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. 2025 Jul 4;25(1):461.
doi: 10.1186/s12872-025-04924-0.

Role of electrograms recorded from mini electrodes in catheter ablation of atrioventricular nodal reentrant tachycardia: a retrospective study

Ungjeong Do  1   2 , Gi-Byoung Nam  3 , Min Soo Cho  4 , Jun Kim  4 , Kee-Joon Choi  4
Affiliations

Role of electrograms recorded from mini electrodes in catheter ablation of atrioventricular nodal reentrant tachycardia: a retrospective study

Ungjeong Do et al. BMC Cardiovasc Disord. .

Abstract

Background: Data on the role of electrograms (EGMs) recorded from mini electrodes (MEs) of the IntellaTip MiFi ablation catheter (Boston Scientific) are limited. We evaluated the additional value of MEs during slow-pathway ablation in atrioventricular nodal reentrant tachycardia (AVNRT).

Methods: Consecutive patients with AVNRT who underwent slow-pathway ablation using the MiFi catheter were included. A combined electroanatomical approach was used to identify the target site. During ablation, operators were blinded to the ME EGMs, and ME EGMs recorded immediately before the first radiofrequency (RF) application were evaluated retrospectively.

Results: Altogether, 61 patients with typical (n = 58), atypical (n = 2), or both (n = 1) of AVNRT were included. Successful slow-pathway ablation or modification was achieved in all patients, and 33 patients (54.1%) demonstrated a junctional rhythm during the first RF application. Atrial EGMs (> 0.05 mV) at the MEs were observed immediately before the first RF in 34 patients (55.7%). A significant association was identified between the presence of atrial EGMs in MEs and the occurrence of junctional rhythm (odds ratio 13.5, P < 0.001). The positive and negative predictive values of atrial EGMs in the MEs for junctional rhythm induction during the first RF were 79.4% (27/34) and 77.8% (21/27), respectively.

Conclusions: Atrial EGMs recorded from MEs before the first RF application could help identify effective ablation sites during slow-pathway ablation. Junctional rhythm was more frequently induced at sites with discernible ME signals, whereas sites without measurable ME EGMs despite adequate bipolar signals were less effective. These findings are limited to the initial RF application and warrant further validation.

Keywords: Atrioventricular nodal reentrant tachycardia; Catheter ablation; Mini electrodes.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: This retrospective study was reviewed and approved by the Institutional Review Board of Asan Medical Center, Seoul, Korea (approval number: 2024 − 0790; approval date: 19 Jun 2024), which waived the requirement for informed consent due to the retrospective nature of the study. All methods were performed in accordance with the relevant guidelines and regulations, including the Declaration of Helsinki. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Ablation catheter used for mapping and ablation. A The IntellaTip MiFi open-irrigated ablation catheter (Boston Scientific, Boston, MA, USA) has three mini electrodes (MEs) at the tip of the catheter, which are 1.3 mm distant from the tip of the catheter. This 7.5-Fr ablation catheter has a 4.5-mm-sized tip electrode and three ring electrodes. B The MEs (marked with arrowheads), surrounded by an insulating ring, are positioned radially with the same inter-electrode distance. A schematic image demonstrating the location of the MEs (displayed with three gray-colored small rounds) of the ablation catheter distal tip is inserted in the right upper corner
Fig. 2
Fig. 2
Representative cases with and without atrial electrograms in mini electrodes. Mini electrode (mini 12, 23, and 31) electrograms (EGMs) of four patients immediately before the first radiofrequency ablation. In the first three patients (A–C), atrial EGMs on the mini electrodes (MEs) were observed, whereas none was detected in the fourth patient (D). An inducible junctional rhythm was observed in the first three patients, but not in the fourth patient. In the first two patients (A, B), the atrial EGM of MEs demonstrated a double component, which was an initial low-frequency, low-amplitude component, followed by a high-frequency, high-amplitude component. The pattern of the double component is only evident in MEs and is not definite in bipolar electrodes (BEs), as demonstrated in panel (B). In the next patient (C), a high-frequency component followed by a low-frequency pattern was observed in the MEs and BEs. Panel D presents the case with good BE EGMs but without definite atrial EGM in the MEs. Only small (<0.05 mV) and delayed noise-like EGMs were visible in the ME, demonstrating a discrepancy between BE and ME. The gain settings of the MEs were the same, and the sweep speed was set to 100 mm/s
Fig. 3
Fig. 3
Dot plots with box plot overlays presenting voltage of mini-electrode bipolar electrogram. The amplitudes of mini-electrode (ME) electrogram (EGM) before the first radiofrequency application were compared. The mean amplitude values are 0.19 ± 0.11 mV and 0.11 ± 0.06 mV in the case with and without inducible junctional rhythm, respectively. The amplitude of the ME EGM was significantly different between the groups (P = 0.035). Each dot represents a single patient’s voltage in the EGM. Solid line = median
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