Electrophysiological characteristics of non-pulmonary vein triggers excluding origins from the superior vena cava and left atrial posterior wall: Lessons from the self-reference mapping technique.

BACKGROUND: The detailed electrophysiological characteristics of atrial fibrillation (AF) initiating non-pulmonary vein (PV) triggers excluding origins from the superior vena cava (SVC) and left atrial posterior wall (LAPW) (Non-PV-SVC-LAPW triggers) remain unclear. This study aimed to clarify the detailed electrophysiological characteristics of non-PV-SVC-LAPW triggers.
METHODS: Among 446 AF ablation procedures at 2 institutions, patients with reproducible AF initiating non-PV-SVC-LAPW triggers were retrospectively enrolled. The trigger origin was mapped using the self-reference mapping technique. The following electrophysiological parameters were evaluated: the voltage during sinus rhythm and at the onset of AF at the earliest activation site, coupling interval of the trigger between the prior sinus rhythm and AF trigger, and voltage change ratio defined as the trigger voltage at the onset of AF divided by the sinus voltage.
RESULTS: Detailed electrophysiological data were obtained at 28 triggers in 21 patients. The median trigger voltage at the onset of AF was 0.16mV and median trigger coupling interval 182msec. Normal sinus voltages (≧0.5mV) were observed at 16 triggers and low voltages (<0.5mV) at 12 triggers. The voltage change ratio was significantly lower for the normal sinus voltage than low sinus voltage (0.20 vs. 0.60, p = 0.002). The trigger coupling intervals were comparable between the normal sinus voltage and low sinus voltage (170ms vs. 185ms, p = 0.353).
CONCLUSIONS: The trigger voltage at the onset of AF was low, regardless of whether the sinus voltage of the trigger was preserved or low.

Introduction

Catheter ablation of atrial fibrillation (AF) has emerged as an effective treatment option and is currently an indication for symptomatic patients with drug refractory AF [1]. Pulmonary vein (PV) isolation is a cornerstone strategy to control AF by ablation [2] and additional substrate ablation failed to show superiority in non-paroxysmal AF patients [3]. Successful elimination of non-PV triggers is still important and contributes to better outcomes in paroxysmal [4] and non-paroxysmal patients [5]. Non-PV triggers from the superior vena cava (SVC) or left atrial posterior wall (LAPW) were usually treated with an isolation strategy. Non-PV triggers excluding origins from the SVC and LAPW (Non-PV-SVC-LAPW triggers) were considered to be related to worse clinical outcomes [6] because those triggers require precise mapping to eliminate them and are known to be difficult to eliminate [7].

Mapping of origins of non-PV triggers is usually performed using a 3-dimentional electro-anatomical mapping system. The techniques for the provocation or localization of non-PV triggers have been previously reported [8], but the detailed electrophysiological data has not been fully evaluated. We previously reported a new technique called self-reference mapping to map origins of non-PV triggers [9, 10]. This technique does not require any other fixed reference catheters and uses the previous earliest activation site as a reference. The operator repeatedly moves a PentaRay NAV (PEN) catheter (Biosense Webster Diamond Bar, CA, USA) to the earliest signal creating a new reference each time to map the non-PV triggers. This method has the advantage of a single-beat analysis, which creates a high-density map of non-PV triggers [11], and the detailed electrophysiological data could be analyzed. Therefore, the purpose of this study was to clarify the detailed electrophysiological characteristics of non-PV-SVC-LAPW triggers.

Methods

Study population

This study was a sub-analysis of the previously reported paper [10], in which the short- and long-term clinical outcomes of the self-reference mapping technique were shown. The study population has previously been reported [10]. In brief, we investigated 446 AF ablation procedures in 431 patients at Osaka Rosai Hospital and JCHO Hoshigaoka Medical Center from January 2017 to March 2019. Patients who had reproducible non-PV-SVC-LAPW triggers were enrolled. In this study, the detailed electrophysiological characteristics were analyzed while synchronizing the log reports of an electro-anatomic mapping system (CARTO 3, Biosense Webster Diamond Bar, CA, USA) and simultaneously recorded polygraph (LABSYSTEMTM PRO EP Recording System, Boston Scientific, Marlborough, MA, USA). All patients provided written informed consent for the AF ablation procedures and the use of their clinical data. The research protocol complied with the ethical guidelines of the Declaration of Helsinki in 1975. The institutional ethics committee of each site approved the study.

AF ablation

All antiarrhythmic drugs were discontinued for at least 5 half-lives prior to the catheter ablation. Amiodarone was not used in this study group. Electrophysiological studies were performed under sedation with propofol and dexmedetomidine. Invasive arterial blood pressure monitoring, oxygen saturation measurements, and surface 12-lead ECGs were monitored during the entire procedure. The transseptal puncture was guided by intracardiac echocardiography to access to the left atrium (LA). All patients underwent a bilateral PV isolation using open irrigation contact catheters (ThermoCool Smart-Touch SF, Biosense Webster, Diamond Bar, CA, USA). The radiofrequency ablation power settings were 20–30 W for the posterior LA and 25–35 W for the anterior LA. After the PV isolation, the induction of non-PV triggers was performed. Additional ablation, including linear or an SVC ablation, was at the operator’s discretion.

Non-PV trigger induction and self-reference mapping of non-PV triggers

Our definition of non-PV triggers was AF initiating triggers. Frequent atrial premature complexes that did not induce AF were not defined as non-PV triggers. Non-PV triggers were induced with a continuous infusion of isoproterenol (ISP, 1–10 μg / min), rapid infusion of ISP (2–20 μg), and/ or adenosine triphosphate (ATP, 40-60mg). If AF was not initiated by the ATP and ISP infusions, sustained AF was induced by programmed atrial burst pacing. Non-PV triggers after restoration of sinus rhythm by intracardiac cardioversion were investigated. Reproducible non-PV triggers were mapped using the following self-reference mapping technique. The non-PV trigger reproducibility was defined by 2 criteria: 1) identical intracardiac atrial electrogram sequences and 2) less than a 10 msec fluctuation in the coupling interval between the prior sinus beat and non-PV trigger.

The details of the self-reference mapping have been previously reported [9, 10]. A summary of this technique is as follows. First, the operator was advised to place a catheter from the lateral right atrium, septal right atrium to the SVC, and coronary sinus. After interpreting the trigger activation sequence, the operator placed the PEN catheter at the earliest possible activation site. Using the PEN multipolar catheter, the operator annotated the earliest site of local activation and placed a reference tag there. The multipolar catheter was then moved to the reference tag and the process was repeated. Finally, we identified a cluster of tags. The origin of the non-PV trigger must be in the area of the previous cluster. Local activation around the oldest activation site was evaluated by high density mapping. Radiofrequency ablation was applied with open irrigation contact force catheters. The power setting was 20–35 W. The endpoint of a successful ablation was the non-inducibility of AF.

Electrophysiological analysis of non-PV triggers

The electrophysiological data at the earliest activation site of AF triggers obtained by the PEN catheter were analyzed. Therefore, the electrogram was obtained by 1-mm electrodes with 2-mm interelectrode spacing. Bipolar electrograms were filtered between 30 and 500 Hz. According to the previous report [12], we evaluated the peak-to-peak electrogram amplitude and defined a low voltage as <0.5mV and normal voltage as ≧0.5mV. The bipolar voltages at the trigger origins were evaluated during sinus rhythm and at the onset of AF. The sinus voltage was assessed at the last sinus rhythm, just before AF initiation. Triggers were divided into 2 groups (normal sinus voltage group and low sinus voltage group) according to the voltage during sinus rhythm. The voltage change ratio was calculated as follows: (voltage change ratio) = (trigger voltage at the onset of AF) / (Sinus voltage of triggers). The trigger coupling interval was evaluated from the onset of the previous sinus beat to the onset of the trigger. An electrophysiological analysis of non-PV triggers is shown in Fig 1. Non-PV triggers from the SVC or LAPW were excluded from this study.

Fig 1

Illustration of the measurement of the electrophysiological characteristics at the earliest activation site.

The electrogram was obtained by a PentaRay NAV catheter (Biosense Webster Diamond Bar, CA, USA) with 1-mm electrodes with 2-mm interelectrode spacing. The bipolar electrograms were filtered between 30 and 500 Hz. At the earliest activation site of the AF initiating trigger, the peak-to-peak electrogram amplitudes during sinus rhythm and at the onset of AF were measured. The trigger coupling interval was evaluated from the onset of the previous sinus beat to the onset of the trigger. CS, coronary sinus; PEN, PentaRay NAV catheter; RA, right atrium; SVC, superior vena cava.

Statistical analysis

The continuous variables were presented as the median [interquartile range], and categorical variables as exact numbers and percentages. Continuous variables were compared using a Mann-Whitney U test and Wilcoxon single-rank test. Categorical variables were performed using a Fisher’s exact test. The correlation of the continuous variables was assessed using the Pearson correlation coefficient analysis. A P <0.05 was considered statistically significant in all analyzes. The statistical analyses were performed using a commercially available statistical package (JMP Pro14, SAS Institute, Inc., Cary, North Carolina, USA).

Results

Clinical characteristics, results of the self-reference mapping, and trigger ablation

A total of 32 non-PV-SVC-LAPW triggers occurred in 23 patients (5%). Polygraph back up data was not available in 1 patient. It was difficult to confirm the earliest trigger site in 1 patient with the synchronization between the CARTO system and polygraph data. The remaining 28 triggers in 21 patients, in whom detailed electrophysiological data were obtained, were enrolled in this study. The patient clinical characteristics are summarized in Table 1. The median age was 69, and there were 15 males (71%), 11 with paroxysmal AF (52%), 5 with re-do sessions (24%), 2 with non-ischemic cardiomyopathy (10%), and 1 with ischemic cardiomyopathy (5%). The median left ventricular ejection fraction was 67% and left atrial diameter 42mm.

Table 1

Patients characteristics and results of self-reference mapping and ablation.

	Values
Patients characteristics	21 patients
Age	69 [61, 75]
Male	15 (71)
Paroxysmal/ Persistent (<12 months)/ long-standing (>12 months)	11/6/4 (52/29/19)
Session (1st/ 2nd/ 3rd)	16/3/2 (76/14/10)
Hypertension	12 (57)
Diabetic mellitus	3 (14)
Heart failure	6 (29)
Non-ischemic cardiomyopathy	2 (10)
Ischemic cardiomyopathy	1 (5)
Chronic kidney disease	4 (19)
Left ventricular ejection fraction (%)	67 [59, 72]
Left atrial diameter (mm)	42 [39, 47]
β blocker	7 (33)
ACEI or ARB	8 (38)
Estimated glomerular filtration rate (ml/min/1.73m2)	66.5 [59.3, 80.9]
BNP (pg/ml)	89.5 [30.2, 152.9]
Self-reference mapping results	21 patients, 28 triggers
Number of mapped triggers
N = 1	16 (76)
N = 2	3 (14)
N = 3	2 (10)
Number of mapping points to detect the origin of the trigger	8 [4.3, 9.8]
Number of the cardioversion to detect the origin of the trigger	8 [5.8, 10]
Mapping time to detect the origin of a trigger (min)	8.9 [2.6, 14.9]
Distribution of triggers
Right atrium	16 (57)
Left atrium	12 (43)
Trigger ablation results	28 triggers
Successful trigger elimination	28 (100)
Number of radiofrequency applications for the trigger ablation	9 [3, 12]
Total radiofrequency time for the trigger ablation (min)	4.3 [2.6, 6.0]
Complication	0 (0)

Data are given as the n (%) or median [quartile 1, 3]. ACEI = angiotensin converting enzyme inhibitor; ARB = angiotensin Ⅱ receptor blocker

Multiple non-PV-SVC-LAPW triggers were observed in 5 patients (24%). The median number of self-reference mapping points to detect the trigger origin was 8 [4.3, 9.8]. The median number of the cardioversion to detect the trigger origin was 8 [5.8, 10]. The median mapping time for the self-reference mapping to detect the trigger origin was 8.9 min. The trigger origin was in the right atrium for 16 triggers (57%) and left atrium for 12 (43%). The distribution of non-PV-SVC-LAPW triggers were shown in Fig 2. All non-PV-SVC-LAPW triggers were eliminated by radiofrequency ablation. The median number of radiofrequency applications and time per each trigger were 9 times and 4.3 min, respectively. No major complications related to the AF ablation procedure were observed. The self-reference mapping and trigger ablation results are summarized in Table 1. Among 23 patients, 5 patients had AF/AT recurrences. Three had re-do session, and none of them had recurrences of the non-PV-SVC-LAPW triggers, which was targeted at the index procedure.

Fig 2

The distribution of non-PV-SVC-LAPW triggers.

Blue tag indicates normal sinus voltage. Orange tag indicates low sinus voltage. CS = coronary sinus; PV = pulmonary vein; LA = left atrium; RA = right atrium; LAA = left atrial appendage.

Electrophysiological characteristics of non-PV triggers

The median sinus voltage at the trigger origins was 0.58mV. A low voltage (<0.5mV) was observed at 12 triggers (43%). The median trigger voltage at the onset of AF was 0.16mV. A low voltage at the onset of AF (<0.5mV) was observed in 27 triggers (96%). The median voltage change ratio was 0.35. The median trigger coupling interval between the prior sinus beat and AF initiation was 182msec. A trigger coupling interval of <200 msec was observed at 18 triggers (64%). The electrophysiological characteristics of the non-PV-SVC-LAPW triggers are summarized in Table 2. The trigger voltage at the onset of AF was significantly more reduced than the sinus voltage (p = 0.005) (Fig 3A). The voltage change ratio was significantly correlated to the trigger coupling interval (R = 0.44, β = 0.44, p = 0.0189) (Fig 3B), whereas the sinus and trigger voltages were not correlated to the trigger interval (p = 0.211 and 0.954, respectively, Fig 3C and 3D).

Table 2

Electrophysiological characteristics of non-PV triggers.

	Values
Sinus voltage at the trigger origin (mV)	0.58 [0.22, 1.02]
Sinus voltage at the trigger origin <0.5mV	12 (43)
Trigger voltage at the onset of AF (mV)	0.16 [0.11, 0.23]
Trigger voltage at the onset of AF <0.5mV	27 (96)
Voltage change ratio	0.35 [0.15, 0.62]
Trigger coupling interval (msec)	182 [153, 222]
Trigger coupling interval <200msec	18 (64%)

Data are given as the n (%) or median [quartile1, 3]. AF = atrial fibrillation

Fig 3

Left panel: Voltage change from the sinus beat to the onset of AF. The trigger voltage at the onset of AF was significantly more reduced than the sinus voltage (0.16 mV vs. 0.58mV, p = 0.005). Right panel: The relationship between the voltage change ratio and trigger coupling interval. The voltage change ratio was significantly correlated to the trigger coupling interval (R = 0.44, β = 0.44, p = 0.0189).

Non-centrifugal activation at the onset of AF

An activation with a preferential like conduction turning around was observed at 1 trigger (Fig 4). The earliest potential recorded by electrode pair PEN15-16 did not conduct to PEN13-14, which was on the same spline of the PEN catheter, but instead conducted to PEN 9–10 and then PEN 13–14 was activated. The surrounding atrial muscle, where the other PEN electrodes were placed, was not activated. The earliest potential was a discrete pre-potential and a single point ablation (started with 25W and up to 30W, 22sec) rendered the AF non-inducible.

Fig 4

Left panel: The intracardiac electrograms during the onset of AF by the non-pulmonary vein trigger. The first beat was sinus rhythm. The earliest potential of the non-pulmonary vein trigger was recorded by PEN15-16 (white arrowhead). The next activated potential was recorded by PEN 9–10 and then PEN 13–14 was activated. Right panel: The location of the PEN. The white arrows show the activation sequence of the non-pulmonary vein trigger. AP, anterior-posterior view; CS, coronary sinus; PEN, PentaRay® NAV catheter.

Difference in the electrophysiological characteristics between the normal sinus voltage and low sinus voltage groups

The normal sinus voltage group consisted of 16 triggers and low sinus voltage group 12 triggers. The sinus voltage at the trigger origin was higher in the normal sinus voltage group than low sinus voltage group (0.86mv vs. 0.20mV, p<0.001). The distribution of the right or left atrium were comparable between 2 groups (p = 0.459). The trigger voltage at the onset of the AF in the normal sinus voltage group was as low as that in the low sinus voltage group (0.17mV vs. 0.13mV, p = 0.137). The voltage change ratio was significantly lower in the normal sinus voltage group than low sinus voltage group (0.20 vs. 0.60, p = 0.002). The trigger coupling interval between the prior sinus beat and AF initiation was comparable between the 2 groups (170ms vs. 185ms, p = 0.353). The number of mapping points to detect the origin of a trigger (8 times vs. 8 times, p = 0.833) and mapping time (8.9 min vs. 8.2 min, p = 0.944) were comparable between the 2 groups. The number of radiofrequency applications for a trigger (8 times vs. 10 times, p = 0.457) and the total ablation time for a trigger (5.4 min vs. 3.7 min, p = 0.624) were comparable between the 2 groups. These results are summarized in Table 3 and Fig 5.

Table 3

Differences in the electrophysiological characteristics between a normal voltage and low voltage during sinus rhythm.

	Normal Voltage during Sinus Rhythm (n = 16 triggers)	Low Voltage during Sinus Rhythm (n = 12 triggers)	P value
Sinus voltage at the trigger origin (mV)	0.86 [0.64, 1.35]	0.20 [0.17, 0.38]	<0.001
Right atrium/ left atrium	8 / 8	8 / 4	0.459
Trigger voltage at the onset of the AF (mV)	0.17 [0.11, 0.35]	0.13 [0.09, 0.21]	0.137
Trigger voltage at the onset of the AF <0.5mV	15 (94)	12 (100)	1.000
Voltage change ratio	0.20 [0.09, 0.39]	0.60 [0.33, 1.04]	0.002
Trigger coupling interval (msec)	170 [149, 216]	185 [153, 263]	0.353
Trigger coupling interval <200msec	11 (69)	7 (58)	0.698
Number of mappings to detect the origin of a trigger	8 [5, 9]	8 [4, 20]	0.833
Mapping time to detect the origin of a trigger (min)	8.9 [2.3, 14.9]	8.2 [3.4, 14.4]	0.944
Number of radiofrequency applications for the trigger ablation	8 [2, 12]	10 [4, 12]	0.457
Total radiofrequency time for the trigger ablation (min)	5.4 [2.7, 7.1]	3.7 [2.6, 5.2]	0.624

Data are given as the n (%) or median [quartile1, 3]. AF = atrial fibrillation

Fig 5

Difference in the electrophysiological characteristics between the normal sinus voltage and low sinus voltage groups.

Discussion

Major findings

Our study was the first to describe the detailed electrophysiological characteristics of the non-PV-SVC-LAPW triggers at the successful ablation sites. The major findings in our study were 1) the trigger voltage at the onset of AF was low (median 0.16mV), 2) the coupling interval of the trigger of the non-PV-SVC-LAPW triggers was median 182 msec, and 3) the voltage change ratio was significantly lower in the normal sinus voltage group than low sinus voltage group (0.20 vs. 0.60, p = 0.002).

Trigger voltage at the onset of the initiation of AF

The trigger voltage at the onset of AF was low (median 0.16mV), even though those electrograms were obtained by a multi-electrode PEN catheter with 1-mm electrodes and a 2-mm interelectrode spacing. Small and closely spaced electrodes are considered to provide a higher mapping resolution and to identify distinct potentials in low voltage areas in both the atria [13] and ventricles [14] as compared to a larger tip ablation catheter. The self-reference mapping technique uses a PEN multi-electrode catheter to cover a wide area as well as possible to detect any small electrograms at the onset of AF. That concept would relate to good results of a complete elimination of reproducible non-PV-SVC-LAPW triggers. Satisfactory long-term clinical success rates after the non-PV-SVC-LAPW trigger ablation based on the self-reference mapping have already been reported [10] in the same population of this analysis. After the self-reference mapping based non-PV-SVC-LAPW trigger ablation, the AF free survival at 1 year was 82.6%. Three patients who received additional ablation procedures for recurrent AF had late acquired non-PV triggers and the non-PV triggers ablated during the previous procedure have not recurred.

We previously reported a possible limitation of this self-reference mapping technique in patients after excessive atrial substrate ablation, because excessive ablation would affect the conduction pattern, and the atrial tissue would not conduct centrifugally [9]. However, in this study we could find a non-centrifugal preferential like turning around activation using the self-reference mapping technique. We think the ability to detect low voltage potentials with the small and closely spaced electrodes contributed to this result.

The non-concentric centrifugal activation pattern of PV triggers was previously described using a 64-pole basket catheter [15]. A blocked wavefront introduced a unidirectional conduction and reentrant circuit in the PV. This report would be accordant with our finding of a preferential like turning around activation at the onset of the AF in the non-PV-SVC-LAPW triggers. Moreover, this non-concentric centrifugal activation would result in difficulty in eliminating non-PV triggers [6, 7] and clinicians should consider the possibility of a preferential like turning around activation with non-PV-SVC-LAPW triggers.

Coupling interval of the AF triggers

Not all premature atrial complexes induced AF. A short coupling interval trigger can introduce conduction block and contribute to a reentrant circuit. Since reentry is considered to be one of the mechanisms of AF [16], it is reasonable that a short coupling interval trigger can induce AF. Kanda et al. reported that AF inducible ectopy (n = 77) has a short coupling interval (mean coupling interval: 201 msec) and the main origin of the ectopy is the pulmonary veins (n = 74, 96%) [17]. Wang et al. reported that a shorter coupling interval of the P waves in AF initiates premature atrial complexes more than non-AF initiation premature atrial complexes [18]. Their AF initiation triggers were from the PVs and SVC. In our study, the P wave overlapped with the QRS complex or T wave because of a high dose of isoproterenol needed to induce the trigger. Therefore, the P wave interval was not optimal to evaluate in our population. To the best of our knowledge, this is the first study to describe a coupling interval of non-PV-SVC-LAPW triggers.

Triggers from normal voltages and low voltages during sinus rhythm

There were some possible explanations for the reasons why the voltage change ratio differed between the normal sinus voltage and low sinus voltage groups. First, during the sinus rhythm, the trigger myocardium depolarizes simultaneously with the surrounding myocardium by the propagation from the sinus node. Therefore, the total current at the trigger reflects the simultaneous depolarization of both the trigger myocardium and the surrounding myocardium. However, at the onset of AF, the trigger myocardium depolarizes at first and could only depolarize the neighboring cells according to the source-sink relationship [19], then the total current recorded at the origin becomes low. Second, our evaluation of the voltage was the sum of the surrounding tissues around an electrode. If damaged low voltage tissue was masked by healthy high voltage tissue during the sinus voltage, the voltage obtained by an electrode was high. If AF initiating triggers occurred from damaged tissue as in the low sinus voltage group, a small potential would precede the other potentials. According to the above-described mechanisms, the voltage change ratio was lower in the normal sinus voltage group than low sinus voltage group. Third, the mechanism of the AF initiating triggers differed. Because the target of our study was reproducible triggers with isoproterenol, the possible mechanisms were reentry and triggered activity [16]. Low voltage areas are known to be related to a reentry mechanism in the ventricular tachycardia field [20, 21] and reentry mechanisms are also described for premature ventricular complexes [22]. Triggered activity initiates arrhythmias in the absence of structural heart disease with catecholamine dependency. Depolarization occurs before full repolarization of the fibers, termed early afterdepolarization, and the fibers arise from a reduced level of the membrane potential and exhibit a reduced voltage [16]. Therefore, the voltage change ratio was lower in the normal sinus voltage group with a triggered activity mechanism than in the low sinus voltage group with a reentry mechanism. However, it was difficult to determine which mechanism initiated AF in the normal sinus voltage and low sinus voltage areas, because pacing maneuvers such as entrainment were not possible during AF.

Clinical implications

Our study demonstrated the detailed electrophysiological characteristics of the non-PV-SVC-LAPW triggers. The triggers at the onset had a low voltage and short coupling interval. The trigger voltage at the onset of AF was low, regardless of whether the sinus voltage of the trigger was preserved or low. Therefore, electrophysiologists should pay attention not to miss small electrograms. Our results of the trigger coupling interval (median 182msec) would be one of the helpful targets for finding the earliest activation site.

Limitations

There were limitations to this study. First, we evaluated the electrophysiological characteristics at the earliest activation site as a trigger origin. There was the possibility that we could not find an earlier activated site. However, we could eliminate all of the triggers with a limited number of radiofrequency applications according to the self-reference mapping results. This result would support our mapping quality. Second, the number of non-PV-SVC-LAPW triggers included in this study was small. Limited number of triggers may have affected the result that no triggers from the left atrial appendage or vein of Marshall were observed. However, the low incidence (0.3%) of the left atrial appendage triggers in 7129 patients has been reported [23] and this result was consistent with our data. Third, the electrophysiological characteristics of the non-PV-SVC-LAPW triggers were not compared to other AF triggers, such as triggers from PV, SVC or LAPW. Our strategy to eliminate these triggers were isolation, and the detailed electrophysiological data were not obtained. Forth, we did not create whole voltage map of the right and left atrium. Therefore, assessment of the voltage other than the non-PV-SVC-LAPW trigger origin was possibly not accurate. However, the voltage assessment at the non-PV-SVC-LAPW trigger must be accurate because this mapping provided high density map around the origin and in fact non-PV-SVC-LAPW triggers were all eliminated by the RF application in a small area. Fifth, the unipolar signals were not recorded during the procedure and not assessed in this study. Finally, there is a possibility of AF initiating triggers induced by the mapping catheter. However, to reduce this possibility, the non-PV trigger reproducibility was robustly assessed, comparing the atrial sequences and trigger coupling interval fluctuation, which was permitted only less than 10 msec.

Conclusion

The trigger voltage at the onset of AF was low, regardless of whether the sinus voltage of the trigger was preserved or low.

Dataset of this study.

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4 Nov 2021

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Additional Editor Comments:

Before sending to external reviewers, please clarify several points:

1. How did the authors ensure that PVs were not associated with the AF initiations? Did the authors place PV catheters during determination of the AF origin?

2. How could the authors draw 3D-maps during the initiation of AFs? Did the author also use non-contact mapping to identify the origin (i.e., snap shots)? I think it is difficult to draw 3D-maps during initiation (i.e., only one beat).

3. Did the authors check voltage maps around the origin of AF? In Fig 1, the signal amplitudes at PEN15-16 keep changing. How were the unipolar signals at the origin of AF?

4. If the authors believe these AFs were not associated with PVs, why did the authors isolate PVs?

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28 Nov 2021

Response to Editor/Reviewer

We appreciate your great advice for making our manuscript more sophisticated. We provided our responses to the reviewer’s comments in a blue non-bold font as follows. We hope this revision process has remedied all of your concerns with the original manuscript (OM). The changes and corrections of the OM are shown in a highlighted text in the revised manuscript (RM). We hope our manuscript will be accepted for publication with this version.

Editor Comments

1. How did the authors ensure that PVs were not associated with the AF initiations? Did the authors place PV catheters during determination of the AF origin?

→Thank you for your comment. Before AF induction, we performed PV isolation. Moreover, if the earliest activation site was near the PV, we placed a catheter inside the PV isolation line and checked whether PV isolation remained.

2. How could the authors draw 3D-maps during the initiation of AFs? Did the author also use non-contact mapping to identify the origin (i.e., snap shots)? I think it is difficult to draw 3D-maps during initiation (i.e., only one beat).

→Thank you for your comment. I completely agree with your opinion. We used the self-reference mapping technique, reported in Reference #10. In this technique, we don’t draw an activation map. We place a tag at the earliest activation site among a multi-electrodes catheter, and using the earliest activation site as a reference, we move the multi-electrodes catheter to find earlier activation site as shown in the following figure. This figure was reported in Reference #10 and contained in "Response to Reviewers" file.

3. Did the authors check voltage maps around the origin of AF? In Fig 1, the signal amplitudes at PEN15-16 keep changing. How were the unipolar signals at the origin of AF?

→Thank you for your comment. We did not make voltage maps. However, as shown in “Limitations” section, the voltage assessment at the non-PV-SVC-LAPW trigger must be accurate because this mapping provided high density map around the origin and in fact non-PV-SVC-LAPW triggers were all eliminated by the RF application in a small area.

As you kindly pointed out, voltage maps were not able to obtain during AF storm, non-regular sinus rhythm, like Fig1. Therefore, we evaluated the sinus voltage just before AF initiation. The unipolar voltage was not recorded during the procedure.

According to your suggestion, we added the following sentences.

Page 8, Line 9-10

“The sinus voltage was assessed at the last sinus rhythm, just before AF initiation.”

Page 18, Line 9-7

“Fifth, the unipolar signals were not recorded during the procedure and not assessed in this study.”

4. If the authors believe these AFs were not associated with PVs, why did the authors isolate PVs?

→Thank you for your comment. According to the guideline (2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation), PV isolation is the most important first step to treat AF with ablation. Therefore, we performed PV isolation before AF induction in all cases.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

5 Jan 2022

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PLOS ONE

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Reviewers' comments:

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Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

Reviewer #3: (No Response)

**********

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The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

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Reviewer #2: Partly

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

Reviewer #3: I Don't Know

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors examined the coupling interval and the voltage of the non-PV-SVC-LAPW triggers initiating AF and compared the voltage of them with that of the sinus rhythm. I think this study is interesting. However several issues should be clarified.

1. The authors concluded that Non-PV-SVC-LAPW triggers had a short coupling interval (Page2, Line18). Compared with what was the coupling interval of the AF triggers short? Since it is obvious that the coupling interval of the AF trigger is shorter than the cycle length of the sinus rhythm, the coupling interval of the AF trigger should be compared with those of atrial premature beats not initiating AF that were observed in the 21 patients.

2. The authors described the self-reference mapping technique (Page6, Line4). However, I think that the triggers originating from certain locations such as the CS, region near the tricuspid annulus are cumbersome to map using the PEN catheter alone. Were all the non-PV triggers able to be mapped using the PEN catheter alone without ablation catheter?

3. The authors found that the median number of self-reference mapping points to detect the trigger origin was 8 (Page8, Line12). Was external or internal electrical cardioversion used to restore the sinus rhythm during the mapping? What is the median number of the cardioversion needed to detect the non-PV trigger origin in each patient?

4. The authors showed the activation like preferential conduction (Page9, Line 13). Was the PEN catheter located at the right atrial septum (near the fossa ovalis)? It looks like that the earliest small potential was followed by the large sharp potential at Pen 15-16. The earliest small potential may be caused by ectopy from the LA septum. Was the electrogram of the LA septum simultaneously recorded using the ablation catheter during the mapping?

Reviewer #2: This is a sub-study of their previous report that showed clinical outcomes of their unique technique called self-reference mapping. In the present study, the authors evaluated the electrophysiological characteristics of the AF triggers, excluding origins from the PV, SVC, and LA posterior wall (non-PV-SVC-LAPW).

The authors showed that the non-PV-SVC-LAPW triggers had a short coupling interval and the voltage at the onset of AF was low regardless of the voltage during sinus rhythm.

I found the manuscript to be insightful and well-written. The authors adequately responded to the comments of the previous reviewer. Here, I would like to raise just one but critical issue.

The authors speculated two possible explanations regarding the mechanisms of the voltage change of the trigger site in terms of the voltage during sinus rhythm. They speculated that damaged low voltage tissue might be masked by healthy high voltage tissue during the sinus voltage. I think there were no evidence to support this hypothesis because they did not create whole voltage map and compare the voltage between the trigger and the other intact area.

On the other hand, the authors also presented that the voltage at the onset of AF was consistently low regardless of the voltage during sinus rhythm (Table 3, 0.17 vs. 0.13 mV, p=0.137).

The source-sink relationship could also be the reason for the low voltage at the onset of AF. During the sinus rhythm, the trigger myocardium depolarizes simultaneously with the surrounding myocardium by the propagation from the sinus node. Therefore, the total current at the trigger reflects the simultaneous depolarization of both the trigger myocardium and the surrounding myocardium. However, at the onset of AF, the trigger myocardium depolarizes at first and could only depolarize the neighboring cells, then the total current recorded at the origin becomes low.

I would like to recommend the authors to check the review by Dr. Peter Spector (Circ Arrhythm Electrophysiol. 2013;6:655-661) and consider incorporating this possible mechanism into the discussion.

Reviewer #3: Authors described the electrophysiological characteristics of non-PV trigger excluding the triggers from left atrial posterior wall (LAPW) and superior vena cava (SVC) using the self-reference mapping technique. Thirty-two non-PV-SVC-LAPW triggers were documented in 23 out of 446 patients (5%), and 28 triggers were evaluated in this study. Authors found 1) the trigger voltage at the onset of AF was low, and 2) coupling interval from the non-PV-SVC-LAPW was short. Non-PV-SVC-LAPW trigger appeared from not only the low voltage area but also normal voltage area. Non-PV-SVC-LAPW origin trigger are difficult to map the origin accurately and their electrophysiological characteristics are not well understood. Overall, the manuscript was well written and some findings were very informative to the reader. However, reviewer has some questions and comments.

Major comments

1. Authors divided the non-PV-SVC-LAPW triggers into 2 groups according to the voltage during sinus rhythm. The voltage change ratio was lower in the group with normal voltage during sinus rhythm than the group with low voltage during sinus rhythm. This finding is natural because the voltage of trigger was comparable between 2 groups and authors defined the group according to the voltage during sinus rhythm. What is the difference of electrophysiological significance of the voltage change ratio compared to the voltage during sinus rhythm at the part of the triggers?

2. Authors showed the relationship between the voltage change ratio and trigger coupling interval in Figure 3 right panel. Please create and analyze the diagrams of the relationship between the voltage at the trigger part during sinus rhythm and trigger coupling interval, and the relationship between the voltage of trigger and coupling interval.

3. Please show the outcome of the patients in this study after the procedure. If redo-procedures were performed in recurrent cases, please show the electrophysiological finding of redo-procedure.

Minor comments

1. Authors defined the non-PV trigger as AF initiating triggers and mapped average 8 times to detect the origin of the trigger. That’s means authors required the cardioversion at least average 8 times. Please show the number of cardioversion which authors performed.

2. Please mention the potential of AF initiating triggers induced by the mapping catheter.

**********

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Reviewer #2: No

Reviewer #3: No

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20 Jan 2022

Response to Reviewer #1

We appreciate your great advice for making our manuscript more sophisticated. We provided our responses to the reviewer’s comments in a blue non-bold font as follows. We hope this revision process has remedied all of your concerns with the original manuscript (OM). The changes and corrections of the OM are shown in a highlighted text in the revised manuscript (RM). We hope our manuscript will be accepted for publication with this version.

Reviewer #1: The authors examined the coupling interval and the voltage of the non-PV-SVC-LAPW triggers initiating AF and compared the voltage of them with that of the sinus rhythm. I think this study is interesting. However, several issues should be clarified.

1. The authors concluded that Non-PV-SVC-LAPW triggers had a short coupling interval (Page2, Line18). Compared with what was the coupling interval of the AF triggers short? Since it is obvious that the coupling interval of the AF trigger is shorter than the cycle length of the sinus rhythm, the coupling interval of the AF trigger should be compared with those of atrial premature beats not initiating AF that were observed in the 21 patients.

→Thank you for your comment. I totally agree with your comment. I should have used “short” comparing to something. As you suggested, we should have compared coupling interval with the non-AF initiating PACs. But we did not map the origin (earliest activation site) of the non-AF initiating PACs. Therefore, it is not possible to compare coupling interval of the AF initiating triggers and the non-AF initiating PACs. We deleted the sentence “Non-PV-SVC-LAPW triggers had a short coupling interval” from the “Conclusions” (Page2, Line18, Page 18, Line 12 in the OM)　and other pages (Page 13, Line 2, Page 15, Line 2, Line 12, Page 17, Line 6 in the OM).

2. The authors described the self-reference mapping technique (Page6, Line4). However, I think that the triggers originating from certain locations such as the CS, region near the tricuspid annulus are cumbersome to map using the PEN catheter alone. Were all the non-PV triggers able to be mapped using the PEN catheter alone without ablation catheter?

→Thank you for your great comment. It is an important point to do the self-reference mapping. As shown in “Methods/ Non-PV trigger Induction and Self-reference Mapping of non-PV triggers” (Page7, Line11-13), the first step of the mapping is to speculate the earliest activation site by interpreting the atrial sequence of the fixed catheters at the lateral RA, septal RA-SVC and CS. When there were multiple possible earliest activation sites, we compared them using the PEN and ablation catheter or else as shown below figure (Reference #8, Matsunaga-Lee Y, et al. Int J Cardiol 2020; 321: 81-87). After these steps, the last step to find the earliest activation site was performed using the PEN in all cases, including the origins from the CS and near the tricuspid annulus.

3. The authors found that the median number of self-reference mapping points to detect the trigger origin was 8 (Page8, Line12). Was external or internal electrical cardioversion used to restore the sinus rhythm during the mapping? What is the median number of the cardioversion needed to detect the non-PV trigger origin in each patient?

→Thank you for your comment. As you mentioned, we used internal electrical cardioversion to restore sinus during AF trigger mapping. The number of the cardioversion was similar to the number of the mapping, but slightly different because in PAF patients, AF terminated spontaneously. In non-paroxysmal AF patients, they were almost same. According to your comment, we added the following description in “Result” and changed Table1 and Supplemental Table (dataset of this study) to include the information of the cardioversion.

Page 8, line 12-13 in the RM

“The median number of the cardioversion to detect the trigger origin was 8 [5.8, 10].”

Table 1

Self-reference mapping results 21 patients, 28 triggers

Number of mapped triggers

N = 1 16 (76)

N = 2 3 (14)

N = 3 2 (10)

Number of mapping points to detect the origin of the trigger 8 [4.3, 9.8]

Number of the cardioversion to detect the origin of the trigger 8 [5.8, 10]

Mapping time to detect the origin of a trigger (min) 8.9 [2.6, 14.9]

Distribution of triggers

Right atrium 16 (57)

Left atrium 12 (43)

4. The authors showed the activation like preferential conduction (Page9, Line 13). Was the PEN catheter located at the right atrial septum (near the fossa ovalis)? It looks like that the earliest small potential was followed by the large sharp potential at Pen 15-16. The earliest small potential may be caused by ectopy from the LA septum. Was the electrogram of the LA septum simultaneously recorded using the ablation catheter during the mapping?

→Thank you for your comment. The PEN was located at the RA septum near sinus venosus area, not near the fossa ovalis (FO). However, intracardiac echocardiography was not used to mark the FO. Before locating PEN at this position, we compared the LA and RA septum and found that the RA was earlier activated than the LA. The result that the only single-point RF from the RA side rendered AF non-inducible also supported that the trigger origin was from the RA.

Response to Reviewer #2

We appreciate your great advice for making our manuscript more sophisticated. We provided our responses to the reviewer’s comments in a blue non-bold font as follows. We hope this revision process has remedied all of your concerns with the original manuscript (OM). The changes and corrections of the OM are shown in a highlighted text in the revised manuscript (RM). We hope our manuscript will be accepted for publication with this version.

Reviewer #2: This is a sub-study of their previous report that showed clinical outcomes of their unique technique called self-reference mapping. In the present study, the authors evaluated the electrophysiological characteristics of the AF triggers, excluding origins from the PV, SVC, and LA posterior wall (non-PV-SVC-LAPW).

The authors showed that the non-PV-SVC-LAPW triggers had a short coupling interval and the voltage at the onset of AF was low regardless of the voltage during sinus rhythm.

I found the manuscript to be insightful and well-written. The authors adequately responded to the comments of the previous reviewer. Here, I would like to raise just one but critical issue.

The authors speculated two possible explanations regarding the mechanisms of the voltage change of the trigger site in terms of the voltage during sinus rhythm. They speculated that damaged low voltage tissue might be masked by healthy high voltage tissue during the sinus voltage. I think there were no evidence to support this hypothesis because they did not create whole voltage map and compare the voltage between the trigger and the other intact area.

On the other hand, the authors also presented that the voltage at the onset of AF was consistently low regardless of the voltage during sinus rhythm (Table 3, 0.17 vs. 0.13 mV, p=0.137).

The source-sink relationship could also be the reason for the low voltage at the onset of AF. During the sinus rhythm, the trigger myocardium depolarizes simultaneously with the surrounding myocardium by the propagation from the sinus node. Therefore, the total current at the trigger reflects the simultaneous depolarization of both the trigger myocardium and the surrounding myocardium. However, at the onset of AF, the trigger myocardium depolarizes at first and could only depolarize the neighboring cells, then the total current recorded at the origin becomes low.

I would like to recommend the authors to check the review by Dr. Peter Spector (Circ Arrhythm Electrophysiol. 2013;6:655-661) and consider incorporating this possible mechanism into the discussion.

→Thank you for your great recommendation. I agree with your hypothesis. The source-sink mismatch could be the best reason for the low voltage at the AF initiation. I adopted this hypothesis as a first possible mechanism in the “Discussion” as follows.

Page 13, line 17〜page 14, line 3 in the RM

“During the sinus rhythm, the trigger myocardium depolarizes simultaneously with the surrounding myocardium by the propagation from the sinus node. Therefore, the total current at the trigger reflects the simultaneous depolarization of both the trigger myocardium and the surrounding myocardium. However, at the onset of AF, the trigger myocardium depolarizes at first and could only depolarize the neighboring cells according to the source-sink relationship [19], then the total current recorded at the origin becomes low.”

New reference #19

Spector P. Principles of cardiac electric propagation and their implications for re-entrant arrhythmias. Circ Arrhythm Electrophysiol. 2013;6(3):655-61. Epub 2013/06/20. doi: 10.1161/CIRCEP.113.000311. PubMed PMID: 23778249.

Response to Reviewer #3

We appreciate your great advice for making our manuscript more sophisticated. We provided our responses to the reviewer’s comments in a blue non-bold font as follows. We hope this revision process has remedied all of your concerns with the original manuscript (OM). The changes and corrections of the OM are shown in a highlighted text in the revised manuscript (RM). We hope our manuscript will be accepted for publication with this version.

Reviewer #3: Authors described the electrophysiological characteristics of non-PV trigger excluding the triggers from left atrial posterior wall (LAPW) and superior vena cava (SVC) using the self-reference mapping technique. Thirty-two non-PV-SVC-LAPW triggers were documented in 23 out of 446 patients (5%), and 28 triggers were evaluated in this study. Authors found 1) the trigger voltage at the onset of AF was low, and 2) coupling interval from the non-PV-SVC-LAPW was short. Non-PV-SVC-LAPW trigger appeared from not only the low voltage area but also normal voltage area. Non-PV-SVC-LAPW origin trigger are difficult to map the origin accurately and their electrophysiological characteristics are not well understood. Overall, the manuscript was well written and some findings were very informative to the reader. However, reviewer has some questions and comments.

Major comments

1. Authors divided the non-PV-SVC-LAPW triggers into 2 groups according to the voltage during sinus rhythm. The voltage change ratio was lower in the group with normal voltage during sinus rhythm than the group with low voltage during sinus rhythm. This finding is natural because the voltage of trigger was comparable between 2 groups and authors defined the group according to the voltage during sinus rhythm. What is the difference of electrophysiological significance of the voltage change ratio compared to the voltage during sinus rhythm at the part of the triggers?

2. Authors showed the relationship between the voltage change ratio and trigger coupling interval in Figure 3 right panel. Please create and analyze the diagrams of the relationship between the voltage at the trigger part during sinus rhythm and trigger coupling interval, and the relationship between the voltage of trigger and coupling interval.

→Thank you for your great comment #1 and #2. I think it is preferable to reply to comments at the same time. I added the relationship between the sinus/trigger voltage and trigger coupling interval as follows. Also, we added Fig 3 C and D. To answer your comment #1, this analysis was important. The sinus/trigger voltage were not correlated to the trigger coupling interval, however voltage change ratio was correlated to the coupling interval. Therefore, even there was an adequate amount of myocardium during long coupling interval (sinus rhythm), only small amount of myocardium could activated at the small coupling interval (AF initiation). This might be explained by the mechanism of the triggered activity (Reference #16, Zipes DP. Mechanisms of clinical arrhythmias. J Cardiovasc Electrophysiol. 2003;14(8):902-12.), as shown in the “Trigger from normal voltages and low voltages during sinus rhythm” in the Discussion part. This is why we analyzed the voltage change ratio, not only the sinus/trigger voltage.

Page 9, line 12-14 in the RM

“The voltage change ratio was significantly correlated to the trigger coupling interval (R=0.44, β=0.44, p=0.0189) (Fig 3 B), whereas the sinus and trigger voltages were not correlated to the trigger interval (p=0.211 and 0.954, respectively, Fig 3 C and D).”

3. Please show the outcome of the patients in this study after the procedure. If redo-procedures were performed in recurrent cases, please show the electrophysiological finding of redo-procedure.

→Thank you for your suggestion. I also wanted to add the outcomes including the re-do procedure. However, in the initial report of the self-reference mapping (Reference #10, Matsunaga-Lee Y, et al. Int J Cardiol 2020; 321: 81-87), we have already reported the clinical outcomes and re-do procedure. (Shortly summarized, 5 patients had AF/AT recurrences. Three had re-do session, and none of them had recurrences of the non-PV-SVC-LAPW triggers, which was targeted at the index procedure.) If we included these data, there might be large overlapping description between current and initial report. Therefore, we were afraid to write them again and added the shortly summarized description in the “Result”.

Page 8, line 19〜page 9, line 2 in the RM

“Among 23 patients, 5 patients had AF/AT recurrences. Three had re-do session, and none of them had recurrences of the non-PV-SVC-LAPW triggers, which was targeted at the index procedure.”

Minor comments

1. Authors defined the non-PV trigger as AF initiating triggers and mapped average 8 times to detect the origin of the trigger. That’s means authors required the cardioversion at least average 8 times. Please show the number of cardioversion which authors performed.

→Thank you for your advice. As you mentioned, we used internal electrical cardioversion to restore sinus during AF trigger mapping. The number of the cardioversion was similar to the number of the mapping, but slightly different because in PAF patients, AF terminated spontaneously. In non-paroxysmal AF patients, they were almost same. According to your recommendation, we added the following description in “Result” and changed Table1 and Supplemental Table (dataset of this study) to include the information of the cardioversion.

Page 8, line 12-13 in the RM

“The median number of the cardioversion to detect the trigger origin was 8 [5.8, 10].”

Table 1

Self-reference mapping results 21 patients, 28 triggers

Number of mapped triggers

N = 1 16 (76)

N = 2 3 (14)

N = 3 2 (10)

Number of mapping points to detect the origin of the trigger 8 [4.3, 9.8]

Number of the cardioversion to detect the origin of the trigger 8 [5.8, 10]

Mapping time to detect the origin of a trigger (min) 8.9 [2.6, 14.9]

Distribution of triggers

Right atrium 16 (57)

Left atrium 12 (43)

2. Please mention the potential of AF initiating triggers induced by the mapping catheter.

→Thank you for your comment. I added following sentences in the “Limitations”.

Page 16, line 8-12 in the RM

“Finally, there is a possibility of AF initiating triggers induced by the mapping catheter. However, to reduce this possibility, the non-PV trigger reproducibility was robustly assessed, comparing the atrial sequences and trigger coupling interval fluctuation, which was permitted only less than 10 msec.”

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

31 Jan 2022

Electrophysiological Characteristics of Non-Pulmonary Vein Triggers Excluding Origins from the Superior Vena Cava and Left Atrial Posterior Wall: Lessons from the Self-reference Mapping Technique

PONE-D-21-34553R2

Dear Dr. Nishino,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Tomohiko Ai, M.D., Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

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Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for the revision. I think the conclusions has been revised to be reasonable. I have no further comment.

Reviewer #2: The authors have adequately responded to the comment and adopted the source-sink mismatch as the first possible mechanism of the voltage change of the trigger site.

Reviewer #3: I appreciate the authors significant efforts to clarify and address this reviewer's questions. Hopefully the revised manuscript has been strengthened as a result. I have no further comments.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: Yes: Taku Nishida

Reviewer #3: No

28 Mar 2022

PONE-D-21-34553R2

Electrophysiological Characteristics of Non-Pulmonary Vein Triggers Excluding Origins from the Superior Vena Cava and Left Atrial Posterior Wall: Lessons from the Self-reference Mapping Technique

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