Europace Advance Access originally published online on April 7, 2007
Europace 2007 9(6):401-406; doi:10.1093/europace/eum031
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CRYOABLATION
Transvenous cryo-ablation of the slow pathway for the treatment of atrioventricular nodal re-entrant tachycardia: a single-centre initial experience study
Rhythmology Unit, Cardiology Institute, Pitie-Salpetriere Hospital, Paris 75015, France
Manuscript submitted 28 December 2006. Accepted after revision 7 February 2007.
* Corresponding author. Tel: +33 145409530; fax: +33 323243118. E-mail address: antoniodesisti{at}yahoo.fr
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Abstract |
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Aims Within the last several years, transvenous cryo-ablation has become an alternative method to perform ablation of the slow-pathway. This study evaluated the acute and long-term safety and effectiveness of atrio-ventricular nodal re-entrant tachycardia (AVNRT) cryo-ablation.
Methods and results The first 69 consecutive patients with AVNRT (60 slow–fast, 4 fast–slow, and 5 slow–slow) who underwent slow-pathway cryo-ablation were included. Mean age was 37 ± 15, body weight 68 ± 14 kg, symptom duration 125 ± 104 months, and number of ineffective antiarrhythmic (AA) drugs 1.8 ± 1.4. A 7 Fr cryo-catheter (Cryocath®) was used, with initially 4-mm-tip and later with 6-mm-tip electrode. Cryo-mapping (n = 7.9 ± 8.4 per pt) was performed at the temperature of –30°C to test the effect on the target ablation site. Successful cryo-mapping was defined as abolition of nodal conduction jump or AV nodal refractory period prolongation. Cryo-ablation (n = 5.1 ± 4.9 per pt) was then applied by freezing to –75°C for 4 min in duration if no AV-block occurred. Acute procedural success (defined as AVNRT non-inducibility) after the first cryo-ablation attempt was achieved in 60/69 patients (87%). During cryo-ablation, inadvertent transient AV-block was encountered in 14 patients (five I AV-block and nine II–III AV-block). A mid-septal target site was the only variable correlated with inadvertent AV-block occurrence during cryo-ablation (P < 0.02). Long-term clinical success after cryo-ablation was globally achieved in 56/66 (85%) with a mean follow-up of 18 ± 9 months (3 pts dropped-out). After the first procedure, 41/66 (62%) had no relapse, eight had a dramatic reduction in AVNRT duration-frequency and considered themselves cured, and five needed previously ineffective AA (with no relapse in three, drastic reduction in AVNRT duration-frequency in two). The five last patients needed one or more procedures, after which one had no recurrence and one had reduction in duration-frequency. Absence of recurrence after the first procedure was positively correlated with 6-mm-tip cryo-catheter use (<0.001) and negatively with acute procedural success (<0.001). At multivariate analysis, both were independently significant (<0.04 and <0.008, respectively). Long-term clinical success was correlated only with 6-mm-tip cryo-catheter use (<0.001).
Conclusions Slow pathway cryo-ablation is associated with an acute success but a higher recurrence rate. A 6-mm-tip cryo-catheter seems to assure during cryo-ablation a large acute and long-term success. AV-block seems non-guaranteed by a negative cryo-mapping, stressing on need of a careful surveillance. Nevertheless, the theoretical advantage of avoiding the risk of permanent AV-block when compared with radiofrequency needs larger series to be demonstrated.
Key Words: Atrioventricular node, Tachycardia, Mapping, Catheter ablation
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Introduction |
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Radiofrequency catheter ablation of the slow pathway is an established and effective therapy for atrioventricular nodal re-entrant tachycardia (AVNRT). Although acute and long-term success rate of radiofrequency is high, there is a small risk of inadvertent non-reversible complete AV-block during the procedure, evaluated 1–2% in large series.1
,2 Following initially successful experiences with cryo-surgery,3,4 transcatheter cryo-ablation has recently been introduced for the treatment of supraventricular tachycardia. Potential advantages compared with radiofrequency ablation include decreased risk of thromboembolism and perforation, less patient discomfort, more sharply demarcated lesions, and decreased risk of inadvertent damage to adjacent structures due to the ability to test electrophysiologic (EP) lesion effects prior to permanent tissue damage.5–8 Within the last several years, transvenous cryo-ablation has become an alternative method to perform ablation of the slow-pathway.9–15 This study evaluated the acute and long-term safety and effectiveness of AVNRT cryo-ablation. |
Methods |
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Study and patients
All patients referred to our centre for catheter ablation of AVNRT were included in the study.
Procedure
After giving informed consent, patients were investigated in the fasting state without sedation. Antiarrhythmic (AA) drugs were discontinued for at least five half-life periods. A standard EP study was performed. Dual AV nodal physiology was identified by a sudden AH or HA jump of at least 50 ms in response to programmed atrial or ventricular extrastimulation. AVNRT was diagnosed on the basis of standard diagnostic criteria.16 If sustained tachycardia could not be induced, isoproterenol was infused to facilitate tachycardia induction. A combination of intracardiac electrograms and anatomical approaches was conducted to identify appropriate target sites for ablation of the slow pathway in the Koch triangle.16,17 Procedural success was defined as non-inducibility of AVNRT with or without isoproterenol administration or complete elimination of the slow pathway in the case of AVNRT non-inducibility at basical EP study.
Ablation was performed by using a 7 Fr cryo-catheter (Cryocath®) with initially 4-mm and later with 6-mm-tip electrode. Cryo-mapping was carried out first at a cryo-catheter tip temperature of –30°C for a maximal duration of 60 s to test the EP effect on the target sites by using programmed stimulation which reproducibly demonstrated dual nodal physiology or induced AVNRT. In case of ineffective results or AV-block, cryo-mapping was terminated and then repeated at new target sites. Cryo-ablation, which created a permanent lesion by cooling the tip temperature to –75°C for 4 min, was initiated immediately following successful cryo-mapping defined as abolition of the slow pathway or AVNRT non-inducibilty. If AVNRT was still inducible or AV-block occurred, cryo-ablation was stopped and cryo-mapping at new target sites was repeated. EP study was repeated after a waiting period of 30 min after cryo-ablation to check the effectiveness of the slow pathway ablation at baseline and during isoproterenol infusion.
Post-ablation management and follow-up
After cryo-ablation, all AA drugs were withdrawn except for beta-blocking agents in patients with ischaemic heart disease. During the follow-up, patients underwent assessment of symptoms, rest ECG, and 24-h Holter recording at 3 and every 6 months in our centre or by their referring physicians. Relapse was defined as recurrence of index arrhythmia-typical symptoms of tachycardia with sudden onset or tachycardia documented with ECG. The minimal observational period was set at 6 months.
Study endpoints
Endpoints of this study were the evaluation of acute procedural success (defined as AVNRT non-inducibility, or slow pathway abolition in patients with non-inducible AVNRT during the procedure), reversible and permanent complete AV-block, recurrence of AVNRT after first procedure, and global clinical success (defined as a composite of no recurrence or dramatic reduction in AVNRT duration-frequency whatever the given AA treatment or number of cryo-ablation attempts).
Statistical analysis
Continuous variables were expressed as mean ± SD. Comparison for coupled data used two-tailed paired t-test. Univariate analysis of acute procedural variables used ANOVA to compare continuous variables, and 
2 test for discrete variables. Multivariate analysis used logistic regression model. Correlation between long-term results in the follow-up and the different variables used Cox's regression model for univariate and multivariate analysis. Following univariate analysis, factors with associated P-value <0.10 were tested in multivariate analysis. A stepwise regression procedure was used to determine independent predictors. The P-value for entry or removal of a variable from the regression model were 0.05 and 0.10, respectively. A P-value <0.05 was considered significant. Statistical analysis was performed using SPSS 13 for Window.
Parameters included in the analysis
Clinical demographic parameters: age (years), sex ratio (M/F), body weight (kg), symptoms duration before cryo-ablation (months), underlying heart disease (pts), number of ineffective AA drugs prescribed before cryo-ablation (n), previously ineffective radiofrequency and ineffective cryo-ablation attempts (pts), and drugs given at hospital discharge (pts) or after the first disabilitating AVNRT recurrence (pts).
Baseline and post-cryo-ablation electrophysiologic parameters: AVNRT type, arrhythmia cycle (ms), PR, AH, and HV interval, jump (pts), AVNRT induction (pts), nodal effective refractory period (ERP), and Wenckebach AV block cycle length (ms).
Cryo-ablation procedural parameters: electrophysiologist (1-4), catheter tip size (6-mm and 4-mm-tip), small Koch triangle (pts) defined as a X-ray distance <11 mm between His and coronary sinus Os catheter, mid-septal effective site (pts), X-ray exposition time (min), procedural time (min), number of cryo-mapping (n), cryo-ablation attempt (n), cryo-mapping duration (s), cryo-ablation duration (s), AV-block during cryo-mapping, AV-block during cryo-ablation (pts), AV-block during cryo-ablation necessitating procedural interruption with cryo-ablation duration at the last effective site less then 4 min (pts), adjunctive consolidation application at effective site using a freezing–rewarming–freezing cycle (pts), and procedural complications (pts).
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Results |
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Patient characteristics
A total of 69 patients, mean age 37 ± 15 years, 45 women and 24 men, with frequent drug-refractory AVNRT were included in this study. AVNRT episode frequency was daily in 11, weekly in 8, monthly in 48, and several episodes per year in the remaining 2 patients. Episode duration ranged from minutes to hours. Symptom duration was 125 ± 104 months, number of previously ineffective AA drugs 1.8 ± 1.4, and body weight was 68 ± 14 kg. Twelve patients had underlying heart disease or hypertension. Five patients had undergone an unsuccessful radiofrequency attempt in other institutions (Table 1).
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Clinical and electrophysiologic procedural variables
Baseline characteristics
A slow–fast AVNRT was diagnosed in 60 patients, fast–slow in 4, and slow–slow in 5. The mean AVNRT cycle length was 334 ± 63. PR interval was 145 ± 31 ms, AH 79 ± 31 ms, HV 45 ± 10 ms, Wenckebach AV-block cycle length 340 ± 66 ms, and AV nodal ERP 275 ± 55 ms. A jump was elicited in 57 patients, and AVNRT was induced in 65/69 patients.
Procedural variables
A 6-mm-tip catheter was used in 61 patients, and 4-mm-tip in the remaining 8. The number of cryo-mapping was 7.9 ± 8.4 and cryo-ablation 5.1 ± 4.9 per patient. Cryo-mapping and cryo-ablation duration were 231 ± 208 and 862 ± 708 s, respectively. Fourteen patients had a small Koch's triangle. In 10 patients, the effective cryo-ablation site was located at mid septum, and in the remaining at its lower part anteriorly to the coronary sinus Os. The procedure and fluoroscopy times were 154 ± 53 and 27.7 ± 13 min, respectively. A freezing–rewarming–freezing cycle of 4+4 min was performed in 23 patients (Table 2).
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Electrophysiologic modification after the first cryo-ablation procedure
AV nodal ERP and Wenckebach AV-block cycle length were significantly prolonged when compared with baseline values (<0.001 for both). Acute procedural success, defined as AVNRT non-induction, was achieved in 60/69 (87%) patients. When considering only patients in whom a 6-mm-tip catheter was used the procedural success was achieved in 56/61 (92%). A residual jump was elicited in 13 of 57 patients who had baseline dual AV physiology. No junctional ectopy occurred during cryo-mapping or cryo-ablation (Table 3).
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AV-block at first cryo-ablation
During cryo-mapping, seven patients had transient AV-block. During cryo-ablation, inadvertent different degrees of AV-block was encountered in 14 (20%) patients (five I AV-block and nine II–III AV-block), ranging in duration from 2 to 30 s, but one remained with a first degree AV-block up to 4 days. In 10 of them, the procedure was interrupted for AV-block at the only effective site during the last cryo-ablation attempt after <4 min (mean 119 ± 81 s; range 30–200 s) in freezing duration.
Acute procedural success predictive factors
In patients with AVNRT non-inducibility after cryo-ablation, the use of 6-mm-tip catheter was more frequent (56/61 pts vs. 4/8 pts; P < 0.001) and body weight lower (66.3 ± 14.7 vs. 77 ± 9 kg; P < 0.04). The former was independently significant (<0.01).
Correlation between AV-block and procedural variables
Incidence of inadvertent AV-block during cryo-ablation was more frequent when effective target was the mid-septal site (5/10 vs. 9/59 pts; P < 0.02). No difference was found in other parameters.
Complications
In one patient, manipulation of a diagnostic catheter in the right ventricle caused pericardial effusion requiring pericardiocentesis.
Follow-up after first cryo-ablation
No AA drug was prescribed at hospital discharge except beta-blocking agents in four patients with ischaemic heart disease. Three patients were lost in the follow-up. During a mean follow-up of 18 ± 9 months, 41/66 (62%) patients were free of AVNRT recurrence. Time to first recurrence was 3 ± 2.4 months (within 3 months in sixteen patients). When considering only patients in whom a 6-mm-tip catheter was used, 40/59 (68%) were free of recurrence (Table 4).
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Predictors of no recurrence after the first procedure
Absence of recurrence after the first procedure was positively correlated with 6-mm-tip cryo-catheter use (<0.001) and negatively with acute procedural success (<0.001). At multivariate analysis, both were independently significant (<0.04 and <0.008, respectively) (Table 5).
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Global cryo-ablation procedure results
As five patients with recurrence underwent one or more re-intervention procedures, a total of 76 cryo-ablation procedures were performed. Acute procedural success was achieved in 64/76 cases (84%).
Predictive factors of acute procedural success
The rate of AVNRT non-inductibility was lower in the case of 6-mm-tip catheter use (58/64 vs. 6/12 pts; P < 0.001), previously unsuccessful radiofrequency and cryo-ablation attempt (8/12 vs. 56/64 pts; P < 0.07), and lower body weight (66.7 ± 14.6 vs. 75.6 ± 9.3 kg; P < 0.05). At multivariate analysis, 6-mm-tip catheter use was the only independent significant predictive factor (<0.007).
Predictive factors of inadvertent AV-block
Inadvertent AV-block occurred in 16 patients (21%). The incidence was higher with 6-mm-tip catheter (16/64 vs. 0/12 pts; P = 0.05), as well as in the case of mid-septal effective target site (5/11 vs. 11/65 pts; P < 0.04). No one was independently significant.
Long-term clinical results
Long-term clinical effects
In total, 14 patients received an AA treatment: 4 with ischaemic pathology after the first cryo-ablation and 10 after the first clinical disabilitating recurrence in the follow-up. Long-term clinical success after cryo-ablation was globally achieved in 56/66 (85%). In fact, after the first procedure, 41 (62%) had no relapse, eight had a dramatic reduction in AVNRT duration-frequency and considered themselves cured, and five needed previously ineffective AA (with no relapse in three, drastic reduction in AVNRT duration-frequency in two). After a second procedure, one had no recurrence and one had reduction in duration-frequency (Table 4).
The only variable correlated with long-term clinical success was a 6-mm-tip cryo-catheter use (B 2.43, SE 0.68; P < 0.001). In fact, in patients who underwent cryo-ablation with 6-mm-tip catheter clinical success was globally achieved in 54/59 (91.5%).
Patients with previous history of unsuccessful radiofrequency
Among five patients with previous RF, four were free of relapse after the first cryo-ablation and one had recurrence and no changing in clinical status after the first cryo-ablation, immediately followed by a successful RF attempt.
Cryo-ablation re-intervention
One or more cryo-ablation re-interventions were performed in five patients (none of them had had a previous RF attempt). Two had two ineffective cryo-ablation attempts per patient and no changing in clinical status in the follow-up. One had a second ineffective cryo-ablation and an RF attempt also ineffective. One had a dramatic reduction in AVNRT duration-frequency episodes without AA drugs after a second cryo-ablation, and an other was definitely cured after a second successful cryo-ablation with no recurrence successively.
Radiofrequency after unsuccessful cryo-ablation
Four patients had an RF procedure after one or more unsuccessful cryo-ablation attempt. Three patients had recurrence and no modification in clinical status, and one was definitely cured.
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Discussion |
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The present study shows that cryo-ablation therapy of the slow pathway for AVNRT is safe and effective in terms of acute and long-term success. In the literature, there are no many articles concerning slow-pathway ablation for AVNRT. In these published series, in which a 4-mm-tip catheter was almost exclusively used, the acute success rate has been reported between 85 and 99% (Table 6),8
–15 not so far from acute success described in radiofrequency series.1,2 In our study, acute success was lower than some other series, but when considering only patients treated with a 6-mm-tip catheter (the vast majority in our population) the results were quite similar. In studies using radiofrequency, the incidence of recurrence is low, 3–5% of the cases, but permanent AV-block necessitating PM implant has been reported to be 1–2% in experimented centres.1,2 Recurrence rate in studies involving cryo-ablation is reported within 7 and 20%, therefore higher than radiofrequency, and significantly higher in three studies comparing the two methods.10,14,15 In our population, recurrence rate after the first cryo-ablation appears higher than in other series. However, the results are in the same range when taking into account the overall clinical success, including not only the absence of recurrence but also a drastic reduction of duration-frequency of AVNRT episodes, whatever the AA drug used or number of cryo-ablation attempts. Some factors could explain these results. Our data show that cryo-ablation using a 4-mm-tip catheter appears to be inferior to 6-mm in both acute and long-term success. Because of cryo-adherence during ablation (otherwise safe with regard to AV complication), the catheter is not passively sliding along a larger area, as under radiofrequency ablation. The higher recurrence rate in 4-mm-tip catheter patients is probably related to smaller lesion size created when compared with 6-mm-tip. Catheter handling during ablation was mostly done by less experienced physicians, with the senior electrophysiologist operating the EP lab. A 4-mm-tip catheter, used mainly at the beginning of our experience combined with a learning courbe effect, could also explain our results. The mean age of our patients was sensibly lower than in other studies, when excluding pediatric patients series,14 and young age has been reported as a risk factor of recurrence after a radiofrequency procedure for AVNRT ablation.18 Additionally, our population consisted of patients with very frequent, disabilitating, and drug refractory AVNRT episodes, whereas in the other series the clinical characteristics of AVNRT episodes are not clearly reported. Finally, the follow-up duration was longer than in other studies, and although the time to recurrence was generally within 3 months after the procedure, this fact can contribute to explain our higher recurrence rate.
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Adverse but still reversible effects on AV conduction may be observed during cryo-ablation despite no evidence of previous deleterious effects of cryo-mapping. (Table 6) As underlined by Fischbach et al.,5
this experience demonstrates that the cryo-lesion created during cryo-ablation may expand relative to that suggested by cryo-mapping. In our study, as in other series, all inadvertent AV-blocks encountered during cryo-ablation were reversible, but one persisted as prolonged PR interval for 4 days. The incidence of transient inadvertent AV-block seems higher in the case of 6-mm-tip catheter, (largely used in the present study), which creates larger lesions. In fact, no patients in whom a 4-mm-tip catheter was used presented with inadvertent AV-block during cryo-ablation. Obviously, application of cryo-energy at the mid-septum increased the risk of AV-block. Concerning the other series, Zrenner,10 despite a 4-mm-tip catheter use, had 17% of transient inadvertent AV-block, whereas Jensen-Urstad13 encountered some complication in 8% of the cases using a 6-mm-tip catheter.
Clinical implications
It has been assumed that the cornerstone of cryo-technology is the capability to test its effect by creating a reversible lesion at a less critical temperature and therefore assessing a risk of AV-block. Cryo-adherence prevents dislodgement of the catheter tip and therefore avoids unwanted energy delivering at the compact AV node or His bundle. Junctional ectopy, a sensitive marker of successful RF ablation,19 does not occur during cryo-ablation, which facilitates monitoring the completeness of the fast pathway. If this is the case, there will be a significant proportion of patients, especially the young ones and those with abnormal AV node anatomy, in whom a reduced efficacy may be preferred over the risk for a pacemaker implantation, a disastrous event in this population. Nevertheless, in our study, some procedures were interrupted for an AV-block after <4 min of cryo-energy application at the effective target site. Additionally, a short duration of cryo-energy was not correlated with acute and long-term failure of the procedure. In fact, there were some patients in whom a very short application of cryo-energy assured non-inductibility and no recurrence in the follow-up. It has been recently observed in an animal model that the minimal application of cryo-energy for obtaining complete nodal AV-block was 10 s in duration.20 These data stress the need for a careful attention also when ablating by cryo-energy instead of radiofrequency.
Experimentally, a freezing–rewarming–freezing cycle has been described to be associated with more extensive lesions.21 In our study, an adjunctive consolidation application of cryo-energy using this strategy was not correlated to recurrence and clinical success, nor a higher AV-block risk. It is possible also that a duration shorter than 4 min of cryo-ablation in enough to assure a permanent lesion, as recently performed by Jensen-Urstad13 with a maximal duration of 2 min of cryo-ablation.
Limitations of the study
In our population, there was a lack of homogeneity concerning different types of AVNRT, but this fact was statistically indifferent. Patients ablated by 4-mm-tip and 6-mm-tip catheter were not randomized, as well as patients in whom a freezing–rewarming–freezing cycle application of cryo-energy was done. Our results are limited by a lack of a control group treated by radiofrequency, especially when evaluating AV-block complications.
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Conclusions |
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Slow-pathway cryo-ablation is associated with a considerable acute success rate but a higher recurrence rate. A 6-mm-tip cryo-catheter seems to assure a large acute and long-term success rate than 4-mm-tip, but this eventual different effect of catheter size should be evaluated in a randomized study. AV-block appears often non-guaranteed by a negative cryo-mapping, stressing on need for a careful surveillance during cryo-ablation. Nevertheless, the theoretical advantage of avoiding the risk of permanent AV-block when compared with radiofrequency needs larger series to be demonstrated.
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References |
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