Europace Advance Access originally published online on June 13, 2006
Europace 2006 8(8):601-606; doi:10.1093/europace/eul067
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ELECTROPHYSIOLOGY
Electrocardiographic predictors of long-term outcomes after radiofrequency ablation in patients with right-ventricular outflow tract tachycardia
1 Division of Cardiology, Department of Medicine, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand; 2 Division of Cardiology, Her Majesty Cardiac Center, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand; 3 Division of Cardiology, Department of Research Promotion, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
Manuscript submitted 16 November 2005. Accepted after revision 14 April 2006.
* Corresponding author. Tel: +66 1 805 9992; fax: +66 2 412 7412. E-mail address: sirkt{at}mahidol.ac.th
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Abstract |
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Aims The objectives of this study were to identify electrocardiographic (ECG) predictors of long-term outcomes after radiofrequency (RF) ablation in patients with right-ventricular outflow tract (RVOT) tachycardia.
Methods and results We correlated ECG characteristics with RF ablation outcomes in 144 patients with RVOT tachycardia who underwent RF ablation for >1 year. Unfavourable RF ablation outcomes were predefined as unsuccessful RF ablation or recurrence of tachycardia requiring repeated ablation. RF ablation was not successful in 11 (7.6%) patients and 16 (12%) patients had arrhythmia recurrence requiring repeated ablation. Average follow-up time was 72.2±28.4 months. Selected parameters from univariate analysis included number of RF applications, pacemapping, application of bonus burn, procedure time, monophasic R-wave in lead I, QS pattern in leads I and aVL, QRS duration in leads II and V2, and right axis deviation, in ventricular tachycardia. From logistic regression analysis, only monophasic R-wave in lead I remained in the final equation (P=0.004, odds ratio 12.9).
Conclusion Monophasic R-wave in lead I during RVOT tachycardia is associated with unfavourable outcomes after RF ablation. This finding may help clinicians in the selection of patients for RF ablation and for the prediction of RF ablation outcome.
Key Words: ECG, RF ablation, RVOT tachycardia, Ventricular tachycardia
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Background |
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Ventricular arrhythmia with electrocardiographic (ECG) morphology of left bundle branch block and inferior axis usually originates from the right-ventricular outflow tract (RVOT). Patients with RVOT tachycardia may have varying degrees of symptom severity. Most patients have no evidence of structural heart disease. RVOT tachycardia may be treated with medication or radiofrequency (RF) ablation. Results of RF ablation are excellent with an overall success rate of 80–90% and a recurrence rate of 10–15%.1
–4 Prognosis of patients with RVOT tachycardia is excellent.5 However, some of these patients may later develop arrhythmogenic right-ventricular dysplasia.6 The objective of this study was to identify the ECG predictors of long-term outcomes after RF ablation. |
Methods |
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Study population
This study was approved by the Ethics Committee for Human Rights Research. We studied patients with RVOT tachycardia who had a typical left bundle branch block and inferior axis QRS morphology during tachycardia who underwent RF ablation and had a follow-up duration for >1 year. Clinical tachycardia was documented prior to ablation in all patients. Holter monitoring was performed in 93 patients (64.6%) before RF ablation. The density of arrhythmia was on an average of 21990±12922 beats in 24 h. Ventricular tachycardia was detected from Holter monitoring in 19 patients. Patients with structural heart disease were excluded.
ECG evaluation
Twelve-lead ECG was performed by the conventional technique at a paper speed of 25 mm/s. The following ECG characteristics were studied: transitional zone in V2 or V3, delta wave appearance during tachycardia, the presence of R-wave in lead V1, monophasic R-wave in leads I and aVL, QS pattern in leads I and aVL, QRS duration in leads II and V2, and right axis deviation during tachycardia.
RF catheter ablation
Antiarrhythmic medications were discontinued at least five half-lives before the procedure. The electrophysiological study was performed in the fasting state under light sedation. Surface ECG leads I, aVF, V1, and V6 and intracardiac electrograms were simultaneously displayed and recorded on a multichannel oscilloscopic recorder (Prucka Engineering, Sugar Land, TX, USA). In patients with spontaneous ventricular arrhythmia, 12-lead ECG morphology of ventricular arrhythmia was saved and printed for documentation of the clinical arrhythmia and for comparison during mapping (pacemapping). Induction of ventricular arrhythmia was performed by rapid ventricular pacing and programmed electrical stimulation. Isoprenaline 1–5 µg/min was infused, if ventricular arrhythmia could not be induced, and the induction protocol was repeated.
Mapping was performed around the RVOT. Mapping for the target site of ablation was guided by activation mapping and pacemapping. Activation mapping was to search for the site with the earliest local electrical signal. Target sites usually have a local electrical signal at least 30 ms earlier than the onset of the ectopic QRS complex. Pacemapping was performed by the comparison of 12-lead QRS morphology during pacing and during clinical arrhythmia. The target site of ablation was required to have at least 11 of 12 leads with matching morphology, paced complexes vs. during clinical arrhythmia. There were no special mapping systems used in this study. Radiofrequency power was applied to the target site using the temperature-guided tip of the ablation catheter, trying to maintain the temperature at the tip of the catheter 
50–55°C during ventricular tachycardia or during premature ventricular complexes of the same morphology. If no beneficial effect was observed, RF power was discontinued at 20–30 s. If a beneficial effect was observed with either suppression of ventricular arrhythmia or initially irritable arrhythmia followed by suppression, the RF power was maintained for 60 s. Whenever possible, a bonus burn was applied at the successful site for another 60 s to make sure the target site was completely eliminated. However, it was not applied if the operator had already observed immediate elimination of the tachycardia or if the ablation catheter position had changed after successful ablation. Successful ablation was defined as complete elimination of spontaneous or inducible ventricular arrhythmias with and without isoprenaline infusion at least 30 min after successful ablation. The successful site of RF ablation was anatomically recorded as being on the septum or free wall by using fluoroscopic images in both right anterior oblique and left anterior oblique views. Procedure time, fluoroscopic time, number of RF applications, and complications were recorded. Patients were observed overnight in hospital and discharged the next day. Patients were followed in the outpatient department every 3 months for 1 year after the procedure. Patients were instructed to return to the clinic whenever they had recurrent symptoms, to determine whether they had recurrent arrhythmia. Patients with recurrent ventricular tachycardia were encouraged to undergo another electrophysiological procedure for a possible repeat RF ablation.
Statistical analysis
Continuous variables were described as mean±standard deviation and categorical variables were described as frequencies and percentages. A comparison of continuous variables was made by the unpaired t-test and comparison of categorical variables was made by the 
2 test. In all tests, the criterion for statistical significance was two-sided P
0.05. The selected ECG parameters were evaluated for the association with RF ablation outcome. We also included age, gender, and ventricular tachycardia for analysis. Unfavourable RF ablation outcomes were predefined as an unsuccessful RF ablation or arrhythmia recurrence requiring another RF ablation. Although both types of outcome may be caused by a different aetiology, both of them are considered unfavourable outcomes and should be taken into account when considering RF ablation in patients with RVOT tachycardia. Univariate analysis was performed to determine factors that influence outcomes from ECG parameters and clinical parameters. Logistic regression analysis was performed to determine the most fitted model for the parameters that influence the outcomes. Survival analysis was performed for significant variables from logistic regression analysis. In all tests, the criterion for statistical significance was two-sided P<0.05.
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Results |
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There were 33 men (22.9%) and 111 women (77.1%) with an average age of 42±10.8 years enrolled in this study. Baseline characteristics are shown in Table 1.
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Results of RF ablation
During RF ablation, the arrhythmia was confirmed and had a similar morphology in all patients. RF ablations were successful in 133 patients (92.4%), unsuccessful in 9 (6.3%), and not attempted in 2 (1.4%) because of multiple ventricular tachycardia morphologies and unstable haemodynamics. There was no major complication. Four patients (2.8%) had minor complications including right bundle branch block in two, groin haematoma in one, and pericardial effusion in one. Earliest activation at site of RF application was 36.6±7.8 ms. Pacemapping showed ECG match of 12, 11, 10, and 8 leads in 118 (81.9%), 21 (14.6%), 2 (1.4%), and 1 (0.7%), respectively. Bonus burns were given in 93 patients (64.6%). The average number of RF applications was 11.8±12.8 and average power used was 25.2±8 W. Location of successful ablation was recorded in 104 patients: in 84 patients, it was at RVOT septum and 20 patients at RVOT free wall. It was not recorded in 29 patients because of incomplete data from fluoroscopic images or change in the ablation catheter position after successful ablation. Eight patients had associated cardiac arrhythmia: atrioventricular nodal re-entrant tachycardia in three, atrial tachycardia in three, atrial flutter in two, and atrioventricular reciprocating tachycardia using concealed bypass tract in one. One patient had atrial tachycardia and atrioventricular nodal re-entrant tachycardia. Associated arrhythmias were successfully ablated. Total procedure time was 130±67.6 min. Total fluoroscopic time was 32.5±29.7 min.
Association between ECG parameters and RF ablation outcomes
Patients were followed up for an average of 72.2±28.4 months. Ninety-four patients (65.3%) were followed up at the hospital and 50 patients (34.7%) were contacted by telephone. Twenty patients (13.9%) had symptoms of recurrent tachycardia. The presence of arrhythmia was determined by ECG during symptoms in 16 patients and by Holter monitoring in 4 patients. Four patients (2.8%) had minimal symptom and chose medication, whereas 16 patients (11.1%) agreed to undergo further ablation. Repeat RF ablation was successful in 14 patients (87.5%). Median time of recurrence was 4.5 months (average 8.9±10 months). Therefore, 27 patients (18.8%) had unfavourable outcomes (unsuccessful RF ablation or arrhythmia recurrence). Fourteen of 16 patients who underwent a second procedure had the same QRS morphology during tachycardia as that before ablation. All of them had a successful second procedure. However, the other two patients who had recurrent RVOT tachycardia with different QRS morphology had an unsuccessful second procedure and underwent defibrillator implantation. During ablation, all patients with similar QRS morphology during recurrent tachycardia had successful ablation at the same site.
Univariate analysis of baseline parameters, RF ablation parameters, and ECG characteristics for the prediction of long-term outcomes is shown in Tables 2 and 3. From univariate analysis, we selected variables with P-value of 0.1 for further analysis. From multiple logistic regression analysis, only monophasic R-wave in lead I as demonstrated in Figure 1 remained in the final equation with the P-value of 0.004 and odds ratio of 12.9. No significant differences were detected for other selected variables including the number of RF applications (odds ratio 1.044, P=0.175), pacemapping (odds ratio 0.507, P=0.117), application of bonus burn (odds ratio 0.335, P=0.087), procedure time (odds ratio 1.002, P=0.826), QS pattern in leads I (odds ratio 0.274, P=0.120) and aVL (odds ratio 0.456, P=0.437), right axis deviation (odds ratio 0.603, P=0.081), QRS duration in leads II (odds ratio 1.015, P=0.741) and V2 (odds ratio 1.012, P=0.812), and the presence of ventricular tachycardia (odds ratio 2.014, P=0.312). The number of RF applications was not different in patients with and without monophasic R-wave in lead I (14±16 vs. 11±11 attempts, P=0.198). Survival analysis demonstrated significant difference in the recurrence rate between patients with and without monophasic R-wave in lead I with P-value of <0.0001 by log-rank test (Figure 2). Among the 104 patients with successful ablation who had the anatomical site recorded, there was a significant correlation between monophasic R-wave in lead I and RVOT free-wall locations. RF ablation was successful at free-wall location in 16 of 26 patients (61.5%) with monophasic R-wave in lead I when compared with 4 of 78 (5.1%) of those without (P<0.001) (Figure 3).
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We also performed univariate and logistic regression analysis separately for unsuccessful RF ablation and arrhythmia recurrence requiring another RF ablation to understand whether monophasic R-wave in lead I predicts that the focus is less likely to be located in the RVOT or it predicts that applications at the site of origin are less effectively applied. There are no variables in the final equation of logistic regression analysis that can predict unsuccessful RF ablation. However, for arrhythmia recurrence, monophasic R-wave in lead I was the only factor in the final equation of logistic regression analysis (odds ratio 6.089, P=0.009).
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Discussion |
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TopAbstractBackgroundMethodsResultsDiscussionReferences |
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In this study, we demonstrated that certain ECG characteristics were associated with long-term outcomes after RF ablation in patients with RVOT tachycardia. Many ECG variables during tachycardia were predictors of outcomes by univariate analysis, including monophasic R-wave in lead I, QS pattern in leads I and aVL, right axis deviation, and QRS duration in leads II and V2. From multiple logistic regression analysis, monophasic R-wave in lead I was the only ECG predictor for RF ablation outcome.
Previous studies have reported ECG predictors of RF ablation outcomes. Rodriguez et al.1 reported that a delta wave-like beginning of the QRS, >1 morphology of induced ventricular tachycardia, and pacemap correlation <11 of 12 leads were predictors for unsuccessful RF ablation in 35 patients with RVOT tachycardia. They also demonstrated that a good pacemap was more important than an early endocardial activation time, which is similar to our results. We demonstrated that a wider QRS is associated with a bad outcome, which is similar to data from Vestal et al.2 but different from another report.3 However, QRS width is not an independent predictor of outcome of RF ablation in our study.
Recently, there have been many reports on the unusual sites of tachycardia origin in patients presenting with RVOT tachycardia such as pulmonary artery and other extra-RVOT sites.7–11 These studies have indicated that certain ECG characteristics such as transitional zone8 and R-wave characteristics in V1 and V29–11 were associated with extra-RVOT locations. In our study, we were unable to demonstrate that these ECG characteristics were associated with a bad outcome.
ECG characteristics can be used to identify the site of tachycardia origins. By the use of body surface mapping and 12-lead ECG in 35 patients with RVOT tachycardia, Kamakura et al. 12 were able to localize the origin or the optimum ablation site of idiopathic RVOT tachycardia. Anatomic location of RF ablation of idiopathic RVOT tachycardia could also be focused by the consideration of QRS orientation in lead I and R-wave progression in precordial leads.13 Jadonath et al.14 reported that specific ECG characteristics can be employed to localize the origin of RVOT tachycardia by comparing the 12-lead ECG with pacemapping at different sites of RVOT in 11 patients. A positive R-wave in lead I distinguished the posterior part of septum and free wall from the anterior part.15 In our study, precordial R-wave transition had no effect on the long-term outcome after RF ablation. Therefore, different R-wave transition may just indicate different sites within the RVOT region. Monophasic R-wave in lead I had a significant impact on long-term outcomes in our study. We showed that monophasic R-wave in lead I may reflect the free-wall site of tachycardia. However, not all patients with monophasic R-wave in lead I had successful ablation at a free-wall site. When compared with septal sites, free-wall sites more often have structural disease which may be difficult to detect by echocardiogram. Many studies have shown that structural abnormalities at RVOT, such as localized wall bulging, wall thinning, fatty infiltration, and fibrosis, can be detected by magnetic resonance imaging not only in patients with right-ventricular dysplasia16,17 but also in patients with RVOT tachycardia.18,19 These structural abnormalities may be the reason for recurrent tachycardia in these patients. Free-wall location of the RVOT may be an important predictor of failure and may be the reason why certain ECG characteristics could be related to the outcome of RF ablation. When compared with previous reports, our results were based on a larger sample size and a longer follow-up duration. Mapping and ablation of patients with monophasic R-wave in lead I should be carefully performed. Electroanatomical mapping may help to identify appropriate sites of RF ablation in patients with RVOT tachycardia, especially in difficult cases.20 Besides, it may help to differentiate between RVOT tachycardia and arrhythmogenic right-ventricular dysplasia.21
Unsuccessful procedures and recurrent tachycardia may be caused by a different aetiology. Monophasic R-wave in lead I only predicts arrhythmia recurrence and does not predict unsuccessful RF ablation. Therefore, a different RF ablation strategy such as other settings or energy sources should be considered when targeting this area in order to prevent recurrences.
We conclude that among various ECG parameters, a monophasic R-wave in lead I is associated with unfavourable RF ablation outcomes in patients with RVOT tachycardia. This finding may help clinicians in the selection of patients for RF ablation and for the prediction of RF ablation outcomes.
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References |
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