WHAT IS A PACEMAKERNoran IbrahimTRG, Tanta University

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.

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.

FUNDEMENTALS OF ELECTRICITY OHM’s Law

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 VCurrent (I)

• Current is the flow of the electrical charge and is typically measured in milliamperes or mA.

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.

Did we

get it ??

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.

PACING LEADS

Polarity

Fixation

Steroid eluting

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.

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.

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.

EVOLUTION OF THE PACING THRESHOLD

Steriod eluting leads