Transcript CorePace #3 - Basic Concepts

Basic Concepts—Electricity and Pacemakers
Module 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
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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 (W)
– 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
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
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Voltage and Current Flow
Electrical Analogies
Water pressure in system
is analogous to voltage –
providing the force to
move the current
Spigot (voltage) turned up, lots of
water flows (high current drain)
Spigot (voltage) turned low, little flow
(low current drain)
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?
• High resistance – a knot results in low total current flow
Ohm’s Law
• Describes the relationship
between voltage, current,
and resistance
V
• V=IXR
V
=
I X R
• I=V/R
V
I
I
R
• R=V/I
= R
V
I =
R
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?
Status Check
What happens to current if the voltage is reduced but the
impedance is unchanged?
• Start with:
• Reduce the voltage to 2.5 V
– Voltage = 5 V
– Voltage = 5 V
– Impedance = 500 W
– Impedance = 500 W
– Current = 10 mA
– Current = ?
• Solve for Current (I):
– I = V/R
• Is the current increased/
decreased or unchanged?
– I = 5 V ÷ 500 W = 0.010 Amps
– I = V/R
– Current is 10 mA
– V = 2.5 V ÷ 500 W =
0.005 Amps or 5 mA
• The current is reduced
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Status Check
What happens to current if the impedance is reduced
but the voltage is unchanged?
• Start with:
• Reduce impedance to 250 W
– Voltage = 5 V
– Voltage = 5 V
– Impedance = 500 W
– Impedance = 250 W
– Current = 10 mA
– Current = ?
• Solve for Current (I):
– I = V/R
• Is the current increased/
decreased or unchanged?
– I = 5 V ÷ 500 W = 0.010 Amps
– I = V/R
– Current is 10 mA
– V = 2.5 V ÷ 250 W =
0.02 Amps or 20 mA
• The current is increased
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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 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)
Positive terminal
– A separator, (also an ion conductor) and
– A positive electrode (cathode)
Cathode
Anode
Separator
Negative 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.
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