These findings suggest that inadequate vein isolation, rather than extrapulmonary foci or other mechanisms of initiation and maintenance of atrial fibrillation, is usually responsible for arrhythmia recurrence. More effective isolation should therefore reduce recovery of conduction into the veins and lead to higher long-term success rates.
Irrigated tip catheters have important theoretical advantages over conventional temperature controlled catheters [9]. Surface cooling during energy delivery reduces heating at the point of highest current density where excessive temperatures would normally produce charring, crater formation and impedance rises. Thus, higher levels of energy can be delivered safely using cooled tip ablation with more reliable delivery of radiofrequency current to the tissue.
The efficacy and safety of irrigated tip ablation have been demonstrated in the treatment of several common arrhythmias including recurrent accessory pathways after conventional radiofrequency ablation procedures, atrial flutter and ventricular tachycardia [10–12]. In these examples there is a clear advantage in producing deeper lesions. The findings of the present study strongly suggest that the theoretical advantages of open irrigated tip ablation also translate to improved outcomes for pulmonary vein isolation.
A previous study compared standard ablation catheters with irrigated tip catheters and 8 mm tip electrode catheters [7]. Marrouche et al. found that closed-irrigated tip catheter ablation did not result in improved outcomes when compared with a group using standard ablation catheters. The closed-irrigated tip may be less effective at cooling the tissue surface. This characteristic limits comparison with the present study. Both the present study and that of Marrouche et al. were non-randomized.
The safety of irrigated tip ablation was recently reported by Macle et al. [13]. In their series there was a small risk of serious pulmonary vein stenosis. Open irrigated tip ablation produces larger lesions under experimental conditions [9,18]. The lesion size corresponds to the delivered power [19]. The study by Macle et al. demonstrated that the larger lesions and higher power delivery did not result in a large increase in the incidence of pulmonary vein stenosis, tamponade or coronary artery injury. Our study supports the finding of Macle et al. [13]. In both the studies a low incidence of complications was observed. In our study, a similar incidence of serious pulmonary vein stenosis was detected in the irrigated and non-irrigated catheter groups. Other adverse events were infrequent and evenly distributed between the two groups. A larger study would be required to detect small differences in the incidence of complications.
Limitations
The present study supports previous work suggesting that the open irrigated tip catheter is a safe alternative for pulmonary vein isolation procedures. The major limitation is the use of an historical control group. Improvements in operator technique and differences in the duration of follow-up may account for some of the differences between the groups. The number of lesions was also greater in the group using the irrigated tip ablation catheter. However, the number of lesions employed did not correlate with procedural success and the vast majority of atrial fibrillation recurrences occurred within three months of the pulmonary vein isolation procedure. A further limitation of this study is the relatively short follow-up period.
Clinical implications
The differences between the irrigated and conventional catheter groups detected were highly significant and suggest further study is justified. A randomized comparison would be required to confirm our findings.
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Acknowledgements |
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The authors thank Dr Karen Byth for her assistance with the statistical analysis. We also acknowledge the assistance of Drs R Abraham, TC Choong, MJ Cooper, L Davis, AR Dennis, P Kovoor, M Mardini, DAB Richards, P Russell and JB Uther.
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References |
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