Interpretations

Arch Dis Child Educ Pract Ed: first published as 10.1136/archdischild-2023-326825 on 14 July 2024. Downloaded from http://ep.bmj.com/ on April 16, 2025 at Royal College of
How to use chest radiographs and
ECGs in children with pacemakers
Ian Scott Kendall ‍ ‍,1 Lisa Turkington,2 Jonathan Gillender,1
Andrew J Sands1

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1
Paediatric Cardiology, Royal ABSTRACT or the endocardium of the heart, often
Belfast Hospital for Sick
A child with pacemaker is an uncommon screwed or wedged between cardiac
Children, Belfast, UK
2
Department of Cardiology, presentation to the general paediatric ward, and fibres. Endocardial leads are inserted
Royal Victoria Hospital most clinicians without previous experience may transvenously into the heart chambers.
Laboratory and Mortuary not feel confident in assessing these patients. Epicardial leads are surgically implanted
Services, Belfast, UK
This article provides an overview of paediatric onto the surface of the epicardium. The
Correspondence to
pacemakers and commonly found radiological leads are connected to a pulse generator (a
Dr Ian Scott Kendall; ​ and electrophysiological correlates along with sealed metallic unit with integrated pace-
scttkendall@g​ ooglemail.​com clinical consideration. maker circuitry and battery). The pulse
generator is usually implanted superficial
Accepted 22 June 2024 or deep to pectoralis major (endocardial)
Published Online First
14 July 2024 Pacemakers, while uncommon in chil- or rectus abdominus (epicardial). The
dren, are important devices. Many chil- minimum energy required to successfully
dren with a pacemaker live distant to their depolarise the myocardium is called the
stimulation threshold. Pacemaker leads

Paediatrics and Child Health .

cardiac centre and may present to their
local hospital. The indications, types and may be impregnated with steroid-­eluting
problems associated with paediatric pace- elements to reduce fibrosis leading to
makers differ from adults. This article higher thresholds and shortening gener-
describes common paediatric pacemaker ator lifespan.2
modalities and includes examples of chest Epicardial pacemakers are often
radiographic (CXR) and ECG findings. preferred in smaller children and in
patients with intracardiac shunts or a
single ventricle. Implantation requires
PHYSIOLOGY BACKGROUND
surgery (thoracotomy/sternotomy/subx-
Depolarising current originates in all
iphoid incision). Endocardial pacemakers
cardiac cells with automaticity across
are preferred for larger children, due to the
all the cardiac chambers. Usually, these
longevity of components. However, there
are synchronised by the faster automatic
is an increased risk of venous occlusion,
rate from the sinoatrial node area of
tricuspid regurgitation and endocarditis.2
the right atrium, the heart’s own 'pace-
There are many pacemaker modali-
maker'. The depolarisation wave then
ties for different indications. Indications
propagates across both atria and reaches
include congenital heart block with an
the atrioventricular (AV) node. The
inadequate intrinsic ventricular rate or
AV node is normally the sole route by
acquired AV block, for example, postoper-
which depolarisation can be transmitted
ative block, or single ventricle conditions
to the ventricles via the His bundle. The
with AV node dysfunction. These usually
Purkinje fibres continue as the left and
warrant ventricular or dual chamber
right septal conduction bundles. These
pacing. Atrial pacing is sometimes needed:
rapidly conduct the depolarisation wave
mostly due to sinus node disease which
to the apex of the heart, a short time after
may be congenital or acquired. Patients
the atrial contraction (resulting in the AV
© Author(s) (or their with a single ventricle or history of atrial
employer(s)) 2025. No conduction delay (PR interval)). Contrac-
surgery are more commonly affected, with
commercial re-­use. See rights tion is followed by a short refractory
and permissions. Published by an inadequate rate response to exertion or
period then the cycle repeats.1
BMJ Group. prolonged (symptomatic) pauses.3 Use of
To cite: Kendall IS,
pacemakers for sinus bradycardia in chil-
Turkington L, Gillender J, TECHNOLOGICAL BACKGROUND dren, for example, reflex anoxic seizures,
et al. Arch Dis Child Educ Pacing is achieved using specialised elec- is controversial.3 Some devices have an
Pract Ed 2025;110:70–74. trodes attached either to the epicardium antiarrhythmic function which can be

70    Kendall IS, et al. Arch Dis Child Educ Pract Ed 2025;110:70–74. doi:10.1136/archdischild-­2023-­326825
 Interpretations

Arch Dis Child Educ Pract Ed: first published as 10.1136/archdischild-2023-326825 on 14 July 2024. Downloaded from http://ep.bmj.com/ on April 16, 2025 at Royal College of
Table 1 The revised North American Society of Pacing and Electrophysiology (NASPE)/British Pacing and Electrophysiology Group
(BPEG) generic code for antibradycardia pacing
Position I II III IV V
Chambers
Category Chambers paced sensed Response Rate modulation Multisite pacing
0=none 0=none 0=none 0=none 0=none
A=Atrium A=Atrium T=Triggered R=Rate Modulation A=Atrium
V=Ventricle V=Ventricle I=Inhibited V=Ventricle
D=Dual D=Dual D=Dual D=Dual

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(A+V) (A+V) (T+I) (A+V)

either via antitachycardia pacing or using a special-

ised defibrillator lead and generator (eg, for children
at high risk of dangerous ventricular arrhythmia).4
Recently introduced, leadless pacemakers have also
been used in children, in selected cases.5
Pacemaker function is described by a five-­letter code.
The first letter refers to the chamber paced, the second
to the chamber sensed, the third is the response to the
sensed innate activity. The response can include inhi-
bition of a paced ‘beat’ in response to innate cardiac
activity or triggering further pacing. The fourth letter
is applied if the pacemaker has rate modulation; the

Paediatrics and Child Health .

heart rate increases with increased movement. The
fifth letter refers to multisite pacing, where there are
multiple pacing sites in the atria or ventricle(s). It is
rarely used in paediatrics.6 Usually, only the first three
letters are used (table 1).

COMPREHENSIVE PACEMAKER REVIEW

Pacing follow-­up at cardiac centres varies. It is often
Figure 2 Chest X-­ray demonstrating an endocardial pacemaker.
conducted by pacing technicians, either as part of a Pulse generator is over the left pectoral area, the lead runs from the
dedicated pacing clinic or as a routine part of general generator, into the right subclavian vein, joining the superior vena cava
and entering the right atrium. There is excess curled lead in the right
atrium to allow for growth.

clinic. It now frequently occurs remotely with a

home-­ based monitoring system. Follow-­ up includes
assessment to ensure appropriate sensing, assessment
of stimulation thresholds, estimated battery life and
lead integrity. Technical support can also be provided
by the companies that produce pacemakers.7 Expert
pacemaker technician input is required to: assess the
intrinsic rhythm (and to maximise the potential for
the heart to use it), optimise battery life, ensure pacing
outputs have an adequate safety margin and determine
the best rate settings.8
In children, special attention should be paid to
increases in stimulation threshold or impedance (the
ratio of voltage to current in the electrical circuit).
This may signify lead dysfunction.9 These clinics
Figure 1 Chest X-­ray demonstrating an epicardial pacemaker. The are also an opportunity for pacemaker settings to be
pulse generator is below the diaphragm, the lead is seen to commence altered, including upper and lower heart rates of the
at the generator, cross the diaphragm and terminate at the right pacemaker. For some children, the pacemaker acts as a
ventricular apex. Although in this patient the generator is on the right-­ backup only. During periods when the heart rate will
hand side, it is most often seen inserted on the left-­hand side. likely be lower (eg, during sleep) it can be set to only

Kendall IS, et al. Arch Dis Child Educ Pract Ed 2025;110:70–74. doi:10.1136/archdischild-­2023-­326825 71
 Interpretations

Arch Dis Child Educ Pract Ed: first published as 10.1136/archdischild-2023-326825 on 14 July 2024. Downloaded from http://ep.bmj.com/ on April 16, 2025 at Royal College of
Figure 5 Example of DDD pacing; triggering of both atrium and
ventricle are demonstrated. Note the small atrial pacing spikes (A)
before each P wave and small ventricular pacing spike (V) before each
wide QRS wave.

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Figure 6 Further example of DDD. A ventricular pacing spike is seen
after every native P wave initially. Then at beat 10 there is a longer
pause (as indicated) between the native P wave and a ventricular
pacing spike. This is followed by a paced atrial P wave (P) with a
different morphology, before reverting to native P waves followed by
paced ventricular complexes.

which necessitate intravenous antibiotics and potential

surgical removal.12 While these investigations help to
assess pacemaker function, a full interrogation of the
pacemaker should be performed. This may also help
with the diagnosis of any tachyarrhythmia. Reviewing
telemetry results will help ensure that the base rate
is being achieved and that there is an appropriate

Paediatrics and Child Health .

increase in heart rate on exertion (if programmed).13

CHEST RADIOGRAPHS
In the case of the epicardial pacemaker, the lead(s) will
Figure 3 Lateral chest X-­ray demonstrating a lead fracture. Old be seen to emerge from the pulse generator below the
fractured epicardial bipolar leads (O) (arrow at fracture site), replaced diaphragm and attach to the heart. The lead(s) should
with a new unipolar lead anteriorly (N). This figure highlights the be continuous with no interruption before inserting
importance of carefully tracing each lead individually and comparing onto the atria or ventricle (figure 1). Young children
with previous radiographs as fracture may be quite subtle as in this
may have excess, sometimes coiled, lead to prevent
case.
lead fracture or dislodgement with growth. Ideally,
an extended PA CXR should be obtained to view lead
pace if the spontaneous rate falls below a lower limit position. Lateral films may also help. Comparison
below the programmed lower-­paced rate; this feature with CXRs performed immediately postimplant helps
is known as hysteresis.10 Application of a magnet to a ensure lead and generator position is unchanged.
pacemaker generally causes it to pace asynchronously, An endocardial pacemaker CXR shows the pulse
however, this varies between models.11 generator in the chest (often on the left side) with
the lead following the course of the subclavian vein,
INVESTIGATING PACEMAKER-RELATED joining the superior vena cava and entering the heart
PRESENTATIONS (figure 2).
Children may present with diverse symptoms such
as chest pain, palpitations, syncope or pectoral
muscular twitching prompting CXR and ECG. They
may also have these investigations performed as part
of a workup for unrelated symptoms. Patients may
present with lead erosion or generator site infections

Figure 4 Example of VVI pacing. Note the tall pacing spikes at

a regular interval (120 beats per minute) followed by a negatively
deflected QRS complex. P waves are present (labelled above) but are
dissociated and bear no relation to pacing either. Figure 7 (See question 4).

72 Kendall IS, et al. Arch Dis Child Educ Pract Ed 2025;110:70–74. doi:10.1136/archdischild-­2023-­326825
 Interpretations

Arch Dis Child Educ Pract Ed: first published as 10.1136/archdischild-2023-326825 on 14 July 2024. Downloaded from http://ep.bmj.com/ on April 16, 2025 at Royal College of
Lead fracture (figure 3) is diagnosed when the leads
Clinical bottom lines
are not continuous on a CXR; they may also exhibit
a sudden change in impedance on interrogation.8 In
► Common indications for paediatric pacemakers include
pacing-­dependent children, a lead fracture may neces-
heart block and sinus node disease.
sitate external pacing or placement of a temporary ► Lead fracture can be diagnosed via CXR.
transvenous wire. A CXR can also diagnose complica- ► Knowledge of pacemaker modality aids ECG
tions with implantation, for example, pneumothorax interpretation.
and pericardial effusion.14 ‘Twiddler’s Syndrome’ ► Full pacemaker interrogation is essential if malfunction
describes how a patient may distort a pacemaker by is suspected and may also help with tachyarrhythmia
twisting the leads or pulse generator.15 Cardiac stran- diagnosis.

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gulation is a rare complication of epicardial pace-
makers in which the leads encircle the heart causing
ischaemic, valvar or myocardial dysfunction.16 MRI
Most modern pacemakers are MRI ‘conditional’.
COMMON PACEMAKER SETTINGS Older systems may be unsafe. Consultation with the
VVI manufacturer should be considered before scanning
This setting is often used in epicardial pacemakers in
patients with postoperative heart block or small chil-
dren with congenital heart block. The pacemaker has Test your knowledge
a lead attached to a ventricle which will discharge
a pacing potential unless an intrinsic ventricular 1. The most common indications for pacemakers in the
discharge is sensed within a certain time limit, in paediatric population include
which case it will be inhibited. It is a relatively simple A. Complete heart block
modality, unable to provide AV synchrony (figure 4). B. Asymptomatic bradycardia

Paediatrics and Child Health .

C. First-­degree heart block
DDD D. Brugada syndrome
DDD is another common setting which achieves AV E. Wolff-­Parkinson-­White syndrome
synchrony and is considered more physiological. It 2. Chest radiography can help diagnose which of these
requires atrial and ventricular leads. The atrial lead will pacemaker problems/malfunctions?
either sense a native atrial depolarisation and inhibit a A. Rising stimulation threshold
pacing impulse or if there is no native atrial depolarisa- B. Cardiac strangulation
tion within an elapsed time, pace the atrium. Similarly, C. Pulse generator failure
the ventricular lead will either provide a paced impulse D. Lead fracture
or be inhibited. The AV delay is set to maintain a phys- E. Oversensing
iological response while giving appropriate time to 3. Which code describes a pacemaker which senses both
‘encourage’ a native ventricular response8 (figures 5 the atrium and ventricle and (sometimes) paces both?
and 6). A. VVI
B. AAI
APPROACH TO THE ECG OF A PACEMAKER C. V00
PATIENT D. DDD
A comprehensive analysis of ECGs of paced patients E. A00
is beyond the scope of this article. However, some tips 4. Regarding figure 7, what mode of pacing does this
include: represent?
► When interpreting ECGs of patients with a pacemaker, A. VVI
assess the morphology of P waves, QRS complex and the B. AAI
presence of pacing spikes, noting their relationship to P C. V00
waves and QRS complexes. D. DDD
► A pacing spike before a P wave indicates the atrium is E. A00
paced and a spike before a QRS indicates ventricular
pacing. This assumes that the pacing impulse has depo- 5. Which of these advantages applies to endocardial
larised (captured) the relevant chamber. pacemakers compared with epicardial pacemakers?
► There may be native (non-­paced) waves on the same A. Useful in smaller patients
trace and it is important to distinguish the two. B. Reduced risk of thrombosis
► Native waves may be appropriate in pacemakers with C. Inserted transvenously
inhibitor settings. Two consecutive pacing spikes of the D. Longer lifespan
same type (atrial or ventricular) indicate the paced rate. E. Reduced risk of endocarditis
► Pacing spikes are not always easy to appreciate and
Answers to the quiz are at the end of the references.
changing the gain voltage on the ECG machine may help.

Kendall IS, et al. Arch Dis Child Educ Pract Ed 2025;110:70–74. doi:10.1136/archdischild-­2023-­326825 73
 Interpretations

Arch Dis Child Educ Pract Ed: first published as 10.1136/archdischild-2023-326825 on 14 July 2024. Downloaded from http://ep.bmj.com/ on April 16, 2025 at Royal College of
and the ability to reprogramme the device must be 8 Chiu-­Man C. How pacemakers work and simple
readily available.17 programming: a primer for the non-­electrophysiologist.
Cardiol Young 2017;27:S115–20.
9 Bernstein AD, Daubert J, Fletcher RD, et al. The revised
Funding The authors have not declared a specific grant for this research from NASPE/BPEG generic code for antibradycardia, adaptive rate
any funding agency in the public, commercial or not-­for-­profit sectors. and multisite pacing. Pacing Clin Electrophys 2002;25:260–4.
10 Park MK, Salamat M. Park’s the paediatric cardiology
Competing interests None declared.
handbook. Elsevier, 2022:358–67.
Patient consent for publication Not applicable.
11 Jacob S, Panaich SS, Maheshwari R, et al. Clinical applications
Ethics approval Not applicable. of magnets on cardiac rhythm management devices. Europace
Provenance and peer review Not commissioned; externally peer 2011;13:1222–30.

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reviewed. 12 García-­Izquierdo E, Vilches S, Castro V. Is this pacemaker
functioning abnormally? Circulation 2017;135:711–3.
ORCID iD
13 Czosek RJ, Meganathan K, Anderson JB, et al. Cardiac
Ian Scott Kendall http://orcid.org/0000-0001-9452-0629
rhythm devices in the pediatric population: utilisation and
complications. Heart Rhythm 2012;9:199–208.
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74 Kendall IS, et al. Arch Dis Child Educ Pract Ed 2025;110:70–74. doi:10.1136/archdischild-­2023-­326825