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Cooled-tip vs. 8 mm-tip catheter for circumferential pulmonary vein ablation: comparison of efficacy, safety, and lesion extension

Maria Matiello, Lluis Mont, David Tamborero, Antonio Berruezo, Begoña Benito, Eric Gonzalez, Josep Brugada
DOI: http://dx.doi.org/10.1093/europace/eun144 955-960 First published online: 30 May 2008

Abstract

Aims In many laboratories, cooled-tip catheters have replaced 8 mm-tip catheters due to their theoretical advantage of achieving larger lesions and avoiding charring. However, direct comparisons between the catheters in the subset of atrial fibrillation (AF) ablation are scarce. The aim of this study was to compare the efficacy, safety, and lesion extension created by 8 mm-tip vs. cooled-tip catheter with different energy settings for circumferential pulmonary vein ablation (CPVA).

Methods and results A series of 221 consecutive patients with symptomatic AF were included in the study. Circumferential pulmonary vein ablation was performed using an 8 mm-tip catheter (55 W, 50°C) in 90 patients (Group 1), a cooled-tip (30 W, 45°C) in 42 (Group 2), and a cooled-tip (40 W, 45°C) in 89 (Group 3). In a subgroup of 60 patients, troponin I (TpnI), creatinine kinase, and myoglobin values were obtained before and at 12 and 24 h after ablation. At 1 year follow-up, the probability of being arrhythmia-free after a single procedure was 53, 35, and 55% in patients from Groups 1, 2, and 3, respectively. Ablation with a cooled-tip catheter at 30 W led to a higher recurrence rate (P = 0.030) and was identified in Cox regression analysis as an independent predictor of AF recurrence (HR, 1.713; 95% CI, 1.02–2.90; P = 0.045). There were no differences in intra-procedure complications (2.2 vs. 5.6 vs. 4.9%, P = 0.542). The myocardial lesion according to TpnI was smaller in Group 2 (P = 0.02).

Conclusion The cooled-tip catheter at 30 W was less efficacious than both the 8 mm catheter and the cooled-tip with a 40 W power setting.

Keywords
  • Atrial fibrillation
  • Arrhythmia
  • Radiofrequency catheter ablation

Introduction

Atrial fibrillation (AF) ablation has been shown to be an effective treatment for refractory AF.14 However, reported success rates and complications vary widely from series to series.510 Several factors have been proposed to explain the differences, some of which are related to operator abilities (the learning curve) or patient selection and post-procedure monitoring; however, most of them refer to procedural differences due to a non-standardized ablation technique. One factor influencing outcome is the depth and extension of lesion, which is directly influenced by the catheter type and radiofrequency (RF) energy settings.

Experimental studies have shown that the cooled-tip catheter may produce deeper and larger lesions without carbonization of the tip.1113 Therefore, it could improve AF ablation outcome, achieve larger lesions, and minimize complications such as thrombus formation. Although the choice of a cooled-tip catheter seems justified, previous clinical studies are controversial and have failed to demonstrate better results with this catheter technology in AF ablation.1416

The aim of the present study was to compare the efficacy, safety, and lesion extension created by 8 mm-tip and cooled-tip catheters with two different energy settings in the context of circumferential pulmonary vein ablation (CPVA).

Methods

Study population

A series of 221 consecutive patients (169 men, mean age 52 ± 11 years) with documented symptomatic refractory paroxysmal (62%), persistent (24%), and permanent (14%) AF, who were referred to our institution for ablation, were included in the study.

Exclusion criteria were age <18 or >75 years, anteroposterior left anterior descending artery at transthoracic echocardiography >55 mm, presence of left anterior (LA) thrombus on transesophageal echocardiography, and the presence of a mechanical prosthetic heart valve.

Written informed consent was obtained from all patients. Antiarrhythmic drug therapy was stopped at least five half-lives before the ablation, except in patients receiving amiodarone. Patients on oral anticoagulation stopped medication 3 days prior to the procedure and low-molecular-weight heparin was administered up to 12 h before the ablation. Patients underwent cardiac resonance imaging and transesophageal echocardiography prior to ablation.

Ablation procedure

Catheters were introduced percutaneously through the femoral vein and a transseptal puncture was performed to access the left atrium. After transseptal access, a bolus of 5000 IU of heparin was administered, along with an additional bolus to maintain an activated clotting time of between 200 and 250 s. Ablation was performed under intravenous sedation with propofol and analgesia with meperidin and phentanyl. Oxygen saturation and invasive arterial blood pressure were monitored throughout the procedure.

A three-dimensional map was constructed using an electroanatomical mapping system (either with CARTO, Biosense-Webster, or NAVX, St Jude Corporation) to support the creation and validation of RF lesions.3

Continuous RF lesions were delivered surrounding each ipsilateral PV as described previously.10 Ablation lines were also deployed along LA roof and LA posterior wall joining contralateral encircling lesions. The endpoint was the disappearance of the local electrogram inside the whole surrounded areas and it was assessed during sinus rhythm whenever it was possible, performing electrical cardioversion when necessary. Additionally, mitral isthmus ablation was anatomically performed by creating an RF line from the postero-lateral aspect of the left-sided encircling lesions to the mitral valve.

In the first 90 patients (Group 1), RF lesions were made using a thermocouple-equipped 8 mm-tip catheter (Celsius, Biosense-Webster) at a target temperature of 55°C and a maximum output of 50 W. For the next 131 patients, we used a saline cooled-tip catheter (Celsius Thermocool, Cordis, Biosense-Webster) at 45°C temperature and 30 W power output in 42 of them (Group 2) and at 45°C/40 W in the remaining 89 (Group 3). Irrigation was done with saline solution at a rate of 16 mL/min during energy delivery at room temperature.

In order to assess myocardial injury related to RF catheter ablation, serum levels of cardiac lesion biomarkers [creatinine kinase (ck), troponin I (TpnI), and myoglobin] were obtained in a subgroup of 60 patients (24 from Group 1, 18 from Group 2, and 18 from Group 3) before and at 12 and 24 h after ablation.1719 The time of RF application was also monitored.

Follow-up

Follow-up consisted of outpatient visits and 24 h Holter monitoring at 1, 4, and 7 months, and every 6 months thereafter if the patient remained asymptomatic. Patients were also asked to report any symptoms of arrhythmia between scheduled visits and encouraged to document recurrences by an ECG performed at their emergency service. A transthoracic echocardiogram and a magnetic resonance angiography were routinely performed 4 months after ablation.

All patients continued on oral anticoagulation to maintain an international normalized ratio of between 2.0 and 3.0 for a minimum of 2 months. Previous antiarrhythmic therapy was maintained for at least 1 month in order to manage early recurrences and then discontinued if there were no recurrences 1–3 months after ablation.

Any documented episode of AF or left atrial flutter presenting after the 3 month healing period was considered as a recurrence. Arrhythmic episodes within the first 3 months after the procedure were not considered in the evaluation of final success rates because they are often described as transient recurrences related to atrial inflammatory processes following RF lesions.20

Statistical analysis

Continuous variables were expressed as mean ± SD and compared by analysis of variances. Categorical variables were expressed as percentages and were compared by chi-squared analysis or with Fisher's exact test. Arrhythmia-free survival ratio was calculated by the Kaplan–Meier method, assessing differences by the log-rank test. Univariate and multivariate analyses were performed using the Cox proportional hazards regression model to determine clinical predictors of arrhythmia recurrence. A P-value of <0.05 was considered statistically significant. Statistical analysis was performed using SPSS for Windows Version 12.0 (SPSS Inc., Chicago, IL, USA).

Results

Patient characteristics

There were no baseline differences between the groups in terms of patients' characteristics. Baseline clinical and echocardiographic pre-procedure characteristics are depicted in Table 1.

View this table:
Table 1

Baseline characteristics of patients included in the study

Baseline characteristics8 mm-tip catheter (88)Cooled-tip catheter 30 W (54)Cooled-tip catheter 40 W (105)P-value
Age (years) (mean ± SD)50.8 ± 11.454.5 ± 10.952.8 ± 11.30.204
Male gender [n(%)]76 (83.3%)29 (70.7%)67 (75.3%)0.105
Left atrial diameter (mm)41.7 ± 5.740.7 ± 7.141.9 ± 5.20.635
Structural heart disease [n (%)]16 (17.7%)8 (19.0%)15 (16.9%)0.946
Hypertension [n (%)]29 (32.2%)15 (35.7%)35 (39.3%)0.311
Type of AF [n (%)]0.133
 Paroxysmal57 (63.3%)27 (64.3%)53 (59.5%)
 Persistent26 (28.9%)7 (16.7%)19 (21.3%)
 Permanent7 (7.8%)8 (19.0%)17 (19.1%)

Ablation procedure

A total of 98 patients (44%) started the procedure in AF. Of these, 28 patients (29%) recovered sinus rhythm during RF application. Average procedure time was 128 ± 31 min, with 27 ± 8 min of fluoroscopy and 2197 ± 944 s of RF application.

Study outcome

Mean follow-up of each group was 20 ± 10, 14 ± 6, and 9 ± 3 months, respectively. Probability of remaining arrhythmia-free after a single procedure at 1 year follow-up, based on Kaplan–Meier estimates, was 53% in Group 1, 35% in Group 2, and 55% in Group 3. A total of 7 (8%), 4 (10%), and 13 (15%) of the patients of each group were taking one antiarrhythmic drug despite they had no recurrences beyond the blanking period.

Arrhythmia recurred AF in 32% of patients from Group 1, 55% from Group 2, and 40% from Group 3, whereas left atrial flutter (LAF) was documented in 20, 25, and 14%, respectively. Some patients had both AF and LAF documented after ablation (Figure 1AC).

Figure 1

Arrhythmia-free survival curves of any arrhythmia occurrence (A), atrial flutter (B) and AF (C).

Overall arrhythmia recurrences were significantly higher in Group 2 patients (log-rank P = 0.030). The percentage of patients who were free of recurrences during follow-up did not differ between Groups 1 and 3 (log-rank P = 0.366). There were no differences in the incidence of LAF recurrence in Group 2 (P = 0.752) or Group 3 (P = 0.255) compared with Group 1.

Among all the analysed variables, only anteroposterior atrial diameter (HR, 1.105; 95% CI, 1.05–1.19; P = 0.001) and cool-tip ablation with a 30 W power setting (HR, 1.713; 95% CI, 1.02–2.90; P = 0.045) were independent predictors of arrhythmia recurrence.

There were no significant differences in intra-procedure complications (2.2 vs. 5.6 vs. 4.9%, respectively, P = 0.542). Complications are listed in Table 2.

View this table:
Table 2

Intra-procedure complications related to RF application

P = 0.5428 mm-tip catheter (88)Cooled-tip catheter 30 W (54)Cooled-tip catheter 40 W (105)
Dysphagia001
Transient vascular accident112
Tamponade100
Pericarditis413
Transient ST elevation012
Pulmonary vein stenosis*000
  • *PV narrowing of >50%.

Myocardial lesion

Baseline values of ck, myoglobin, and TpnI obtained in a subgroup of patients from Groups 1, 2, and 3 were all in the normal range before procedure. At 12 and 24 h post-ablation, serial values of TpnI were above the normal range in all patients. The maximum TpnI values were obtained at 24 h after ablation.

The subgroup of patients from Group 3 showed the largest myocardial lesion as estimated by TpnI maximum value, followed by Groups 1 and 2 (P = 0.02). Myocardial lesion did not correlate with the number of RF applications. Indeed, in Group 2, there was a trend towards greater RF application time in order to achieve the ablation endpoint.

Biochemical lesion markers and RF data are depicted in Table 3 and Figure 2.

Figure 2

Troponin I serial values 12 and 24 h after CPVA.

View this table:
Table 3

Biochemical lesion markers data

8 mm-tip catheter (88)Cooled-tip catheter 30 W (54)Cooled-tip catheter 40 W (105)
CK (30–140 UI/L)
 12 h226.32 ± 73.63194.63 ± 74.33239.35 ± 123.27
 24 h200.38 ± 67.48190.59 ± 87.91248.00 ± 129.06
Myog (0–80 ng/mL)
 12 h67.24 ± 28.9857.61 ± 25.7899.91 ± 68.91
 24 h55.27 ± 28.2145.31 ± 15.2655.97 ± 25.12
TpnI (0–0.1 ng/mL)
 12 h3.14 ± 1.392.00 ± 1.004.40 ± 2.14
 24 h4.26 ± 2.372.68 ± 1.105.62 ± 2.31
  • myog, myoglobin.

  • *Normal range between parentheses.

Discussion

The main finding of the present study is that the efficacy of ablation catheter was strongly related to power settings. A power setting of 30 W for a cooled-tip catheter seems to be less efficacious when compared with the other groups.

Atrial fibrillation was initially ablated with a 4 mm catheter.1 The high initial recurrence rate, partly related to incomplete ablation lines and conduction recovery, led to the use of catheter technologies able to deliver higher power in order to achieve complete and deeper lines, as in the case of 8 mm-tip or cooled-tip catheters.2125

Furthermore, the risk of severe complications related to RF application, such as thrombus formation, PV stenosis, and atrium perforation, showed that better RF energy control was necessary.2628 The solutions proposed in order to minimize these RF-related complications included the use of intra-cardiac echocardiograms to control micro-bubbles and consequent thrombus formation with 8 mm-tip catheters, power titration during the procedure, raising power while applying to the anterior wall, lowering it in zones with a high risk of complication such as posterior wall and around pulmonary vein ostia, or limiting the RF power delivered.29,30

In this context, 8 mm-tip catheters were also replaced by cooled-tip catheters, as they have the theoretical advantage of less charring formation and better preservation of endocardial surface, as the use of saline irrigation allows delivery of greater power and the cooling effect minimizes impedance rises and avoids overheating of tissue interface and consequent thrombus formation.11,12 However, although saline irrigation could have several advantages, it also poses the additional risk of emboli due to air bubbles.

Previous studies comparing efficacy of cooled-tip vs. 8 mm-tip catheters in AF ablation showed apparently contradictory results.1416 This fact seems to be related to the different power settings and is consistent with our results. When irrigated catheter output power was programmed <35 W, the efficacy was lower when compared with the 8 mm-tip catheter,14,15 whereas the efficacy was comparable when the cooled-tip catheter power output was programmed to 50 W.15,16 However, cooled ablation at 50 W was associated with higher cardiovascular and gastrointestinal risks.15 In our study, an intermediate RF setting of 40 W power output in the cooled-tip catheter showed the same efficacy than the 8 mm-tip catheter without increasing the complications.

Myocardial injury as assessed by the enzymatic lesion curve showed a coherent relationship between the estimated lesion formation and clinical outcomes. Higher values were observed in Group 3 and fewer applications were necessary to achieve the ablation endpoint.

Although, as pointed out previously, intra-procedure energy titration or intra-cardiac echocardiograms are feasible options to control energy application, we believe that a fixed RF setting helps to standardize the procedure and power-limited cooled ablation at 40 W offers a reasonably safe method given that this is an extra-ostial PV ablation procedure.

Study limitations

The main limitation of the study is the lack of randomization. Since patients were included consecutively and each group belonged to a different chronological period, the learning curve and different follow-up periods of each group could have influenced the results. To assess the former question, we have included in the multivariate analysis a variable dividing the population into four categories of 55 patients each, according to the historical period when the procedure was performed. Arrhythmia predictors after introducing this variable in the multivariate model did not change. This should suggest no significant influence of the learning curve in the results of this study.

On the other hand, to assess whether recurrence risk was underestimated in the last group due to a shorter follow-up period, binomial multivariate regression was performed to find predictors of arrhythmia recurrence at 6 month follow-up. The results were consistent with those obtained using survival analyses, since the same independent predictors were raised: LA diameter [OR: 1.11 (1.04–1.18), P = 0.001] and to use 30 W output irrigated catheter [OR: 3.3 (1.4.−8.0), P = 0.007]. This should suggest no significant influence of the different follow-up periods between groups, and this was probably related to the fact that, in this series, time to first recurrence rarely was beyond the 6th month after ablation procedure.

Another limitation is the activated clotting time (ACT) times. Although several groups have been using an ACT of 200 to 250 s, a recent consensus document recommends higher levels of anticoagulation (ACT >300); therefore, some of the observed transient cerebrovascular accidents may be attributable to relatively low anticoagulation rather than to the ablation catheter itself. Finally, these results refer to CPVA and may not be applicable to other AF ablation approaches.

Conclusions

At 30 W, the cooled-tip catheter was less efficacious than the 8 mm-tip. Raising power settings up to 40 W increased the efficacy of the cooled-tip catheter without a significant increase in the risk of complications. Power settings may therefore exert a strong influence on ablation outcomes.

Conflict of interest: none declared.

Funding

The study was funded in part by a grant from the Carlos III Health Institute, Madrid, Spain (Fondo Investigación Sanitaria—PI050081).

References

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