The effect of different power radiofrequency ablations in treatment and postoperative pain in patients with atrial fibrillation: a retrospective study

Abstract

Background

There has been no consensus on what power of radiofrequency energy can be used to produce the best surgical results in patients with atrial fibrillation. In addition, patients undergoing local anesthesia and fentanyl analgesia may experience pain when radiofrequency ablation is performed. This study investigated the effect of different power radiofrequency ablations in treatment and postoperative pain in patients with atrial fibrillation.

Methods

A retrospective study was performed with 60 patients who underwent radiofrequency ablation for atrial fibrillation between January and June 2023. Patients were divided into 2 groups according to the power of the radiofrequency ablation catheter used, with 30 patients in the conventional power group (35 W) and 30 patients in the high-power group (50 W). The cardiac electrophysiological indexes and postoperative pain of the 2 groups were compared.

Results

Most of the procedural key parameters between the 2 groups had no significant differences. However, the total application time during radiofrequency ablation and pulmonary vein isolation time in the high-power group were significantly shorter than those in the conventional power group (p < 0.001). Patients in the high-power group reported significantly less pain than those in the conventional power group in the immediate postoperative period and the late postoperative period (p < 0.001).

Conclusions

High-power radiofrequency ablation showed a shorter treatment time, and could reduce postoperative pain compared to conventional power ablation.

Background

Atrial fibrillation (AF) is a common arrhythmia characterized by irregular and ineffective atrial contraction with typical electrocardiograph changes of absolute inequality in the R-R interval and absence of significant repetitive P waves, which can lead to reduced cardiac ejection, increased risk of heart failure, and myocardial infarction [1]. With an in-depth study of the pathogenesis of AF, Haissaguerre et al. found in 1997 that focal electrical activity originating from the pulmonary veins could trigger/drive the development of AF, and suggested that AF could be treated by catheter ablation [2]. Since then, radiofrequency ablation has received much attention.

In recent years, with the increasing research on the theory and technology of catheter ablation, it has become an important method in the treatment of AF and even arrhythmia. Radiofrequency ablation, cryoballoon ablation, and pulsed field ablation are the most commonly used catheter ablation methods, among which radiofrequency ablation is a mature, safe, and standard treatment of AF in China. It was much more effective than conventional drug therapy in maintaining sinus rhythm in patients with AF, and was regarded as the first-line treatment for AF in the latest guidelines for the treatment of AF. It is a breakthrough in cardiac electrophysiology technology and a hot spot in the field of cardiac treatment in recent years. Pulmonary vein electrical isolation, the basis of AF catheter radiofrequency ablation, can destroy myocardial tissue by generating heat with adjustable current, causing irreversible coagulation and degenerative necrosis of local myocardial tissue, resulting in the formation of non-conductive scar tissue, thus destroying the AF trigger and maintaining the matrix [3, 4]. Sustained, irreversible transmural injury is the key to successful ablation, and the stability of the catheter and its apposition are the most important factors affecting the ablation results. Patients often experienced abrupt changes in respiratory rate and body movement based on different pain tolerance levels, as local anesthesia and fentanyl analgesia during surgery were used in China, which was different from that in western countries where general anesthesia and analgesia were used. Sudden changes in respiratory rate during surgery could seriously affect real-time catheter apposition, thus increasing the risk of pericardial tamponade and reducing the effectiveness of ablation. The body movement of some patients could also affect the accuracy of 3D modeling of the atria, which greatly prolonged the operation time. Therefore, how to optimize perioperative pain management in patients with AF is a current research hotspot and difficult point. The main cause of intraoperative pain was the damage of tissues (especially the epicardium and esophagus) caused by ablation energy. Therefore, the ablation energy was one of the most important factors affecting the depth and extent of ablation injury. However, there has been no consensus on what power of radiofrequency energy should be used intraoperatively to produce the best surgical results. Theoretically, with stable catheter-myocardial apposition and constant pressure, the increased output power and decreased ablation time resulted in the increased impedance heat and decreased conduction heat, leading to larger and shallower ablation target diameters and better inter-target articulation, which was helpful to achieve complete electrical isolation of the pulmonary veins, avoid collateral damage to surrounding tissues during ablation, and reduce pain associated with the surgery [5]. In addition, compared with conventional low-power ablation (typically 25–35 W), high-power ablation could significantly reduce the single-ablation time and increase the single-circle isolation rate of the pulmonary vein. Moreover, conventional power radiofrequency ablation might cause lasting damage such as tissue edema and increased the risk of complications [6]. Therefore, this study investigated the effectiveness of high- and low-power radiofrequency ablations in the treatment of AF and the alleviation of postoperative pain in patients.

Methods

Study population

A retrospective study utilizing Zhongshan Hospital (an A-level tertiary hospital in Shanghai, China) information system database was performed. Sixty patients with paroxysmal AF admitted between January and June 2023 were selected from the database. The inclusion criteria were patients who were compliant with the diagnostic criteria for AF in the 2020 ECS/EACTS Guidelines for the Diagnosis and Management of Atrial Fibrillation [7], aged 18 years and above, could communicate and interact normally, and were eligible for catheter radiofrequency ablation treatment strategy after failure in pharmacological treatment. Patients with left atrial or left atrial appendage thrombosis confirmed by transesophageal echocardiography, with acute pulmonary edema, acute hemorrhagic/ischemic stroke, and other diseases that could not tolerate the surgery, with severe bleeding tendency, being allergic to atropine, isoprenaline or low molecular heparin, and having undergone catheter radiofrequency ablation were excluded. Written informed consent was obtained from all the participants. The study complied with the principles of good clinical practice and with the Declaration of Helsinki for investigation in human beings, and was approved by the institutional review board of Zhongshan Hospital.

Surgical procedure

Ablation index (AI)-guided radiofrequency ablation with ST-SF catheter was used in Zhongshan Hospital. The patients’ AI was set to 450–500 for the anterior wall and 350–400 for the posterior wall to achieve bilateral pulmonary vein isolation. Under 1% lidocaine local infiltration anesthesia, the right femoral vein was punctured, and a ten-stage fixed curved diagnostic electrophysiology catheter was placed into the coronary sinus under X-ray guidance. The foramen ovale of the atrial septum was punctured using an atrial septum puncture needle, followed by the intravenous injection of 100 U/kg heparin after successful puncture and an additional 1000 U/h, accompanied by controlling the activated prothrombin time at 300–350 s. The foramen ovale was then punctured in the same manner as described above and delivered into an 8.5 F puncture sheath. The Pentaray star mapping catheter and the ST-SF catheter were delivered into the left atrium through the 8.5 F septal puncture sheath, and the Pentaray star mapping electrode was applied to construct an anatomical model of the left atrium and pulmonary vein under the guidance of the Carto3 3D mapping system, after which the catheter was placed at the left inferior pulmonary vein antrum to adjust respiratory gating. The ablation parameters in the high-power group were set, with power as 50 W, contact force as 5–10 g, application time as 15–20 s for the anterior wall and 6–10 s for the posterior wall, saline-irrigated flow rate as 15 ml/min for ablation and 2 ml/min for nonablation. The power, contact force, and application time were set as 35 W, 5–10 g, and 20–35 s, respectively, when using the conventional power strategy for ablation, with the saline-irrigated flow rate being adjusted to 8 ml/min for ablation and 2 ml/min for nonablation.

The Visitag point parameter was set during ablation. The Visitag point was displayed with a radius of 3 mm and the distance between two points was less than 6 mm. The ablation was performed point by point starting from the anterior wall of the left upper pulmonary vein, and the endpoint of ablation was the attainment of the efferent block at the pulmonary vein potential displayed on the Pentaray star mapping electrode. During the operation, fentanyl analgesia was given intravenously, and blood pressure, heart rate, and respiration were monitored.

Measurements

General information including age, gender, education level, body mass index (BMI), hospital anxiety and depression scale (HADS) score [8], left atrial volume, and left atrial inner diameter were collected. Procedural key parameters included total number of ablation points, the maximum decrease in cardiac tissue impedance, the average decrease in impedance, total intracardiac vascular perfusion, procedure time (the interval from venous puncture to extubation at the end of the surgery), total application time during the radiofrequency ablation surgery, pulmonary vein isolation time, number of applications stopped during the surgery due to patient pain, and doses of fentanyl used during the surgery. Pain were measured within 6 h after surgery (immediate postoperative period) and between 6 and 24 h after surgery (late postoperative period) using the numeric pain rating scale (NRS) scores [9].

Statistical analyses

All statistical analyses were performed using IBM SPSS Statistics, version 22 (IBM Corporation, Armonk, NY). Continuous variables with normal distribution were expressed as mean and standard deviation (SD). Categorical variables were expressed as frequency and percentage. The t-test (normally distributed continuous variables) and chi-square test were used to compare different characteristics of patients. A 2-sided p valued of < 0.05 was considered statistically significant.

Results

A total of 60 patients were included with 30 patients in the conventional power group and 30 patients in the high-power group. The type of AF and the surgical procedure in both groups were matched 1:1. There were 20 men and 10 women in the conventional power group with the mean age of 61.4 ± 9.4 years. There were 23 men and 7 women in the high-power group with the mean age of 60.1 ± 11.8 years. There were no statistically significant differences in general information between the 2 groups (p > 0.05), as shown in Table 1.

Table 1 General information of patients (n = 60)

Most of the procedural key parameters between the 2 groups had no significant differences, such as the total number of ablation points, maximum decrease in cardiac tissue impedance, the average decrease in impedance, total intracardiac vascular perfusion, procedure time, number of applications stopped due to patient pain during surgery, and doses of fentanyl used during surgery. However, the total application time during radiofrequency ablation and pulmonary vein isolation time in the high-power group were significantly shorter than those in the conventional power group (p < 0.001), indicating higher surgical efficiency (Table 2).

Table 2 Comparison of the procedural key parameters between 2 groups (n = 60)

Further analysis of the effect of different powers on patients’ postoperative pain showed that patients in the high-power group reported significantly less pain than those in the conventional power group in the immediate postoperative period and the late postoperative period (p < 0.001) (Table 3).

Table 3 Comparison of postoperative pain between 2 groups (n = 60)

Discussion

There were many causes of AF with old age being an independent risk factor [9]. As the world population is aging, the number of AF patients is expected to continue to increase in the future, and the incidence of AF in China is approximately 0.77% [10]. AF can cause a variety of hazards, including thromboembolism and heart failure, which can seriously affect the physiological function of patients. It also imposes an economic burden on families and social health care to a certain extent. With the increasing prevalence and mortality of AF, it has been a major public health problem.

Radiofrequency ablation is an important method for maintaining sinus rhythm in patients with AF, especially those with symptomatic AF. The key to successful radiofrequency ablation is the formation of continuous and transmural tissue damage, which depends on the depth and extent of irreversible cellular damage caused at each ablation target. However, the success rate of AF operations, especially in terms of relieving patient pain after ablation, is currently suboptimal due to an incomplete understanding of the pathogenesis of AF and the limitations of radiofrequency ablation techniques. Although radiofrequency ablation therapy for AF has been developing and progressing in recent years, patients often have significant pain during ablation and even after surgery. Some researchers have concluded that the possible reason for pain in patients might be that the current ablation operation was basically performed in the left atrium, which had a relatively weak posterior wall and was adjacent to the tracheoesophageal [11]. Additionally, some researchers found by autopsy that the vagus nerve in the posterior wall of the left atrium was the most distributed and abundant [12]. Higher vagus nerve density at the site of radiofrequency ablation might lead to pain sensitivity due to the uneven distribution of the vagus nerve in the left atrium. This might better explain the fact that most of the painful points in radiofrequency ablation of AF were located in the posterior wall of the left atrium. To improve the short/long-term efficacy of radiofrequency ablation as well as to reduce the postoperative pain of patients, performing ablation by increasing the radiofrequency output power and reducing the ablation time point by point were proposed.

Although there were no uniform criteria regarding high- and low-power radiofrequency ablation operations, many studies have shown that high-power radiofrequency ablation could reduce adjacent tissue damage with significant advantages compared to low-power ablation. An animal study showed that ablation with output power/duration of 50 W/5s and 60 W/5s appeared to be more likely to achieve effective transmural injury without increasing surgical complications compared to that of 40 W/30s [13]. Pambrun et al. found that high-power ablation (40–50 W) was shallower in depth and wider in ablation diameter than low-power ablation (25–30 W) [14]. The high-power ablation line had higher integrity and a wider damage range at the same depth of injury. It was also shown that the high-power ablation strategy could achieve adequate continuity without increasing the ablation depth. A study comparing the effects of different power ablation strategies on the degree of injury in isolated pig hearts under the same pressure conditions found that the ablation strategy of 50 W/13s was sufficient to meet the needs of left atrial ablation, could minimize the damage to adjacent organs and tissues such as the left atrial posterior wall and esophagus, ensured good tightness and effective ablation depth between each target point, thus reducing pain [15]. To the best of our knowledge, this is one of the few studies in China to investigate the effect of different power radiofrequency ablations in treatment and postoperative pain in AF patients. The effectiveness of the high-power ablation strategy for the treatment of AF was confirmed in this study. There were no significant differences in the number of ablation points and some intraoperative electrophysiological indicators between different power groups. However, the high-power group was superior to the conventional power group in terms of total application time and pulmonary vein isolation time, suggesting that the high-power ablation strategy could further improve the surgical efficiency on the basis of effectiveness. The results echoed with those reported in a meta-analysis with high-power ablation reducing ablation time and fluoroscopy time [6]. However, the definition of high-power was not consistent. In the meta-analysis, high-power was defined as possessing a power of more than 40 W, while high-power referred to a power of 50 W in this study. While, some recent studies have shown similar results of this study. In those studies, pulmonary vein isolation time was shorter in high-power short-duration group compared to standard-power long-duration group [16, 17].

This study also analyzed the effect of radiofrequency ablation with different powers on patients’ postoperative pain, which were few studied in western countries where general anesthesia and analgesia were used. The results showed that high-power ablation reduced patients’ immediate and late postoperative pain, which might be due to better continuity and shorter duration of the ablation process at a certain ablation range and depth, and it was conducive to reducing tissue and nerve damage. As local anesthesia and fentanyl analgesia were used during radiofrequency ablation surgery in China, patients inevitably experienced pain, which could affect real-time catheter apposition, prolong the operation time, and reduce the effectiveness of ablation. Chen et al’s study found that high-power ablation was as safe as low-power with a low rate of complications [6]. This study further confirmed that the high-power ablation strategy seemed to increase patient comfort on the basis of better safety, which had a direct favorable impact on patients.

The findings in this study should be interpreted with consideration of the study limitations. Firstly, the sample was from a single hospital with a small sample size. A prospective study with a large sample size is needed in the future. Secondly, only procedural key parameters were collected. The follow-up data, such as AF recurrence rate and anticoagulant dose, were not collected. Finally, postoperative pain was measured no more than 24 h after surgery. A follow-up study could be conducted to determine the long-term effect of different power radiofrequency ablations in treatment and postoperative pain in AF patients.

Conclusions

This study showed that the high-power ablation shortened the total application time and pulmonary vein isolation time, and reduced postoperative pain. These results had some implications for the management of radiofrequency ablation of AF in China. Without compromising the treatment effectiveness, high-power ablation improved the surgical efficiency and reduced the pain of patients. Therefore, high-power radiofrequency ablation might be considered to increase operation speed, favor operators and supporting staff, create a better patient experience, and facilitate early rehabilitation and early discharge of patients, thereby improving quality of life, reducing medical burden, and improving the quality of medical services.