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International Journal of Arrhythmia 2014;15(3): 4-12.
ORIGINAL ARTICLES
Prognosis of Atrial Flutter Alone
Ablation in Patients who Show
Typical Atrial Futter with or without
Rarely Documented Paroxysmal
Atrial Fibrillation

 




Introduction

Atrial fibrillation (AF) and atrial flutter (AFL) are the most common sustained atrial arrhythmias and often coexist. Both arrhythmias have similar pathological features including electrical remodeling1 and shortened action potential duration2 as well as similar clinical predictors such as hypertension, heart failure, and pulmonary disease.3,4 The AFL macroreentrant circuit is localized in the right atrium between the tricuspid valve and the crista terminalis.5 Therefore, in a majority of patients, a line of block (LOB) is needed between both vena cavae to prevent short-circuiting.6,7 Ablation of AFL interrupts the circuit at its narrowest portion the cavotricuspid isthmus (CTI). Current guidelines established CTI ablation as Class I therapy for recurrent AFL.8 In a previous study, 12-26% of patients developed AF during the follow-up period after ablation of typical AFL, which was performed within 2 years after CTI ablation.9,10 AF and AFL are known to coexist. Waldo et al.11,12 hypothesized that burst episodes of AF initiate AFL by creating an LOB between the vena cavae. Thus, ablation of the CTI may unmask underlying episodes of AF. Ablation of AF and AFL in patients with both arrhythmias is beneficial,13 but data on prophylactic AF ablation in patients with AFL alone are lacking. Therefore, the purposes of this study were (1) to examine the longterm outcome after ablation of typical AFL with or without rarely documented paroxysmal AF, and (2) to investigate the predictors of recurrent atrial arrhythmia after catheter ablation of the CTI.

Methods

Study Population

Patients were enrolled between March 2010 and June 2012. The inclusion criterion was symptomatic persistent typical AFL or typical AFL with rarely documented paroxysmal AF (PAF). AFL recognition was based on the typical saw-tooth appearance on the surface 12-lead electrocardiogram (ECG). AFL was considered persistent if it sustained for at least 1 week. Rarely documented PAF was defined as the occurrence of ECG or Holter monitoring-proven short runs of AF less than three times. All patients underwent chemical or electrical cardioversion. Failure of at least one antiarrhythmic drug or postcardioversion was required before performing catheter ablation. Exclusion criteria were inability or unwillingness to take warfarin, left ventricular (LV) dysfunction on echocardiogram (ejection fraction [EF] <40%), pregnancy, and non-inducible typical AFL at the electrophysiological study. Because sinus rhythm could be the presenting rhythm during the electrophysiological study, it was considered an inclusion criterion and used to induce AFL and demonstrate CTI participation.

Study Design

CTI ablation alone was performed in 36 consecutive patients (age, 63.3 ± 1.3 years; 34 men), of whom 26 had typical AFL alone (AFL-alone group) and 10 showed mainly typical AFL with rarely documented PAF episodes (mixed group) prior to ablation. The procedure was performed under conscious sedation with midazolam or propofol. For patients who were in sinus rhythm at the time of the ablation, AFL was induced by atrial burst pacing. Typical AFL was confirmed by entrainment mapping maneuvers. Lack of demonstration of CTI-dependent flutter during the electrophysiological study was considered an exclusion criterion. Surface ECG signals and intracardiac electrograms were filtered at 30-500 Hz and recorded simultaneously using the Prucka Cardiolab EP system (General Electric Co., Fairfield, CT, USA). All antiarrhythmics were discontinued 5 half-lives before the procedure. Patients were administered warfarin for at least 1 month before ablation to achieve effective oral anticoagulation. Administration of warfarin was stopped at admission and replaced by intravenous heparin before the ablation; heparin administration was continued for 2 days after the procedure. Warfarin was restarted on the night of the procedure and continued for at least 2 months to maintain an international normalized ratio between 2 and 3.

Ablation of AFL

Intracardiac catheters were placed percutaneously under fluoroscopic guidance. Two standard quadripolar catheters (inter-electrode spacing 5-5-5 mm; St. Jude Medical, Inc., MN, USA) were placed at the right ventricle and right atrium through the right femoral vein. Coronary sinus recordings were taken using a 6-Fr decapolar catheter (inter-electrode spacing 2-8-2 mm; St. Jude Medical, Inc., MN, USA) advanced through the right jugular vein. A standard quadripolar catheter (inter-electrode spacing 5-5-5 mm; St. Jude Medical, Inc., MN, USA) was placed at the His bundle region through the left femoral vein. CTI ablation was performed using a bidirectional 4-mm-tip catheter (Cool Path Duo mid curve, St. Jude Medical, Inc., MN, USA) in a dragging motion every 10 seconds, targeting a power of up to 30 W and temperature of 35°C. The procedure endpoint was a bidirectional block, which was assessed by an activation detour by pacing either side of the line and by differential pacing techniques as described in the literature.10,14

Post-ablation Follow-up

After ablation, all patients were followed up at our clinic. When the patients experienced symptoms suggestive of tachycardia, ECG, 24-hour Holter monitoring, or cardiac event recording were performed again to define the cause of clinical symptoms. A questionnaire including the following questions was then administered to the patients: (1) Did the patient still have clinical symptoms suggestive of arrhythmias? (2) Were the symptoms the same as those experienced before ablation? (3) When did the symptoms first appear after ablation? (4) Did the patient go to the clinic, undergo ECG examination, and receive a diagnosis? (5) What kind of therapy was used to treat the symptoms? The responses to the questionnaire were reviewed, and the medical history of all patients was obtained.

Statistical Analysis

Continuous variables are expressed as mean ± standard deviation and were compared using the Mann-Whitney test. A Chi-square test or Fisher’s exact test was used to compare categorical variables. A P value <0.05 was considered statistically significant. SPSS 17.0 (statistical package for Mac, Chicago, IL) was used for statistical analysis.

Results

Arrhythmia and survival of EAM

CTI ablation alone was performed in the 36 consecutive patients (age, 63.3 ± 1.3 years; 34 men), of whom 26 had typical AFL alone and 10 showed mainly typical AFL with rarely documented PAF episodes prior to ablation.
Baseline characteristics were not significantly different between the AFL-alone group and the mixed group; the social history, associated diseased, and past medical history are presented in Table 1. Further, the baseline echocardiographic parameters did not differ in interventricular septal wall thickness, LV posterior wall thickness, left atrial (LA) dimensions, and LV EF (Table 2).




The mean follow-up duration was 20.8 ± 17.3 months. In the AFL-alone group, atrial tachyarrhythmia recurred in 9 (34.6%) patients. AFL recurrence and new-onset AF were noted in 8 (30.8%) and 2 (7.5%) patients, respectively. In the mixed group, atrial arrhythmia was noted in 9 (90%) patients. AFL and AF recurrence was noted in 5 patients each (50% for both). Further, AFL and AF recurrence within 1 year was noted in 4 patients each (15.3% and 40%, respectively) (Table 3).
In the subgroup analysis of the AFL-alone group, those who experienced recurrence had larger LA dimensions (42.24 ± 2.09 mm vs. 48.22 ± 2.24 mm, p=0.05) and a higher incidence of dyslipidemia (0% vs. 33.3%, p=0.01) than those who did not experience recurrence (Table 4). Concomitant AF at baseline, increased left atrial diameter, and dyslipidemia were significantly associated with the recurrence of atrial tachyarrhythmia.

Discussion

In the present study, atrial tachyarrhythmia was noted in 9 (34.6%) patients in the AFL-alone group, and atrial arrhythmia was noted in 9 (90%) patients in the mixed group. During the follow-up period, recurrent AFL was noted in 30.8% and AF, in 7.5% of the patients in AFL-alone group.



AFL ablation is very effective when a bidirectional block is achieved at the CTI.15,16 The occurrence of AFL after successful CTI ablation in typical AFL patients has been reported to be approximately 30%. Moreover, spontaneous AF prior to CTI ablation and structural heart disease has been consistently associated with an increase in the recurrence of AF after the procedure.17,18 Therefore, AFL ablation is traditionally considered more effective in patients with AFL alone.19,20
Since the prior history of AF plays an important role in the prediction of early or late AF occurrence after AFL ablation, we analyzed the risk of AF during the follow-up period in patients with or without a prior history of rarely documented PAF after AFL ablation. Previous studies demonstrated that successful ablation of AFL decreased the AF recurrence in 50-75% of patients with a prior history of AF.21 The underlying mechanism of the effects of AFL ablation on AF is still unknown. Some studies reported that AFL transformed into AF, which provides a basis for AF eradication after CTI ablation.3,22,23 Thus, CTI ablation seemed to modify the atrial substrate for AF and changed the natural course of AF in patients with typical AFL.
We further analyzed the risk of AF during the follow-up period in patients without a prior history of AF after the ablation of AFL alone. Subgroup analysis of the AFL-alone group showed that those who experienced recurrence had larger LA dimensions than those who did not experience recurrence. In a previous study, CTI ablation failed in only 3% of the patients, and atrial enlargement was the only predictor of unsuccessful ablation. A larger atrium has a wider isthmus, thus leading to a higher failure rate in these patients.24,25 Therefore, if the patients with typical AFL were treated with CTI ablation before the LA dimension was not enlarged, the recurrence of atrial tachyarrhythmia might have reduced.
The occurrence of AF is still a major problem after successful ablation of the CTI. Previous studies have reported that 12-26% of patients developed AF during the follow-up period after successful ablation of typical AFL.9,10 The electrical isolation of the 4 PVs (pulmonary veins) in addition to CTI ablation in patients with mainly typical AFL with intermittent PAF episodes might reduce the recurrence of AF.



Despite the important findings, our study has a few limitations that need to be acknowledged. It is difficult to estimate the incidence of AF in patients with typical AFL. Therefore, the incidence of prior AF may be underestimated. After ablation of AFL, we did not perform Holter monitoring or event recording routinely to detect asymptomatic AF, and patients with asymptomatic recurrence of atrial arrhythmias may be lost to follow-up. Therefore, the incidence of recurrent AF or AFL may be underestimated. Because this was a retrospective study, we could not ensure a balance between genders. As a result, the number of women in the study population was very less (only 2), which could have led to a selection bias. And there was a limitation that ECG monitoring before ablation could not be adequate to detect short-run of AF.
In conclusion, close, regular follow-up might be needed for patients with typical AFL after CTI ablation owing to a high recurrence of atrial tachyarrhythmia. In addition to CTI ablation, more aggressive treatment such as pulmonary vein isolation might be needed for patients presenting with mainly typical AFL and rarely documented PAF episodes.




References

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