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Open Heart
Open Heart
openhrt
openhrt
Open Heart
2053-3624
BMJ Publishing Group BMA House, Tavistock Square, London, WC1H 9JR

39304298
10.1136/openhrt-2024-002873
openhrt-2024-002873
Original Research
Arrhythmias and Sudden Death
1506
Empirical superior vena cava electrical isolation guided by quantitative ablation index improves outcomes of radiofrequency catheter ablation for paroxysmal atrial fibrillation
http://orcid.org/0000-0002-7019-3042
Guan Wenchi 1wenchi.guan@outlook.com

http://orcid.org/0000-0002-9353-4604
Liu Jun 2liujundoctor@163.com

Chen Keping 1chenkeping@263.net

http://orcid.org/0000-0002-4003-4323
Yao Yan 1ianyao@263.net.cn

1 Fuwai Hospital, Chinese Academy of Medical Sciences, Beijing, People's Republic of China
2 Fuwai Hospital, Chinese Academy of Medical Sciences; Fuwai Shenzhen Hospital,Chinese Academy of Medical Sciences, Beijing, People's Republic of China
Dr; liujundoctor@163.com
None declared.

2024
19 9 2024
11 2 e00287303 8 2024
04 9 2024
Copyright © Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

Abstract

Background

The value of empirical superior vena cava isolation (SVCI) following pulmonary vein isolation (PVI) to improve the efficacy of radiofrequency catheter ablation (RFCA) for paroxysmal atrial fibrillation (PAF) remains controversial.

Objective

To evaluate the efficacy and safety of quantitative ablation index (AI)-guided empirical SVCI, in addition to PVI, for patients with PAF.

Methods

Patients with symptomatic PAF who underwent RFCA between October 2021 and May 2023 were retrospectively analysed. Patients were categorised into PVI-only group and PVI+SVCI group based on the intraoperative ablation strategy. RFCA was guided by quantitative AI in both groups. Regular clinical follow-ups were conducted to detect AF recurrence, defined as any episode of atrial fibrillation, atrial flutter or atrial tachycardia lasting >30 s.

Results

A total of 246 patients were enrolled, with 108 patients in the PVI group and 138 patients in the PVI+SVCI group. Compared with the PVI group, patients in the PVI+SVCI group had a higher prevalence of coronary artery disease (p=0.04), stroke (p=0.02) and a smaller left atrial diameter (p<0.01). After a follow-up period of 16±6 months, the ablation success rate was significantly higher in the SVCI+PVI group compared with the PVI group (91.3% vs 81.5%, p=0.02). Multivariable logistic regression analysis indicated that SVCI was an independent predictor of reduced AF recurrence postablation (Relative Risk [RR] 0.4, 95% CI 0.19 to 0.90, p=0.026). No significant difference in complication rates was observed between the groups.

Conclusion

Quantitative AI-guided empirical SVCI, in addition to PVI, improves the success rate of RFCA for PAF without increasing the risk of complications.

atrial fibrillation
ablation techniques
atrial flutter
Clinical Research Special Fund for Central High-level Hospital 2023-GSP-GG-33
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pmcWHAT IS ALREADY KNOWN ON THIS TOPIC

The superior vena cava (SVC) is one of the most common non-pulmonary venous trigger foci for paroxysmal atrial fibrillation (PAF), and plays an important role in the recurrence of atrial fibrillation (AF) after radiofrequency ablation; however, previous randomised studies failed to demonstrate a decrease in AF recurrence rate with the empirical addition of SVC isolation (SVCI) to pulmonary vein isolation (PVI) for PAF.

WHAT THIS STUDY ADDS

By using quantitative ablation index-guided SVC ablation, we demonstrated a 100% acute success rate of SVCI and an improved success rate for PAF ablation, without increasing the risk of complications.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

Our study provides a promising approach to increasing the success rate of PAF ablation.

Future prospective randomised clinical trials are needed to further validate these findings and potentially influence clinical practice and guidelines.

Instruction

The superior vena cava (SVC) is one of the most common non-pulmonary venous trigger foci for paroxysmal atrial fibrillation (PAF).1 SVC trigger is a significant mechanism for atrial fibrillation (AF) recurrence, especially in Asian population. However, the value of empirical SVC isolation (SVCI) following pulmonary vein isolation (PVI) to improve the success rate of radiofrequency catheter ablation (RFCA) for PAF remains controversial. Most experts recommend limiting SVCI to patients with clear evidence of SVC triggers. However, the success rate of AF provocative tests used to identify SVC triggers in clinical practice is not satisfying. For instance, the success rate of isoproterenol, the most commonly used drug during the electrophysiological test, is only 35.1%.2 Additionally, the high rate of SVC reconnection after ablation3 and the risk of damage to the sinus node (SN) and phrenic nerve (PN) during ablation4 are also concerns that limit the use of SVCI in clinical practice.

Despite these concerns, previous studies have suggested that empirical SVCI may improve the outcome of RFCA for PAF.57 Furthermore, to address the potential risks of SVCI, we proposed the concept of ‘SCVI guided by quantitative ablation index (AI)’.8 Our previous study showed that a target AI value ranging from 350 to 400 is both safe and effective for completing SVCI. Therefore, we conducted this retrospective study to investigate whether empirical SVCI guided by quantitative AI value can improve the success rate of RFCA for PAF.

Patients and methods

Study population

Patients with symptomatic PAF who underwent single-operator RFCA at Fuwai Hospital between October 2021 and May 2023 were retrospectively analysed. Exclusion criteria were as follows: (1) patients without PAF; (2) prior catheter ablation for any type of arrhythmia; (3) SN dysfunction or other indications for permanent pacemaker implantation. Based on the intraoperative ablation strategy, the patients were divided into two groups: the PVI-only group and the PVI+SVCI group. Preoperative CT and/or trans-oesophageal echocardiography of the left atrium were performed to rule out intracardiac thrombosis. Common cardiac parameters, such as the left atrial diameter, were measured by transthoracic echocardiography. All patients received standard perioperative management of AF ablation during hospitalisation, and oral anticoagulants were administered without interruption throughout the perioperative period.8 9

Electrophysiological test and RFCA

The RFCA procedure was completed under local anaesthesia. First, PVI was performed under the guidance of quantitative AI, with an AI value of over 500 for the anterior wall and over 400 for the posterior wall.8 10 Additional atrial linear ablation was performed in the patients with concurrent atrial flutter (AFL). Patients who failed to return to sinus rhythm (SR) after ablation received pharmacological or electrical cardioversion. Patients in the PVI+SVCI group then underwent SVCI in SR, as described in our previous studies8 (figure 1). Briefly, the anatomy and electrical activity of right atrium (RA) and SVC in SR were reconstructed by the Carto 3 electro-anatomical mapping system (Biosense Webster, California, USA). The functional SN region was defined as the first 10 ms of activity on the isopotential map. Subsequently, a catheter (SmartTouch SF, Biosense Webster) was used for point-by-point pacing with a contact force of 10–20 g along the PN alignment. The anatomical sites with PN capture or loss of capture were identified by observing diaphragmatic movement. Finally, SVCI was completed under the guidance of AI values (350-400). RF energy was delivered in power-control mode (power 40 W, temperature 43°C, saline irrigation 15 mL/min, contact force 5–20 g). Real-time automated display of radiofrequency applications (Visitag, Biosense Webster) was used with predefined settings of catheter stability (2 mm for 3 s) and minimum contact force (25% of time >3 g). Once the target AI values were achieved, the catheter was moved to the next site, with a maximum interlesion distance of 5 mm. The ablation end point was complete electrical isolation between the RA and the SVC, confirmed by pacing from RA or SVC with evidence of bidirectional conduction block. Both the PVI and the SVCI were revalidated after a 15 min waiting period postablation.

Figure 1 Ablation index (AI)-guided pulmonary vein electrical isolation (PVI) and superior vena cava electrical isolation (SVCI). This figure shows a three-dimensional anatomical reconstruction of the left atrial and pulmonary veins, alongside a three-dimensional electrical-anatomical reconstruction of the right atrium. The left side presents a posterior-anterior (PA) view, while the right side provides a right lateral (RL) view. Red dots indicate AI values >450, pink dots indicate AI values >350. Yellow dots mark sites where the phrenic nerve could be captured, and white dots mark sites where the phrenic nerve could not be captured. The red area of the right atrium represents the anatomical location of the functional sinus node. AP, Anteroposterior view; LAO, Left Anterior Oblique view; RAO, Right Anterior Oblique view; LL, Left Lateral view; INF, Inferior view; SUP, Superior view.

Clinical follow-up

All anti-arrhythmic drugs, except beta-blockers when necessary, were discontinued both before the procedure and after the 3-month blanking period. This approach allowed us to evaluate the efficacy of the ablation procedure without the influence of anti-arrhythmic medications. Outpatient follow-up was performed at 3, 6 and 12 months after the procedure, and then anually thereafter. Follow-up included screening for AF recurrence by a 14-day duration ECG. Recurrence of AF was defined as episodes of AF or AFL or atrial tachycardia lasting >30 s. The presence of SN impairment, PN palsy, stroke and other complications associated with RFCA was also observed.

Statistical methods

Continuous variables with normal distribution were presented as mean±SD, with comparisons made using the Student’s t-test. Continuous variables with non-normal distribution were expressed as median (Q5, Q95), and comparisons were made using the non-parametric tests (Mann-Whitney U test). Discrete variables were expressed as percentages, with comparisons made using the χ2 test or Fisher’s exact probability test. The Kaplan-Meier method was used to compare the effect of RFCA treatment between the two groups, and survival curves were plotted. Both univariate and multivariate Cox regression were to identify clinical factors associated with postoperative AF recurrence and to calculate HRs. A p value of <0.05 was considered statistically significant. Statistical analysis was performed using SAS software (V. 9.1, SAS Institute, Cary, North Carolina, USA).

Results

Baseline data

A total of 246 patients were enrolled, with 108 patients in the PVI group and 138 patients in the PVI+SVCI group. The patients in the PVI+SVCI group had a higher proportion of coronary artery disease (p=0.04) and stroke (p=0.02), as well as a smaller left atrial diameter (p<0.01). The prevalence of other comorbidities did not differ significantly between the two groups (table 1).

Table 1 Baseline characteristics

	PVI group (n=108)	PVI+SVCI group (n=138)	Total (n=246)	P value	
Male (n/%)	68/63.0	97/70.3	165/67.1	0.2249	
Age (year)	60±9	61±10	61±10	0.5015	
Hypertension (n/%)	63/58.3	74/53.6	137/55.7	0.4605	
Diabetes mellitus (n/%)	24/22.2	34/24.6	58/23.6	0.6578	
Coronary artery disease (n/%)	17/15.7	37/26.8	54/22.0	0.0374	
Heart failure (n/%)	1/0.9	5/3.6	6/2.4	0.1735	
Prior stroke (n/%)	5/4.6	19/13.8	24/9.8	0.0165	
Left atrial diameter (mm)	39±5	37±4	38±5	0.0059	
Left ventricular ejection fraction (%)	65±4	64±5	65±4	0.4320	
CHA2DS2-VASc score†	1.5±1.1	1.9±1.5	1.7±1.4	0.0271	
 0	20/18.5%	26/18.8%	45//18.7%		
 1	40/37.0%	40/29.0%	80/32.5%		
 2	32/29.6%	31/22.5%	63/25.6%		
 ≥3	16/14.8%	41/29.7%	58/23.6%		
HAS-BLED score‡	1.1±0.8	1.3±0.9	1.2±0.9	0.1484	
 0	30/27.8%	36/26.1%	66/26.8%		
 1	43/39.8%	49/35.5%	92/37.4%		
 2	31/28.7%	36/26.1%	67/27.2%		
 ≥3	4/3.7%	17/12.3%	21/8.5%		
† C: Congestive Heart Failure (or Left Ventricular Dysfunction); H: Hypertension (high blood pressure); A: Age ≥ 75 years (2 points); D: Diabetes Mellitus; S: Stroke or Transient Ischemic Attack (TIA) (2 points); V: Vascular Disease (e.g., prior myocardial infarction, peripheral artery disease, or aortic plaque); A: Age 65-74 years (1 point); Sc: Sex Category (female gender gets 1 point).

‡ H: Hypertension (uncontrolled, systolic BP >160 mmHg). A: Abnormal renal and liver function (1 point each); Renal: chronic dialysis, renal transplant, or serum creatinine ≥200 µmol/L (2.26 mg/dL); Liver: chronic liver disease (e.g., cirrhosis) or bilirubin >2x normal with AST/ALT/ALP >3x normal. S: Stroke (previous history). B: Bleeding history or predisposition (e.g., prior major bleeding or tendency to bleed). L: Labile INR (unstable or high International Normalized Ratio if on warfarin). E: Elderly (age >65 years). D: Drugs or alcohol (1 point each), Drugs: concomitant use of drugs like antiplatelets, NSAIDs; Alcohol: excessive alcohol use.

PVIpulmonary vein isolationSVCIsuperior vena cava isolation

Ablation parameters

At the beginning of the procedure, the majority of patients (66.3%) were in SR, while the remaining were in AF. SR was restored in 26.0% of cases through ablation, 4.1% through pharmacological conversion and 1.6% through electrical cardioversion. Additional linear ablation was performed in some patients due to AFL, including mitral isthmus (2.0%) and tricuspid isthmus (21.5%). The PVI group received more additional linear ablation (p=0.02) and had a higher percentage of SR recovery by RFCA. Two patients in the PVI group fail to complete PVI due to pain intolerance, resulting in an acute ablation success rate of 98.2% for PVI. The immediate ablation success rates were 100% in the PVI+SVCI group (table 2).

Table 2 Ablation parameters

	PVI group (n=108)	PVI+SVCI group (n=138)	Total (n=246)	P value	
Rhythm on beginning					
 Under SR (n/%)	66/61.1	97/70.3	163/66.3	0.1308	
 Under AF (n/%)	42/38.9	41/29.7	83/33.7	0.1308	
Success rate of PVI (n/%)	106/98.2	138/100	244/99.2	0.2281	
Additional ablation					
 Tricuspid isthmus line (n/%)	31/28.7	22/15.9	53/21.5	0.0154	
 Mitral isthmus line (n/%)	5/4.6	–	5/2.0	0.0155	
 Left roofline (n/%)	6/5.6	7/5.1	13/5.3	0.8665	
SR recovery by					
 Ablation (n/%)	35/32.4	29/21.0	64/26.0	0.0432	
 Pharmacological cardioversion (n/%)	5/4.6	5/3.6	10/4.1	0.6916	
 Electrical cardioversion (n/%)	3/2.8	1/0.7	4/1.6	0.2064	
AFatrial fibrillationPVIpulmonary vein isolationSRsinus rhythmSVCIsuperior vena cava isolation

Clinical follow-up

After a mean follow-up of 16±6 months, the success rate of ablation was higher in the PVI+SVCI group compared with the PVI group (91.3% vs 81.5%, p=0.023). All recurrent cases presented with AF, with no recurrence of AFL or atrial tachycardia. The survival analysis showed a higher success rate of maintaining SR postoperatively in the SVCI group compared with the PVI group (figure 2). The multivariate logistic regression analysis showed that after adjusting for gender, age, left atrial diameter, hypertension and diabetes mellitus, SVCI was associated with fewer AF recurrences compared with the PVI alone group (RR 0.4, 95% CI 0.19 to 0.90, p=0.026). See details in table 3.

Figure 2 Survival curve of postoperative success in maintaining sinus rhythm between the PVI group (the black line) and the PVI+SVCI group (the red line). AF, atrial fibrillation; PVI, pulmonary vein isolation; SVCI, superior vena cava isolation; SR, sinus rhythm.

Table 3 Univariate and multivariate Cox regression analysis of atrial fibrillation recurrence

	Univariate Cox analysis	Mutivariate Cox analysis	
HR (95% CI)	P value	HR (95% CI)	P value	
Age	0.992 (0.957, 1.028)	0.5405			
Male	0.550 (0.233, 1.297)	0.1720			
Hypertension	0.4495 (0.331, 1.632)	0.5720			
Diabetes mellitus	0.660 (0.267, 1.631)	0.3682			
Left atrial diameter	1.040 (0.964, 1.121)	0.3111			
Superior vena cava isolation	0.235 (0.106, 0.519)	0.0004	0.209 (0.100, 0.440)	<0.001	

Complication

Complications occurred in nine patients (3.7%), including four (2.8%) patients in the PVI group and five (2.4%) patients in the PVI+SVCI group. All complications recovered spontaneously (table 4).

Table 4 Procedure complications

	PVI group (n=108)	PVI+SVCI group (n=138)	Total (n=246)	
Death	0	0	0	
Stroke	0	0	0	
Pulmonary vein stenosis	0	0	0	
Atrial oesophageal fistula	0	0	0	
Pericardial tamponade	0	0	0	
Pericardial effusion without drainage	3/2.7%	2/1.4%	5/2.0%	
Superior vena cava stenosis	0	0	0	
Sinoatrial node injury	0	1/0.7%	1/0.4%	
Phrenic nerve injury	0	0	0	
Femoral pseudoaneurysm	1/0.9%	2/1.4%	3/1.2%	
Total (n/%)	4/2.80%	5/4.85%	9/3.66%	
PVIpulmonary vein isolationSVCIsuperior vena cava isolation

Discussion

In this retrospective study, we evaluated the efficacy and safety of quantitative AI-guided SVCI in addition to PVI for patients with PAF. The results showed that SVCI can improve the success rate of RFCA for PAF without increasing the risk of complications.

The pulmonary veins serve as the most important trigger foci for AF, making the PVI the cornerstone of catheter ablation for AF. Except for the pulmonary veins, other areas such as SVC, atrial appendage and coronary sinus were also found to be trigger foci for AF. Among these, the SVC stands out as the most common source of non-PV triggers,1 particularly among Asian patients. Theoretically, additional SVCI can help to improve the efficacy of AF ablation. However, previous meta-analyses have not demonstrated significant improvements in AF ablation success rates with empirical SVCI.11 Consequently, the role of empirical SVCI for patients with PAF remains a topic of debate and is not currently recommended by clinical guidelines.

The negative results of the previous meta-analysis about SVCI plus PVI could be explained by two aspects. On one hand, the proximity of the SVC to crucial structures, such as SN and PN, raises concerns regarding potential injury during ablation procedures (ie, SN dysfunction, PN palsy and stenosis of the SVC). Prior studies reported that the incidence of PN injury during cryoablation of SVCI was as high as 19.2%, and the SN injury rate reached up to 7.7%.4 These safety concerns often prompt operators to inadvertently reduce ablation energy to mitigate risks, potentially resulting in insufficient ablation. For example, Kawano et al12 found a significant need for touchup ablation points in areas adjacent to the SVC and SN, particularly along the anterior and lateral walls, with rates of 12.6% and 7.8%, respectively. On the other hand, insufficient ablation results in a high rate of electrical reconnection, diminishing the clinical benefit of SVCI. Miyazaki et al3 have demonstrated an electrical reconnection rate of SVC as high as 74% following the first ablation, with the most common site located in the anterior lateral wall, an area closely associated with the SN. Even after a second ablation, the rate of electrical reconnection remains substantial at 29%. Gianni et al13 used a new SVCI strategy to improve safety, however, the rate of electrical reconnection of SVC remains considerable, reaching up to 38.4%.

To address the aforementioned problems, we proposed the concept of ‘SCVI guided by quantitative AI’,8 offering a solution that effectively solves the problem of intraoperative safety and efficacy of SVCI. The concept of quantitative ablation originated from the application of AI-guided values in PVI. The AI, which incorporates contact force (CF), time and power in a weighted formula, helps to control the release of RFCA energy,14 which can achieve precise atrial myocardial injury while minimising adjacent tissue damage. At present, the recommended target value of AI during PVI by RFCA is between 400 and 500.15 With this quantitative AI strategy, the immediate success rate of single-loop PVI was as high as 90%, and the clinical follow-up success rate was around 82%.10 Therefore, the quantitative AI-guided strategy for PVI with RFCA is widely used in clinical practice. We applied the concept of quantitative AI to SVCI and identified a target AI range of 350–400 by both retrospective analysis and prospective validation studies.8 Using this strategy, we achieved a remarkable 100% immediate success rate in the SVCI procedure without any complications. Our experiences with this AI value were similar to previous studies—Kawano et al12 used a low power of 20–25 W for SVCI, and found that the optimal AI was above 350, they observed that all ablation sites requiring additional treatment had AI values <308; Kusa et al16 conducted a post hoc analysis of SVCI using a high-power (50 W) strategy, identifying AI values of ≤300 for lateral wall and ≤400 for non-lateral wall as optimal parameters.

Our study showed that empirical SVCI guided by quantitative AI, in addition to PVI, can increase the success rate of RFCA for PAF without increasing the risk of complications. Our finding about efficacy of empirical SVCI is consistent with several previous studies. For instance, Ejima et al5 compared empirical SVCI with non-empirical SVCI (ie, only those with clear evidence of SVC trigger), and found that the AF recurrence rate was lower in the empirical SVCI group. Zhang et al7 also reported that empirical SVCI in patients with recurrent PAF could improve the success rate of RFCA therapy. Furthermore, by introducing the quantitative AI to the SVCI procedure, we were able to balance between achieving effective isolation and minimising the risk of procedural complications. Overall, the quantitative AI-guided SVCI provides a promising approach to increase the success rate of PAF ablation, and should be validated by prospective random clinical trials in the future.

Limitations

The study has several limitations. First, this study is a single-operator, retrospective study without matching between the two groups. Differences in LA diameter, the frequency of empirical extra-PV linear ablation and cavotricuspid isthmus ablation (29% vs 16%) may affect the clinical results. Second, the study is retrospective in nature and single-centred with a relatively small sample size. The incidence of procedural complications might be underestimated, as no postprocedural imaging exam was systematically performed. However, no patient reported clinical symptoms potentially related to these complications. Our ongoing randomised study (ClinicalTrials.gov, NCT:05908955) will further address these issues. Third, the recurrence rate of AF may be underestimated, as some patients may experience short-duration, asymptomatic AF episodes between follow-up visits. We have employed 14-day ambulatory ECG during follow-up to maximise the detection of potential AF episodes. Previous studies have also used this approach during follow-up. Indeed, compared with the 14-day ambulatory ECG, the implantable cardiac monitor (ICM) is more accurate for assessing AF recurrence. However, in clinical practice, the use of ICM is limited due to its invasive nature and high cost, patients are reluctant to undergo the procedure, which restricts its application in routine clinical practice.

Conclusion

Quantitative AI-guided empirical SVCI, in addition to PVI, can improve the success rate of RFCA for PAF, without increasing the risk of complications.

Data availability statement

No data are available.

Funding: This work was supported by the Clinical Research Special Fund for Central High-level Hospital (2023-GSP-GG-33).

Patient consent for publication: Not applicable.

Ethics approval: This study was approved by the Ethics Committee of Fuwai Hospital, Chinese Academy of Medical Sciences (project number: 2023–2119). The study protocol adhered to the ethical principles for medical research involving human subjects established by the Declaration of Helsinki, protecting the privacy of all the participants as well as the confidentiality of their personal information. Participants gave informed consent to participate in the study before taking part.

Provenance and peer review: Not commissioned; externally peer reviewed.
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