design has improved to provide greater stability
at the interface with the myocardium, and less
susceptibility to fl exion damage. Where Arne
Larsson’s fi rst device provided only one pacing
mode – asynchronous VOO pacing – modern
microprocessor-driven devices are increasingly
sophisticated and can employ various algorithms
to optimise the pacing mode, depending on the
patient’s needs. 2
Today, permanent pacemaker implantation has
become routine for bradyarrhythmia management.
Worldwide, more than 700,000 pacemakers are
implanted annually, with around 35,000
implanted in the UK. 3,4 Although it has become
a routine procedure and is very safe for most
patients, problems relating to the leads, venous
access or the pocket may occur. In the immediate-
to short-term, the most signifi cant potential
complications include haematoma, pneumothorax,
lead displacement or, rarely, cardiac perforation
and tamponade. 5 Device infection, which in turn
may lead to septicaemia and endocarditis, carries
a mortality of up to 35% and normally warrants
device extraction, with its own inherent risk of
myocardial or vascular injury. 6 Other, longer-term
complications, such as chronic lead failure from
insulation damage or lead fracture, warrant
a repeat procedure to replace the faulty lead. The
risk of complications increases with the number
of procedures required during a patient’s lifetime.
A pacemaker recipient in his/her early 50s, for
example, might expect to have a further three
of four battery change procedures on top of the
initial implantation, and with each opening of the
pocket, the risk of infection rises.
Leadless pacemakers
Although there have been continuous
developments in pacemaker technology over the
last 60 years, a standard transvenous pacemaker
today consists, in essence, of the same components
it ever has: a pulse generator, including battery
and circuitry, and at least one lead to deliver an
electrical stimulus to the myocardium and to
transmit any signals of intrinsic myocardial
electrical activity back to the generator.
Table 1
Characteristics of the Nanostim™ LCP, Micra™ TPS and single chamber
transvenous system
Parameter Nanostim™ LCP Micra™ TPS Dimensions (mm)
Volume (cm 3 )
Weight (g)
Fixation mechanism 42 x 5.99
1.0
2.0
Screw-in helix 25.9 x 6.7
0.8
2.0
Four nitinol tines Polarity
Estimated battery
longevity
• Standard settings*
• Alternative settings†
Major complications
overall
Hospitalisation
System revision
Cardiac injury
Access site complication Bipolar Bipolar Single chamber
transvenous system
(Medtronic Azure S SR
MRI SureScan)
42.6 x 50.8 x 7.4
12.25
22.5
Active lead: screw-in
helix
Passive lead: tines
Bipolar or unipolar
9.8 years
14.7 years
6.7% 4.7 years
9.6 years
4.0% 14.3 years
–
7.4%
–
1.9%
1.6%
1.2% 2.3%
0.4%
1.6%
0.7 3.9%
3.5%
1.1%
1.6%
* Longevity based on fi xed programming at the ISO International Organisation for Standardisation (ISO 14708) standard guidelines for
reporting pacemaker battery duration longevity: 2.5V, 0.4ms, 600 Ω, 60 beats/min, 100% pacing.
† Longevity based on nominal settings: 1.5V, 0.24ms, 500 Ω, 60 beats/min, 100% pacing
LCP Leadless cardiac pacemaker
TCP Transcatheter pacing system
12
HHE 2018 | hospitalhealthcare.com
Figure 2
A standard single chamber
pacemaker with the
Micra™ Transcatheter
Pacing System.
Reproduced with permission
of Medtronic, Inc.