The Journal of the Arkansas Medical Society Med Journal March 2019 Final 2 | Page 11

expanding tiles to fix it into the RV myocardium. It
differs from the Nanostim device in that it is not re-
trievable, but it is small enough that another device
can be introduced when the battery dies. It utilizes
a VVIR pacing system, with the rate response based
on a three-axis accelerometer rather than the tem-
perature sensors. Pacing with low pulse allows for
longer battery life, and it is programmed via radio-
frequency transmission. The other important fea-
ture is that it is MRI safe.
Advantages & Disadvantages
Despite their widespread use, conventional
device complications remain high. Up to 10% of
patients undergoing pacemaker device implan-
tation develop complications, with 6% chance of
major complications such as venous thrombosis or
tricuspid valve regurgitation. 8
Electrical leads are very reliable and flexible,
yet they are accountable for a majority of these
complications. At the time of implantation, the inci-
dence of traumatic events, including pneumothorax
and cardiac perforation, can go up to 1-2.7%. 9,10
Lead dislocation rates at the time of implantation
and within 30 days are 2.4-3.3% (9,10). Long-term
risks include lead fracture (1-4%) (11), venous ob-
struction (8-21%),1 2 tricuspid regurgitation (5%), 8
and infection (1-2%). 13 Furthermore, pocket-infec-
tion rates for TV systems are 1-2% at initial implant
and 3-4% after generator changes. 13
Leadless systems can also be very helpful in
patients with complicated vascular access where
conventional pacemakers cannot be utilized. Com-
paring the rates of complications, the reported rate
of pericardial effusion associated with conventional
pacemakers is 1% versus 1.5% in LCP and 1.6%
in TPS implants. 9,14)
Dislocation of the leadless system is not un-
common as well. Six dislocations of the Nanostim
device occurred 1-14 days after implantation: four
in the pulmonary artery and two in the femoral
vein, 15 but no long-term dislocations occurred. All
devices were then successfully removed without
complication by using snares. 5 No dislodgements
were reported from the Micra study.1 5
The most significant limitation of the Nanostim
and Micra devices is the restriction to single-cham-
ber, ventricular pacing. Single-chamber pacemak-
ers, both atrial and ventricular devices, make up
less than 10% of pacemaker implants. 16 The most
common reasons for implantation in the Leadless II
Study were chronic atrial fibrillation with slow ven-
tricular response (56%), sinus rhythm with infre-
quent pauses or syncope (34%) and sinus rhythm
with high-grade AV block (9%). 5 In the Micra study,
advanced AV block was the most common indi-
cation (49%), followed by sinus node dysfunction
(43%). 15 Dual-chamber pacing allows for atrioven-
tricular synchrony, which has been shown to mini-
mize pacemaker syndrome. Furthermore, chronic
ventricular pacing can lead to ventricular dyssyn-
chrony and systolic heart failure. 16
Indications & Contraindications
The most common indications for permanent
pacemaker implantation are sinus node dysfunc-
tion and high-grade, or symptomatic, atrioven-
tricular (AV) block. This is no different from leadless
systems, with the previously discussed drawback
of being only single-chamber pacers. Guidelines for
implantation of cardiac pacemakers have been es-
tablished by a collaboration of the American College
of Cardiology, the American Heart Association, and
the Heart Rhythm Society (ACC/AHA/HRS). 16 The
need for permanent pacing in patients with sinus
node dysfunction is based largely upon the correla-
tion of bradycardia with symptoms or symptomatic
chronotropic incompetence. Acquired AV block is
the second most common indication for permanent
pacemaker placement. 16 Other less common indi-
cations are congenital heart block, neuromuscular
disease, long QT syndrome, HOCM, or heart failure.
Other similar contraindications are syncope
of undetermined etiology, which requires exten-
sive investigations before putting a pacemaker; si-
nus bradycardia without significant symptoms, or
sinoatrial block / sinus arrest, without significant
symptoms. Asymptomatic, prolonged RR intervals
with atrial fibrillation or other causes of transient
ventricular pause are also not an indication for
pacing. 16
Asymptomatic, second-degree Mobitz I
(Wenckebach) AV block, reversible AV block such
as those associated with electrolyte abnormalities,
Lyme disease, sleep apnea, enhanced vagal tone,
and some cases that occur postoperatively usually
do not require permanent pacing. 16
Future Research
It is evident that the absence of a TV lead
decreases the complications of these devices’ in-
sertion, and since they are fairly new to practice,
more research and studies are needed to further
validate their use in practice guidelines. Areas of
research should include developing smaller and
less traumatic delivery systems to avoid mechani-
cal complications. Development of multi-chamber
or dual-chamber devices would eliminate hesitancy
involved in choosing the leadless system for pa-
tients. More research is warranted to further formu-
late their efficacy.
Conclusion
Despite their recent introduction into practice,
leadless cardiac devices have shown promising
results and encouraging outcomes in terms of ad-
dressing patients’ morbidities. Even though their
revolutionary design stands out, more research
and studies are needed to follow up on their long-
term complications and to overcome their design
limitations.
References:
1. Landegren J, Elmqvist R, Petterson S. Artificial
pacemaker for treatment of Adams-Stokes
syndrome and slow heart rate. American Heart
Journal. 1963;65(6):731-48.
2. Mond HG, Proclemer A. The 11th World Sur-
vey of Cardiac Pacing and Implantable Car-
dioverter-defibrillators: Calendar Year 2009
– a World Society of Arrhythmia’s project.
Pacing – Clinical Electrophysiology: PACE.
2011;34:1013-27.
3. El-Chami MF, Merchant FM, Leon AR. Leadless
Pacemakers. American Journal of Cardiology.
2017;119(1):145-8.
4. Reddy VY, Knops RE, Sperzel J, Miller MA, Petru
J, Simon J, et al. Permanent leadless cardiac
pacing: Results of the LEADLESS trial. Circula-
tion. 2014;129(14):1466-71.
5. Doshi R, Bunch TJ, Tomassoni GF, Friedman PA,
Estes NAM, Ip J, et al. Percutaneous Implanta-
tion of an Entirely Intracardiac Leadless Pace-
maker. 2015:1125-35.
6. Duray GZ, Ritter P, El-Chami M, Narasimhan
C, Omar R, Tolosana JM, et al. Long-term per-
formance of a transcatheter pacing system:
12-Month results from the Micra Transcatheter
Pacing Study. Heart Rhythm. 2017;14(5):702-9.
7. Reddy VY, Miller MA, Neuzil P, Butter C, Seifert
M, Delnoy PP, et al. Cardiac Resynchronization
Therapy With Wireless Left Ventricular Endo-
cardial Pacing. 2017;69(17).
8. Kirkfeldt RE, Johansen JB, Nohr EA, Jørgensen
OD, Nielsen JC. Complications after cardiac
implantable electronic device implantations:
an analysis of a complete, nationwide cohort in
Denmark. 2014. p. 1186-94.
9. Udo EO, Zuithoff NPA, Hemel NMV, Cock CCD,
Hendriks T, Doevendans PA, et al. Incidence
and predictors of short- and long-term compli-
cations in pacemaker therapy : The FOLLOW-
PACE study. HRTHM. 2012;9(5):728-35.
10. Ellenbogen KA, Hellkamp AS, Wilkoff BL, Camu-
nas JL, Love JC, Hadjis TA, et al. Complications
arising after implantation of DDD pacemakers:
the MOST experience. The American Journal of
Cardiology. 2003;92(6):740-1.
Contact AMS for a complete list of references.
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