Clinical outcome of left atrial ablation for paroxysmal atrial fibrillation is related to the extent of radiofrequency ablation
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- Katritsis, D., Ellenbogen, K.A., Giazitzoglou, E. et al. J Interv Card Electrophysiol (2008) 22: 31. doi:10.1007/s10840-008-9247-9
The exact mechanism of eliminating atrial fibrillation (AF) by catheter ablation techniques is not known. We investigated whether the extent of atrial damage conferred by radiofrequency lesions is a predictor of success after ablation, regardless of the method employed for ablation.
Ninety consecutive patients with paroxysmal AF subjected to ostial–antral pulmonary vein isolation (n = 41) or circumferential (n = 49) catheter ablation were studied.
At 1 year follow-up, 16 out of 41 patients (39%) with ostial–antral ablation and 16 out of 49 patients (32.6%) with circumferential ablation had AF recurrences (p = 0.5). The mean duration of radiofrequency ablation lesions was statistically significantly shorter in patients with recurrence of AF compared to those with sinus rhythm 1 year after ablation (22.3 ± 4.2 min vs. 27.2 ± 4.5 min, respectively, p value < 0.001). Radiofrequency ablation time was inversely associated with the risk of recurrence of AF 1 year after ablation and this relationship remained even after adjustment for potential confounding factors such as age, sex, left atrial size, and type of ablation technique (ostial–antral or circumferential; HR = 0.80, 95% CI: 0.72–0.87, p < 0.001).
Duration of radiofrequency energy delivery is an independent predictor of clinical outcome at 1 year follow-up both among patients undergoing circumferential as well as ostial–antral ablation.
The exact mechanism of eliminating atrial fibrillation (AF) by catheter ablation techniques is not known. Although re-emergence of AF following pulmonary vein (PV) disconnection procedures is usually due to recurrence of PV conduction, [1–3] complete electrical isolation of the PVs may not be necessary for a successful outcome. [2, 4–8] Nonencircling left atrial lesions created by catheter ablation have been found equally effective with circumferential ablation in eliminating permanent AF , and tailored catheter approaches that either target triggers and drivers of AF  or aim at non-inducibility of the arrhythmia can produce favourable long-term results with [11, 12] or without [12, 13] verification of PV isolation. Electrogram-guided ablation may also produce favorable clinical results  although the mechanism of eliminating AF appears to be different than that of circumferential ablation . It has been suggested that the extent of left atrial ablation (average 30%) is a marker of success rather than PV isolation , but no specific data relating clinical efficacy of various ablation techniques with the duration of radiofrequency lesions exists.
The present study investigated the relationship between clinical efficacy of various ablation techniques with the extent of left atrial lesions performed in patients with paroxysmal atrial fibrillation.
Consecutive patients with symptomatic, paroxysmal atrial fibrillation subjected to catheter ablation according to different techniques and in whom no second ablation attempt was performed throughout a 1-year follow-up period were included in the study. Patients who underwent a repeat ablation attempt for AF recurrence or ablation-induced atrial flutter or focal tachycardia were excluded from this analysis. Detailed data regarding radiofrequency energy delivery (number of lesions, and energy delivery time) were kept for all patients. The trial was approved by our Institutional Review Board and all patients had provided a written, informed consent.
Ablation procedures were performed following IV enoxaparin (1 mg/Kg) with a conventional 4 mm catheter tip and 2.5 mm interelectrode spacing (Cordis-Webster), at a preset electrical power of 40 Watts, aiming at a target temperature of 52°C (for ostial–antral ablation), and an irrigated-tip ablation catheter (infusion rate of 17 ml/min) with a 4 mm tip and 2.5 mm interelectrode spacing (Cordis-Webster) electrical power of 30 W and aiming at a target temperature of 46°C (for circumferential ablation).
As part of our routine AF ablation protocol, all but two patients with chronic obstructive pulmonary disease were receiving beta blockers, whereas all patients were kept on amiodarone and warfarin for 6 weeks post-ablation. Patients were subjected to monthly clinical assessment and ambulatory electrocardiographic monitoring up to 1 year. All patients were instructed to maintain personal records with descriptions of every episode of symptomatic palpitations and, in case of persistent arrhythmia episodes, to obtain trans-telephonic or electrocardiographic documentation of the underlying rhythm. A successful outcome over the follow-up period was defined as the lack of electrocardiographically recorded AF, and no PAF on Holter, and subjective symptomatic improvement after a 6-week blanking period. Patients we reviewed both by fellows who were blinded to treatment and at least two members of the ablation team. Final decisions regarding clinical outcome was made by consensus among the ablation team. Trans-esophageal echocardiography and magnetic resonance imaging of the PVs were also performed in all patients at completion of follow-up to exclude PV stenosis.
1.2 Statistical analysis
Shapiro–Wilk test was used to evaluate the normality of continuous variables (i.e. age, left atrial size, radiofrequency time) and because no variable was skewed, all of them are presented as mean±SD while categorical variables are summarized as absolute and relative (%) frequencies. Associations between categorical variables were tested with the chi square test, and associations between continuous and categorical variables were tested with Student's t test. Freedom from recurrent AF was determined using Kaplan–Meier analysis and differences in AF-free survival were evaluated using the log-rank test. Cox proportional hazard model was used to evaluate the association between the extent of left atrial ablation (extent of radiofrequency time in minutes) and the recurrence of AF 1 year post-ablation, after controlling for potential confounders such as type of ablation technique and ablation catheter type, age, sex, and left atrial size. Separate models were fitted using radiofrequency time as continuous and as binary variable (short vs. long time). Appropriate plot used to assess the proportional hazards assumption revealed that this was valid. All reported p values were based on two-sided tests and were compared to a significant level of 5%.
2.1 Clinical characteristics
Characteristics of patients with respect to radiofrequency time of ablation
Short radiofrequency time (<median)
Long radiofrequency time (≥median)
54.7 ± 8.2
54.8 ± 9.5
Males (n, %)
Cause of atrial fibrillation
Coronary Artery Disease
Left atrial size
40.5 ± 4.8
40.9 ± 4.08
Characteristics of patients by type of ablation technique
Ostial–antral Ablation (n = 41)
Circumferential Ablation (n = 49)
52 ± 10
57 ± 7
Males (n, %)
Cause of atrial fibrillation
Coronary artery disease
Left atrial size
40.1 ± 2.3
41.2 ± 5.6
2.2 Procedural characteristics
Procedural characteristics are presented in Table 2. The mean±SD of radiofrequency time among all patients recruited in the study was 25.4 ± 4.9 min (range: 14.5–37.5 min, median: 25.4 min). No statistical difference was observed in radiofrequency time between patients who underwent ostial–antral ablation and those in whom circumferential ablation was performed (Table 3).
Cumulative radiofrequency current delivery, procedure and fluoroscopy times
Ostial–antral Ablation (n = 41)
Circumferential Ablation (n = 49)
RF time (minutes)
25.9 ± 3.6
25.1 ± 5.8
Fluoroscopy time (minutes)
56.3 ± 7.9
28.2 ± 6.1
Procedure time (minutes)
208.8 ± 26.9
180.1 ± 18.4
2.3 Clinical outcome and radiofrequency time
Radiofrequency time for patients with sinus rhythm and those with AF recurrence, stratified by sex, cause of AF and type of ablation technique In brackets we present the number of patients for each group
Sinus rhythm (n = 58)
AF recurrence (n = 32)
27.2 ± 4.5
22.3 ± 4.2
24.5 ± 3.8 (11)
23.3 ± 4.0 (4)
27.8 ± 4.4 (47)
22.1 ± 4.2 (28)
Cause of AF
26.8 ± 4.3 (31)
22.6 ± 4.7 (19)
Coronary artery disease (16)
29.3 ± 4.8 (8)
22.9 ± 3.2 (8)
Lone AF (24)
26.8 ± 4.6 (19)
20.1 ± 2.7 (5)
Type of ablation technique
27.6 ± 2.9 (25)
23.1 ± 2.9 (16)
26.8 ± 5.4 (33)
21.5 ± 5.1 (16)
Since sex distribution among patients who received low and high amount of ablation was different (Table 1), remained confounding may exists. Therefore, we performed stratified analysis by gender. Cox proportional hazard models showed that among men the one minute increase in radiofrequency time is associated with 16% reduction in risk for AF recurrence (HR = 0.84, 95% CI: 0.77–0.90), while no association was observed among female patients (HR = 0.91, 95% CI: 0.66–1.25). The small number of women among the total study population may account for this finding.
Our results suggest that elimination of the electrical activity of the left atrium is a powerful predictor of AF-free survival in patients subjected to catheter ablation, regardless of the ablation technique employed. This is in keeping with the observations of Pappone and colleagues in the setting of circumferential ablation . Our study indicates that the amount of ablated atrial myocardium is also critical in the ostial–antral ablation approach.
Our results can be interpreted within the context of the multi-factorial aetiology of AF [19, 20]. There is now substantial evidence that apart from the PVs, other parts of the left atrium such as the PV-left atrial junction , the posterior left atrial wall , and areas rich in sympathetic  or parasympathetic  innervation may also contribute to triggering and maintaining of AF through various mechanisms [21, 22, 25, 26]. One might therefore speculate that the more extensive the ablation-induced damage, the higher the possibility of intervening with one of these mechanisms. An effect on rotors and AF nests as probably happens with real-time frequency analysis- and complex fractionated electrogram-guided ablation [14, 27] cannot be ruled out with extensive left atrial ablation. Nevertheless, mere elimination of the left atrial tissue below the critical amount required for reentry  may also theoretically affect clinical outcomes. Perhaps it is not surprising that in a recent report, single ablation end-points such as PV disconnection or voltage abatement did not to persist over time and did not predict clinical outcome .
However, our results should be considered with caution. The effect of ablation on left atrial transport function is still debated [29, 30] and left atrial voltage reduction  and fibrosis  may predispose to AF development. Risk of complications may also be increased with prolonged ablation procedures. We certainly do not advocate an unnecessarily prolonged procedure with delivery of an unrestricted number of ablation lesions. Theoretically, clinical outcomes should be optimized by performing the minimum amount of ablation and left atrial damage. Further studies are necessary to address this important issue.
3.1 Study limitations
Our study has several limitations. First, asymptomatic episodes after catheter ablation of AF are well documented [33, 34]. Nevertheless, this limitation applies almost to all reports on AF ablation and results in overestimation of the true success rate. Second, achieved temperatures for each individual lesion and in each patient have not been recorded for comparative purposes. Thus, actual left atrial damage can only be inferred from total ablation time. However, although theoretically expected, an increase in duration of radiofrequency energy application may not necessarily indicate a larger mass of left atrial tissue ablated. Third, patients subjected to different ablation techniques were not randomized. They were, however, consecutive patients who were subjected to the technique that used to be our clinical practice at time of recruitment. Finally, our small sample size might have been responsible for an overestimation of the association between time of ablation and recurrence of AF, such as the observed 16% reduction in the odds of AF recurrence for one additional minute of ablation.
Acknowledging these limitations, our study indicates that the extent of left atrial damage is the main determinant of clinical success following catheter ablation techniques, regardless of the method employed for ablation. It also supports the notion of several, different mechanisms being implicated in the genesis and perpetuation of AF.
Conflict of interest statement
There is no conflict of interest to be disclosed for any author.