3
ORIGINAL SCIENTIFIC ARTICLE
Early atrial ectopic beats and atrial conduction delay predict atrial fibrillation
Copyright (c) 2025 Slovenian Medical Journal. This work is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.
Early atrial ectopic beats and atrial conduction delay 
predict atrial fibrillation
Zgodnji preddvorni ektopični utripi in upočasnjen preddvorni prevod napovedujejo 
preddvorno fibrilacijo
Matjaž Šinkovec,1,2 Bor Antolič,1,2 Martin Rauber,1,2 Jana Ambrožič,1,2 Marta Cvijić,1,2 Luka Klemen,1 David Žižek,1,2 
Janez Toplišek,1,2 Andrej Pernat1,2
Abstract
Background: Atrial fibrillation/flutter (AF/AFl) is commonly diagnosed arrhythmia, associated with increased morbidity 
and mortality. Therefore, we have to improve our early AF/AFl diagnostics. Several studies indicated association between 
conduction delay, excessive atrial ectopic beats (AEBs) and AF/AFl onset. Association with some other AEB features is less 
clear.
Objective: To validate the role of early AEBs from Holter-ECG in relation to documented AF/AFl events.
Methods and Results: We enrolled 14 consecutive patients (6 female, median 60.5 years) with documented AF/AFl during 
or within 6 months after Holter-ECG (AF-group). Control group consisted of 10 clinically similar consecutive patients (5 
female, median 64.5 years), without any evidence of AF/AFl, but with comparable burden of AEBs. Holter-ECGs were ex-
amined with 3-channel Holter system (Schiller, Darwin2 software). 24-hour data were analyzed for number and/or burden 
(%) of: a) AF/AFl, b) AEBs, c) early-AEBs (coupling interval cut-off <530 ms), d) AEB pairs, triplets, runs, and e) bigeminy. In 
addition, P-wave duration (cut-off <130 ms), PQ, QRS, and QTc were measured. AF-group had higher burden of early-AEBs 
(p<0.03) and longer P-waves (p<0.05) than controls. In both groups, non-conducted and aberrantly-conducted early-AEBs, 
AEBs in bigeminy, pairs, triplets and runs were found, as-well-as no difference for PQ, QRS, and QTc (p=NS). The majority 
of 243 AF/AFl events started during day-time and in 83% with early-AEBs. Before AF onset, outbursts of early-AEBs were 
encountered in 58% of patients.
Conclusion: A higher burden of early AES in the Holter ECG and a longer P-wave duration predict the occurrence of AF/AU.
1 Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
2 Department of Cardiology, Division of Internal Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia
Correspondence / Korespondenca: Matjaž Šinkovec, e: matjaz.sinkovec@guest.arnes.si
Keywords: atrial fibrillation; atrial ectopic beats; electrocardiogram; holter-monitoring
Ključne besede: atrijska fibrilacija; preddvorni ektopični utripi; elektrokardiogram; holtersko monitoriranje
Received / Prispelo: 27. 3. 2024 | Accepted / Sprejeto: 18. 11. 2024
Cite as / Citirajte kot: Šinkovec M, Antolič B, Rauber M, Ambrožič J, Cvijić M, Klemen L, et al. Early atrial ectopic beats and atrial 
conduction delay predict atrial fibrillation. Zdrav Vestn. 2025;94(1–2):3–15. DOI: https://doi.org/10.6016/ZdravVestn.3532
eng slo element
en article-lang
10.6016/ZdravVestn.3532 doi
27.3.2024 date-received
18.11.2024 date-accepted
Cardiovascular system Srce in obtočila discipline
Original scientific article Izvirni znanstveni članek article-type
Early atrial ectopic beats and atrial conduction 
delay predict atrial fibrillation
Zgodnji preddvorni ektopični utripi in upočasnjen 
preddvorni prevod napovedujejo preddvorno 
fibrilacijo
article-title
Early atrial ectopic beats and atrial conduction 
delay predict atrial fibrillation
Zgodnji preddvorni ektopični utripi in upočasnjen 
preddvorni prevod napovedujejo preddvorno 
fibrilacijo
alt-title
atrial fibrillation, atrial ectopic beats; electro-
cardiogram; holter-monitoring
atrijska fibrilacija, preddvorni ektopični utripi, 
elektrokardiogram, holtersko monitoriranje kwd-group
The authors declare that there are no conflicts 
of interest present.
Avtorji so izjavili, da ne obstajajo nobeni 
konkurenčni interesi. conflict
year volume first month last month first page last page
2025 94 1 2 3 15
name surname aff email
Matjaž Šinkovec 1 matjaz.sinkovec@guest.arnes.si
name surname aff
Bor Antolič 1,2
Martin Rauber 1,2
Jana Ambrožič 1,2
Marta Cvijić 1,2
Luka Klemen 1
David Žižek 1,2
Janez Toplišek 1,2
Andrej Pernat 1,2
eng slo aff-id
Faculty of Medicine, University 
of Ljubljana, Ljubljana, Slovenia
Medicinska fakulteta, Univerza v 
Ljubljani, Ljubljana, Slovenija 1
Department of Cardiology, 
Division of Internal Medicine, 
University Medical Centre 
Ljubljana, Ljubljana, Slovenia
Klinični oddelek za kardiologijo, 
Interna klinika, Univerzitetni 
klinični center Ljubljana, 
Ljubljana, Slovenija
2
Slovenian Medical Journallovenian Medical Journal
4
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1 Introduction
Atrial fibrillation (AF) is a commonly diagnosed 
arrhythmia in clinical practice. It is associated with 
an increased risk of stroke, heart failure, and cognitive 
decline, contributing to high morbidity and mortality 
rates in these patients (1,2). Therefore, in clinical prac-
tice, it is important to improve our early AF diagnos-
tics with a view toward early AF treatment (3,4).
Atrial ectopic beats (AEBs) are common in the 
general population (5,6). However, several studies and 
meta-analyses in recent years indicated an association 
between excessive AEBs and AF (7,8,9), stroke (8,10) 
pacemaker implantation (11), and mortality (8,11,12). 
In addition, standard ECG data had been recently re-
viewed, confirming a strong predictive value of atri-
al and AV-conduction delay parameters for AF onset 
(13,14). From clinical practice, it is evident that some 
patients with excessive AEBs will develop AF and oth-
ers will not, possibly depending on the severity of atri-
al cardiomyopathy (15). The diagnostic value of some 
additional AEB features (except high AEB burden) 
that could reveal patients with AF remains partially 
studied.
Therefore, this pilot observational case-control 
study was aimed to validate some AEB features and 
conduction delay markers from Holter-ECG record-
ings with documented AF.
2 Methods
2.1 Patients
Between September 2022 and October 2023, we 
recruited consecutive patients of both genders from 
the waiting list for catheter ablation of AF at our insti-
tution (AF-group). All had documented paroxysmal 
AF/atrial flutter (AF/AFl) during or within 6 months 
after Holter recordings. The control group consisted of 
clinically similar consecutive patients from the same 
time period, without any evidence of AF, without an-
tiarrhythmic drug treatment, but with a comparable 
burden of AEBs. They were selected from outpatients’ 
lists with available Holter and clinical data. The study 
was approved by the National Ethics Committee of 
the Republic of Slovenia (KME 0120-65/2022/6). An 
informed consent was obtained from all study partici-
pants prior to investigations.
2.2 Methods, ECG parameters, and definitions
We used the Holter system (Schiller, Medilog AR 
Professional) with EASI 5-electrode set-up for 3 or-
thogonal lead tracings (16). Continuous ECG data 
were stored for later automatic analysis, review, and 
manual measurements (Darwin2 Professional Soft-
ware). We analysed 24-hour data for: a) the number 
Izvleček
Izhodišča: Preddvorna fibrilacija/undulacija (AF/AU) je pogosta motnja srčnega ritma, ki je povezana z višjo umrljivostjo 
in obolevnostjo. Zato jo je treba čim prej diagnosticirati. Rezultati več raziskav kažejo na povezavo med upočasnjenim 
preddvornim prevodom, velikim številom preddvornih ektopičnih utripov (AES) in pojavom AF/AU. Manj jasna je povezava 
z nekaterimi drugimi značilnostmi AES.
Cilj raziskave: Vrednotiti smo želeli pomen zgodnjih AES pri holterskem elektrokardiogramu (EKG) v povezavi z zabeleže-
nimi epizodami AF/AU.
Metode in rezultati: V pilotsko raziskavo smo vključili 14 zaporednih bolnikov (6 žensk, mediana starost 60,5 leta) z doku-
mentirano AF/AU v zapisu holterskega EKG ali do 6 mesecev po njem (skupina z AF/AU). V kontrolni skupini je bilo 10 zapo-
rednih bolnikov s podobno klinično sliko (5 žensk, mediana starost 64,5 leat) brez AF/AU v anamnezi, vendar s podobnim 
bremenom AES. Holterski EKG smo beležili s 3-kanalnim sistemom (Schiller, Darwin2 software). V 24-urnih zapisih EKG 
smo analizirali število in/ali breme (%) naslednjih parametrov: a) AF/AU, b) AES, c) zgodnjih AES (vezni interval < 530 ms), 
d) AES v parih, tripletih in salvah in e) prisotnost bigeminije; poleg tega pa še trajanje vala P (normalna vrednost < 130 ms), 
PQ, QRS in QTc. Skupina z AF/AU je imela večje breme zgodnjih AES (p< 0,03) in daljši val P (p< 0,05) kot kontrolna skupina. 
V obeh skupinah smo zabeležili neprevedene in aberantno prevedene AES, AES v bigeminiji, parih, tripletih in salvah. Prav 
tako ni bilo razlike v trajanju PQ, QRS in QTc (p=NS). Večina od 243 primerov AF/AU se je sprožila v dnevnem času, v 83 % z 
zgodnjo AES. Pri 58 % smo zabeležili pred pojavom AF/AU porast števila zgodnjih AES.
Zaključek: Večje breme zgodnjih AES v holterskem EKG in daljše trajanje vala P napovedujejo pojav AF/AU.
5
ORIGINAL SCIENTIFIC ARTICLE
Early atrial ectopic beats and atrial conduction delay predict atrial fibrillation
Figure 1: Frequent early atrial ectopic beats (*) in bigeminy, 
conducted with aberrancy, before induction of atrial 
fibrillation. The coupling interval of atrial ectopic beat is 
about 460 ms.
Source: archive of the Department of Cardiology, University 
Medical Centre Ljubljana.
and burden of all AEBs presented as singles, pairs, 
and triplets (the burden was defined as % of all beats 
during sinus rhythm), b) early-AEBs burden of >50 %, 
and <50 % (from all AEBs), c) number of pairs, triplets 
and non-sustained (<30 s) AEB runs of (4‒8 beats and 
>8 beats), d) presence or absence of AEB bigeminy (at 
least 3 consecutive AEBs coupled with sinus beats), e) 
number and onset time of AF/AFl events, f) AF/AFl 
burden (% of time in AF/AFl), and g) number of sus-
tained atrial tachycardias (AT). In addition, we manu-
ally measured durations of P-wave, PQ-interval, QRS, 
at heart rate of 55‒65/min, and analysed automatic 
measurements of QTc (Fridericia correction, 5-minute 
average). AF and flutter events were analysed togeth-
er since these arrhythmias frequently interchanged 
between each other in the same subject. AF/AFl was 
defined according to current international guidelines 
(1,2). AF was a varying, low amplitude, rapid (300‒500 
beats/min) atrial rhythm with chaotic ventricular re-
sponse. AFl was a rapid atrial rhythm with a constant 
Figure 2: Non-conducted early atrial ectopic beats (*) in 
bigeminy, with coupling interval of 430 ms. The last one is 
conducted aberrantly and followed by atrial fibrillation (AF).
Source: archive of the Department of Cardiology, University 
Medical Centre Ljubljana.
rate (220‒350 beats/min), “flutter” P-wave morpholo-
gy, and regular ventricular response. AT was regular 
atrial rhythm at a constant rate of >100 beats/min with 
discrete altered P waves and longer PR-interval than 
during sinus rhythm. We defined that early-AEBs 
fire before completed atrial repolarisation, which is 
at an AEB coupling interval of <500 ms in those with 
a P-wave duration of <130 ms, and <530 ms in those 
with a P-wave duration >130 ms (Figures 1 and 2). In 
case of uncertainty in the Holter-ECG analysis, the de-
cision was made by consent.
2.3 Statistics
We used a t-test for normally distributed metric 
data, the Mann-Whitney rank-sums test for non-nor-
mally distributed data, and a Chi-squared test for pro-
portion analysis. Anderson-Darling normality test 
was applied. Value P < 0.05 was considered significant.
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3 Results
3.1 Patients
We included 14 patients (6 female, median age of 
60.5 years (45‒72, range)) (Table 1). Twelve patients 
had documented AF/AFl events during Holter-ECG 
Legend:
* Propafenone, flecainide, sotalol, amiodarone
** More than 50% of atrial ectopic beats are early (eAEBs); AEB coupling interval of <500‒530 ms was considered “early”
LAVI – left atrial volume index; normal values are according to Lang et al. (2015) (17).
AF group Control group P value
N (Female) 14 (6) 10 (5) NS
Average age (years)
(median, range) 60.5 (45-72) 64.5 (58-72) NS
CHA2DS2-VASc 1.5 (0-4) 2 (0-6) NS
Increased LAVI (>34 ml/m2) 7/14 3/10 NS
*Antiarrhythmic drugs 6/14 0/10
Number of Holter-ECG recordings 26 (1-4/patient) 10 (1/patient)
Duration of all Holter-ECG recordings (hours) 2427 400
AF/AFl number of events 243 0
24-hour AF burden (%)
(median, range) 10 (0-67) 0
24-hour AEB burden (%)
(median, range) 0.39 (0.0001-6.3) 1.14 (0.13-7.23) <0.03
24-hour AEB number
(median, range) 381 (3-3937) 1219 (125-7998) <0.01
**>50 % eAEB burden 9/14 1/10 <0.03
24-hour AEB runs
(median, range) 3 (0-151) 2 (1-59) NS
24-hour AEB pairs, triplets
(median, range) 6 (0-174) 9 (2-233) NS
AEB bigeminy 23/26 6/10 NS
AEB aberrant conduction 21/26 7/10 NS
P-wave duration (ms) 
(mean ± SD) 143 ± 20.3 129 ± 13.0 <0.05
PQ duration (ms)
(mean ± SD) 183 ± 40.2 172 ± 18.5 NS
QRS duration (ms)
(mean ± SD) 100 ± 13.4 98 ± 12.4 NS
QTc duration (Fridericia)
(mean ± SD 438 ± 21 426 ± 23 NS
Table 1: Clinical data and results of our observations.
monitoring, and two patients 2 weeks and 4 months 
after the monitoring, respectively. The control group 
consisted of 10 clinically similar patients (5 female, 
median age of 64.5 years (58‒72, range)) without any 
evidence of AF, without antiarrhythmic drug treat-
ment, but with a comparable burden of AEBs (Table 
1).
7
ORIGINAL SCIENTIFIC ARTICLE
Early atrial ectopic beats and atrial conduction delay predict atrial fibrillation
In the AF group, 26 continuous ECG recordings 
were analysed (1‒4 recordings per patient, median 
195.8 hours (23‒279, range, together 2427 hours). In 
the control group, we analysed 10 recordings of a me-
dian of 23.4 hours per patient (19‒143 range), together 
400 hours.
3.2 ECG parameters
The results are shown in Table 1. We identified 
243 AF/AFl events. Patients from the AFgroup had 
asignificantly higher burden of early,AEBs than con-
trols (p < 0.03) (Figure 3), as well as longer P-wave 
duration (p < 0.05). In both groups, some early AEBs 
were conducted to ventricles with aberrancy or were 
even non-conducted (Figures 1 and 2). The repetitive 
forms of AEBs in bigeminy or trigeminy were fre-
quently found in both groups, as well as were AEBs in 
pairs, triplets and runs. Sustained AT was not associ-
ated with AF/AFl induction since it has been found in 
controls only. AF was induced with early AEBs in the 
majority of patients (10/12, 83%) (Figures 1 and 2); in 
some, it was the second beat in the row, after the late 
first AEB (2/12, 17%). The AF/AFl started most fre-
quently during the day and particularly in the evening 
(Figure 4). As expected, some early AEBs were related 
to higher heart rates (not shown). Before AF onset, the 
increasing numbers of singles, pairs, triplets and runs 
of early AEBs were encountered in 7/12 (58%) pa-
tients, like an outburst of an “electrical storm”. A short 
AF/AFl event typically preceded the more sustained 
AF/AFl event.
The prolonged P-wave and PQ interval durations 
were frequently observed with longer AEB coupling 
intervals and more regular activity of AF/AFl events 
(Figure 5). In 5/14 (36%) patients from the AF group 
and in 1/10 (10 %) control, night-time QT-interval > 
454 ms was documented (P = NS), and one patient 
had short PQ-interval (< 120 ms). Late AEBs were 
mainly related to slow repetitive ectopic activity and 
non-sustained atrial rhythms and were unrelated to 
AF/AFl onset (not shown).
4 Discussion
4.1 Early atrial ectopic activity
In this pilot case-control observational study, we 
demonstrated an association between early-AEB bur-
den and AF/AFl events (p < 0.03). The arrhythmo-
genic potential of early AEBs may be explained with 
firing before completed atrial repolarization. The cut-
off values for early AEBs were arbitrarily derived from 
Holmquist et al. (2009) (18), who reported data on 
Figure 3: Patients from the AF group had a significantly higher burden of early AEBs than the controls.
p < 0.03
Control GroupAF Group
1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10
%
0
25
50
75
100
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atrial repolarisation time in patients with a complete 
AV-block. The average P-Ta duration was 449‒512 ± 
55‒60 ms (mean ± SD), which is in agreement with 
our data. In addition, in 58% of AF-group patients, 
AF/AFl induction correlated with a distinct pattern of 
outbursts of early AEBs and AEB runs. This “electri-
cal storm” activity, however, predicted AF/AFl events 
in the time frame of minutes to hours (not shown). It 
seems however, that long-term prediction of AF/AFl 
events could also be feasible (e.g., for weeks or even 
months in two of our patients) but should be proven 
in a larger group of patients. However, we suspect that 
diagnostic sensitivity for 24-hour recordings might be 
low since a high and low burden of early AEBs and 
AF/AFl events had been encountered in a single pa-
tient (not shown). Nevertheless, high burden of ear-
ly AEBs may be considered a manifestation of an ar-
rhythmogenic state.
Others had long ago demonstrated the importance 
of early AEBs in triggering AF/AFl events (19). It has 
been reported recently that in patients with crypto-
genic stroke, 7 or more non-conducted early AEBs 
in 24-hour Holter-ECG predict AF (with a sensitivity 
of 62.5% and a specificity of 97.7%) (20). The mini-
mum prematurity index of the AEBs (48% or less) at 
12 months after catheter ablation of AF was shown to 
be an independent predictor of AF recurrence (21). 
On the other side, our observations suggest that late 
AEBs are related to slower repetitive atrial ectopic ac-
tivity, such as we see with abnormal focal automatici-
ty, which has, in our opinion, a low proarrhythmic or 
predictive potential for AF/AFl events.
The number of early AEBs in this study was prob-
ably underestimated since conduction from PVs to 
atria may be delayed in some cases (e.g., in patients 
with prolonged P-wave duration (Figure 5)) and ec-
topic atrial activity may not be visible behind QRS 
complex or in some leads. Therefore, we considered a 
longer cut-off value for early AEBs (coupling interval 
530 ms) in patients with prolonged P-wave duration. 
For clinical practice, an alerting ECG sign of early, ar-
rhythmogenic AEBs are non-conducted and aberrant-
ly conducted AEBs. However, isolated AV-conduction 
abnormalities must first be excluded (e.g., a prolonged 
PQ interval or an incomplete bundle-branch block).
Figure 4: The majority of atrial fibrillation or flutter (AF/AFl) events started in the evening and rarely in the night between 
1 and 6 o’clock. Most events recorded between 4 and 5 o’clock (n = 16) occurred in a single patient. The adrenergic drive 
seems more important than cholinergic as the autonomic modulator of AF/AFl induction in our patient.
Time of AF/AFI firing
N
um
be
r o
f A
F/
AF
I f
iri
ng
s
1:
00
2:
00
3:
00
4:
00
5:
00
6:
00
7:
00
8:
00
9:
00
10
:0
0
11
:0
0
12
:0
0
13
:0
0
14
:0
0
15
:0
0
16
:0
0
17
:0
0
18
:0
0
19
:0
0
20
:0
0
21
:0
0
22
:0
0
23
:0
0
0:
00
10
3 3
16
17
12
7
10
17
7
13
18
11
10
18
13
15 15
27
33
18
22
9
ORIGINAL SCIENTIFIC ARTICLE
Early atrial ectopic beats and atrial conduction delay predict atrial fibrillation
Figure 5: The sinus beat on the left shows a prolonged P wave (170 ms) and PQ interval (250 ms) due to slow atrial and 
AV-conduction. However, the coupling interval of early atrial ectopic beat is at the cut-off value of 530 ms which is still 
aberrantly conducted (*). More regular atrial fibrillation/flutter activity is induced on the background of atrial structural 
disease in this patien.
Source: archive of the Department of Cardiology, University Medical Centre Ljubljana.
4.2 Atrial conduction delay
It is well documented that atrial conduction delay 
represents a marker and electro-anatomical substrate 
for the development of AEBs and AF/AFl events; it 
was also named the “Bayes’ syndrome” (13,14,22). The 
P-wave duration of >120 ms was predictive of AF in a 
large group of patients who were followed for 5.3 years 
(Perez 2013) (23). Our data confirm that a prolonged 
P-wave duration is associated with AF/AFl events (Ta-
ble 1, Figure 5). Therefore, P-wave duration combined 
with early AEBs burden might be a useful Holter-ECG 
predictor of the near-future AF/AFl events. Neverthe-
less, the P-wave duration in our patients revealed an 
appropriate cut-off value at about 130 ms, similar to 
Holmquist’s measurements (18).
4.3 Atrioventricular conduction
The study by Nilsen, et al. (2013) showed that long 
and also short PQ-intervals (< 130 ms) predict a new 
onset of AF (24). We saw a short PQ interval in on-
ly one patient from the AF group. In the majority, we 
demonstrated prolonged PQ intervals; however, the 
difference was not statistically significant, possibly due 
to a small patient sample and a high data variability. 
As mentioned above, there were some patients with 
normal or even short PQ intervals. In patients with a 
short PQ interval, it is obvious that aberrant conduc-
tion of early AEBs is less evident.
4.4 Source of atrial fibrillation firing
It has long been known that pulmonary veins are 
the major source of AF firing (PVs) (25). Therefore, it 
is highly probable that the majority of early AEBs orig-
inate from PVs, as we also observed in our patients 
during catheter ablation (Figure 6). It is interesting 
that localised reentry activity at this location may be 
an important triggering mechanism for AF/AFl onset. 
The coronary sinus (and vein of Marshall) with its di-
verse muscle fiber coating and the terminal crest with 
complex pectinate muscle anatomy are among other 
potential sources of AF/AFl triggering in about 10% of 
patients (26). An example of AF onset triggered from 
the terminal crest is shown in Figure 7.
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Figure 6: Two examples of triggered and reentry activity from the left pulmonary vein (PV) antrum. In this location, bipolar 
electrograms from the circular diagnostic catheter are marked by “LASO/LASSO”. The first sinus beat (*) on the left upper 
tracing is fused with the ectopic beat (arrow). The second ectopic beat is not conducted to the ventricle, and the third 
is conducted aberrantly. After the third ectopic beat, a short reentry antral activity terminated spontaneously (arrows). 
Below, in another patient, a similar sequence of events induced atrial fibrillation, which is less regular in CS than in the left 
PV antrum.
Legend: ABLD – electrogram from ablation catheter; CS – bipolar electrograms from the coronary sinus.
Source: archive of the Department of Cardiology, University Medical Centre Ljubljana.
11
ORIGINAL SCIENTIFIC ARTICLE
Early atrial ectopic beats and atrial conduction delay predict atrial fibrillation
4.5 Mechanisms of atrial fibrillation triggering
The electrophysiological basis of AEBs is triggered 
activity, either by early afterdepolarisation in the case 
of prolongation of the action potential or by delayed 
afterdepolarisation in the case of increased heart rate 
(27). The reported leading mechanisms of AF induc-
tion were: a) triggered activity, which includes Ca2+ 
handling abnormalities, mainly by delayed after-depo-
larisations; b) reentry activity in structurally remod-
eled atria; and c) inflammatory signaling in some con-
ditions (28). In addition, atria are highly innervated 
by the autonomic nervous system via the ganglionated 
plexi (29). Both the sympathetic and parasympathetic 
systems are involved in the occurrence of AEBs and 
AF by increasing the calcium transient and heteroge-
neous shortening of action potentials (30,31,32). The 
prevailing daytime firing of AF/AFl in our patients 
suggests the important role of sympathetic predomi-
nance before induction. Early AEBs seem to be related 
to fast repetitive activity from PVs as the main source, 
with triggered activity (and localized reentry) as the 
main mechanism of AF/AFl induction (Figure 6). The 
AF induction was also associated with long nocturnal 
Figure 7: Early atrial ectopic beat from terminal crest (the first arrow on the left) is followed by fast regular atrial activity 
(AT) with fragmentation (cycle up to 160 ms), which converts to atrial fibrillation (AF) as first seen on the 10-polar catheter 
in the coronary sinus (CS). AF is most likely induced in CS or the left atrium. Sinus beats are marked with stars (*).
Legend: ABLD, ABLP – bipolar electrograms from ablation catheter positioned on the upper terminal crest of the right atrium; 
RVAD, RVAP – bipolar electrograms with His and right bundle electrograms (H).
Source: archive of the Department of Cardiology, University Medical Centre Ljubljana.
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QT intervals in one-third of our patients. If we specu-
late that a long QT interval is also a marker of abnor-
mal atrial repolarisation (due to localised autonomic 
nerve dysfunction), primary atrial repolarisation ab-
normality might be involved in AF/AFl induction in 
some of our patients. In the majority however, pro-
longed P-wave duration (and PQ interval) suggests 
that primary abnormality was an atrial conduction de-
lay, possibly on the grounds of atrial cardiomyopathy 
with reentry as another important mechanism of AF/
AFl induction and perpetuation (15). Furthermore, it 
seems that the location of AEBs firing may be clini-
cally meaningful. In a swine model, AEBs originating 
from the lateral left atrium were associated with lon-
ger P-wave duration, greater echocardiographic atrial 
mechanical dyssynchrony, and longer induced AF du-
ration than from the septal AEBs or after regular left 
atrial pacing at 130 beats/min (Higuchi 2024) (33).
Another mechanism for early AEB firing and AF 
induction has to be mentioned, i.e., the so-called 
“mechano-electrical feedback”, proposed by Tse et al. 
(2001) (34). Early AEBs occur during atrial and ven-
tricular contractions and atrial relaxation. The systol-
ic traction on antral parts of PVs and changing blood 
flow directions might contribute to electrical trigger-
ing (Figure 8). This haemodynamic trigger of AF in-
duction may play particular role in conditions with 
increased left ventricular filling pressures. An example 
is hypertensive cardiac disease, the most frequent co-
morbidity in patients with non-valvular AF (1,2).
Figure 8: Pulsed-wave Doppler tracings (in yellow) of the right upper pulmonary venous flow with simultaneous ECG 
tracings. Reversal of blood flow with atrial contraction (Ar) at the end of ventricular diastole is followed by fast inflow 
during ventricular systole (S), the time of early atrial ectopic beats firing.
Legend: D – diastolic wave.
Source: archive of the Department of Cardiology, University Medical Centre Ljubljana.
13
ORIGINAL SCIENTIFIC ARTICLE
Early atrial ectopic beats and atrial conduction delay predict atrial fibrillation
4.6 The normal burden of atrial ectopic beats 
in Holter-ECG monitoring
There is currently no widely accepted consensus on 
reference ranges for 24-hour Holter-ECG AEB activity 
to guide interpretation. A threshold of 500 AEBs/24 h 
has been proposed in a consensus paper (35). Howev-
er, a recent meta-analysis in a healthy adult popula-
tion, although on limited available data, demonstrated 
that AEBs of >1000/24 hours increased with age, from 
0 (95% CI 0–0%) in those aged 18–39 years to 6% (95% 
CI 0–17%) in those aged 60–79 years. Episodes of any 
AEB runs (minimum 3‒5 beats) increased from 3% 
(95% CI 1–6%) in those aged 18–39 years to 28% (95% 
CI 9–52%) in those aged 60–79 years (6). In our pa-
tients, the median number of AEBs (in singles, pairs, 
and triplets) was below the suggested cut-off value of 
500/24 hours (Table 1).
4.7 Limitations
Our pilot observational study has some limita-
tions. The accuracy of readings and measurements of 
so many events and parameters over long time periods 
may be limited. Nevertheless, our results are reason-
ably accurate since we carefully checked the automatic 
analysis results many times. We assessed the burden 
of early AEBs in a semiquantitative way since it was 
almost impossible to count out correct numbers from 
thousands of events. Nevertheless, the separating val-
ue of more than 50% of early AEBs (of all AEBs in a 
24-hour Holter-ECG recording) was evident (Figure 
3). Also, in 4 out of 6 patients from the AF group who 
were taking antiarrhythmic drugs, P-wave duration 
was prolonged, and this effect may not be neglected. 
In addition, the selection of the control group of pa-
tients may be biased since some of them had had cath-
eter ablation of focal sustained atrial tachycardia 
before. This arrhythmia, however, was not associat-
ed with AF/AFl events, thus confirming its different 
electrophysiological mechanism. Further, some pa-
tients from control group might have had a silent AF/
AFl event before inclusion. Finally, the AF/AFl event 
would also be revealed in the control group if the du-
ration of Holter-ECG recordings was similar to that of 
patients from the AF group. However, the difference 
between the groups would be even less evident in this 
case. Nevertheless, the diagnostic value of proposed 
Holter-ECG parameters for predicting AF/AFl events 
has to be re-evaluated in a larger group of patients.
5 Conclusions
The results of this pilot case-control observational 
study suggest that the increased burden of early AEBs 
over 50%, combined with prolonged P-wave duration 
beyond 130 ms, may be a useful Holter-ECG predictor 
for a near-future AF/AFl event.
Conflict of interest
None declared.
Acknowledgements
We express our sincere gratitude to Benjamin 
Jezernik, Ingrid Tušar and Matic Cesar for their thor-
ough and pedantic work with data recording and 
collection.
This work was supported by the research grant No. 
20210004, UMC Ljubljana.
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