Canan Ayabakan MD, Eric Rosenthal MD FRCP
Evelina Children's Hospital, Guy’s & St Thomas’ Hospital Trust,
Lambeth Palace Road, London SE1 7EH, UK.
Address for
correspondence: Dr Eric Rosenthal MD FRCP MRCPCH, Consultant
Paediatric Cardiologist, Evelina Children's Hospital, Guy’s & St
Thomas’ Hospital Trust, Lambeth Palace Road, London SE1 7EH, UK.
E-mail:
eric.rosenthal@kcl.ac.uk
Abstract
Transvenous pacemaker lead
implantation is the preferred method of pacing in adult patients. Lead
performance and longevity are superior and the implantation approach
can be performed under local anaesthetic with a very low morbidity. In
children, and especially in neonates and infants, the epicardial route
was traditionally chosen until the advent of smaller generators and
lead implantation techniques that allowed growth of the child without
lead displacement. Endocardial implantation is not universally
accepted, however, as there is an incidence of venous occlusion of the
smaller veins of neonates and infants with concerns for loss of venous
access in the future. Growing experience with lower profile leads,
however, reveals that endocardial pacing too can be performed with low
morbidity and good long-term results in neonates and infants.
Key Words: Pacemaker;
Endocardial pacing; Epicardial pacing; Lead extraction
Cardiac pacing in infants and children has evolved considerably since
the initial implants over half a century ago. Pacemaker generators have
become smaller and are now easily accommodated subcutaneously or
submuscularly either in the chest or the abdominal wall in the smallest
of infants. Improvements in lead technology have enabled lower chronic
thresholds with greater mechanical and electrical integrity and
longevity of the leads and the pacemaker system. While endocardial
leads have consistently proven to be superior to epicardial leads both
mechanically and electrically, the development of steroid eluting
epicardial leads has improved the effectiveness of epicardial systems
1. The child who receives a pacemaker will
undergo several additional interventions to replace the generator with
or without the lead itself during his/her lifetime. Special
consideration should therefore be given when selecting the most
appropriate pacing system in the very small.
The choice of
the method of permanent pacing is determined by the patient’s size, and
presence of structural heart disease. While a large body of opinion
holds that neonates and infants should receive epicardial pacing systems
2-4, experience with
endocardial leads in the smallest of infants is building up (
Figure 1). The favourable outcome of
endocardial leads in small infants is not limited to anecdotal case
reports
5-10.
The largest experience to date from two centres (Guy’s Hospital and
Wilhelmina Children’s Hospital) in 39 infants ≤ 10kg was published
recently by Kammeraad et al
11.
After a relatively long follow-up period of a median 4.3 years (up to
15.3 years), 31 of 36 patients (86%) continued with an endocardial
system and 27 of them had the original endocardial lead. Two
endocardial systems had to be replaced with epicardial systems and
pacing therapy was stopped in three patients because it was no longer
indicated. Lead survival was excellent with 87% of those with their
first or second generator continuing with the original lead -
comparable to the results of epicardial leads in older children
12. Indeed in a similarly aged cohort, a
significant number of epicardial lead failures were reported in
neonates within the first year of implantation due to acute exit block
and lead fractures
13.
Figure
1. Left panel shows lead position in a baby with congenital
complete heart block who was born prematurely with hydrops. A
transvenous endocardial pacemaker was implanted at the age of 8 weeks
when she weighed 2.95 kg. At 5 years of age (weight 17.2 kg), she still
has the initial lead and generator (right panel). The redundant loop of
lead formed in the right atrium has not yet been taken up and will
allow generator replacement without the need for lead advancemenrt.
Venous obstruction
Endocardial
leads are increasingly preferred for small infants in other centres as
well
14-16.
The reasons for this preference are lower acute and chronic threshold
values and decreased surgical morbidity from the procedure. The risk of
venous occlusion, however, is the major drawback of endocardial lead
placement in neonates and infants. If an adequate amount of slack is
not left in the heart to cater for growth and the lead cannot be
advanced, then replacement will be needed. If the lead cannot be
replaced due to venous occlusion then the contralateral subclavian vein
will need to be used and this may reduce the options for venous access
in the future. Although transfemoral and transhepatic pacing can be
performed with good results, few centres advocate these routinely
17-18. Accordingly some
centres still prefer to implant epicardial leads in children less than
10 kg
2-4,13.
In some centres the policy is one of replacing epicardial systems
electively with an endocardial system at the end of life of the first
generator due to an increase in lead fractures with time
13.
Studies
specifically comparing pacing via the endocardial route versus the
epicardial route in small infants are lacking. The incidence of venous
obstruction and occlusion has rarely been addressed. Venous obstruction
due to endocardial leads in a small group of newborns and infants was
assessed by Stojanov et al
16.
In 12 children younger than 12 months, who had endocardial leads
implanted via the cephalic vein, only two had ultrasonographic evidence
of partial (up to 20%) venous occlusion at the end of a mean follow-up
of 85.2 pacing months. Only four patients were reported to have
asymptomatic venous occlusion during lead extraction among the 36
neonates and infants reported by Kammeraad et al
11. Asymptomatic venous occlusion was not
systematically looked for however, and the incidence may therefore be
higher in this cohort who had their leads implanted via a subclavian
puncture. Even in older children, the incidence of venous occlusion may
be as high as 21% in endocardial leads depending on the lead diameter,
body surface area and the introduction site (subclavian vein versus
cephalic vein) of the lead
19.
Stojanov et al
promote a cephalic vein cut down rather than a subclavian puncture
approach in the very small
15.
It may be that avoidance of the relatively large sheath needed for a
subclavian puncture to introduce the lead tip, which is larger than the
lead body, has an advantage. Whether late venous obstruction depends
more on the size of the subclavian introducer and acute trauma produced
at the time of vein puncture or the diameter of the lead left in
the vein has not been systematically investigated.
Lead Extraction
Endocardial
pacing in neonates is not for the faint-hearted as lead replacement is
likely to be needed in at least some of the patients. While extracting
11 leads uneventfully in nine patients (including atrial leads placed
at the second or third system), Kammeraad et al
11
had to abandon a ventricular lead,
which was adherent to the atrial myocardium. Extraction techniques are
continuing to improve and lead replacement through an occluded
subclavian vein is now possible using countertraction sheaths. A
technique for femoral extraction that allows preservation of guidewire
access across an occluded subclavian vein (
Figure 2) is described by Kammeraad
et
al
11. Downsizing extraction
countertraction sheaths for smaller leads may allow their safe use even
in small children. In older children, standard diathermy and laser
extraction sheaths can be used safely.
Figure 2. An infant with
congenitally corrected transposition (cTGA) developed heart failure
with the onset of complete heart block and was paced at 6 weeks of age (a). At 4 years the generator reached
its end of life with some remaining lead slack (b). During the generator change, the
lead was inadvertently damaged and had to be replaced. Angiography
revealed an occluded subclavian vein (c).
To avoid the use of large countertraction sheaths from the subclavian
approach, a coronary guidewire was passed into the lead stylet channel
and was drawn out the femoral sheath with the lead after snaring the
lead with the help of a tip deflector wire (d). Over the subclavian-femoral
guidewire circuit, a new sheath was placed to implant a new ventricular
lead (e).
Although
epicardial leads do not carry a risk of venous thrombosis, there is an
increased perioperative morbidity
13.
Patients who are already a candidate for a sternotomy or thoracotomy
for the correction of heart defects may benefit from epicardial leads
especially when dual chamber pacing is required for atrioventricular
synchrony to improve the postoperative hemodynamics. However
postoperative infections and pericarditis may preclude epicardial lead
placement, in which case an endocardial pacing system is the best choice
11,13. While some
surgical heart block patients require dual chamber pacing, the majority
of infants and neonates who require pacing, are well served by a single
chamber system that can be implanted endocardially. Transvenous dual
chamber pacing is possible but generally avoided due to the increased
risks of venous occlusion
11,14.
Early pacing with a dual chamber system may lead to a cardiomyopathy
due to pacing induced ventricular dysynchrony which is aggravated by
the higher rates found with atrial tracking in the very young
20,21
Conclusions
Neither the
epicardial nor the endocardial approach in permanent pacing is free
from complications. The experience reported with endocardial pacing in
neonates and infants while encouraging is limited and no directly
comparative data with epicardial pacing are available. Although the
clear advantage of endocardial pacemaker implantation over the
epicardial approach has yet to be demonstrated, the growing experience
indicates that endocardial pacing is feasible and effective even in
neonates and small infants - and it is an acceptable alternative to
epicardial systems. The current disadvantages of endocardial leads may
be overcome in the future by downsizing of the leads and extraction
systems. The ultimate approach in very small children currently will
depend on the facilities and experience of the surgeons and
cardiologists in each centre.
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