A pacemaker is an electronic device implanted in the body to regulate the heart rhythm. It consists of a battery and electronic circuit enclosed in a sealed can that delivers electrical stimuli to the heart through leads and electrodes. The pacemaker contains a lithium-iodide battery, circuit board, telemetry coil, and header ports enclosed in a titanium casing. Pacemaker leads can be unipolar or bipolar, referring to the number of electrodes, and use fixation mechanisms like tines or an active helix to attach to the heart muscle.

1. WHAT IS A PACEMAKER
Noran Ibrahim
TRG, Tanta University

2. WHAT IS A PACEMAKER
 A pacemaker is an electronic
device implanted in the body
to regulate the heart rhythm.
 It consists of a battery and
electronic circuit enclosed
within a sealed can. It
delivers the electrical stimuli
over leads with electrodes at
their ends in contact with the
heart.

3. PULSE GENERATOR
 Contains a lithium iodide battery which is used to
produce electricity.
 The hybrid is the circuit board necessary for the
pacing and sensing.
 The telemetry coil is used by the programmer to
communicate with the implanted device.
 The header containing the ports for the leads.
 Outer casing made of
titanium as it is biocompatible
and rarely provokes patient allegy.

4. FUNDEMENTALS OF ELECTRICITY
 OHM’s Law

5. VOLTAGE (U)
 Voltage is defined as the
difference in electrical potential
between two points, but for device
clinicians, we can think of voltage
as the push or force that causes
electrons to move through a
circuit. It is measured in volt (V).
 Normal battery voltage at
implantation is 2.8 V, as we reach
th EOL the voltage becomes 2.1-
2.4 V
Current (I)
• Current is the flow of the
electrical charge and is typically
measured in milliamperes or mA.

6. RESISTANCE (R)
 Resistance is the opposition to the current flow and is
measured in units called ohms (Ω). Can also be
expressed as impedence. The resistance comprises
that of the leads and the cardiac tissue.

8. BATTERY
 Modern
pacemakers rely
on a lithium-iodide
battery, a very
long-lived battery
with a reliable
discharge curve,
that is, they
behave in very
predictable ways.

10. PACING LEADS
Polarity
Fixation
Steroid
eluting

11. POLARITY
 Pacing systems are either unipolar or bipolar, which refers to how many poles are
on the distal end of the lead, that is, whether the lead has one electrode (unipolar)
or two electrodes (bipolar) at the tip.
 The unipolar pacing system uses the tip electrode on the lead as the cathode and
the pacemaker itself as the anode. On the other hand, a bipolar pacing system uses
the tip electrode as the cathode and a ring electrode on the lead as the anode.

12. WHICH IS BETTER ??
• Before technological advances made today unipolar
leads were much thinner but nowadays bipolar leads are
nearly just as thin as unipolar leads.
 Bipolar leads offer a redundancy advantage, in that if the outer
conductor should fracture, the lead can still be used by programming
the system to unipolar. If a unipolar lead loses its one conductor, it
can no longer function.
 Myopotentials refer to electrical signals generated from the muscles
of the body. Muscle noise occurs in everybody, particularly in active
people. A unipolar pacemaker—with its wide antenna going from tip
electrode to can—is far more sensitive to myopotentials than a
bipolar pacemaker. A unipolar pacemaker may sense a myopotential
and misinterpret it as a cardiac signal. If the pacemaker senses a
myopotential and perceives it as a cardiac signal, it will
inappropriately inhibit the pacing output pulse.

14. FIXATION
 Passive-fixation
mechanisms are
protrusions at the lead tip,
usually tines or fins, which
embed themselves into
the trabeculae within the
heart. The fixation is
passive, that is, nothing is
attached; the lead is just
snagged into the dense
fiber-like structures inside
the heart. Over time, the
lead will fibrose itself into
place.
• An active-fixation lead
has a helix or corkscrew
at the tip, which is
actively twisted into place
to affix the lead to the
myocardium.
• An active lead is easier to
extract because there is
less fibrosis.

15. EVOLUTION OF THE PACING THRESHOLD
Steriod
eluting
leads