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 Table of Contents  
GUIDELINE
Year : 2021  |  Volume : 6  |  Issue : 2  |  Page : 77-84

The interpretation of cryoballoon ablation of atrial fibrillation: Consensus of Chinese experts (English version)



Date of Submission13-Oct-2021
Date of Decision01-Nov-2021
Date of Acceptance03-Nov-2021
Date of Web Publication28-Dec-2021

Correspondence Address:
Congxin Huang
Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan University, Wuhan 430060, Hubei Province

Dejia Huang
Department of Cardiology, West China Hospital, Sichuan University, Chengdu 610041, Sichuan Province

Shu Zhang
State Key Laboratory of Cardiovascular Disease, Cardiac Arrhythmia Center, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100037

Dr. Zulu Wang
Department of Cardiology, General Hospital of Northern Theater Command, Shenyang 110016, Liaoning Province

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijhr.ijhr_12_21

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  Abstract 


Atrial fibrillation (AF) is the most common tachycardia arrhythmia in clinical practice. Catheter ablation has been one of the most effective established therapies for AF. In recent years, cryoballoon ablation (CBA) is a novel technique of AF treatment. Much experience in the operations, therapeutic parameters, and the prevention against complications has been gained during the process of clinical application and promotion. Chinese Society of Pacing and Electrophysiology and Chinese Society of Arrhythmias organized experts, jointly initiated, and compiled “The interpretation of CBA of AF: Consensus of Chinese experts,” aiming to standardize and promote the clinical application of CBA. Based on the real-world situation in China, this article interprets and reviews the important contents of this consensus, combined with the domestic and overseas guidelines, consensus, and recent literature on AF management.

Keywords: Atrial fibrillation, catheter ablation, cryoballoon, expert consensus, interpretation


How to cite this article:
Wang Z, Huang C, Huang D, Zhang S. The interpretation of cryoballoon ablation of atrial fibrillation: Consensus of Chinese experts (English version). Int J Heart Rhythm 2021;6:77-84

How to cite this URL:
Wang Z, Huang C, Huang D, Zhang S. The interpretation of cryoballoon ablation of atrial fibrillation: Consensus of Chinese experts (English version). Int J Heart Rhythm [serial online] 2021 [cited 2022 May 24];6:77-84. Available from: https://www.ijhronline.org/text.asp?2021/6/2/77/334127



This manuscript is an English version based on the Chinese Society of Pacing and Electrophysiology, Chinese Society of Arrhythmias. The interpretation of cryoballoon ablation of atrial fibrillation: Consensus of Chinese experts. Chin J Cardiac Arrhyth 2020;24(3):259-64. DOI: 10.3760/cma.j.cn. 113859-20200512-00118. The second publication of this manuscript has obtained the permission from Chinese Journal of Cardiac Arrhythmias.


  Table of Contents Top


1. INTRODUCTION

2. EXTENDED INDICATIONS OF CRYOBALLOON ABLATION FOR ATRIAL FIBRILLATION TREATMENT

2.1. Paroxysmal atrial fibrillation

2.2. Persistent atrial fibrillation

2.3. Atrial fibrillation in the elderly

3. MORE DETAILED AND COMPREHENSIVE PREOPERATIONAL PREPARATION

4. PERIOPERATIVE ANTICOAGULATION MANAGEMENT THROUGHOUT THE WHOLE PROCEDURE

4.1. Preoperative anticoagulation management

4.2. Anticoagulation management during the procedure

4.3. Postoperative anticoagulation management

5. DETAILED, COMPREHENSIVE, AND PRACTICAL SUGGESTIONS ON THE ABLATION PROCEDURE

5.1. Establishing the vascular access

5.2. Establishing the transseptal access to left atrium

5.3. Precautions of the preparation for cryoballoon catheter system

5.4. Cryoballoon catheter positioning and pulmonary vein occlusion procedure

5.5. Suggestions on pulmonary vein antrum isolation

6. MULTI-ASPECT EVALUATION ON THE EFFICACY OF CRYOABLATION AND EMPHASIS ON THE IMPORTANCE OF TIME-TO-ISOLATION

6.1. Temperature

6.2. Time-to-isolation

6.3. Cryoablation dosing and times

6.4. Time to thaw

7. PREVENTION AGAINST COMPLICATIONS AS TOP PRIORITY

7.1. Phrenic nerve injury

7.2. Esophageal injuries

7.3. Cardiac tamponade

7.4. Femoral arterial injuries

8. CLOSE ATTENTION TO POSTOPERATIVE FOLLOW-UP AND MANAGEMENT OF PATIENTS WITH RECURRENT ATRIAL FIBRILLATION

9. ENHANCED TRAINING FOR OPERATORS AND ENGINEERING TECHNICIANS


  1. Introduction Top


Atrial fibrillation (AF) is the most common tachycardia arrhythmia in clinical practice. Catheter ablation has been one of the most effective established therapies for AF, and pulmonary vein (PV) isolation (PVI) has been a cornerstone strategy of AF ablation. However, due to the high recurrence rates after poor PVI durability, many studies focused on the development of safe and durable PVI techniques, including the single-shot energy delivery strategy. Cryoballoon ablation (CBA), representing the single-shot delivery technique, has been popularized in other countries and become one of the standard techniques to achieve PVI since it came into the market in Europe in 2005. In China, CBA began to be applied for AF ablation in 2013, and in 2016, the second-generation cryoballoon (Arctic Front Advance, Medtronic Inc., USA) was updated from the first-generation cryoballoon. To date, CBA has been performed in more than 20,000 cases in China. Some studies have shown the safety and efficacy of CBA in the treatment of AF, with a short learning curve and fewer serious complications, but more standardized techniques and workflow, training, promotion, and quality control remain demanded to further improve the safety and efficacy of CBA in AF treatment.

Therefore, the Chinese Society of Pacing and Electrophysiology and Chinese Society of Arrhythmias organized experts, jointly compiled, and published “Cryoballoon ablation of AF: Consensus of Chinese experts” in Chinese Journal of Cardiac Arrhythmias and Chinese Journal of Cardiac Pacing and Electrophysiology in April 2020.[1],[2] This consensus was divided into 10 sections, including background, principles and features, indications and contraindications, preoperative preparation, perioperative anticoagulation management, recommendation on operational procedures, efficacy evaluation of CBA, prevention of complications, postoperative follow-up and recurrent AF management, and suggestions on training, involving the whole procedure of CBA for AF. Based on the real-world situation in China, this article interprets and reviews the important contents of this consensus, combined with the domestic and overseas guidelines, consensus, and recent literature on AF management.


  2. Extended Indications of Cryoballoon Ablation for Atrial Fibrillation Treatment Top


In this consensus, the indications of CBA include the following four points.

2.1. Paroxysmal atrial fibrillation

For antiarrhythmic drug-resistant, frequent, and symptomatic paroxysmal AF, catheter ablation is recommended as Class I indication by the domestic and overseas guidelines.[3],[4],[5] In the early stage of AF catheter ablation, radiofrequency ablation (RFA) was widely applied. Since CBA was allowed in the treatment of paroxysmal AF, both techniques of AF ablation have been being performed during the same period. Thus, the studies which worked on the difference of the safety and efficacy between CBA and RFA were expected. FIRE AND ICE Trial evaluated the safety and efficacy of CBA, compared to RFA combined with three-dimensional (3D) mapping system, for the treatment of drug-refractory paroxysmal AF. This trial demonstrated noninferior safety and efficacy, shorter operative time, and shorter procedural time in the left atrium (LA) but a little longer fluoroscopy time in CBA group than in RFA group.[6] In addition, the secondary analysis showed fewer events of hospitalization from any cause, cardiovascular rehospitalization, direct current cardioversion, and repeat ablation, supporting that CBA might be superior to RCA for patients with paroxysmal AF.[7] However, in FIRE AND ICE Trial, the radiofrequency catheter was updated from an ordinary irrigated-tip catheter to contact force sensing catheter while the cryoballoon was updated from the first generation to the second generation. Thus, it was difficult to obtain definite conclusions about the current dominant ablation approaches, which referred to the comparison of the safety and efficacy between contact force sensing catheter and second-generation cryoballoon. Recently, the long-term follow-up outcomes of CBA for paroxysmal AF have been reported, overall, which were comparable to those of RFA.[8],[9] Based on the characteristics of using CBA for PVI, such as safety, efficacy, simplification, and reproducibility, CBA has been recommended as one of the conventional methods by the domestic and overseas guidelines. It is believed that CBA will be applied widely in more AF ablation centers and the cases will significantly increase with the popularity and promotion of CBA techniques.

2.2. Persistent atrial fibrillation

It remains unclear whether either CBA or RFA is the better ablation strategy. PVI is still the current cornerstone of catheter ablation for different types of AF. Several studies discovered that for patients with persistent AF, who underwent CBA using only PVI approach, the single-procedure success rate after 1-year follow-up was 67–69%.[10],[11],[12] Besides PVI, some experienced operators attempted substrate modification using second-generation cryoballoon, such as LA roof linear ablation, LA ridge ablation, left atrial appendage electrical isolation, etc. The results suggested that those ablation strategies can improve the success rate, but randomized controlled trials are lacking at the present.[13] The current domestic and overseas guidelines recommend Class IIa indication for symptomatic, drug-resistant, persistent AF, and Class IIb indication for symptomatic, drug-resistant, long-standing persistent AF, respectively.[3],[4],[5] Except for PVI, the efficacy and optimization of other supplemental ablation approaches remain further discussion.

2.3. Atrial fibrillation in the elderly

The prevalence of AF increases significantly with age. Under the circumstances of population aging, the number and percentage of elderly patients with AF obviously increase. It is safe and feasible to deliver CBA in elderly patients (over 75 years old).[14] Also, CBA was being easily tolerant with low demand for anesthesia or deep sedation and analgesia, and short operative time, which might be more suitable for elderly patients with AF. However, in the real-world clinical practice, it is necessary to weigh the risks to benefits in individuals, because some elderly AF patients have poor physical conditions with more comorbidities and increased operational risks.

2.4. Atrial fibrillation combined with heart failure

AF and heart failure (HF) often coexist, which is related to poor prognosis like mortality. In addition, AF could contribute to significantly increased risks of hospitalization in HF patients, and the medication treatment, aiming to control the ventricular rate or restore and maintain sinus rhythm, failed in improving the prognosis. CASTLE-AF Trial demonstrated that for AF patients combined with HF, RFA resulted in significantly lower rates of all-cause mortality and hospitalization, when compared to medication treatment.[15] In another multi-center study, second-generation cryoballoon was applied for achieving PVI in HF patients with left ventricular ejection fraction ≤40% and in patients without HF, which showed comparable perioperative safety and 1-year follow-up success rate in both groups but better improved left ventricular ejection fraction on average in HF group.[16] However, there was a lack of randomized control trials working on RFA in AF patients combined with HF as well as the head-to-head studies between RFA and CBA. Furthermore, the causes of AF combined with HF, the impacts of AF on the development of HF, cardiac and other organs' conditions, and whether to use medication or device therapies were varying from individuals. Thus, this consensus suggests that those patients before catheter ablation should receive the overall evaluation on physical conditions in case of the safety issue. Although for AF patients with HF, some current guidelines recommend the same Class IIa indication as those without HF,[3],[4] Class IIb indication is suggested by the remaining guidelines.[17]

It is important to point out that RFA should be the primary option when other cardiac arrhythmias, including supraventricular tachycardia, preexcitation syndrome, typical atrial flutter, etc., are combined with AF and demand catheter ablation meantime.


  3. More Detailed and Comprehensive Preoperational Preparation Top


Preoperational preparation includes patient preparation and operating room setup. CBA has the same preoperational preparation as RFA, but this consensus emphasizes the importance of 3D imaging of LA/PVs. At the present, CBA should be guided using 2D X-ray imaging during the procedure, because the anatomy of PVs is varying from individuals, which could be not demonstrated clearly using the selective or nonselective pulmonary angiography. Therefore, this consensus suggests using multi-slice spiral enhanced computed tomography or magnetic resonance imaging for 3D reconstruction of LA/PVs and storing multi-body images, which are helpful to understand the number, branches, morphology, and anatomic variants of the PVs, explore the diameter and the location of the proximal PVs, and screen the thrombus of LA and left atrial appendage. In some experienced centers, the 3D reconstruction of LA/PVs/esophagus is performed meantime to understand the anatomic relations between PVs (especially left inferior PV [LIPV]) and esophagus, which also supplies the reference for the time and frequency of cryoablation, and the minimum temperature at which the ablation is stopped.


  4. Perioperative Anticoagulation Management throughout the Whole Procedure Top


CBA has the same anticoagulation strategies for AF as RFA.[3],[5]

4.1. Preoperative anticoagulation management

This consensus gave the suggestions on the anticoagulation strategies before CBA procedure and transesophageal echocardiographic, which were used for screening LA thrombus (those patients who are not tolerant to transesophageal echocardiographic could receive intracardiac ultrasound instead of transesophageal echocardiographic); patients with warfarin administration reaching the target international normalized ratio do not need to discontinue warfarin but maintain an international normalized ratio range of 2.0–3.0; in general, novel oral anticoagulants are not necessary to be stopped before the operation. However, this consensus does not discuss the administration of different types of novel oral anticoagulants in detail. Current overseas consensus recommends that dabigatran (I, A) or rivaroxaban (I, B) cannot be discontinued or stopped once or twice (IIa, B). Without the discontinuation of anticoagulation treatment, many issues should be adequately considered in the centers, including the femoral vein access guided by the vascular ultrasound, the available idarucizumab as a specific reversal agent for dabigatran, and the formal monitoring of activated clotting time.

4.2. Anticoagulation management during the procedure

This consensus suggests immediate delivery of heparin after the transseptal puncture, periodic monitoring (every 20–30 min) of activated clotting time, and dose adjustment to maintain the activated clotting time at a range of 250–350 during the procedure. At the present, X-ray fluoroscopy is applied to assist in the transseptal puncture in China. In general, after succeeding in the transseptal puncture, the initial loading dose of 100 IU/kg of heparin is administered using intravenous bolus; in some centers, 2000–3000 IU of heparin is administered for preliminary anticoagulation before transseptal puncture, and extra enough doses of heparin are added after the successful puncture. However, the efficacy and safety of this later strategy remain further verification.

4.3. Postoperative anticoagulation management

After the sufficient postoperative hemostasis for 4–6 h is finished and the local bleeding at the puncture site, hematoma, cardiac tamponade, and pericardial effusion are excluded, the systematic anticoagulation treatment should restart immediately. When novel oral anticoagulants or warfarin does not discontinue before the procedure, the original anticoagulation strategy should continue after the procedure; when warfarin is not administered for anticoagulation until the operation is completed, low molecular weight heparin is used for bridging before the target international normalized ratio is reached. At least 2 months of continuous anticoagulation treatment is needed, and whether the following anticoagulation therapy continues or not is determined by the assessment of stroke risks and the recurrence conditions of AF.


  5. Detailed, Comprehensive, and Practical Suggestions on the Ablation Procedure Top


In this consensus, four aspects during the ablation procedure are suggested: Establishing the vascular access and the transseptal access to LA, precautions of the preparation for cryoballoon catheter system, cryoballoon catheter positioning, and PV occlusion procedure, and PV antrum ablation. These suggestions are very detailed, comprehensive, and extremely practical.

5.1. Establishing the vascular access

This consensus recommends that the puncture site of the femoral vein should avoid the inguinal ligament in case that it is difficult to have access through the groin area using a deflectable sheath of an outer size of 15 F. Because the deflectable sheath is too thick, it is important to avoid hurting the femoral artery when puncturing the femoral vein.

5.2. Establishing the transseptal access to the left atrium

(1) Intracardiac ultrasound is not regularly used to guide the transseptal puncture in China, and some risks are expected when the puncturing location is close to the anterior or inferior sites under fluoroscopy. To avoid unnecessary complications, the regular puncture sites should be suggested, except for the experienced operators; (2) For the skillful operators, the selective or nonselective pulmonary angiography can be omitted when the computed tomography or magnetic resonance imaging results of LA-PVs are obtained before the procedure; (3) When the adjustable bent sheath tube is replaced, short sheath tubes of 11–16F or long sheath tubes used in mitral valve adaptation can be chosen to predilate and go through the groin area for the difficult cases in some centers; (4) Continuous irrigation through the sheath tubes with heparinized saline should be equipped with infusion pumps or regular infusion bags. When pressure infusion bags are used, the alarm device for intravenous infusion should be applied to avoid the serious complications caused by the air entering the body.

5.3. Precautions of the preparation for cryoballoon catheter system

(1) 28 mm cryoballoon catheter is the priority option for cryoablation; (2) Circular Achieve mapping catheter should be advanced outside the long sheath tube before the cryoballoon catheter. During the cryoballoon catheter operation, the soft Achieve catheter should be positioned at the tip of the cryoballoon to provide protection and avoid the trauma in the LA walls from the cryoballoon catheter tips.

5.4. Cryoballoon catheter positioning and pulmonary vein occlusion procedure

(1) To isolate the superior PV, the Achieve catheter should be advanced toward its superior branch as priority; to isolate the inferior PV, the Achieve catheter should be advanced toward its inferior branch as priority, which could contribute to better balloon-to-PV contact and easier PV occlusion; but in some cases, individualized choices should be made based on the detailed anatomy of PVs and the balloon imaging post PV occlusion; (2) Deep seating the balloon, inflating the balloon or ablating inside the PV is not allowed to protect against the mechanic trauma to the intimal layers of PVs; (3) Achieve mapping catheter could provide additional support for the cryoballoon, but in fact, the balloon-PV engagement is controlled mostly through the deflectable FlexCath Advance sheath. During cryoablation, the sheath can be advanced to the distal hemisphere of the balloon for enough support and satisfactory balloon-to-PV contact; (4) The deflectable sheath should be aligned with the angle of the target PV to make the balloon achieve PV occlusion more easily; (5) The occlusion should be sufficient, and when the retention of contrast agents is visible, the cryoablation process should not start immediately. Proximal-seal technique is recommended to make the balloon close to PV antrum, achieving wide-area circumferential PVI and lessening the risks of neighboring tissue injuries;[18] (6) For some PVs, when complete occlusion cannot be made after repeated adjustment of the balloon position, segmental ablation approach should be considered.[19] Intracardiac ultrasound used for guiding this procedure could clearly identify the contact area of cryoablation. Whereas, in China, contrast injection with the assistance of X-ray is used during this process and there are some limitations; (7) Upon the best-fit occlusion, the Achieve mapping catheter could be used to obtain PV potential recordings for real-time monitoring. Withdrawal and torque can be applied to the Achieve catheter to prolapse the circular mapping poles at the tip toward the antrum to be able to record PV potentials. Meantime, the time-to-isolation (TTI) can be assessed.

5.5. Suggestions on pulmonary vein antrum isolation

(1) Using the second-generation CBA, the initial ablation with CBA lasts no longer than 180 s and the minimum temperature is not colder than −55°C; (2) Maneuvering of the cryoballoon after initiation of ablation should be avoided. A “post-cryo initiation” may increase the risk of mechanical trauma; (3) After freeze application, allow the balloon and tissue interface to thaw. The postablation thawing process can be slow. Do not move the balloon catheter until the catheter temperature reading reaches 35°C; (4) During the second freeze, allow the balloon to enlarge and stiffen, then engage the PV ostium. Proximal-seal technique can help expand the antral location of the intended lesion.


  6. Multi-Aspect Evaluation on the Efficacy of Cryoablation and Emphasis on the Importance of Time-To-Isolation Top


Cryoballoon energy transfer is dependent on the source of cryoenergy, balloon-tissue contact area, collateral warming, and time.[18] The main evaluation parameters of cryoablation include temperature, TTI, cryoablation dosing and times, and time to thaw. In current clinical studies, the parameters in CBA application adopted by different operators are not consistent. Recently, with the improvement of mapping techniques and the advance in ablation devices, the number of patients and the percentage of PVs with recorded PVI during cryoablation have significantly increased. After all, the recorded PVI during cryoablation is the most direct parameter to evaluate the efficacy of CBA. Therefore, TTI is paid close attention to as the parameter of CBA evaluation in recent years.[20]

6.1. Temperature

(1) Temperature can reflect the contact between the balloon and the PV, which is used to evaluate the efficacy of cryoablation.[13] Especially, when TTI cannot be recorded, temperature is regarded as an effective evaluation parameter. Overall, the temperature of the left superior PV and right superior PV is lower than that of LIPV and right inferior PV, but it does not mean that LIPV and right inferior PV cannot achieve effective and durable PVI; (2) To some extent, temperature is meaningful to the safety of cryoablation. Much lower temperature might lead to unnecessary damages to these tissues other than PVs as well as increased risks of complications. This consensus points out that it is reasonable to control the cryoablation temperature with the minimum temperature not colder than −55°C for the second-generation CBA. Besides the nadir temperature, the temperature drop rate during cryoablation should be concerned. If the balloon temperature during the first 30 s reaches below −40°C, a rapid descent in temperature is indicated, maybe resulting in a higher likelihood of the collateral tissue injury.[21]

6.2. Time-to-isolation

Since the release of second-generation cryoballoon, the percentage of PVs with recorded TTI has increased. TTI is an important variable to predict the effective PV occlusion and PVI. When the occlusion is satisfactory, PVI can be achieved within 60 s for most PVs, and 96.4% of PVs could achieve the permanence of cryoablation lesions after 120 s.[22] This consensus proposes that TTI is used to predict the success rate and durability of PVI. In clinical practice, individualized ablation strategies are established based on the actual situations of each PV, aiming to lower the cryoablation dosing and reduce the complications when the effective PVI is achieved.

6.3. Cryoablation dosing and times

Regarding the cryoablation dosing and times of PVI using CBA, there are no consistent standards at the present. The second-generation cryoballoon is designed with eight refrigerant jets, which can achieve greater cryorefrigerant density than the first-generation one with only four refrigerant jets. Therefore, the ablation strategy of the second-generation cryoballoon has been shortened to 180 s for two cryoablation applications instead of 240 s.[20] Combined with the results from the domestic and overseas studies and experts' suggestions, this consensus recommends as below. (1) When TTI is achieved at 60 s or less, the initial freezing cycle is 180 s and the repeat strengthened one is 120 s. (2) When TTI is achieved at over 60 s, the cryoablation should be stopped and the balloon position should be modified. (3) If TTI cannot be recorded, the initial freezing cycle is 120 s under the conditions of satisfactory PV occlusion; if PVI is achieved after thawing, another repeat application should be performed with a freezing cycle of 180 s. (4) If the PV occlusion is still not satisfactory, segmental cryoablation should be considered. (5) Under any circumstances, the temperature at colder than −55°C shown on the cryoablation instrument indicates that cryoablation should be terminated in case of related complications. The new cryoablation dosing and times recommended by this consensus remain further verification and optimization. Meantime, the complex anatomic characteristics of PVs and the anatomical relations between esophagus and PVs (especially LIPV) should be considered individually. In the cited literature, where the abovementioned ablation strategies were used, the specificity and sensitivity of their prediction for durable PVI is 83–87%, indicating the necessity and possibility to be improved;[20] in several studies on the shortened cryoablation dosing, the sample size was not large enough, and more of them made the comparisons about the success rate and recurrence rate. The design for improving the safety of CBA was not powerful; the differences in the absolute values of some main results were big but were not statistically significant, probably owing to the insufficient efficacy in the study design, the homogeneity between different clinical studies, and the discrepancy between the clinical studies and real-world clinical practice. In addition, over-interpretation might contribute to major limitations and misunderstanding. For example, in the AD-balloon study, the patients who underwent CBA were divided into two groups: If PVI was achieved after being treated with a single 3-min freezing, one group received another 3-min freezing for strengthening, but the other group did not. The 1-year success rate was 87.3% and 89.1%, respectively (P > 0.05). Delayed enhancement MRI imaging showed 46% and 36% of PV gaps, respectively, but with no statistical significance (P > 0.05). The absolute difference in the rates of PV gaps reaches 10%, indicating that further research and long-term follow-up remain demanded.[23]

6.4. Time to thaw

Monitoring the time to thaw is helpful to predict the long-term PVI,[24],[25] and the much shorter time to thaw (−30°C to 15°C) is the predictive factor of PV reconnection.[24] Aryana et al.[25] discovered that the most effective thawing interval to predict the PV reconnection is the duration from the freezing termination to 0°C (iTT0); the multivariate analysis showed TTI ≤60 s and iTT0 ≥10 s as the significant predictors of long-term PVI durability, and PV reconnection was much less possible when both standards were met together.[26]


  7. Prevention against Complications as Top Priority Top


The incidences of AF cryoablation-related adverse events are low. In the FIRE AND ICE trial, the incidence of major adverse events was 6.2% in CBA group. Among them, the incidence of phrenic nerve paralysis was 2.7% (10/374), most of which recovered in 6 months.[6] The incidence of cardiac tamponade/pericardial effusion was only 0.3% (1/374), and atrial esophageal fistula (AEF) did not occur. Apart from phrenic nerve injury (PNI), the incidences of other adverse events, including the inguinal puncture area-related complications, cardiac tamponade, recurrent atrial flutter, and atrial tachycardia after ablation were lower in CBA group than those in RFA group.

7.1. Phrenic nerve injury

PNI is the most common complication associated with CBA and mainly occurred during the cryoablation of right-sided PVs (especially right superior PV). Mild PNI is asymptomatic, and patients with severe PNI have dyspnea and shortness of breath after activity. No better treatment for PNI is available, but most patients could recover during the procedure or postprocedural follow-up.[6] Prevention is the key to PNI. In China, the most common monitoring method of phrenic nerves is to pace the right phrenic nerve and monitor the activity of diaphragm. Long-lasting or permanent PNI is infrequent. In this case, the cryoballoon position is too deep inside the right-sided PVs, which were close to the right phrenic nerve, and the disappearance and inactivity of the diaphragm could not be found in time or misjudged (the cryoablation could not be terminated immediately because the pacing leads are displaced), leading to the too long freezing time and other else. Overseas studies reported that Proximal-seal technique or PV antrum ablation techniques could be applied to avoid the deep cryoablation inside the PVs and reduce the risks of PNI.

7.2. Esophageal injuries

Esophagus is close to the posterior wall of LA. Esophagus injury is a complication observed in both RFA and CBA procedures, manifesting as esophageal erythema, esophageal ulcer, and AEF based on different degrees of esophageal injuries. The incidence of AEF related to CBA is rare (lower than 1/10,000). After analyzing the AEF cases associated with CBA, almost all AEF cases occurred during the cryoablation at the LIPVs. Too long freezing time (over 4 min), too many cryoablation times, and too low nadir temperature might cause injuries of the neighboring tissues, especially during the cryoablation at the LIPV, which should be especially concerned. The precautions to protect against the esophageal injuries related to CBA include monitoring the esophageal temperature during CBA procedures, avoiding continuous repeat ablation at the same PV target, controlling the cryoablation dosing, demonstrating the position of esophagus using esophageal barium swallow, using proton pump inhibitors, and decreasing the contact force but there is no definite current evidence.

7.3. Cardiac tamponade

Except for the cardiac tamponade caused by transseptal puncture, the incidence of cardiac tamponade during cryoablation is low, but the imprudent operation in LA might cause atrial perforation or laceration, probably leading to cardiac tamponade. The following consideration should be given during the CBA procedure in LA: (1) The soft annular Achieve (or the novel generation of Achieve Advance) mapping catheter should maintain outside the catheter tip. The tip of cryoballoon catheter is rigid and stiff in case that LA roof or LA appendage is perforated by the violent operation when the Achieve catheter is not at the tip; (2) When the balloon is incarcerated in PVs or LA appendage, cryoablation should be avoided in case of their laceration; (3) It should be careful when the distal end of annular Achieve mapping catheter is reversely folded. If this folded part (about 14 cm away from the tip of annular Achieve mapping catheter; about 11 cm away from the tip of annular Achieve Advance mapping catheter) is hardened, caution should be made during the procedure. Although it is rare, the cases of PV damage or the fractured tip of the annular mapping catheters left in PVs have been reported; (4) After the cryoablation is terminated, the catheter should be removed after sufficient thawing (at least 35°C) between the balloon and the tissue. If the time to thaw is too long, “late-adhesion” phenomenon should be excluded with the guide of X-rays.

7.4. Femoral arterial injuries

Once the deflectable FlexCath advance steerable sheath with an outer size of 15F is advanced into the femoral artery by mistake, it is difficult to close the wound and achieve the hemostasis by pressing. Seriously, a huge hematoma and hemorrhagic shock might be life-threatening. Most patients should receive urgent vascular surgery. Therefore, precaution is the most essential. During the femoral vein puncturing, no femoral arterial injuries should be confirmed based on blood color, blood pressure, bleeding rate near the puncture needle or guidewire, and guidewire path tracking under fluoroscopy before 8F SL1 transseptal sheath is delivered. In some centers, 6F short sheath is used to verify the access before the 8F transseptal sheath is delivered. When it is being replaced by 15F FlexCath Advance sheath, it should be rechecked that whether the femoral artery is entered by mistake. At present, many domestic and overseas centers use the peripheral vascular ultrasound to guide femoral vein puncture, which can significantly reduce the injuries of local vessels.


  8. Close Attention to Postoperative Follow-Up and Management of Patients with Recurrent Atrial Fibrillation Top


Postoperative follow-up and management for patients who underwent CBA should pay attention to the following issues: (1) The recurrence rate is high. Recurrent arrhythmia should be treated, including the antiarrhythmic drugs during the early stages and the repeat ablation during the late stages; (2) Anticoagulation treatment and management should be valued post cryoablation; (3) Early and late complications post CBA procedures should be identified, evaluated, and managed. In this consensus, this part emphasized the importance and contents of postoperative follow-up after CBA and proposed that the focus in the early follow-up stages should be paid on the procedure-related complications, especially to identify the symptoms and signs which require urgent evaluation and treatment, such as bleeding from the puncture site, delayed cardiac tamponade, postoperative embolism, AEF, and PNI. During the postoperative follow-up, special attention should be given to the prevention and early identification of AEF, and proton pump inhibitors or histamine type 2 receptor blockers should be administered for 4–6 weeks after AF ablation, aiming to protect against AEF. AEF might occur in several days or 1–2 months postcryoablation. Although AEF is rare in patients who receive CBA for AF treatment, its mortality is high (60–80%), which demands close attention. The patients who experience CBA and recurrent AF have their own features, which is a low likelihood of iatrogenic atrial flutter or atrial tachycardia after the second-generation CBA.[6],[7] Thus, the mechanism of late recurrence (more than 3 months but less than 1 year) and long-term recurrence (more than 1 year) is more associated with PV reconnection. Another explanation is about non-PV triggers, which might be the main reason, especially in patients without observed PV reconnection. However, the ablation strategies for the recurrent AF after CBA are not consistent. Whether CBA or RFA guided by 3D mapping system is chosen as the repeat ablation for recurrent AF is lacking in research. Most centers might adopt the latter one, but it remains unknown that whether supplemental ablation or wide-area circumferential isolation should be chosen to achieve PVI for the patients with observed PV reconnection.


  9. Enhanced Training for Operators and Engineering Technicians Top


In this consensus, it emphasizes that the standardized training should be enhanced for the physicians and engineering technicians working on CBA, aiming to improve the safety and success of this ablation therapy.

In conclusion, “The interpretation of CBA of AF: Consensus of Chinese experts” summarizes the evidence-based medicine, real-world studies, and clinical evidence in the field of CBA for AF treatment in recent years, to provide detailed suggestions and regulations, involved with theoretical basis, perioperative management, procedural workflow, technique tips, evaluation on the efficacy of CBA, prevention of complications, postoperative follow-up, and the management of patients with recurrent AF. With the development and popularization of the CBA therapy techniques, it has been one of the indispensable catheter ablation techniques in the treatment of AF. However, there is still much room for research, innovation, and development, including the extension of indications, improvement of cryoballoon and mapping electrodes, studies on the ablation strategies other than PVI, and the ablation strategies for recurrent AF cases, etc. We are looking forward to more high-quality research evidence, including that from the Chinese population, to provide more reliable evidence for clinical practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Table of Contents
1. Introduction
2. Extended Indi...
3. More Detailed...
4. Perioperative...
5. Detailed, Com...
6. Multi-Aspect ...
7. Prevention ag...
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