The study included patients 18 to 80 years of age with AT undergoing de novo or redo CA procedure using the integrated AcQMap-RMN system. The inclusion criteria were documented AT on 12-lead ECG, Holter monitoring, or previous CA procedure with documented recurrences. This inclusion criterion allowed to enter patients planned for de novo, post-PVI and post-MAZE procedures, too. For further subgroup analysis, the study population was divided into three groups based on the utilized mapping modality during ablation procedures as follows: group 1, SPM performed exclusively, group 2, AMPM performed exclusively, group 3, both SPM and AMPM performed. Further, patients were divided into groups based on arrhythmia mechanism, localization and type of procedure. Additionally, the study population was compared to historical procedural and outcome data of RMN guided procedures performed with sequential 3D mapping (CARTO control group). The institutional medical ethics committee approved the data collection and analysis for this study and concluded that it did not fall under the Medical Research Involving Human Subjects Act (SERCA-2, MEC-2021–0299). The authors declare that all data that support the findings of this study are available from the corresponding author upon reasonable request.

The primary hypothesis of this study was that the AcQMap-RMN integration is safe and provides high acute and long-term success with low recurrence rates. Furthermore, we hypothesized that the novel AMPM feature offers improvements in source identification during CA procedures, leading to improved outcomes by offering high resolution in propagation maps of electrical activation. The primary endpoints of this study were safety, characterized by intra- and post-procedural complications and efficacy, characterized by acute procedural success. The secondary endpoint was procedural effectiveness characterized by recurrence during a 12-month follow-up and assessing the differences in procedure characteristics and outcome between the study groups.

Major complications were defined as any procedure-related adverse event, which were life threatening, requiring significant surgical intervention and prolonged hospital stay or resulted in death. Minor complications were defined as procedure-related adverse events, which resulted in minimal transient impairment of a body function or damage to a body structure, or which did not require any intervention or further therapy. We defined de novo procedures as first-time CA of AT, redo procedures as repeat procedure after one or more failed initial procedure or after documented recurrence. Total procedure time was defined as the time passed from first venous puncture until the removal of sheaths. Acute success was defined as non-inducibility of the treated arrhythmia. Recurrence was defined as any documented AT regardless of its duration. We included short-lived ATs ranging from premature atrial contractions (PACs) to 124 beats documented on 24 h-72 h Holter monitoring, when sequential mapping was unlikely possible. Short-lived ATs in our center are specifically planned with the AcQMap system.

Baseline demographic, clinical characteristics and procedural data from patients were collected from our prospective database using the electronic health records (HiX version 6.1) and analyzed in accordance with the hospital institutional review board policies. We collected safety data such as acute intra-procedural and post-procedural adverse events. The following demographic and procedural data were collected: age, sex, height, weight, BMI, date of procedure, procedure duration time, number of applications, application duration, radiation dose, rhythm at the end of procedure. Further, we collected and analyzed clinical data, such as left atrial dimension, left ventricular ejection fraction, comorbidities, and antiarrhythmic medication. Mapping data were collected from the AcQMap workstation.

The AcQMap system is a noncontact charge density-based mapping technology that combines ultrasound-based 3D endocardial anatomy reconstructions with high-resolution propagation history maps of electrical activation and allows visualization of global atrial activation. The 48-pole noncontact mapping catheter (AcQMap catheter, Acutus Medical, Carlsbad, CA) has six splines, each spline incorporating eight biopotential electrodes and eight ultrasound transducers. The basket catheter is manually controlled in the mapped atrium. The ultrasound-generated 3D endocardial chamber surface reconstruction corresponds to the end-diastolic size and shape of the atrium and it is created within 2–3 min. Unipolar intracardiac potentials are sensed from the biopotential electrodes of the basket catheter and are processed by an inverse solution to derive the dipolar charge sources at the endocardial surface. The waves of activation are displayed across the 3D anatomy reconstruction through time as high-resolution propagation history maps. The noncontact modality of the AcQMap system allows for two modalities of mapping: single position mapping (SPM) and aggregated multiposition noncontact mapping (AMPM). SPM can be applied as single-beat analysis to map short non-sustained ATs or PACs (Fig. 1 and 2). While AMPM enables mapping of both non-sustained and sustained repetitive atrial rhythms (Video 1). After hovering the basket catheter around the cardiac chamber, multiple noncontact catheter positions are time aligned based on coronary sinus (CS) activation (Fig. 3). The utilized mapping modality was chosen at the discretion of the operator if the arrhythmia lasted long enough. In cases of short-lived ATs and PACs only SPM was possible.

– EGMs and propagation history map (SPM). Spread EGM signals from 48 electrodes during single position mapping are shown in panel A. Stacked EGM signals are shown in panel B. Single position isochronal map is shown in panel C

– SPM for brief episodes of AT. Patient with short-runs of AT present on ECG (on the left). Single beat single position map was acquired (right) and identified a focal firing source nearby the base of right atrial appendage (RAA)

– SPM versus AMPM. Two separate cases of AT, both mapped with SPM and AMPM, too. In Panel A the SPM shows the exit of the isthmus, the propagation in CCW direction and no retrograde conduction because of the line, which contains the isthmus. However, the signal of the isthmus itself (conduction through the isthmus) is only visible on the AMPM. In panel B the SPM isochronal map shows less detail (circle), compared to the AMPM on the right, the yellow arrow shows a more detailed localization

All procedures were performed using the Niobe ES robotic system (Stereotaxis, St. Louis, MO, USA). An initial standard diagnostic EP study was performed for every patient. After the presence of slow-pathway or accessory pathway mediated reentrant arrhythmias was excluded, attempts of AT induction were made including atrial programmed extrastimulation and burst atrial pacing. If this was unsuccessful or when AT did not occur spontaneously, isoproterenol was administered. The AcQMap mapping catheter was introduced via a 12.4F deflectable sheath (AcQGuide sheath, Acutus Medical, Carlsbad, CA). After reconstructing the endocardial anatomical surface, we overlaid high resolution charge density based maps of electrical activation using the AcQMap mapping system (Video 2). After identification of the chamber of origin, mechanism and the exact location of the substrate, ablation was performed using the MagnoFlush (Medfact, Germany) ablation catheter. The following settings were used: 45-50W (posterior wall—anterior wall, respectively), 17 mL/min flow rate, maximum 43℃. Intravenous heparin was administered for anticoagulation, guided by activated clotting time (> 350 s for LA and > 300 s for RA). We interpreted propagation history maps, identified atrial activation patterns, and performed targeted ablation. A standard of 30 min waiting time was applied to all procedures. After the procedures, patients were continuously monitored, and pre-discharge echocardiography was performed in all patients in order to exclude post-procedural complications.

A follow-up visit at 3 months after the procedure was planned for every patient. In cases where there was no recurrence at the follow-up visit, the patients were discharged and were re-evaluated 12 months after the ablation. The post-PVI/post-MAZE AT patients were followed up based on the PVI follow-up protocol with a routine 6- and 12-month hospital visit. During the follow-up visits 24-h (3 and 6 months) and 7-day Holter recordings (12 months) were analyzed for documentation of recurrent arrhythmias. Patients with recurrences were considered for repeated CA procedure or were identified as ablation failures.

Categorical variables were described as percentages, whereas continuous variables were expressed as mean ± SD for normally distributed data or as medians (interquartile range /IQR) for skewed data. Groups were compared using the student t test, the Mann–Whitney U test, and ANOVA analysis, respectively. Statistical analysis was performed using the SPSS (version 25.0) software.