Atrial fibrillation (AF) is a prevalent tachyarrhythmia in clinical practice, with rapidly increasing incidence and prevalence rates [1]. AF is associated with elevated risks of thromboembolism, heart failure, and other cardiovascular events, leading to higher mortality and disability rates [2]. AF treatment strategies include rhythm and heart rate control therapy, which are crucial components in comprehensive treatment approaches [3]. Some scholars stated there was a probability of spontaneous conversion to sinus rhythm in AF patients, so a score was developed and validated to determine the probability in patients with hemodynamically stable, symptomatic, and recent-onset AF [4]. However, a few patients with AF can convert to sinus rhythm spontaneously and have a high possibility of recurring and maintaining AF rhythm, meaning transcatheter radiofrequency ablation (RFA) has emerged as a significant treatment option for controlling rhythm, alleviating symptoms and enhancing the quality of life in patients with paroxysmal atrial fibrillation (PAF) (Ia) [5]. However, literature reports show a recurrence rate of approximately 11%–30% within 1–5 years after RFA [6, 7, 8, 9]. Thus, to optimize AF treatment strategies, predicting AF recurrence after RFA is essential. Common risk factors for AF recurrence after RFA include left atrial enlargement, prolonged AF duration, and impaired left atrium storage function. Researchers have developed several predictive models to improve the accuracy of predicting AF recurrence after RFA. For instance, Mesquita et al. [10] constructed and validated the ATLAS score to estimate the recurrence rate of AF after RFA, and Kornej et al. [11] developed the APPLE score to identify patients with low, medium, and high risks of AF recurrence, Winkle et al. [12] created the CAAP-AF scoring system to estimate AF recurrence within 2 years after RFA and Mujović et al. [13] established the MB-LATER clinical score to predict very late recurrence of AF occurring $>$12 months. Lohrmann et al. [14] concluded that in patients with continuous monitoring undergoing RFA, only CHA2DS2-VASc scores $\ge$5 could predict higher AF recurrence, and Letsas et al. [15] stated that a CHA2DS2-VASc score $\ge$2 was an independent predictor of AF recurrence during the follow-up. Peigh et al. [16] and Nayak et al. [17] established and validated the ability of a high SCALE-CryoAF score to specifically predict the first AF recurrence over one year and very late recurrence of AF after cryoballoon ablation. Cay et al. [18] developed a PAT2C2H score to identify patients likely to benefit most from cryoballoon ablation of PAF and who should be monitored more closely for arrhythmia recurrence at 12 months. Jastrzębski et al. [19] compared six risk scores for predicting AF recurrence after cryoballoon-based ablation and developed the 0-1-2 PL score to predict AF recurrence, which was simplified without compromising accuracy. However, there remains a need for simple and practical recurrence markers in this context.

Dynamic electrocardiography is a commonly used method for detecting arrhythmias in medical practice. This technology offers several advantages: simplicity, cost-effectiveness, and non-invasiveness. Furthermore, the average ventricular rate obtained from a dynamic electrocardiogram can more accurately reflect a patient’s cardiac activity. Research has demonstrated the significance of the average ventricular rate in guiding optimal heart rate control treatment and adjusting drug dosage in patients with AF when obtained from a 24-hour dynamic electrocardiogram; moreover, it can provide comprehensive information on AF burden and the onset of AF [20]. Another study [21] has suggested that a 24-hour dynamic electrocardiogram can serve not only in diagnosing AF but also in independently correlating ST segment depression with the occurrence of AF, thereby identifying patients with AF who are either at high or low risk.

A prospective cohort study conducted in Norway based on the general population with a follow-up period averaging 20 years has reported that individuals with a higher resting heart rate ($>$60 bpm) have a lower risk of developing AF compared to those with a lower resting heart rate (50 bpm) [22]. Wu et al. [23] found that in PAF patients over 65 years who underwent RFA, a preoperative low resting heart rate is an independent predictor of AF recurrence. In addition, another study [24] demonstrated that in patients with paroxysmal and persistent AF, a high postoperative average heart rate (AHR) is significantly correlated with a high preoperative AHR, while a high postoperative AHR is significantly associated with a reduced clinical recurrence rate of AF.

This study retrospectively examined the 24-hour dynamic electrocardiogram of patients with PAF before undergoing RFA and analyzed the correlation between the AHR in the sinus rhythm state and postoperative recurrence of AF. The objective was to provide guidance for adjusting preoperative antiarrhythmic drug (AAD) usage while also enabling early identification and targeted intervention for patients at high risk of postoperative recurrence.

The findings of this study revealed that for patients with PAF, the recurrence rate of AF decreased with an increase in the AHR in the sinus rhythm state after achieving ventricular rate control before RFA.

In recent years, the management of AF has undergone revolutionary changes. Transcatheter RFA has become a first-line treatment option for drug-resistant and symptomatic PAF patients [5]. However, the high rate of AF recurrence after RFA often diminishes the benefits of ablation. Therefore, the early identification of risk factors for AF recurrence is crucial for detecting and treating such arrhythmias to prevent complications such as stroke.

The guidelines from the American Heart Association [28] suggest long-term administration of a $\beta$-receptor blocker or ND-CCB to control ventricular rate in patients with PAF and achieve the resting heart rate goal of 80 bpm, to enhance clinical symptoms, preserve cardiac function, improve quality of life and prognosis. Nonetheless, the guidelines do not address the potential influence of a low resting heart rate on the onset of AF and the recurrence of AF after ablation.

Several scholars have researched the relationship between heart rate and the development or recurrence of AF and found that a low heart rate can increase the risk of both AF occurrence and postoperative recurrence. For example, O’Neal et al. [29] showed that a decreased resting heart rate is associated with an increased risk of AF, and this finding is consistent in subgroups of age, gender, race, and coronary atherosclerotic heart disease. Other two large independent cohort studies, namely the Copenhagen Electrocardiographic Study [30] and the Tromsø Study [22], have discovered that a low resting heart rate (50 bpm) is an independent predictor of AF. Furthermore, Goff et al. [31] demonstrated a negative correlation between an increase in postoperative resting heart rate and the recurrence of AF one year after ablation, highlighting that patients with a postoperative resting heart rate increase of more than 15 bpm have a reduced risk of AF recurrence. Another study [24], including patients with paroxysmal AF and persistent AF, likewise concluded that an increase in resting heart rate after RFA is negatively associated with AF recurrence. Yu et al. [32] proposed that a high postoperative AHR is linked to a reduced risk of AF recurrence, and a high preoperative AHR is one of the strongest predictive factors for a high postoperative AHR. Wu et al. [23] found that a preoperative low resting heart rate (50 bpm) is an independent predictor of postoperative recurrence in patients with PAF who are 65 years or older. von Olshausen et al. [33] confirmed that patients with a sinus heart rate change 11 bpm (pre-ablation to 3 months post-ablation) were at higher risk of recurrences during one-year post-ablation. Vassallo et al. [34] stated that AF ablation with high-power–short-duration incidental cardiac parasympathetic denervation identified that patients with lower heart rate increase are prone to recurrence, whereas those with higher heart rate increase had higher maintenance of sinus rhythm at a long-term follow-up. The results of this study aligned with previous research.

As previously mentioned, several studies demonstrated that patients with significantly increasing AHR post-ablation had a lower recurrence rate of AF. The cardiac autonomic nervous system (ANS) plays an important role in the pathophysiology of AF [5]. The intrinsic part of the ANS is located primarily in the ganglionated plexus (GP) [35], which primarily contains parasympathetic but also sympathetic neurons [36], considered to influence the sinus rate, atrial refractory period and atrioventricular conduction [37]. Most of the GP lie near the pulmonary vein ostia and left atrium junction [38, 39], where pulmonary vein isolation is operated. Therefore, inadvertent ablation of the GP is possible, which then contributes to the increase in post-ablation heart rate through parasympathetic denervation and could ultimately be relative to a lower recurrence rate of AF.

In this study, we demonstrated that the AHR in the preoperative sinus rhythm state in patients with PAF was negatively associated with the risk of postoperative AF recurrence, which various biological mechanisms can explain. Firstly, it was observed that patients with lower AHR had significantly larger LAD compared to those with higher AHR. This can be attributed to left atrial enlargement, which promotes electrical and anatomical remodeling of the left atrium and leads to the secretion of inflammatory factors, subsequent fibrosis, left atrial matrix remodeling [40], increased P-wave dispersion [41], prolongation of intra-atrial and inter-atrial conduction times [42], and significant atrioventricular block.All these changes increase sensitivity to AF. Secondly, maintaining sinus rhythm for at least three months after ablation is crucial for electrical and anatomical reverse remodeling of the left atrium. However, in patients with low preoperative AHR, the routine use of AAD becomes contraindicated, or the dosage is limited after ablation. This may result in difficulty maintaining sinus heart rate and delayed reverse remodeling of the left atrium, which can easily result in AF recurrence. Lastly, a low resting heart rate is associated with ANS activity or subclinical sinoatrial node dysfunction [29, 32]. On the one hand, the ANS activity is an important modulating factor in the perpetuation of AF [43]. Increased ANS activity shortens the duration of the action potential by increasing acetylcholine-dependent potassium current while also leading to calcium transients by increasing norepinephrine secretion [44, 45]. The above two factors jointly increase early post-depolarization potential, contributing to the formation of AF trigger potential [46] and subsequently increasing the recurrence rate of AF. Meanwhile, lower AHR could be an indicator of increased ANS activity, which may make successful GP ablation more difficult, while the addition of GP ablation has been confirmed to be related to reduced arrhythmia recurrence in PAF patients in a meta-analysis [47]. On the other hand, subclinical sinus node dysfunction is related to sinoatrial node dysfunction and age-related changes and fibrosis in the cardiac conduction system outside the atrial myocardium and sinoatrial node. These anatomical changes create a substrate for the development of AF. Additionally, the accompanying bradycardia further facilitates AF development by increasing the probability of atrial arrhythmias and dispersion of refractory periods [48].

Limitations: Firstly, this study was a retrospective cohort study conducted at a single center. The sample size was relatively small, and the follow-up period was short. Secondly, the multivariate logistic regression model included several potential confounding factors that could influence the development of AF. However, as with other epidemiological studies, residual confounding factors were still possible. For instance, our model did not fully adjust for the duration and severity of certain conditions, such as hypertension, diabetes, and blood pressure and blood sugar control. Moreover, previous studies have shown that less postoperative heart rate increases compared to preoperation may be associated with higher postoperative AF recurrence [24, 31, 33, 34]; we will incorporate postoperative heart rate change parameters in the future to explore the risk of AF recurrence and possible mechanisms. Furthermore, the relationship between left atrial size and AF recurrence has been proved by several studies. In contrast, this study stated that left atrial size had no significant correlation with the recurrence of AF; this result may be relevant to the small sample and less left atrial remodeling in patients with PAF. In future research, we will expand the samples’ quantity and refine the evaluation of left atrial by adding left atrial volume and left atrial strain parameters to better explore the relationship between left atrial and AF recurrence. Finally, the mechanism underlying the occurrence of low preoperative AHR and postoperative recurrence in AF patients is currently unknown. Therefore, large-scale, multicenter, prospective case–control trials are still required to establish the correlation and mechanism between preoperative AHR and postoperative recurrence in patients with PAF.

In summary, the correlation between preoperative AHR in sinus rhythm state and the likelihood of postoperative AF recurrence offers valuable insights for risk stratification and clinical management of AF. Moreover, it serves as scientific evidence supporting the adjustment of preoperative AAD, intraoperative additional ablation of GP, and the identification and early intervention of high-risk patients prone to postoperative recurrence. In the case of AF patients with a low preoperative AHR, it is necessary to administer AAD with caution and to perform additional ablation of GP during RFA.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

MX designed the study and carried out the study, data collection and analysis. XF contributed to acquisition and interpretation of data and drafted the manuscript. LY made substantial contributions to conception and design and revised the manuscript. ZY and YM designed part of the experiments. MG and JM collected the PAF patients. All authors reviewed the manuscript. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

This study was approved by the Ethics Committee of the Third Affiliated Hospital of Soochow University (2016TNo. 44). All patients or their families/legal guardians gave their written informed consent before they participated in the study.

This study was supported by Changzhou Health Commission Youth Project (QN202208) and Top Talent of Changzhou “The 14th Five-Year Plan” High-Level Health Talents Training Project (2022260).

The authors declare no conflict of interest.