1. Basic Concepts—Electricity and Pacemakers Module 3
Student Notes
An introduction to the fundamental electrical concepts used in pacing and defibrillation.
This module will teach you the baseline information necessary for working toward more advanced knowledge in pacemaker operation.
It is possible that you may want additional supplemental materials to enhance your knowledge or provide more practice. If you feel this is necessary for you, ask your instructor for suggestions on books or other tools.
Instructor Notes
This module should take approximately 2 hours to cover.
To deliver this module, the following materials are recommended:
Printed participant guides for each participant
Overhead projector and screen
Optional: Whiteboard or flip chart
While delivering the module, engage the learners by asking questions and getting them to talk about the subject based on their previous knowledge.
Evaluate the learners by delivering the knowledge check at the end of this module. An acceptable score is 100% (there are only two questions, and both must be answered appropriately).
World Headquarters
Medtronic, Inc.
710 Medtronic Parkway
Minneapolis, MN
USA
Internet:
Tel: (763)
Europe
Medtronic International Trading Sàrl
Route du Molliau
Ch Tolochenaz
Switzerland
Tel: (41 21)
Asia-Pacific
Medtronic International, Ltd.
16/F Manulife Plaza
The Lee Gardens, 33 Hysan Avenue
Causeway Bay
Hong Kong
Tel: (852)
Canada
Medtronic of Canada Ltd.
6733 Kitimat Road
Mississauga, Ontario L5N 1W3
Tel: (905)
Toll-free: 1 (800)
Medtronic USA, Inc.
Toll-free: 1 (800)
(24-hour technical support for physicians and medical professionals)
Latin America
Medtronic USA, Inc.
Doral Corporate Center II
3750 NW 87th Avenue Suite 700
Miami, FL 33178
USA
Tel: (305)
UC d EN
Medtronic, Inc.
Minneapolis, MN
December 2007

2. Objectives Upon completion you will be able to:
Describe the relationship between voltage, current, and resistance
Describe the clinical significance of alterations in voltage, current, and resistance
Student Notes
Instructor Notes
Read and discuss the objectives.
Why is understanding these relationships significant to the audience?
This is the foundational information required to evaluate pacemaker performance and make some of the most basic and significant programming decisions.

3. Voltage Current Impedance
Characteristics of an electrical circuit: Including a pacemaker circuit
Voltage
Current
Impedance
Student Notes
Instructor Notes

4. Voltage
Voltage is the force, or “push,” that causes electrons to move through a circuit
In a pacing system, voltage is:
Measured in volts (V)
Represented by the letter “V”
Provided by the pacemaker battery
Often referred to as amplitude or pulse amplitude
Student Notes
The terms “amplitude” and “voltage” are often used interchangeably in pacing, undoubtedly to express “Voltage Amplitude,” which refers to the voltage output.
Instructor Notes

5. Current The flow of electrons in a completed circuit
In a pacing system, current is:
Measured in milliamps (mA)
Represented by the letter “I”
Determined by the amount of electrons that move through a circuit
Student Notes
Current: The movement of electricity, or free electrons, through a circuit. Current is measured in amperes and represented by the symbol I (capital I). One ampere is a unit of electrical current produced by 1 volt acting through a resistance of 1 ohm.
In pacing we express current as milliamps:
1 Ampere = 1000 milliamps
Instructor Notes

6. Impedance The opposition to current flow
In a pacing system, impedance is:
Measured in ohms (W)
Represented by the letter “R”
The measurement of the sum of all resistance to the flow of current
Student Notes
Impedance is the sum of all resistance to the flow of current. The resistive factors to a pacing system include:
Lead conductor resistance
The resistance to current flow from the electrode to the myocardium
Polarization impedance, which is the accumulation of charges of opposite polarity in the myocardium at the electrode-tissue interface
Instructor Notes
Resistance is a term used to refer to simple electric circuits without capacitors, and with constant voltage and current. Impedance is a term used to describe more complex circuits with capacitors and with varying voltage and current. Therefore, the use of the term impedance is more appropriate than resistance when discussing pacing circuits, although both are used.

7. Voltage, Current, and Impedance are Interdependent
The interrelationship of the three components is analogous to the flow of water through a hose
Voltage represents the force with which . . .
Current (water) is delivered through . . .
A hose, where each component represents the total impedance:
The nozzle, representing the electrode
The tubing, representing the lead wire
Student Notes
In this analogy, voltage can be thought of as water pressure delivered by the system. Current is analogous to the amount of water delivered at the end of the hose, and resistance is the sum of all the forces opposing this flow of water. For example, the restriction at the nozzle, the friction along the hose and pipes, even the atmospheric pressure the water must flow through once it exits the hose.
Increasing the force of the water (opening the valve more, or somehow increasing the water pressure) will deliver more water to the hose, but it will also increase some of the resistance (for example, the friction within the hose and pipes).
Instructor Notes
Each of these three components in an electrical circuit are interdependent – this analogy may help you understand the relationship.

8. Voltage, Current, and Impedance Recap
Voltage: The force moving the current (V)
In pacemakers it is a function of the battery chemistry
Current: The actual continuing volume of flow of electricity (I)
This flow of electrons causes the myocardial cells to depolarize (to “beat”)
Impedance: The sum of all resistance to current flow (R or W or sometimes Z)
Impedance is a function of the characteristics of the conductor (wire), the electrode (tip), and the myocardium
Student Notes
On this slide we have a review of the main terminology used to this point, and the symbols used to represent this concept in calculations, or perhaps in a medical record.
Instructor Notes

9. Voltage and Current Flow Electrical Analogies
Spigot (voltage) turned up, lots of water flows (high current drain)
Water pressure in system is analogous to voltage – providing the force to move the current
Student Notes
Using the garden hose as an analogy, the higher the voltage, the greater the push, or “flow” of electrons (and the greater the current drain).
Instructor Notes
This slide provides more information about the analogy on a mouse click. First ask the following question:
Ask: When the spigot is turned up, is there more or less water flow?
More—which is analogous to high current drain
Click your mouse to provide more information about the analogy.
Spigot (voltage) turned low, little flow (low current drain)

10. Resistance and Current Flow Electrical Analogies
Normal resistance – friction caused by the hose and nozzle
Low resistance – leaks in the hose reduce the resistance
More water discharges, but is all of it going to the nozzle?
Student Notes
Resistance affects current flow. Leads with an insulation breach, such as the garden hose pictured in the middle, will measure a low resistance reading with a resultant high current drain, and possible premature battery depletion. Conversely, if there is a high resistance, such as a lead conductor break (represented by the knot), the current flow will be low or non-existent.
Instructor Notes
An analogy for the effect of resistance on current flow.
High resistance – a knot results in low total current flow

11. V I R Ohm’s Law V = I X R I = V / R R = V / I V = I X R V R = I V I =
Describes the relationship between voltage, current, and resistance
V = I X R
I = V / R
R = V / I V = I X R V I R V R I =
Student Notes
If any two values are known, the third may be calculated (cover the value you are seeking and the others appear in the appropriate format to calculate the unknown value).
Instructor Notes V I = R

12. So What? Ohm’s law tells us:
If the impedance remains constant, and the voltage decreases, the current decreases
If the voltage is constant, and the impedance decreases, the current increases
So What?
Student Notes
Ohm’s Law provides the rationale for many of the decisions we will make when evaluating pacing systems and making programming decisions.
Instructor Notes
Ask: So, what is the CLINICAL significance to all this information?
Proper management of electrical characteristics is important for patient safety and device longevity

13. Status Check Start with: Solve for Current (I):
What happens to current if the voltage is reduced but the impedance is unchanged?
Start with:
Voltage = 5 V
Impedance = 500 W
Current = 10 mA
Solve for Current (I):
I = V/R
I = 5 V ÷ 500 W = Amps
Current is 10 mA
Reduce the voltage to 2.5 V
Voltage = 5 V
Impedance = 500 W
Current = ?
Is the current increased/ decreased or unchanged?
I = V/R
V = 2.5 V ÷ 500 W =
Amps or 5 mA
The current is reduced
Student Notes
If: Voltage = 2.5 V
Impedance = 500 ohms
1 Ampere = 1000 milliamps
Then use the formula I = V ÷ R to find I (the current).
The amount of current that flows through a pacemaker system is very small:
Use milliamps as a unit of measurement rather than amps. Convert amps to milliamps by multiplying amps by 1000 (or move the decimal three places to the right).
Instructor Notes
The clinical significance of reducing the current:
Ask: What affect will this have on the longevity of the pacemaker battery?
It will increase device longevity by reducing the drain on the battery
Ask: Will the pacing output still reliably capture the myocardium?
The less current the less likely you are to reliably capture the myocardium

14. Status Check
What happens to current if the impedance is reduced but the voltage is unchanged?
Start with:
Voltage = 5 V
Impedance = 500 W
Current = 10 mA
Solve for Current (I):
I = V/R
I = 5 V ÷ 500 W = Amps
Current is 10 mA
Reduce impedance to 250 W
Voltage = 5 V
Impedance = 250 W
Current = ?
Is the current increased/ decreased or unchanged?
I = V/R
V = 2.5 V ÷ 250 W =
0.02 Amps or 20 mA
The current is increased
Student Notes
If: Voltage = 5 V
Impedance = 250 ohms
1 Ampere = 1000 milliamps
Then use the formula I = V ÷ R to find I (the current).
The amount of current that flows through a pacemaker system is very small:
Use milliamps as a unit of measurement rather than amp. Convert amps to milliamps by multiplying amps by 1000 (or move the decimal three places to the right).
Instructor Notes
The clinical significance of increasing the current:
Ask: What effect will this have on device longevity?
It will increase battery drain and decrease device longevity.
Ask: Will the pacemaker reliably capture the myocardium?
The higher the current the more likely it is to capture the myocardium.
Ask: Could the patient notice any ill effects from increasing the current?
Yes, other muscles in the area of the pacing leads could be stimulated as well, for example the diaphragm.

15. Other terms Cathode: A negatively charged electrode
For example, the electrode on the tip of a pacing lead
Anode: A positively charged electrode
Examples:
The “ring” electrode on a bipolar lead
The IPG case on a unipolar system
More on this later (see: Pacemaker Basics)
Anode
Cathode
Student Notes
The cathode (more commonly called the tip electrode) is negatively charged, and the other electrode is positively charged. The anode may be the ring electrode on the lead, or it may be the case of the pacemaker when a unipolar lead system is used.
If the cathode is negative, and the anode is positive – what is the path the current (or electrons) take?
From cathode to anode.
Some other terms used are:
Charge: The quantity of electricity that has flowed
Charge (Coulombs or watt/hrs) = I x T (time)
Since voltage is relatively constant over battery life, “Charge” is essentially what is consumed as the battery depletes
Energy: The result of multiplying the force times the time
Energy (Joules) = V x I x T
Instructor Notes

16. Battery Basics So where does the current come from?
A battery produces electricity as a result of a chemical reaction. In its simplest form, a battery consists of:
A negative electrode (anode)
An electrolyte, (which conducts ions)
A separator, (also an ion conductor) and
A positive electrode (cathode)
Negative terminal
Anode
Separator
Cathode
Positive terminal
Student Notes
Using a typical “D” cell battery as an illustration:
When the battery is connected to an external load (e.g., myocardium):
A chemical reaction in the battery is initiated when a load is applied to the battery
For example, when a pacing pulse is applied
This reaction frees up electrons on the cathode
The electrons pass through the separator, and are conducted to the anode via the electrolyte where they collect on the anode
They flow from the anode through the myocardium and return back to the cathode
Via the myocardium
This electrons depolarize the muscle cells causing them to contract
When the external load is removed (i.e., the pacing stops), the chemical reaction in the battery ceases. Obviously, pacemakers and defibrillators do not use “D” cell or even wet-cell batteries, but the concepts for generating and moving electrons is the same.
Instructor Notes
Ask: Why not use rechargeable batteries?
The re-charging circuitry takes up space, making the devices ultimately significantly larger
They are not reliable enough to be used as a power source in circumstances that might be life-saving

17. Brief Statements Indications
Implantable Pulse Generators (IPGs) are indicated for rate adaptive pacing in patients who ay benefit from increased pacing rates concurrent with increases in activity and increases in activity and/or minute ventilation. Pacemakers are also indicated for dual chamber and atrial tracking modes in patients who may benefit from maintenance of AV synchrony. Dual chamber modes are specifically indicated for treatment of conduction disorders that require restoration of both rate and AV synchrony, which include various degrees of AV block to maintain the atrial contribution to cardiac output and VVI intolerance (e.g. pacemaker syndrome) in the presence of persistent sinus rhythm.
Implantable cardioverter defibrillators (ICDs) are indicated for ventricular antitachycardia pacing and ventricular defibrillation for automated treatment of life-threatening ventricular arrhythmias.
Cardiac Resynchronization Therapy (CRT) ICDs are indicated for ventricular antitachycardia pacing and ventricular defibrillation for automated treatment of life-threatening ventricular arrhythmias and for the reduction of the symptoms of moderate to severe heart failure (NYHA Functional Class III or IV) in those patients who remain symptomatic despite stable, optimal medical therapy and have a left ventricular ejection fraction less than or equal to 35% and a QRS duration of ≥130 ms.
CRT IPGs are indicated for the reduction of the symptoms of moderate to severe heart failure (NYHA Functional Class III or IV) in those patients who remain symptomatic despite stable, optimal medical therapy, and have a left ventricular ejection fraction less than or equal to 35% and a QRS duration of ≥130 ms.
Contraindications
IPGs and CRT IPGs are contraindicated for dual chamber atrial pacing in patients with chronic refractory atrial tachyarrhythmias; asynchronous pacing in the presence (or likelihood) of competitive paced and intrinsic rhythms; unipolar pacing for patients with an implanted cardioverter defibrillator because it may cause unwanted delivery or inhibition of ICD therapy; and certain IPGs are contraindicated for use with epicardial leads and with abdominal implantation.
ICDs and CRT ICDs are contraindicated in patients whose ventricular tachyarrhythmias may have transient or reversible causes, patients with incessant VT or VF, and for patients who have a unipolar pacemaker. ICDs are also contraindicated for patients whose primary disorder is bradyarrhythmia.

18. Brief Statements (continued)
Warnings/Precautions
Changes in a patient’s disease and/or medications may alter the efficacy of the device’s programmed parameters. Patients should avoid sources of magnetic and electromagnetic radiation to avoid possible underdetection, inappropriate sensing and/or therapy delivery, tissue damage, induction of an arrhythmia, device electrical reset or device damage. Do not place transthoracic defibrillation paddles directly over the device. Additionally, for CRT ICDs and CRT IPGs, certain programming and device operations may not provide cardiac resynchronization. Also for CRT IPGs, Elective Replacement Indicator (ERI) results in the device switching to VVI pacing at 65 ppm. In this mode, patients may experience loss of cardiac resynchronization therapy and / or loss of AV synchrony. For this reason, the device should be replaced prior to ERI being set.
Potential complications
Potential complications include, but are not limited to, rejection phenomena, erosion through the skin, muscle or nerve stimulation, oversensing, failure to detect and/or terminate arrhythmia episodes, and surgical complications such as hematoma, infection, inflammation, and thrombosis. An additional complication for ICDs and CRT ICDs is the acceleration of ventricular tachycardia.
See the device manual for detailed information regarding the implant procedure, indications, contraindications, warnings, precautions, and potential complications/adverse events. For further information, please call Medtronic at and/or consult Medtronic’s website at
Caution: Federal law (USA) restricts these devices to sale by or on the order of a physician.

19. Brief Statement: Medtronic Leads
Indications
Medtronic leads are used as part of a cardiac rhythm disease management system. Leads are intended for pacing and sensing and/or defibrillation. Defibrillation leads have application for patients for whom implantable cardioverter defibrillation is indicated
Contraindications
Medtronic leads are contraindicated for the following:
ventricular use in patients with tricuspid valvular disease or a tricuspid mechanical heart valve.
patients for whom a single dose of 1.0 mg of dexamethasone sodium phosphate or dexamethasone acetate may be contraindicated. (includes all leads which contain these steroids)
Epicardial leads should not be used on patients with a heavily infracted or fibrotic myocardium.
The SelectSecure Model 3830 Lead is also contraindicated for the following:
patients for whom a single dose of 40.µg of beclomethasone dipropionate may be contraindicated.
patients with obstructed or inadequate vasculature for intravenous catheterization.

20. Brief Statement: Medtronic Leads (continued)
Warnings/Precautions
People with metal implants such as pacemakers, implantable cardioverter defibrillators (ICDs), and accompanying leads should not receive diathermy treatment. The interaction between the implant and diathermy can cause tissue damage, fibrillation, or damage to the device components, which could result in serious injury, loss of therapy, or the need to reprogram or replace the device.
For the SelectSecure Model 3830 lead, total patient exposure to beclomethasone 17,21-dipropionate should be considered when implanting multiple leads. No drug interactions with inhaled beclomethasone 17,21-dipropionate have been described. Drug interactions of beclomethasone 17,21-dipropionate with the Model 3830 lead have not been studied.
Potential Complications
Potential complications include, but are not limited to, valve damage, fibrillation and other arrhythmias, thrombosis, thrombotic and air embolism, cardiac perforation, heart wall rupture, cardiac tamponade, muscle or nerve stimulation, pericardial rub, infection, myocardial irritability, and pneumothorax. Other potential complications related to the lead may include lead dislodgement, lead conductor fracture, insulation failure, threshold elevation or exit block.
See specific device manual for detailed information regarding the implant procedure, indications, contraindications, warnings, precautions, and potential complications/adverse events. For further information, please call Medtronic at and/or consult Medtronic’s website at
Caution: Federal law (USA) restricts this device to sale by or on the order of a physician.

21. Disclosure
NOTE:
This presentation is provided for general educational purposes only and should not be considered the exclusive source for this type of information. At all times, it is the professional responsibility of the practitioner to exercise independent clinical judgment in a particular situation.