A functional–anatomic mapping protocol for cardioneuroablation: A mechanistic case series

Abstract

Background

Radiofrequency catheter ablation of ganglionated plexi has been used for more than 2 decades as an alternative to pacemaker implantation in patients with functional bradycardia. Despite potential efficacy and a favorable safety profile, the optimal procedural strategy remains debated, particularly regarding the identification of critical targets and the need for unilateral vs biatrial ablation. Most centers perform cardioneuroablation (CNA) using combined left and right atrial access, although emerging evidence indicates that single-atrial approaches may be sufficient in selected cases.

Objective

This study aimed to develop a functional–anatomic mapping approach combining extracardiac vagal stimulation and endocardial high-frequency stimulation, repeatedly applied throughout the procedure, to reveal critical vagal pathways.

Methods

In this prospective mechanistic series, 5 consecutive patients with cardioinhibitory Vasovagal Syncope International Study 2B vasovagal syncope underwent CNA using the functional–anatomic protocol. Dynamic changes in responses to extracardiac vagal stimulation and high-frequency stimulation after lesion delivery were used to infer critical vagal connections to the sinoatrial and atrioventricular nodes.

Results

5 distinct functional profiles were identified, enabling individualized strategies: 3 patients underwent right atrial–only ablation, 1 had a single left atrial approach, and 1 underwent a biatrial procedure. All patients met the heart rate increment endpoint (>15%) and showed a significant standard deviation of normal-to-normal interval attenuation. No symptom recurrence was observed over a follow-up of 13.4 ± 3.2 months. Furthermore, functional mapping revealed asymmetrical vagal innervation patterns and interganglionated plexus connectivity influencing sinoatrial and atrioventricular modulation, which aided in tailoring the procedure.

Conclusion

This functional–anatomic methodology can be used to define ablation extent and procedural laterality, providing a framework to standardize CNA.

Graphical abstract

Key Findings.

• ▪Patient-specific functional mapping allowed tailored ablation: distinct vagal innervation patterns guided individualized strategies—3 patients required right atrial ablation, 1 left atrial approach, and 1 biatrial procedure—demonstrating heterogeneity in cardiac autonomic anatomy.
• ▪Effective modulation of cardiac nodes: all patients achieved a heart rate increase of >15% and a significant standard deviation of normal-to-normal interval reduction, with no recurrence of syncope over a mean follow-up of 13.4 ± 3.2 months.
• ▪Asymmetrical vagal innervation was revealed: left and right vagus nerves contributed differently to sinoatrial (SA) and atrioventricular (AV) node control, highlighting the importance of functional assessment over purely anatomic targeting.
• ▪Critical interganglionated plexus pathways were identified: connections such as left inferior ganglionated plexus (GP) to right inferior GP via the coronary sinus pathway for AV node control and left superior GP to right anterior GP for SA node control informed ablation extent and laterality decisions.
• ▪Feasibility of targeted, physiology-guided ablation: combined extracardiac vagal stimulation and endocardial high-frequency stimulation reliably mapped key pathways, enabling precise ablation while minimizing unnecessary lesions.

Introduction

It has been 20 years since radiofrequency (RF) catheter ablation of ganglionated plexi (GP) was first used to treat functional bradycardia as an alternative to pacemaker implantation.¹ Since then, variations of the technique have demonstrated potential efficacy and a favorable safety profile.^2,3 Nevertheless, issues regarding target identification and procedural laterality remain unresolved, limiting the widespread adoption of this procedure as a standard treatment.

The necessity of a biatrial approach, as opposed to a single-atrial procedure, is probably the most significant unresolved issue. Most centers perform cardioneuroablation (CNA) by targeting GPs with combined left and right atrial (RA) access.1, 2, 3, 4, 5, 6, 7, 8, 9, 10 However, some authors argue that ablation confined exclusively to the RA may be sufficient to prevent sinus pauses and functional atrioventricular (AV) block,11, 12, 13 whereas others have reported favorable outcomes with a restricted left atrial (LA) ablation approach.^14,15

Who is correct? Given the complexity and variability of the intrinsic cardiac autonomic network, these seemingly contradictory conclusions may all be valid, depending on the functional anatomy of cardiac innervation. Rather than identifying the main GPs as isolated anatomic domains and ablating them indiscriminately, a more precise approach involves mapping the functional connections both among GPs and between GPs and the effectors (sinoatrial and AV nodes).

This can be achieved by combining extracardiac and intracavitary stimulation to repeatedly evoke vagal responses throughout the procedure. Observing changes in these responses after ablating each targeted area allows inference of a personalized map of vagal pathways.

This study aimed to describe how to create a functional–anatomic map of cardiac vagal innervation during CNA procedures. This approach may help establish a more comprehensive and objective protocol for CNA, defining whether a unilateral or biatrial approach is necessary and, potentially, enabling better outcomes.

Methods

Study design and population

This was a prospective mechanistic case series designed as a proof-of-concept to evaluate a functional–anatomic mapping protocol for CNA.

5 consecutive patients diagnosed as having cardioinhibitory Vasovagal Syncope International Study 2B vasovagal syncope on tilt table test (TTT) and referred for CNA were treated using the functional mapping protocol. All patients demonstrated a positive response to atropine before the procedure. Holter monitoring was obtained within 1–2 weeks before the procedure to provide a baseline assessment and again within 24–48 hours after the procedure to evaluate the early effects of CNA and to allow comparison.

The study was approved by the institutional review board, and all patients provided a written informed consent for the procedure.

Extracardiac vagal stimulation

Before ablation, right and left extracardiac vagal stimulation (ECVS) was performed to register the pristine evoked response. As previously described,⁵ ECVS was performed with a decapolar steerable electrode catheter within the right and then left internal jugular vein at the level of the jugular foramen, guided by radiograph. Energy was delivered by using fixed stimulation parameters throughout the procedure (pulse duration 5 seconds; frequency 30 Hz; pulse width 50 μs; amplitude 0.5–1 V/kg). On each side, the stimulation catheter was positioned at the level of the jugular foramen, and minor positional adjustments were made to identify the site producing the most intense and reproducible vagal response. Once identified, this site and stimulation parameters were kept unchanged throughout the procedure. Baseline (“pristine”) responses were defined as preablation responses obtained under these standardized conditions and served as the reference for subsequent comparisons.

When necessary, the influence of ECVS on AV nodal conduction was assessed by concurrently delivering RA pacing at a fixed cycle length of 500 ms.

Target identification and high-frequency stimulation

Endocardial GP sites were identified based on presumed anatomy^{3,4,6,12,13,15} and on functional mapping. In the RA, the right anterior GP (RA GP) was considered to be located at the septal region of the atriocaval junction, and the right inferior (RI) GP in the posterior aspect of the coronary sinus ostium. In the LA, the RA GP can be reached at the upper septal region, and the RI GP near the right inferior pulmonary vein (PV) ostium. Before ablation, high-frequency stimulation (HFS) was systematically applied to these regions to elicit autonomic responses, with ≥10 applications per region, spaced 2–3 mm apart and covering an area of approximately 1–1.5 cm².

When an evoked autonomic response was observed, HFS was extended stepwise to adjacent sites until the responsive area was fully delineated by surrounding negative responses. HFS parameters were a pulse duration of 5 seconds, a frequency of 30 Hz, a pulse width of 50 μs, and an amplitude of 0.5–1 V/kg. An HFS-elicited sinus pause of >2 seconds and/or any AV block was considered a positive response.

Other (nonseptal) regions, such as the left superior (LS) GP (close to the LS PV ostium) and left inferior (LI) GP (close to the LI PV ostium), were considered as additional targets if local signal fragmentation or evoked responses to local HFS were observed.

Procedural protocol

RF pulses (40°C, 20–30 W) were delivered with a TactiFlex 3.5-mm tip irrigated Ablation Catheter SE (Abbott) or a Thermocool Smarttouch SF catheter (Biosense Webster) until the lesion size index value of 4.5–5.0 or a Surpoint value of 450–500 has been reached.

ECVS and local HFS were repeated after completing a cluster of RF applications within a given GP region, to reassess global vagal input. The procedure was deemed complete after RF pulses had been applied to all sites considered targets, a modified or suppressed response to ECVS had been achieved, and an increase in heart rate (HR) of >15% was observed. An atropine bolus test (0.04 mg/kg) was performed at the end of the procedure. Full methodological details and additional data are presented in the Supplemental Appendix.

A priori physiological assumptions

To accurately interpret the phenomena observed during each procedure and to develop the corresponding functional map, a few fundamental principles previously described^10,11,16, 17, 18, 19 were acknowledged and accepted a priori:

• 1.The superior GPs (RA GP and LS GP) predominantly innervate the sinoatrial (SA) node, whereas the inferior GPs (RI GP and LI GP) selectively innervate the AV node.
• 2.The left vagus nerve is the primary source to the left ganglia (LS GP and LI GP), whereas the right vagus nerve supplies the right ganglia (RA GP and RI GP).
• 3.Some neural pathways may connect the main GPs before proceeding to the SA and AV nodes, such as connections between the LS GP and RA GP before reaching the SA node and between the LS GP and RI GP before innervating the AV node.²⁰

A priori, patients 1–3 underwent an initial RA approach, whereas patients 4–5 underwent an initial LA approach. The initial chamber was not evidence mandated, given that there are currently no data supporting the superiority of starting in either atrium; therefore, the starting chamber was assigned for demonstration purposes. The study protocol did not mandate a priori biatrial mapping in all patients. Instead, mapping was intentionally tailored and initiated arbitrarily in 1 atrium, with extension to the contralateral chamber driven exclusively by the functional profile.

There is currently no universally accepted standard regarding the order of GP ablation during CNA. Because the primary objective of this study was to explore functional connections between specific GPs and their cardiac effectors, the sequence of ablation was intentionally varied across cases.

The research reported in this paper adhered to the Declaration of Helsinki guidelines.

Statistical analysis

A paired t test was used to compare Holter variable values before and after the procedure. Statistical significance was set at P < .05.

Case descriptions and functional maps

Patient 1: RA approach

A 56-year-old woman presented with recurrent syncope. Clinical and Holter characteristics are presented in Table 1 and Supplemental Table 1. She exhibited a sinus pause of 30.8 seconds at the 25th minute of the TTT.

Table 1.

Clinical and procedural data

PIN	Age/sex	Syncope episodes (12 mo before procedure)	AE (mm) / LVEF (%)	Syncope mechanism at TTT	Approach	Target identification method	RF (pulses, n/duration, s)	HR pre/post	WCL pre/post	Atropine,pre/post, increase (%)
1	56/F	3	38/71	Sinus pause (30.8 s)	RA	Anat + evok	22/480	76/92	420/310	92/92 (0)
2	57/F	3	36/63	Sinus pause (4.5 s)	RA	Anat + evok + fragm	23/512	53/75	720/460	75/96 (30.6)
3	22/F	4	34/64	Sinus pause (28.2 s)	RA	Anat + evok + fragm	31/663	53/85	540/410	85/85 (0)
4	44/F	2	36/60	Sinus pause (23 s)	LA	Anat + evok + fragm	24/529	66/73	480/410	73/73 (0)
5	41/F	3	35/61	AV block (31 s)	Biatrial	Anat + evok	30/660	68/78	480/400	78/78 (0)

AE = adverse event; anat = anatomy; AV = atrioventricular; evok = evoked response; F = female; fragm = fragmented potential; HR = heart rate; LA = left atrium; LVEF = left ventricular ejection fraction; PIN = patient identification number; RA = right atrium; RF = radiofrequency; TTT = tilt table test; WCL = Wenckebach cycle length.

Intervention: RA approach

Before ablation, right ECVS induced predominant AV block (3:1) with only minimal sinus slowing, whereas left ECVS triggered prolonged sinus pauses (10.3 seconds) and a high-degree AV block (12:1). These findings demonstrate that, from the outset, the left vagus nerve (red vectors) innervated both the SA and AV nodes, whereas the right vagus nerve (blue vectors) innervated predominantly the AV node (Figure 1A).

Figure 1.

Case 1. A: Functional–anatomic map before ablation. Vagal effects on the SA and AV nodes were semiquantitatively graded using an ordinal scale (3+ to 0+), reflecting the relative intensity of the response. B: The electroanatomic map of the right atrium identified small areas of fragmented potentials (clear areas) in the interatrial septum. Rounded areas represent the presumed anatomy of GP. C: Vagal evoked responses (green tags) were recorded at the proximal coronary sinus region. D: Ablation sites (red tags). E: Functional–anatomic map after ablation. AV = atrioventricular; CS = coronary sinus; IVC = inferior vena cava; L = left; LS = left superior; LI = left inferior; R = right; RA GP = right anterior ganglionated plexus; RI = right inferior; SA = sinoatrial; SVC = superior vena cava.

Signal fragmentation (clear areas) was found in small areas of the interatrial septum (Figure 1B). Endocardial HFS in the RA triggered evoked responses (Figure 1C) in the coronary sinus region (green tags).

RF pulses applied exclusively to the right side of the interatrial septum—12 pulses to the superior GP and 10 pulses to the inferior GP (Figure 1D)—resulted in an immediate increase in HR from 76 to 92 beats per minute (bpm) and a reduction in Wenckebach cycle length (WCL) from 420 to 310 ms. Evoked endocardial responses previously identified were eliminated.

Right and left ECVS no longer elicited sinus pauses or AV block (Figure 1E). At the end of the procedure, the atropine test did not produce any additional HR increase.

Case 1: Interpretation and outcome

• •The vagus nerves provided asymmetrical input to the cardiac nodes: right vagus nerve stimulation triggered a short AV block and only minimal sinus slowing, whereas the left vagus nerve strongly innervated both the SA and AV nodes.
• •Ablation of the RA GP and RI GP resulted in complete suppression of responses to both right and left ECVS, suggesting that innervation from the LS GP and LI GP either was of minor functional significance or occurred indirectly, likely via initial connections to the right-sided GPs. Therefore, in this patient, the RA GP and RI GP acted as final common pathways to the effectors (see Supplemental Figures 1 and 2 for electrogram tracing recordings throughout the procedure).
• •No syncope recurrences occurred after 19 months of follow-up. A repeat TTT showed attenuation of the cardioinhibitory response: a drop in HR was observed, but no sinus pauses or AV block were detected.

Patient 2: RA approach

A 57-year-old female with recurrent traumatic syncope was referred for CNA. Clinical and Holter characteristics are presented in Table 1 and Supplemental Table 1. A 4.5-second sinus pause associated with syncope occurred at the 19th minute of the TTT.

Intervention

Before ablation, right ECVS triggered an 8.4-second sinus pause and 9:1 AV block; left ECVS triggered a mild sinus pause (1.8 seconds) and 10:1 AV block, defining the initial functional map (Figure 2A). Sites of interest were identified by fragmented potentials (large clear area, Figure 2B), HFS-evoked responses (green tags, Figure 2C), and presumed anatomy.

Figure 2.

Case 2. A: Functional–anatomic map before ablation. B and C: Fragmented potential areas (clear areas) and high-frequency stimulation–evoked responses (green tags) were observed at the coronary sinus proximal segment. D: Ablation sites (red tags). E: Functional–anatomic map after ablation. Abbreviations as in Figure 1.

After ablation (RA GP 14 pulses; RI GP 9 pulses) (Figure 2D), the HR increased from 53 to 75 bpm, and WCL decreased from 720 to 460 ms. Full suppression of endocardial evoked responses (green tags) was observed. Right ECVS still triggered mild sinus bradycardia (maximum RR interval reduced from 8.4 to 1.6 seconds) and advanced AV block, whereas left ECVS elicited no responses (Figure 2E). The atropine test produced a slight increase in HR (from 75 to 96 bpm). Given that the autonomic state and the ECVS responses had been significantly modified, the procedure was concluded.

Case 2: Interpretation and outcome

• •Again, asymmetrical innervation was observed. In this instance, stimulation of the left vagus nerve elicited only a modest effect on the SA node, whereas right vagal stimulation produced a more pronounced sinus slowing. This indicates a relatively weaker left vagal connection to the SA node.
• •Postprocedure inspection indicated that RF pulses intended to ablate the RI GP were inadvertently delivered to the proximal coronary sinus. This likely disrupted the connection between the LI GP and the RI GP while sparing the body of the RI GP. This explains why left vagal input to the AV node was abolished, but right vagal stimulation still caused AV block. Therefore, the coronary sinus may carry neural fibers connecting the LI GP to the RI GP before reaching the AV node.
• •Similarly, ablation of the right aspect of the cavoatrial junction disrupted the connection between the LS GP and the RA GP without fully destroying the RA GP body (possibly owing to insufficient transmurality). As a result, right ECVS still caused mild sinus bradycardia, but left ECVS did not (see Supplemental Table Figures 3 and 4 for electrogram tracing recordings throughout the procedure).
• •No syncope recurrences occurred after 13 months of follow-up. A postprocedural TTT was negative. Holter recording data are presented in Table 1.

Patient 3: RA approach

A 22-year-old female experienced a 28.2-second sinus pause resulting in a syncopal episode at the 24th minute of the TTT and was referred for CNA. Clinical and Holter information are presented in Table 1 and Supplemental Table 1.

Intervention

Although designated to an RA approach, LA functional–anatomic mapping was also possible in this patient because a patent foramen ovale was present, allowing LA access without transseptal puncture. However, the ablation protocol was strictly adhered to and confined to the RA. Areas of fragmented potentials (Figure 3A and 3B) were detected in the posterior aspect of the cavoatrial junction (RA GP), posterior to the coronary sinus ostium (RI GP), and in the upper septal region of the LA. Endocardial HFS-evoked vagal responses in the proximal segment of the coronary sinus and in the septal aspect of the left interatrial septum (green tags, Figure 3A and 3B).

Figure 3.

Case 3. A and B: Electroanatomic maps of the right atrium (RA) (A, posterior view) and left atrium (B, anterior view) showing fragmented potential areas (clear areas) and local high-frequency stimulation–evoked response sites (green tags). C: Functional–anatomic map before ablation. D: Electroanatomic map of the RA with a restricted ablation of the proximal coronary sinus segment. E: Functional anatomy status at this point of the procedure. F: Electroanatomic map of the RA showing ablation of the RA GP and RI GP. G: Functional–anatomic map after ablation completed. Abbreviations as in Figure 1.

Before ablation, right ECVS evoked a 6.2-second sinus pause and 13:1 AV block, and left ECVS an 8.4-second sinus pause and 16:1 AV block. The initial functional map is presented in Figure 3C.

To test the hypothesis of a functional connection between the LI GP and the RI GP (raised in case 2), 3 RF pulses were initially applied only to the proximal coronary sinus segment (red tags, Figure 3D). After this restricted ablation, local evoked responses were abolished. Right and left ECVS were repeated and demonstrated that innervation from both sides to the SA node remained unchanged and still triggered long sinus pauses but left vagus nerve innervation to the AV node was abolished (Figure 3E).

Subsequently, RF pulses were delivered in the RA (Figure 3F), specifically at the cavoatrial junction (RA GP 15 pulses) and posterior to the coronary sinus ostium (RI GP 13 pulses), resulting in an HR increase from 53 to 85 bpm and a WCL reduction from 540 to 410 ms. After this second set of applications, neither right nor left ECVS produced any response (Figure 3G), the atropine test was negative, and the procedure was concluded.

Case 3: Interpretation and outcome

• •Targeted ablation of the proximal coronary sinus segment effectively eliminated the left vagus nerve response at the AV node, implying the presence of a functional vagal pathway connecting the LI GP to the RI GP via the coronary sinus.
• •Subsequent RF applications at the anatomic sites of the RI GP and RA GP abolished all responses to right and left ECVS, indicating that the right GPs acted as final pathways to the nodes in this patient (see Supplemental Figures 5–7 for electrogram tracing recordings throughout the procedure).
• •No syncope recurrences were observed 11 months after the procedure.

Patient 4: LA approach

A 44-year-old woman with recurrent syncope presented a 23-second sinus pause resulting in a syncopal episode at the 29th minute of the TTT. Clinical and Holter characteristics are presented in Table 1 and Supplemental Table 1.

Intervention

Endocardial HFS of the LA evoked vagal responses only in the LS GP area and in the upper septum (green dots, Figure 4A and 4B). A small area of signal fragmentation (clear area) was observed in the septum (Figure 4B). Before ablation, right ECVS evoked a 7.9-second sinus pause and 10:1 AV block, and left ECVS a 7.2-second sinus pause and 12:1 AV block (see initial functional map in Figure 4C).

Figure 4.

Case 4. A and B: Electroanatomic maps of the left atrium (LA) showing small areas of signal fragmentation in the upper septum only (clear areas) and sites with high-frequency stimulation–evoked responses in upper septal (RA GP) and posterior wall (LS GP) regions (green tags). C: Functional–anatomic map before ablation. D: Electroanatomic map of the LA with a restricted ablation of the LS GP region. E: Functional anatomy status at this point of the procedure. F: Electroanatomic map of the LA showing additional ablation of the RA GP. G: Functional–anatomic map after ablation completed. Abbreviations as in Figure 1.

In this case, ablation was started at the LS GP (Figure 4D, 8 RF pulses). After this first step, local evoked responses were abolished. Right ECVS no longer produced sinus pauses (but only some residual sinus slowing) and evoked an attenuated AV block (AV block reduced from 10:1 to 3:1), and left ECVS also resulted in mild sinus slowing with no sinus pauses and a milder AV block (AV block attenuated from 12:1 to 2:1). The functional map at this step is depicted in Figure 4E.

Next, the RA GP was targeted through the LA with 16 RF pulses (Figure 4F). After this second step, local responses were suppressed and neither right nor left ECVS elicited any sinus pauses or AV block (Figure 4G). HR increased from 66 to 73 bpm, and WCL decreased from 480 to 410 ms. The atropine test did not produce any further increase in HR.

Case 4: Interpretation and outcome

• •The LS GP served as the terminal vagal pathway to the SA node, given that its ablation completely eliminated all SA responses from both left and right ECVS. This finding suggests that the RA GP did not connect directly with the SA node and implies the existence of a connection between the RA GP and the LS GP before their convergence on the SA node.
• •Subsequent RF application to the RA GP abolished vagal innervation from both vagus nerves to the AV node, indicating that the inferior GPs were dependent on, and functioned downstream of, the superior GPs (see Supplemental Figures 8–10 for electrogram tracing recordings throughout the procedure).
• •No syncope or presyncope recurrences were observed 12 months after the procedure. A TTT repeated 3 months after ablation was normal. The 24-hour Holter data before and after the procedure are presented in Table 1.

Patient 5: LA, then biatrial approach

A 41-year-old woman presented with a 31-second advanced AV block at the 22nd minute of orthostasis during TTT. Clinical and Holter data are presented in Table 1 and Supplemental Table 1.

Intervention

Endocardial HFS of the LA evoked vagal responses at the LA roof and at the septum (green dots, Figure 5A and 5B).

Figure 5.

Case 5. A and B: Electroanatomic maps of the left atrium (LA) showing sites with high-frequency stimulation–evoked responses in septal (RA GP) and LA roof (LS GP) regions (green tags). C: Functional–anatomic map before ablation. D: Electroanatomic map of the LA with a restricted ablation of the LS GP region (red tags). E: Functional anatomy status at this point of the procedure. F: Electroanatomic map of the LA showing additional ablation of the RA GP. G: Functional–anatomic map after ablation of LS GP and RA GP. MV = mitral valve; Other abbreviations as in Figure 1.

Before ablation, right ECVS evoked a 3.9-second sinus pause and 2:1 AV block, and left ECVS produced an 8.1-second sinus pause and 12:1 AV block (see initial functional map in Figure 5C).

Ablation was initiated at the LS GP site with 10 RF pulses (Figure 5D). Although this effectively suppressed local evoked responses, it did not result in significant physiological changes: right ECVS still evoked sinus pauses lasting 2.3 seconds and 2:1 AV block, whereas left ECVS induced an 8.6-second sinus pause and 10:1 AV block. The functional map at this stage is presented in Figure 5E.

Then, RA GP ablation followed (Figure 5F). This step resulted in selective modulation of SA node vagal input: right ECVS triggered no sinus pauses but still evoked 3:1 AV block, and left ECVS also had no effect on the SA node and triggered 9:1 AV block (Figure 5G).

At this stage, only selective denervation of the SA node had been achieved, and therefore, it was decided to proceed with the procedure and target the RI GP using a combined biatrial approach. Electroanatomic mapping of the RA was performed, demonstrating normal endocardial signals and evoked responses exclusively in the proximal region of the coronary sinus and posterior to its ostium (marked with green tags, Figure 6A). Identification of the RI GP was based on a combination of HFS-evoked responses and presumed anatomy. Ablation was then performed at the targeted RI GP site, with a total of 11 RF applications delivered (Figure 6B).

Figure 6.

Case 5(biatrial approach). A and B: Electroanatomic map of the right atrium: posterior view showing absence of scar tissue and sites of evoked responses (A) and posteroseptal view illustrating radiofrequency ablation sites (B). C: Functional anatomy status at the end of the procedure. Abbreviations as in Figure 1.

After this third step, local evoked responses were eliminated, and neither right nor left ECVS elicited sinus pauses or AV block (Figure 6C). HR increased from 68 to 78 bpm, and WCL decreased from 480 to 400 ms. The atropine test was negative, and the procedure was concluded.

Case 5: Interpretation and outcome

• •This was another example of asymmetrical innervation, with relatively weak input from the right vagus nerve to both SA and AV nodes.
• •Left vagal innervation to the SA node traveled through the RA GP instead of the LS GP. As a result, ablation of the LS GP had no effect, but ablation of the RA GP abolished responses from both vagus nerves at the SA node. For this reason, a biatrial procedure was required in this case.
• •The RI GP functioned as the final pathway to the AV node. Vagal connections originating from the LI GP and projecting to the AV node via the RI GP—likely traversing the coronary sinus—were successfully interrupted with RF ablation at the RI GP site (see Supplemental Figures 11–14 for electrogram tracing recordings throughout the procedure).
• •No episodes of syncope occurred during the 12-month follow-up. The TTT performed 3 months after ablation was normal. Holter monitoring data before and after the procedure are presented in Table 1.

Discussion

The present work was designed as a mechanistic, proof-of-concept case series aimed at illustrating how functional–anatomic mapping can be used to identify patient-specific vagal pathways during CNA. No acute or late procedural complications were observed in this case series. However, rather than evaluating clinical efficacy or safety, the primary objective was to demonstrate the feasibility of the protocol.

The data presented outline a methodology for CNA that integrates functional criteria with topographical landmarks to guide the procedure. This approach traces the vagal efferent pathways from extrinsic components (vagus nerves), through the atrial intrinsic units (the GPs), to the final effectors: the SA and AV nodes.

To achieve this, ECVS (traditionally used merely as an endpoint measure) and HFS (usually used solely to localize GPs) were leveraged as complementary tools. This combined strategy enabled the definition of critical functional pathways and the tailoring of the ablation procedure. To the best of our knowledge, this approach has not been previously used for this purpose.

Although the vagal intrinsic components are diffusely distributed across the atrial territory,^20,21 the functional pathways engaged to innervate each node remain distinctly site specific and discrete. To accurately locate these pathways, it is essential to introduce causality into the analysis. Without establishing causal relationships, the mere localization of anatomic structures is insufficient to understand their role in the mechanism of syncope. Therefore, if stimulation of 1 vagus nerve—such as the right vagus—elicits a response (for example, AV block) and ablation of a specific site attenuates this response, this supports the existence of a functional pathway linking the stimulated vagus nerve, the ablated site, and the downstream effector, namely the AV node.

This proof-of-concept series offers a strategy to optimize outcomes while avoiding unnecessarily extensive ablation. Several previous studies have explored variations of CNA, including both simplified and anatomically guided approaches. Aksu and colleagues²² described a simplified CNA technique targeting key GPs to treat reflex syncope, functional AV block, and sinus node dysfunction, demonstrating favorable outcomes with a streamlined procedural strategy in selected patients. Their work highlighted the potential for focused ablation without complete biatrial targeting in carefully selected cases. Similarly, Hu et al¹⁵ emphasized the role of the RA GP as a primary target in CNA, reporting that modulation of this region can yield significant autonomic effects and potentially reduce procedural complexity. These reports support the notion that targeted, limited ablation strategies may be effective when guided by appropriate physiological criteria. However, other authors have acknowledged heterogeneity in vagal innervation and suggested that more extensive ablation, including biatrial approaches, may be necessary in some patients to achieve durable vagal denervation.²³

The functional–anatomic mapping protocol presented in this series helps reconcile these seemingly divergent strategies. Importantly, our findings do not support a uniform ablation strategy; instead, they emphasize that procedural laterality and ablation extent should be guided by functional mapping rather than anatomic assumptions alone. Varying the initial chamber across cases was intentional to illustrate how the same functional–anatomic mapping framework can uncover interindividual vagal pathway configurations that may not be apparent under a single standardized chamber-first strategy.

Previous studies have used repeated ECVS to investigate dynamic changes in vagal responses,⁸ but this approach was not primarily designed to tailor procedural methodology, nor was it integrated with endocardial HFS, which constitutes a critical component of the functional mapping protocol.

In the 5 procedures described here, the functional mapping protocol was used consistently and no symptom recurrence was observed after a follow-up of 13.4 ± 3.2 months. The fact that all patients met the HR increment endpoint (>15%) and exhibited a significant reduction in standard deviation of normal-to-normal interval after ablation (Table 1 and Supplemental Table 1), yet displayed markedly different functional profiles, underscores the importance of precisely characterizing functional anatomy.

This approach revealed several often-overlooked physiological principles (Table 2), including:

• •Asymmetrical innervation patterns of the vagus nerves
• •Evidence that the coronary sinus carries functional connections between the LI GP and the RI GP located upstream of the AV node
• •The presence of functional connectivity between the LS GP and the RA GP (possibly following the course of the sinus node artery²⁴) upstream of the SA node

Table 2.

Summary of functional mapping findings, ablation strategy, and outcomes

PIN	Age/sex	Baseline ECVS pattern	Functional final common pathways	Ablation approach	Targeted GP sites	HR increase (%)	Post-CNA ECVS response	Follow-up (months)	Outcome
1	56/F	Asymmetrical Left vagus → SA + AV; right vagus → AV mostly	RA GP and RI GP ablation blocked LS GP → RA GP and LI GP → RI GP connections, respectively.	RA only	RA GP, RI GP	+21	No SA or AV response	19	No syncope; attenuated TTT response
2	57/F	Asymmetrical Right vagus → SA + AV; left vagus → AV mostly	Partial RA GP ablation disrupted LS GP→ RA GP connection, and proximal CS ablation disrupted LI GP→ RI GP connections.	RA only	RA GP, RI GP (proximal CS)	+42	Mild SA response to right ECVS only	13	No syncope; negative TTT
3	22/F	Bilateral vagus → SA + AV	Proximal CS ablation disrupted LI GP→ RI GP connections. (pathway interruption) RA GP ablation blocked LS GP → RA GP connection.	RA only	Proximal CS, RA GP, RI GP	+60	No SA or AV response	11	No syncope
4	44/F	Bilateral vagus → SA + AV	LS GP ablation blocked connections between RA GP → LS GP and LS GP→ LI GP;RA GP ablation interrupted RA GP→ RI GP connection.	LA only	LS GP, RA GP (via LA)	+11	No SA or AV response	12	No syncope or presyncope
5	41/F	Asymmetrical Left vagus dominant → SA + AV	LS GP ablation had no effect. RA GP ablation blocked LS GP → RA GP connections; RI GP ablation blocked LI GP→ RI GP connections.	Biatrial	LS GP, RA GP, RI GP	+15	No SA or AV response	12	No syncope; normal TTT

AV = atrioventricular; CNA = cardioneuroablation; CS = coronary sinus; ECVS = extracardiac vagal stimulation; F = female; GP = ganglionated plexus; HR = heart rate; LA = left atrium; LI GP = left inferior ganglionated plexus; LS GP = left superior ganglionated plexus; PIN = patient identification number; RA = right atrium; RA GP = right anterior ganglionated plexus; RI = right inferior; RI GP = right inferior ganglionated plexus; SA = sinoatrial; TTT = tilt table test.

It is also worth noting that CNA may have a role in managing other vagally mediated arrhythmias, such as atrial fibrillation.^25,26 In fact, atrial fibrillation–triggering PV automaticity—analogous to the SA and AV nodes—can be considered an additional effector. Incorporating functional mapping protocols into CNA techniques and adapting them to target other relevant effectors may enhance its utility across a broader range of clinical scenarios.

Procedural risks

Although no procedure-related complications were observed in this small series, CNA inherently shares the procedural risks associated with RF catheter ablation. In addition, previously published series have reported an approximately 8.3% incidence of sinus tachycardia after CNA, as well as a 2%–3% risk of sinus node artery occlusion.³

The functional–anatomic mapping strategy described in this study may help mitigate some of these risks by limiting ablation to physiologically relevant targets and avoiding empirical, extensive lesion delivery.

Limitations

The small sample size and relatively short follow-up preclude any definitive conclusions regarding clinical efficacy or long-term safety. Accordingly, the findings should be interpreted as hypothesis generating and mechanistic, rather than outcome driven. Larger, multicenter sham-controlled studies will be necessary to determine whether this functional–anatomic mapping strategy can be standardized and broadly adopted.

The ECVS technique is required to accomplish the functional–anatomic protocol. However, it has been demonstrated that ECVS may not be feasible in a minority of cases (∼10%) owing to anatomic variations,²⁷ and this technical limitation must be acknowledged.

Finally, the extent of ablation was guided by coverage of functionally identified regions rather than by iterative testing after each lesion; therefore, a smaller number of lesions might have been sufficient in some cases.

Conclusion

A functional–anatomic methodology integrating ECVS and HFS can be used to define ablation extent and procedural laterality in CNA, providing a framework to standardize the procedure. This mechanistic case series highlights the heterogeneity of cardiac vagal innervation and supports individualized CNA strategies based on functional mapping.

Disclosures

The authors have no conflicts of interest to disclose.