Cryoablation of substrates adjacent to the atrioventricular node: acute and long-term safety of 1303 ablation procedures

Submyocardial Pacing Threshold Distribution During Cold Saline Application; Exploring Reversible Arrhythmia Inhibition

INTRODUCTION

Cold saline application through an irrigation catheter may induce reversible inhibition of submyocardial excitation, which may be used to identify in advance an ideal site for radiofrequency (RF) energy delivery around delicate areas.

METHODS

An open irrigation catheter was positioned vertically or parallel with 10-g contact on coronary perfusing porcine hearts and the contacted myocardium was cooled by cold saline at 4°C (20 mL/min). A temperature electrode was inserted 2 mm below the myocardial surface (intra-myocardial temperature at approximately 2 mm below the surface [Temp-BS]). Pacing threshold inside the ventricular wall was measured using an eight-pole electrode plunge needle inserted 5-8 mm close to the ablation catheter, and percent increase of the pacing threshold by the cold saline application (%increase-PT) was calculated.

RESULTS

During cooling, pacing at 10 V from the myocardial surface interrupted constant capture in 7/10 experiments in vertical and in 9/10 experiments in parallel ablation catheter contact. Minimum Temp-BS was not different in both catheter contact positions (25.9 ± 4.0°C in vertical vs. 25.4 ± 2.6°C in parallel). Large % increase-PT on the surface myocardium decreased as the myocardial depth became deeper, and > 150% increase was at a depth approximately 2-3 mm from the surface and > 120% increase around 6-7 mm from the surface. After cessation of cold saline application, the increased %increase-PT recovered to the pre-cooling values.

CONCLUSIONS

Cold saline application through an irrigation catheter reversibly inhibited submyocardial excitation. This simple method may have the potential to pre-determine the ideal ablation site in sensitive areas of the heart, although further studies and technological adjustments are required before clinical use.

Novel method to avoid serious injurious effects on the atrioventricular nodal (AVN) conduction during catheter ablation of the AVN slow pathway utilizing cryofreezing energy

BACKGROUND

Slow pathway elimination of the atrioventricular node (AVN) is essential to treat AVN reentrant tachycardia (AVNRT). However, injury to the AVN conduction (IAVN) is one of the serious complications. Cryofreezing energy is expected to reduce the incidence of IAVN. This study aimed to investigate the usefulness of a novel method to avoid IAVN during cryoablation of AVNRT.

METHODS

A total of 157 patients (average age, 65.8 years; male, 71) suffering from AVNRT were included. Once the AVNRT terminated during cryo-ablation, then rapid atrial constant pacing (RACP) was performed during freezing at a rate lower 10 bpm than that inducing Wenchebach AV block in 74 (47.1 %) patients (Group A). The RACP rate was decreasingly reduced by 10 bpm in case of the occurrence of IAVN. When the RACP reached 100 bpm, the cryoablation was prematurely terminated. Group B patients (83 = 52.9 %) underwent cryoablation during sinus rhythm. All patients were allocated in a randomized fashion. We compared the severity of the IAVN between Groups A and B.

RESULTS

There were no significant differences at 12 months regarding the freedom from the AVNRT between Groups A and B. However, the duration of the IAVN was significantly longer in Group B than A (p = 0.02). There were no significant differences regarding the distance between the His recording sites and successful ablation sites between Groups A and B. No permanent IAVN requiring pacemaker implantation was provoked in either group.

CONCLUSION

RACP was useful to avoid sustained and serious IAVN during cryoablation of AVNRT.

Voltage and propagation mapping: New tools to improve successful ablation of atrioventricular nodal reentry tachycardia

INTRODUCTION

Mapping system is useful in ablation of atrioventricular nodal reentry tachycardia (AVNRT) and localization of anatomic variances. Voltage mapping identifies a low voltage area in the Koch triangle called low-voltage-bridge (LVB); propagation mapping identifies the collision point (CP) of atrial wavefront convergence. We conducted a prospective study to evaluate the relationship between LVB and CP with successful site of ablation and identify standard value for LVB.

MATERIALS AND METHODS

Three-dimensional (3D) maps of the right atria were constructed from intracardiac recordings using the ablation catheter. Cut-off values on voltage map were adjusted until LVB was observed. On propagation map, atrial wavefronts during sinus rhythm collide in the site representing CP, indicating the area of slow pathway conduction. Ablation site was selected targeting LVB and CP site, confirmed by anatomic position on fluoroscopy and atrioventricular ratio.

RESULTS

Twenty-seven consecutive patients were included. LVB and CP were present in all patients. Postprocedural evaluation identified standard cut-off of 0.3-1 mV useful for LVB identification. An overlap between LVB and CP was observed in 23 (85%) patients. Procedure success was achieved in all patient with effective site at first application in 22 (81%) patients. There was a significant correlation between LVB, CP, and the site of effective ablation (p = .001).

CONCLUSION

We found correlation between LVB and CP with the site of effective ablation, identifying a voltage range useful for standardized LVB identification. These techniques could be useful to identify ablation site and minimize radiation exposure.

Multi-catheter cryotherapy for the treatment of resistant accessory pathways

OBJECTIVE

To investigate the utility of simultaneous multi-catheter cryotherapy for the treatment of APs that were previously resistant to standard radiofrequency (RF) catheter ablation.

BACKGROUND

Catheter ablation is established in the treatment of accessory pathways (AP), with high rates of permanent procedural success with a single attempt. However, there are still instances of acute procedural failure and AP recurrences with standard RF and cryotherapy methods.

METHODS

Seven consecutive cases of pre-excitation syndromes with prior failed RF catheter ablation had the novel treatment. Cryotherapy was delivered using two 8 mm tip focal cryoablation catheters (Freezor® Max, Medtronic, Minneapolis, Minnesota, USA).

RESULTS

Accessory pathway localisation was septal in 5 cases, left posterolateral in 1, right lateral in 1. In all cases, ablation of the AP was acutely successful with no procedural complications. Median procedure and fluoroscopy durations were 199 and 35 min, sequentially. Median Procedure duration fell significantly in the second half of series (174 min) compared to the first half (233 min, P = 0.05). One patient had evidence of a recurring AP conduction with pre-excitation at 5-week follow up. After a median follow up of 66.8+-6.5 months, 6 out of 7 patients remained asymptomatic and free of pre-excitation.

CONCLUSION

Simultaneous multi-catheter cryotherapy is feasible, safe and can provide definitive cure of accessory pathways that were previously resistant to standard radiofrequency ablation. Further study is required in the assessment of this novel form of advanced cryotherapy to treat complex and resistant arrhythmias.

Cryofreezing for slow-pathway modification in patients with slow-fast AVNRT: Efficacy, safety, and electroanatomical relation between sites of transient AV block and sites of successful cryoablation

INTRODUCTION

Cryoablation has emerged as an alternative to radiofrequency ablation for treating atrioventricular nodal reentrant tachycardia (AVNRT). The aim of this prospective study was to evaluate the efficacy and safety of cryoapplication at sites within the mid/high septal region of Koch's triangle and the relation between sites of transient AV block (AVB) and sites of successful cryoablation.

METHODS AND RESULTS

Included were 45 consecutive patients undergoing slow-fast AVNRT cryoablation. Initial delivery of cryoenergy was to the mid-septal to high septal region of Koch's triangle. Transient AVB occurred during cryoenergy delivery in 62% (28/45) of patients. Median distance between sites at which cryofreezing successfully eliminated slow pathway conduction and sites of AVB was 4.0 (3.25-5.0) mm. Sites of successful cryoablation tended to be to the left and inferior to the AVB sites. The atrial/ventricular electrogram ratio was significantly lower at sites of successful cryoablation than at AVB sites (0.25 [0.17-0.56] vs. 0.80 [0.36-1.25], p < .001). Delayed discrete or fractionated atrial electrograms were recorded more frequently at sites of successful cryoablation than at AVB sites (78% vs. 20%, p < .001). No persistent AV conduction disturbance occurred, and 96% (43/45) of patients showed absence of recurrence at a median follow-up time of 25.0 months.

CONCLUSION

Cryoablation of slow-fast AVNRT and targeting the mid/high septal region of Koch's triangle was highly successful. AVB frequently emerged near the site at which the slow pathway was eliminated but always resolved by regulating the energy delivery under careful monitoring, and it may be distinguishable by its local electrogram features.

Cryoablation of atypical atrioventricular nodal reentry tachycardia

AIM

Data on ablation for atypical recurrent atrioventricular nodal reentry tachycardia (AVNRT) and long-term follow-up are generally sparse. Furthermore, the rate of recurrence and safety of cryoablation for atypical AVNRT has not been established. We compared patients cryoablated for atypical AVNRT and typical AVNRT during long-term follow-up.

METHODS

All patients (n = 2612) who underwent catheter ablation for AVNRT at the Karolinska University Hospital between January 2009 and August 2019 were analyzed. A total of 91 patients undergoing first-time cryoablation for atypical AVNRT were included. A control group with first-time cryoablation for typical AVNRT was matched in a 1:1 ratio. Patients were followed-up for recurrences for a median of 5.0 years (interquartile range: 3.1-7.5 years).

RESULTS

After 5 years, AVNRT recurrence occurred in 10 patients (11.0%) in the atypical AVNRT group and in 8 patients (8.8%) in the typical AVNRT group (hazard ratio: 1.31 [95% confidence interval: 0.52-3.32]; p = 0.568). The duration of the index procedure was significantly longer for atypical compared to typical AVNRT ablation (132.1 ± 49.2 min vs. 110.1 ± 38.8 min; p = 0.001). Transient AV blocks occurred in a similar fashion in the atypical compared to typical group (11 [12.1%] vs. 4 [4.9%]; p = 0.103). However, no ablation induced persistent AV block developed in either group.

CONCLUSION

Cryoablation for atypical AVNRT showed similar rate of recurrences and safety compared to typical AVNRT during long-term follow-up.

Cryoablation vs. radiofrequency ablation of the atrioventricular node in patients with His-bundle pacing

AIMS

Radiofrequency ablation (RFA) of the atrioventricular node (AVN) with His-bundle pacing (HBP) can cause rise in capture thresholds. Cryoablation (CRYO) may offer reversibility in case of threshold rise but has never been tested for AVN ablation in this setting. Our aim was to compare procedural characteristics and outcome of CRYO compared with RFA for AVN ablation in patients with HBP.

METHODS AND RESULTS

Forty-four patients with HBP underwent AVN ablation for an 'ablate and pace' indication. Cryoablation was performed in the first 22 patients and RFA in the following 22 patients. Procedural characteristics, success rates, and change in His capture thresholds were compared between groups. Distance from the ablation site to the His lead was measured using biplane fluoroscopy. Acute success was 100% with both strategies. Median procedural duration was significantly longer for CRYO {50 [interquartile range (IQR) 38-63] min} compared with RFA [36 (IQR, 30-41) min; P = 0.027]. An acute threshold rise of ≥1 V was observed in four CRYO (one complete loss of capture) and three RFA patients (P = 0.38), with all of the applications being within 6 mm of the His lead tip. During follow-up, nine patients had AVN re-conduction (six CRYO vs. three RFA; P = 0.58), but only four patients required a redo procedure (all CRYO; P = 0.09).

CONCLUSION

Cryoablation does not offer any advantage over RFA for AVN ablation in patients with HBP and tended to require more redo procedures. If possible, a distance of ≥6 mm should be maintained from the His lead tip to avoid a rise in capture thresholds.

Catheter ablation via the left atrium for atrioventricular nodal reentrant tachycardia: A narrative review

Background

Since 1996, it has been recognized that catheter ablation for atrioventricular nodal reentrant tachycardia (AVNRT) may require an approach through the left atrium.

Objective

The purposes are to present a case report and to provide a comprehensive narrative review on this topic.

Methods

A literature review of all articles that provided detailed information on patients who underwent catheter ablation via the left atrium for AVNRT was performed. The primary search queried PubMed using Medical Subject Headings (MeSH) terms "atrioventricular nodal reentrant tachycardia" and "left." The secondary search was performed by manual review of reference lists and Google Scholar citations of manuscripts retrieved by the primary search. The review was limited to the English language.

Results

The searches yielded 30 articles that described 79 patients. A case report was added. Therefore, the final review consisted of 80 patients. The prevalence of left atrial ablation for patients with AVNRT undergoing catheter ablation at tertiary care centers was approximately 1%. Failed right atrial ablation, with or without coronary sinus ablation, was the most common indication for left atrial ablation. Pooled data from 3 cohort studies estimated the acute success rate for radiofrequency ablation of the slow pathway at the septal or inferoparaseptal segments of the mitral valve annulus after failed right-sided ablation to be 90%. There were no reports of atrioventricular block requiring permanent pacemaker implantation.

Conclusion

Catheter ablation of the slow pathway via the left atrium is an important technique for AVNRT cases that are refractory to conventional ablation.

Transcatheter cryo-ablation of septal accessory pathways, multicenter observational study in Japan

BACKGROUND

Ablation using radiofrequency energy has to be carefully performed when the arrhythmia substrate is located in close proximity to the atrioventricular (AV) node due to the risk of inadvertent permanent AV block. The aim of this study was to evaluate the efficacy and safety of catheter-based cryo-therapy for septal accessory pathways (APs).

METHODS

A total of eleven patients (median = 56.3 years, range 13-74 years) with septal APs underwent cryoablation. Ice-mapping was performed during sinus rhythm and an AV reciprocating tachycardia utilizing the APs as a requisite limb with cooling of the catheter tip temperature to a maximum of -30℃ for less than 45 s. Cryo-ablation was performed for 4 min at a temperature of -80℃ only if ice-mapping abolished the pre-excitation or retrograde conduction over the AP without injury to the AV nodal conduction.

RESULTS

Cryo-ablation was acutely successful in all eleven patients. No permanent cryo-related complications or adverse outcomes were reported. During the follow-up (range 14-26 months), no patients experienced any arrhythmia recurrences.

CONCLUSION

Ice-mapping was a feasible and reliable method to determine the exact location of the APs owing to the possibility of validating the ablation site. Cryo-ablation of APs located near the AV junction is a safe and efficacious technique with a high success rate over the long term.

IRB INFORMATION

Ethical Committee of Japan Red Cross Yokohama City Bay Hospital #2018-19.

Variation in Pediatric Post-Ablation Care: A Survey of the Pediatric and Congenital Electrophysiology Society (PACES)

Although catheter ablation is a standard treatment for pediatric arrhythmias, there are no consensus guidelines for follow-up care. This study describes the variation in post-ablation practices identified through a survey of the pediatric and congenital electrophysiology society (PACES). Pediatric and congenital electrophysiology society members were invited to participate in an online survey of post-ablation practices in September 2014. Survey questions targeted routine post-ablation practices for three common arrhythmia substrates: atrioventricular nodal reentry tachycardia, concealed accessory pathways (AP), and manifest APs. Significant practice variation was defined as <90% concordance among respondents. There were 70 respondents from 67 centers, 29 (41%) in practice for <10 years. Uniform practices included aspirin after left side ablation by 65 (93%), immediate post-procedure ECG by 63 (90%), and performance of outpatient follow-up in 69 (99%) including ECG in 97-100% depending on substrate. The majority, 57 (81%), have standardized follow-up independent of substrate. Post-procedural observation is highly variable, with 25 (36%) discharging patients on the day of ablation, 22 (33%) observing patients in hospital overnight, and 21 (30%) basing hospitalization on pre-defined criteria. Immediate post-procedure echo is performed after all ablations in only 16 (23%). Discharge from outpatient care occurs at a median time of 12 months for each arrhythmia substrate. Common post-ablation practices are evident among pediatric electrophysiologists. However, they report significant variation in post-procedure monitoring practices and testing. The rationale for these variances, and their impact on costs and outcomes, should be defined.

Cryoablation of atrioventricular nodal re-entrant tachycardia: 7-year follow-up in 515 patients-confirmed safety but very late recurrences occur

Aims

Cryoablation is an alternative method to radiofrequency ablation for treatment of atrioventricular nodal re-entrant tachycardia (AVNRT). This study investigates the long-term safety and efficacy of cryoablation in AVNRT.

Methods and results

We studied 515 consecutive patients (317 women, mean age 50 years, range 13-89 years) undergoing a first cryoablation for AVNRT between 2003 and 2008. Ablations were performed with a 6-mm Freezor Xtra catheter. Six patients were acute failures; 494 out of 509 (97%) primarily successfully ablated patients were followed up for a mean of 7.1 years (range 2-12 years). About 11% (54/494 patients) of patients had recurrences of the index arrhythmia. Time to recurrence varied from days to 9 years; 14 patients (3%) had recurrences later than 2 years, 8 patients (2%) later than 3 years, and 6 patients (2%) later than 4 years. Recurrence rate was higher in patients with slow-slow or fast-slow AVNRT (n = 24) compared with the common slow-fast variant (25 vs. 10%; P = 0.04). Recurrence rate was not higher in patients with residual slow pathway conduction (jump with or without echo beat, n = 199, 39%). Transient atrioventricular (AV) block of the first-, second-, or third-degree during ablation was observed in 45 patients but had no impact on the risk of AVNRT recurrence. No late AV block occurred. Single vs. multiple applications or total amount of cryoenergy delivered did not differ between patients with and without recurrences.

Conclusion

Cryoablation in AVNRT is safe with a long-term efficacy of 88%; however, very late recurrences occur.

Long-Term Follow-Up After Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia in Children

Background—

Catheter ablation of the slow conducting pathway (SP) is treatment of choice for atrioventricular nodal reentrant tachycardia (AVNRT). Although there are abundant data on AVNRT ablation in adult patients, little is known about the long-term results ≥3 years after AVNRT ablation in pediatric patients.

Methods and Results—

Follow-up data from 241 patients aged ≤18 years who had undergone successful AVNRT ablation were analyzed. Median age at ablation had been 12.5 years, and median follow-up was 5.9 years. Radiofrequency current had been used in 168 patients (70%), whereas cryoenergy had been used in 73 patients (30%). Procedural end point of AVNRT ablation had been either SP ablation (no residual dual atrioventricular nodal physiology) or SP modulation (residual SP conduction allowing for a maximum of one atrial echo beat). After the initial AVNRT ablation, calculated freedom from AVNRT was 96% at 1 year, 94% at 3 years, 93% at 5 years, and 89% at 8 years. Age, sex, body weight, the choice of ablation energy, and the procedural end point of AVNRT ablation did not impact freedom from AVNRT. Six of 22 AVNRT recurrences (27%) occurred ≥5 years after ablation. No late complications including atrioventricular block were noted.

Conclusions—

Cumulatively, catheter ablation of AVNRT continued to be effective in >90% of our pediatric patients during the long-term course. A significant part of recurrences occurred >5 years post ablation. Body weight, energy source, and the end point of ablation had no impact on long-term results. No adverse sequelae were noted.

Anatomic Challenges In Pediatric Catheter Ablation

Pediatric patients present unique anatomic challenges for catheter ablation. Small patient size requires special adaptation and understanding to perform safe procedures when clinically indicated. The anatomic variations of congenital heart disease also create problems that require pre-procedural preparation for each case in addition to a specialized understanding of a vast anatomic variation and surgical repairs. This understanding coupled with the knowledge of the pathophysiology of arrhythmia disorders and the biophysics of catheter ablation technology are required to perform successful and safe ablation procedures in this special population.