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J Am Coll Cardiol, 2005; 45:133-136, doi:10.1016/j.jacc.2004.10.049 © 2005 by the American College of Cardiology Foundation |
* Division of Cardiology, Department of Pediatrics, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
Cryocath Technologies Inc., Kirkland, Quebec, Canada
Manuscript received June 21, 2004; revised manuscript received October 14, 2004, accepted October 18, 2004.
* Reprint requests and correspondence: Dr. Joel A. Kirsh, Division of Cardiology, Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada (Email: joel.kirsh{at}sickkids.ca).
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Abstract |
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BACKGROUND: Radiofrequency (RF) ablation has become established therapy for pediatric tachyarrhythmias. However, challenges remain in terms of the safety and efficacy of RF ablation in specific locations; new methods may address these issues.
METHODS: Prospective data were available for 64 patients age 13 ± 4 (mean ± SD) years undergoing cryoablation at 14 centers participating in the Cryocath International Patient Registry. Dysrhythmia duration was 5.0 ± 4.2 years, with diagnoses of atrioventricular node re-entrant tachycardia (AVNRT) (n = 30), anteroseptal (n = 11), midseptal (n = 5), or other (n = 15) accessory pathway (AP) mediated AV re-entry, ventricular tachycardia (VT) (n = 3), and ectopic atrial tachycardia (EAT) (n = 2). Two patients had more than one arrhythmia substrate. Transcatheter cryoablation was offered by cardiologist preference after written informed procedural consent of each patient and/or legal guardian. Cryomapping was performed at –30°C and cryoablation was delivered with 4-min applications at –75°C.
RESULTS: Acute success was achieved in 45 of 65 (69%) cryoablation patients, with best success rates in AVNRT (83%) and right septal AP (75%), and lower success rates in other AP (43%), VT (66%), and EAT (0%). No device-related adverse events were reported. The success of radiofrequency (RF) ablation applied in 14 cryoablation failures was 4 of 4 for AVNRT patients, 1 of 1 for anteroseptal AP patients, 5 of 6 for other AP patients, 0 of 1 for VT patients, and 0 of 2 for EAT patients.
CONCLUSIONS: Transcatheter cryoablation is a safe and well-tolerated alternative to RF ablation in pediatric patients on the basis of our initial experience. Success is highest in AVNRT and in substrates recognized as technically challenging or risky for RF ablation.
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We sought to evaluate the safety and efficacy of early pediatric experience of transcatheter cryoablation as recorded in a prospective multicenter cryoablation procedure registry, as well as attempting to identify whether specific arrhythmia substrates and/or ablation locations were particularly suited to this new method.
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Methods |
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After standard electrophysiologic assessment, a 7-F cryoablation catheter (Freezor 4 mm tip or Freezor Xtra 6 mm tip, CryoCath) was introduced via femoral (62 patients) and/or other (5 patients) venous and/or femoral arterial (1 patient) access. Cryomapping at –30°C for up to 60 s was performed and the arrhythmic substrate re-evaluated. Catheter adherence to the endocardium during the cryomap allowed for extrastimulus testing for inducibility, or in the case of atrioventricular nodal re-entrant tachycardia (AVNRT), assessment of slow pathway function. Cryoablation was performed at –75°C for a 4-min period.
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Results |
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The distribution of arrhythmia substrates, as well as the procedural times and fluoroscopy times, stratified by substrate, are shown in Table 1. Procedural data were unavailable for one of the ectopic atrial tachycardia (EAT) cases. Thirty of the 66 cryoablations were for AVNRT. There were 30 cryoablations of accessory pathways (APs), one-half of which were right anteroseptal or midseptal.
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We evaluated the fate of failed cryoablation attempts (Table 1). Of the five failures of cryoablation in AVNRT, four were successfully treated by RF ablation. Of the four failed cryoablations of anteroseptal and midseptal APs, three were abandoned at the discretion of the clinician, and one anteroseptal AP was successfully RF ablated. Of the eight failed cryoablations for other APs, three were in the right posterior septum, two in the left posterior septum, one within the coronary sinus, and two on the left free wall. Two of these cases were abandoned, and five of the six remaining APs were successfully ablated with RF. All of the failed VT or EAT cryoablations also failed RF ablation.
From the patient's point of view in this series, the procedural success rate for ablation of AVNRT or AP, from any energy source, was 97% for AVNRT and 80% to 86% for APs, most of which were in right septal locations.
Adverse events. There were no complications of electrophysiologic (EP) study or cryoablation, specifically no cardiovascular injury and no permanent AV block. During cryomapping, transient observations of AV conduction abnormalities ranging from first degree AV delay to complete heart block were anecdotally observed, particularly in right septal locations; all of these were immediately reversed upon rewarming. One adverse event of "prolonged hospitalization due to prostatitis" was of uncertain relationship to the initial procedure. By way of comparison, a 3% to 4% overall complication rate for EP study and RF ablation has been shown in the Prospective Assessment after Pediatric Cardiac Ablation (PAPCA) study and its associated registry (17), whereas the reported incidence of AV block caused by RF ablation is 1.2% for AVNRT and 3.6% for all right septal pathways (24). In a review of a single center's experience of 145 septal APs, four cases of permanent AV block in 47 attempted anteroseptal and midseptal ablations were observed, for a site-specific AV block rate of 8.5% (16).
Follow-up. Three-month follow-up data were available for 28 of the 45 acutely successful cryoablations. There were four reported recurrences: two of AV node re-entry, one posteroseptal AP, and one VT. Depending on which denominator one uses, this may suggest somewhere between 9% and 14% recurrence rates. Because the follow-up data are incomplete, a selection bias to follow-up in the recurrence patients would be a reasonable assumption, and thus the recurrence rate may not be dissimilar from the PAPCA experience of 7% and 9% at two and six months, respectively (25).
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Discussion |
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Acute failure of cryoablation. Although there were less impressive acute success rates in posteroseptal and free wall locations, most of these pathways were subsequently successfully ablated using RF energy, suggesting that lesion size and delivery may have played a role in these locations (29,30). In contrast, the failure of RF ablation following attempted cryoablation of VT and EAT suggests that the ablation energy source and mode of delivery were not responsible in these cases.
Unique features of cryoablation. The reversibility of cryomapping provides the opportunity for forgivable test lesions in locations known to be at high risk for heart block during empiric RF ablation. Accompanying this is the ability to formally retest AV nodal physiology as well as arrhythmia inducibility during both cryomapping and cryoablation (28). The intrinsic catheter stability related to cryoadhesion prevents dislodgement during ablation. All of these characteristics are expected to enhance both safety and efficacy (27,31,32).
Issues remaining to be resolved. The disappointing performance during this early cryoablation experience in the ablation of some APs is most likely related to the smaller lesion size with initial versions of the cryoablation catheter, leading to a smaller effective target area being ablated. The issue of convective heat loss during cryoablation on the atrial side of the left AV groove has been suggested as playing a role (30), with some centers reporting better success when using a retrograde approach in adults, although the safety and efficacy of a retrograde approach with the relatively stiff cryoablation catheter has not been evaluated in children (Dr. M. Dubuc, personal communication, March 2003). Newer cryoablation catheters with larger tip surface areas and/or modified coolant gas parameters may offer a benefit in these situations.
Similar to the early experience with RF ablation (26), it is reasonable to expect that a learning curve exists for the attainment of proficiency in utilizing cryoablation. Acute success rates as well as recurrence risks are currently acceptable, but should eventually approach those of established modalities. The established safety of cryoablation in high-risk locations should allow the effective ablation of arrhythmias that otherwise might be abandoned, or perhaps ablated with a requirement for permanent pacing (16).
Conclusions. Cryoablation is a safe and effective alternative to RF ablation and appears to offer unique advantages related to catheter stability during energy delivery, as well as the safety of reversible mapping lesions in high-risk locations.
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This article has been cited by other articles:
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  E. Gonzalez-Torrecilla, A. Arenal, F. Atienza, and J. Almendral Transient atrioventricular block shortly after uneventful cryoablation of atrioventricular nodal re-entrant tachycardias: report of two cases Europace, October 1, 2007; 9(10): 927 - 930. [Abstract] [Full Text] [PDF]
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P. Khairy, P. G. Novak, P. G. Guerra, I. Greiss, L. Macle, D. Roy, M. Talajic, B. Thibault, and M. Dubuc Cryothermal slow pathway modification for atrioventricular nodal reentrant tachycardia Europace, October 1, 2007; 9(10): 909 - 914. [Abstract] [Full Text] [PDF]
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 D J Abrams Invasive electrophysiology in paediatric and congenital heart disease Heart, March 1, 2007; 93(3): 383 - 391. [Full Text] [PDF]
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