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Basic Concepts—Electricity and PacemakersModule 3

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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

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Characteristics of an electrical circuit:Including a pacemaker circuit

• Voltage

• Current

• Impedance

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

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

Impedance

• The opposition to current flow

• In a pacing system, impedance is:

– Measured in ohms (

– Represented by the letter “R”

– The measurement of the sum of all resistance to the flow of current

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

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Voltage, Current, and ImpedanceRecap

• 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 or sometimes Z

– Impedance is a function of the characteristics of the conductor (wire), the electrode (tip), and the myocardium

Voltage and Current FlowElectrical Analogies

Spigot (voltage) turned up, lots of water flows (high current drain)

Spigot (voltage) turned low, little flow (low current drain)

Water pressure in system is analogous to voltage –

providing the force to move the current

Resistance and Current FlowElectrical Analogies

• Normal resistance – friction caused by the hose and nozzle

More water discharges, but is all of it going to the nozzle?

• High resistance – a knot results in low total current flow

• Low resistance – leaks in the hose reduce the resistance

Ohm’s Law

• Describes the relationship between voltage, current, and resistance

• V = I X R

• I = V / R

• R = V / I

VV

II RR

V

R

I

V

R

I

R

V

I =

=

=X

Ohm’s law tells us:

1. If the impedance remains constant, and the voltage decreases, the current decreases

2. If the voltage is constant, and the impedance decreases, the current increases

So What?

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Status Check

• Start with:

– Voltage = 5 V

– Impedance = 500

– Current = 10 mA

• Solve for Current (I):

– I = V/R

– I = 5 V ÷ 500 = 0.010 Amps

– Current is 10 mA

• Reduce the voltage to 2.5 V

– Voltage = 5 V

– Impedance = 500

– Current = ?

• Is the current increased/ decreased or unchanged?

– I = V/R

– V = 2.5 V ÷ 500 =

0.005 Amps or 5 mA

• The current is reduced

What happens to current if the voltage is reduced but the impedance is unchanged?

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Status Check

• Start with:

– Voltage = 5 V

– Impedance = 500

– Current = 10 mA

• Solve for Current (I):

– I = V/R

– I = 5 V ÷ 500 = 0.010 Amps

– Current is 10 mA

• Reduce impedance to 250 – Voltage = 5 V

– Impedance = 250

– Current = ?

• Is the current increased/ decreased or unchanged?

– I = V/R

– V = 2.5 V ÷ 250 =

0.02 Amps or 20 mA

• The current is increased

What happens to current if the impedance is reduced but the voltage is unchanged?

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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

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Battery BasicsSo 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

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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.

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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 1-800-328-2518 and/or consult Medtronic’s website at www.medtronic.com.

Caution: Federal law (USA) restricts these devices to sale by or on the order of a physician.

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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.

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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 1-800-328-2518 and/or consult Medtronic’s website at www.medtronic.com.

Caution: Federal law (USA) restricts this device to sale by or on the order of a physician.

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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.

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.