Pacemakers are implantable devices used to control heart rate and rhythm, and a pacemaker system, at its simplest, comprises body tissue and these components:
- Pulse Generator
- Power source
- Computer system
- Leads
- Deliver the pulse to the electrodes
- Electrodes
- Anode (positive)
- Cathode (negative)
The pulse generator is the main body of the pacing system. It contains the:
- Casing/Can
- Titanium – lightweight, biocompactible, stronger than steel
- Connector/header
- Battery
- Largest single component
- Lithium Iodide
- Circuitry components
Battery
- Low self-discharge rate
- LiI battery
- Long shelf life/ high energy density
In single chamber pacing, longevity sits at circa 7 – 12 years.
Dual chamber is 6 – 10 years
Reducing the output voltage of the battery by half, can increase the battery life of the device by up to 2x
Leads and Electrodes
- Impulse delivery to the heart
- Sensing of depolarisation
Leads are characterised based on their;
- Positioning
- Endocardial/transvenous
- Epicardial
- Applied exteriorly
- Fixation mechanism
- Active/Screw-in
- Screw helix extends into endocardial tissue
- Can be placed anywhere within the heart’s chamber
- Passive/Tined
- Tines become lodged in endocardial trabeculae
- Active/Screw-in
- Shape
- Straight
- “J-shaped”
- Insulator
- Silicon
- Polyurethane
- Polarity
- Unipolar
- Bipolar
Lead electrodes come in many varieties, some examples of which are given below.
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