Europace Advance Access originally published online on June 27, 2006
Europace 2006 8(8):592-595; doi:10.1093/europace/eul051
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ELECTROPHYSIOLOGY
One-year follow-up in a prospective, randomized study comparing radiofrequency and cryoablation of arrhythmias in Koch's triangle: clinical symptoms and event recording
1 Department of Cardiology, Medical Centre Alkmaar, Wilhelminalaan 12, 1815 JD Alkmaar, The Netherlands; 2 Department of Clinical Electrophysiology, Erasmus Medical Centre, Rotterdam, The Netherlands; 3 Department of Pacing and Clinical Elelctrophysiology, Hungarian Institute of Cardiology Hungary
Manuscript submitted 5 June 2005. Accepted after revision 15 March 2006.
* Corresponding author. Tel: +31 72 548 4444. E-mail address: g.p.kimman{at}mca.nl
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Abstract |
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Aims To rely solely on clinical symptoms of recurrent palpitations to evaluate the success of interventional procedures can be misleading. This study was designed to assess the efficacy of event recording in evaluating long-term success in patients treated for atrioventricular nodal reentrant tachycardia (AVNRT) or right posteroseptally located accessory pathways (RPS) either by radiofrequency (RF) or by cryoablation (CA).
Methods and results Sixty-three patients with AVNRT and eight with RPS were randomized. Patients were encouraged to activate an event recorder in the case of recurrent palpitations for the first 3 months. One year after the procedure, patients were asked specific arrhythmia related questions. Thirty-six patients underwent RF and 35 CA. Acute success was finally achieved in 34 (94%) patients in the RF and 33 (94%) in the CA groups. Assessment of long-term success demonstrated a similar proportion of palpitations in the RF and CA groups: 11 (31%) vs. 17 (49%). Only 12 patients activated the event recorder, four patients in RF, including one patient with chest pain, and eight in the CA group. Analysis of recordings revealed recurrent AVNRT or circus movement tachycardia in four patients (one RF and three CA), atrial fibrillation in one RF patient, and sinus tachycardia in six (one RF and five with CA). In addition, a complete 12 lead ECG of a recurrent arrhythmia was made in three RF and two CA patients (in-hospital or after the event recording). A total of seven patients underwent a second procedure (four RF and three CA). Without the event recorder, seven patients would have been misclassified as having recurrent arrhythmia.
Conclusion Event recording enhances the sensitivity of detecting arrhythmia recurrences in evaluating therapy efficacy and should be considered in every interventional follow-up study. Analysis of recordings showed that CA is as effective as RF in the treatment of AVNRT and RPS at long-term follow-up.
Key Words: Atrioventricular reentrant tachycardia, Accessory pathway, Radiofrequency catheter ablation, Cryoablation, Event recording, Long-term follow-up
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Introduction |
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Radiofrequency (RF) catheter ablation has become the first-line therapy for patients with recurrent atrioventricular nodal reentrant tachycardia (AVNRT) and circus movement tachycardia (CMT).1
–4 Although it is highly successful, lesions created by RF energy are inhomogeneous, irreversible, thrombogenic, and potentially proarrhythmic.4–7 Cryoablation (CA) creates homogeneous and smaller lesions and is less thrombogenic.8 Together with the specific tools of ice mapping and cryoadherence, this therapy has proved to be especially useful in AVNRT and (para) septally located accessory pathways to reduce the risk of inadvertent AV block.9–14 After interventional procedures, follow-up is important to assess the long-term success of the procedure. A follow-up based solely on clinical symptoms has a potential risk of misleading results.15–19 The purpose of this study was to evaluate long-term success of patients treated either with RF or with CA using an event recorder and a specific questionnaire conducted at 1 year.
Methods
As described earlier, all consecutive patients with a recurrent tachyarrhythmia, suggestive of AVNRT or CMT with the use of a right posteroseptally located accessory pathway (RPS), were randomized by an independent institution (Cardialysis) to either RF or CA before baseline electrophysiological (EP) study.10 The diagnosis of both dual AV nodal pathways, AVNRT and CMT, was made on the basis of standard diagnostic criteria. The earliest retrograde atrial activation during both tachycardia and premature ventricular complexes was registered. Single premature atrial and ventricular stimuli were applied during tachycardia at the time the His bundle was refractory to assess if tachycardia could be reset. This confirmed the presence or absence of an accessory pathway. In patients with manifest pre-excitation, the site that recorded the earliest ventricular activation was identified. If sustained tachycardia could not be induced, isoprenaline was used. In the case of an accessory pathway, the final classification was made according to the successful ablation site.
Ablation
For RF ablation, a 7Fr 40–60 mm curve, 4 mm tip catheter (Conductr, Medtronic, Minneapolis, MN, USA) was used with a conventional electrosurgical generator (Atakr II, Medtronic) as a source of RF energy. Cryoablation was carried out with a 7Fr 53 mm curve, 4 mm tip catheter (Freezor 3, Cryocath Technologies, Montréal, Canada), and a CCT2 CryoConsole (Cryocath Technologies). For AVNRT, the target in both ablation techniques was slow pathway ablation guided by a combination of intracardiac electrogram criteria and anatomical landmarks. With RF, each ablation was started with low energy (10 W) for 10 s. If no adequate temperature was reached, no accelerated junctional rhythm was observed, and AV conduction was preserved, the administered energy was increased to a maximum of 50 W (maximum temperature 55°C). When accelerated junctional rhythm occurred, atrial overdrive pacing was used for monitoring AV conduction disturbances. With cryothermy, ice mapping was initially performed by cooling to –30°C for a maximum of 60 s. Fluoroscopy was applied until a stable level of –30°C was reached. During these 60 s, atrial extrastimulus testing was done. Disappearance of an AH-jump, termination or non-inducibility of AVNRT was considered to be an identification of a potentially successful ablation site, and subsequently, ablation was performed by cooling to –70°C for a 4 min period to create a permanent lesion. If there was no clear AH-jump, and AVNRT was difficult to induce at baseline, prolongation of the antegrade AV refractory period during atrial extrastimulus testing during ice mapping was used to identify a target site. The endpoint was the same for both RF and CA namely, non-inducibility of AVNRT with or without isoprenaline after a 30 min waiting period. For CMT, in both ablation techniques, mapping was performed, beginning at the anteroseptal region at the His deflection down to the coronary os and further to the right posterior region. In patients with manifest ventricular pre-excitation during sinus rhythm, the site of earliest ventricular activation was identified, characterized by a short-local AV interval, with local ventricular activation preceding the onset of the delta wave on the surface ECG. The earliest retrograde atrial activation was identified during orthodromic CMT and ventricular pacing. With RF, an application was started at 15 s with a maximum power of 50 W and a limited temperature of 55°C. If a sudden loss of ventricular pre-excitaton, a sudden loss of VA conduction change from eccentric to concentric VA conduction, or sudden termination of the tachycardia was seen, the application was continued for 60 s. For cryoenergy, ice mapping was started by cooling to –30°C. Only if this was successful, using the same characteristics as described for RF, a CA was carried out. Patients were also observed for 30 min, and a repeat EP study was performed to confirm the loss of accessory pathway conduction.
Follow-up
After hospital discharge, all patients received an event recorder (Reynolds ST 80, single lead) for 3 months and were encouraged to activate it in the case of recurrent palpitations. If activated, a 1 min single lead registration was obtained. They all visited the outpatient clinic approximately 3 months after the procedure and thereafter were sent to their referring cardiologist. One year after the procedure, all patients were approached by telephone or written letter and asked to answer specific questions related to their symptoms, recurrences, and repeated ablation. If a recurrent arrhythmia was registered, a repeat ablation was scheduled to be performed with the same energy source aiming to be as objective as possible in the comparison between RF and CA.
Statistical analysis
Continuous variables were expressed a mean±standard deviation. Non-parametric data were compared using the Mann–Whitney U test. The level of significance was set at P<0.05.
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Results |
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In 63 patients, a diagnosis of AVNRT was made. Of these patients, 33 were randomized to RF and 30 to CA. In eight other patients, a RPS was diagnosed, in which three were randomized to RF and five to CA, respectively (Table 1). Procedural success in AVNRT was achieved in 30 (91%) patients in the RF and 28 (93%) in the CA groups. In the unsuccessfully treated patients, the procedure was terminated because of its length or long fluoroscopy times.
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Radiofrequency ablation for CMT was successful for all three patients in the RF group and in four of five patients in the CA group. In the one unsuccessfully treated patient in the CA group, only intermittent disappearance of pre-excitation was seen, and the procedure was finally abandoned. For patients with AVNRT, the number of ice maps was 5, and 6 with CMT, respectively. The median number of applications was 5 for RF vs. 2 (P<0.002) for CA for the total group. The median number of applications in the treatment of AVNRT was also significantly lower (P<0.05) in the CA group than in the RF group, namely 2 vs. 7. In the CMT group, two complications occurred, one pneumothorax after a subclavian puncture and one tamponade caused by the RV catheter (a Medtronic, 6416, temporary transvenous, active fixation lead), which was used as reference catheter for the LocaLisa system. During a follow-up of 1 year, long-term success was seen in two patients treated for AVNRT (one in each group) after a failed procedure (Table 2). Therefore, the acute success rate in patients with AVNRT was 31 (94%) in the RF and 29 (97%) in the CA group.
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Recurrent palpitations occurred in 10 patients treated for AVNRT with RF and in 13 patients after CA, as assessed by the questionnaire. Nine of these patients activated an event recorder, three treated with RF and six with CA, respectively. The documented arrhythmia in the RF group was recurrent AVNRT in one patient, atrial fibrillation (AF) in one, and sinus tachycardia in one. In the CA group, recurrent AVNRT was seen in two patients. In four other patients, sinus tachycardia was registered. In patients who underwent ablation for CMT, the questionnaire revealed that five patients had recurrent palpitations, namely one in the RF group and four in the CA group. Of these patients, three activated an event recorder, one with a recurrence of CMT, one with sinus tachycardia, and one with chest pain. In five other patients, recurrent tachycardia was documented in hospital or after the period of event recording. In conclusion, 32 (45%) patients experienced recurrent palpitations. Recurrent AVNRT/CMT was confirmed in only nine of these 32 patients. Without the event recorder, seven patients would potentially have been misclassified as having a recurrence of the treated arrhythmia. A total number of five patients underwent a successful repeat ablation with the same energy source (four with AVNRT and one with CMT) (Table 2). In one patient, who was initially unsuccessfully treated with RF, a successful redo was carried out with CA, and, finally, in one patient initially in the CA group, a successful second procedure with RF was performed. The decision to use another energy source for the second procedure depended on the operator's own insight and experience.
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Discussion |
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Acute success
RF ablation for AVNRT and (para)septally located accessory pathways is accompanied by an increased risk of inadvertent RBBB or complete AV-block.1
–4,20–22 Because cryothermy has the ability to create temporary lesions (ice mapping), prospective ablation sites can be investigated, before a definitive and irreversible lesion is created.9–14 In this study, it was confirmed that CA is as effective as RF ablation in the treatment of these arrhythmias, which is in agreement with other studies.9–14 This was achieved despite the fact that our experience with CA prior to this study was limited and indeed a learning curve was seen, as fluoroscopy time decreased during the course of the study. However, as the target in both AVNRT and CMT was the same for both ablation techniques and the procedures were carried out by the same operators, success rates were comparable. It was also shown that in patients treated for AVNRT, this can lead to less applications and minimize the risk of AV conduction disturbances.9–12 In patients treated for RPS, this could not be confirmed in our study, merely by the fact that the group consisted of only eight patients. As is valid for all interventional studies, an adequate follow-up is important to assess long-term success of the procedure.
Follow-up and the role of an event recorder
To rely solely on clinical symptoms of recurrent palpitations has a potential risk of misleading results.15–19 For example, in studies of catheter ablation for AF, success is defined as the absence of symptoms or less symptoms after treatment.17–19 However, it is well known that up to 50% of the episodes of AF are not experienced as such by the patients, and therefore success rates can be overestimated. On the other hand, as is shown in this study, not all recurrent palpitations are by definition recurrences of the treated arrhythmia. Seventeen patients (49%) treated with CA complained of recurrent palpitations in comparison with 11 patients (31%) treated with RF, assessed by a questionnaire at 1 year. However, only eight patients in the cryo group and four in the RF group activated the event recorder because of identical palpitations post-ablation. Probably, in patients who did not activate the event recorder, the palpitations were not identical in comparison with pre-ablation or were too short lasting. Using the event recorder, recurrence of the treated arrhythmia was registered in seven patients. In one patient in the RF group, AF was documented. Sinus tachycardia was seen in one patient in the RF and five patients in the cryo group. The presence of sinus tachycardia, especially after CA of the slow pathway, as was seen in four patients, is remarkable. It has been mainly associated with fast pathway ablation, most likely caused by damage to autonomic inputs.23 The reason for this observation could be a more anterior position of the ablation catheter, due to the smaller lesions created by cryothermy, or an abnormally located antegrade fast pathway, located in the posteroseptal region, which exists in about 3% of patients presenting with AVNRT.24 Without the event recorder, seven patients (two in the RF group and five in the CA group) would have been misclassified as a recurrence of the treated arrhythmia.
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Conclusions |
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Our data demonstrate that use of event recording and not a questionnaire with specific questions related to their symptoms, enhances the sensitivity of detecting arrhythmia recurrences. This has implications for the interpretation and design of clinical trials in the evaluation of treatment efficacy. On the basis of event recording, CA is as effective as RF for arrhythmias in Koch's triangle during long-term follow-up.
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