Basic Pacing Concepts Part II. Electrical Concepts.

Basic Pacing ConceptsBasic Pacing ConceptsPart IIPart II

Electrical ConceptsElectrical Concepts

Voltage

Current

Impedance

Every Electrical Pacing Circuit Has Every Electrical Pacing Circuit Has the Following Characteristics:the Following Characteristics:

VoltageVoltage

Voltage is the force or “push” that causes electrons to move through a circuit

In a pacing system, voltage is:

– Measured in volts

– Represented by the letter “V”

– Provided by the pacemaker battery

– Often referred to as amplitude

CurrentCurrent

The flow of electrons in a completed circuit

In a pacing system, current is:

– Measured in mA (milliamps)

– Represented by the letter “I”

– Determined by the amount of electrons that move through a circuit

ImpedanceImpedance

The opposition to current flow

In a pacing system, impedance is:

– Measured in ohms

– Represented by the letter “R” (for numerical values)

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

Voltage, Current, and Impedance Voltage, Current, and Impedance Are InterdependentAre Interdependent

The interrelationship of the three components can be likened to the flow of water through a hose

– Voltage represents the force with which . . .

– Current (water) is delivered through . . .

– A hose, or lead, where each component represents the total impedance:

The nozzle, representing the electrode

The tubing, representing the lead wire

Voltage and Current FlowVoltage and Current Flow

Spigot (voltage) turned up(high current drain)

Spigot (voltage) turned low(low current drain)

Resistance and Current FlowResistance and Current Flow

“Normal” resistance

“Low” resistance

“High” resistanceLow current flow

High current flow

Ohm’s Law is a Fundamental Ohm’s Law is a Fundamental Principle of Pacing That:Principle of Pacing That:

VV

II RRV = I X RV = I X RI = V / RI = V / RR = V / IR = V / I

Describes the relationship between voltage, current, and resistance

xx

If you reduce the voltage by half, the current is also cut in half

If you reduce the impedance by half, the current doubles

If the impedance increases, the current decreases

When Using Ohm’s Law When Using Ohm’s Law You Will Find That:You Will Find That:

Ohm’s Law Can Be Used to Find Amounts of Ohm’s Law Can Be Used to Find Amounts of Current Passing Through Pacemaker CircuitryCurrent Passing Through Pacemaker Circuitry

If: Voltage = 5 V

Impedance = 500

What will the current be?

I = V/R

I = 5 V ÷ 500 = 0.010 Amperes

0.010 x 1000 = 10 mA

In This Example, the Voltage is HalvedIn This Example, the Voltage is Halved

If: Voltage = 2.5 V

Impedance = 500

Current = ?

I = V/R

V = 2.5 V ÷ 500 = 0.005 Amperes

0.005 x 1000 = 5 mA

In This Example, the Impedance is In This Example, the Impedance is Reduced By HalfReduced By Half

If: Voltage = 5 V

Impedance = 250

Current = ?

I = V/R

I = 5 V ÷ 250 = 0.020 Amperes

0.020 x 1000 = 20 mA

Impedance Changes Affect Pacemaker Impedance Changes Affect Pacemaker Function and Battery LongevityFunction and Battery Longevity

High impedance reading reduces battery current drain and increases longevity

Low impedance reading increases battery current drain and decreases longevity

Impedance reading values range from 300 to 1,000

– High impedance leads will show impedance reading values greater than 1,000 ohms

Lead Impedance Values Will Change Due to:Lead Impedance Values Will Change Due to:

Insulation breaks

Wire fractures

An Insulation Break Around the Lead Wire An Insulation Break Around the Lead Wire Can Cause Impedance Values to FallCan Cause Impedance Values to Fall

Insulation breaks expose the wire to body fluids which have a low resistance and cause impedance values to fall

Current drains through the insulation break into the body which depletes the battery

An insulation break can cause impedance values to fall below 300

Insulation break

Decreased resistance

A Wire Fracture Within the Insulating Sheath A Wire Fracture Within the Insulating Sheath May Cause Impedance Values to RiseMay Cause Impedance Values to Rise

Impedance values across a break in the wire will increase

Current flow may be too low to be effective

Impedance values may exceed 3,000

Lead wire fracture

Increased resistance

StimulationStimulation

Stimulation ProcessStimulation Process

Time (Milliseconds)100 200 300 400 500

Phase 2

Phase 1

Phase 3

Phase 4

Tra

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-50

0

50

-100

Ph

ase

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Threshold

Stimulation ThresholdStimulation Threshold

The minimum electrical stimulus needed to consistently capture the heart outside of the heart’s refractory period

VVI / 60

Capture Non-Capture

Amplitude

Pulse width

Two Settings Are Used to Ensure Capture:Two Settings Are Used to Ensure Capture:

Amplitude is the Amount of Voltage Amplitude is the Amount of Voltage Delivered to the Heart By the PacemakerDelivered to the Heart By the Pacemaker

Amplitude reflects the strength or height of the impulse:

– The amplitude of the impulse must be large enough to cause depolarization ( i.e., to “capture” the heart)

– The amplitude of the impulse must be sufficient to provide an appropriate pacing safety margin

Pulse Width Is the Time (Duration) Pulse Width Is the Time (Duration) of the Pacing Pulseof the Pacing Pulse

Pulse width is expressed in milliseconds (ms)

The pulse width must be long enough for depolarization to disperse to the surrounding tissue

5 V

0.5 ms 0.25 ms 1.0 ms

The Strength-Duration CurveThe Strength-Duration Curve

The strength-duration curve illustrates the relationship of amplitude and pulse width

– Values on or above the curve will result in capture

DurationPulse Width (ms)

.50

1.0

1.5

2.0

.25S

tim

ula

tio

n T

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sho

ld (

Vo

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0.5 1.0 1.5

Capture

Clinical Usefulness of the Clinical Usefulness of the Strength-Duration CurveStrength-Duration Curve

Adequate safety margins must be achieved due to:

– Acute or chronic pacing system

– Daily fluctuations in threshold

Capture

0.5 1.0 1.5Duration

Pulse Width (ms)

.50

1.0

1.5

2.0

.25

Sti

mu

lati

on

Th

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old

(V

olt

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After Patient Safety, the Second Most Important Goal After Patient Safety, the Second Most Important Goal in Programming is to Extend Battery Lifein Programming is to Extend Battery Life

The best way to extend the service life of a battery is to lower voltage settings while maintaining adequate safety margins

– Amplitude values greater than the cell capacity of the pacemaker battery require a voltage multiplier, resulting in decreased battery longevity

Lead impedance

Amplitude and pulse width setting

Percentage paced vs. intrinsic events

Rate responsive modes programmed “ON”

Factors That Affect Battery Factors That Affect Battery Longevity Include:Longevity Include:

Electrode Design May Also Impact Electrode Design May Also Impact Stimulation ThresholdsStimulation Thresholds

Lead maturation process

Lead Maturation ProcessLead Maturation Process

Fibrotic “capsule” develops around the electrode following lead implantation

Steroid Eluting LeadsSteroid Eluting Leads

Steroid eluting leads reduce the inflammatory process and thus exhibit little to no acute stimulation threshold peaking and low chronic thresholds

Porous, platinized tipfor steroid elution

Silicone rubber plugcontaining steroid

Tines forstablefixation

Lead Maturation ProcessLead Maturation Process

Effect of Steroid on Stimulation Thresholds

Pulse Width = 0.5 msec

03 6

Implant Time (Weeks)

Textured Metal Electrode

Smooth Metal Electrode

1

2

3

4

5

Steroid-Eluting Electrode

0 1 2 4 5 7 8 9 10 11 12

Vol

ts

General Medtronic Pacemaker DisclaimerINDICATIONS

Medtronic pacemakers are indicated for rate adaptive pacing in patients who may benefit from increased pacing rates concurrent with increases in activity (Thera, Thera-i, Prodigy, Preva and Medtronic.Kappa 700 Series) or increases in activity and/or minute ventilation (Medtronic.Kappa 400 Series).

Medtronic 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.

9790 Programmer

The Medtronic 9790 Programmers are portable, microprocessor based instruments used to program Medtronic implantable devices.

9462

The Model 9462 Remote Assistant™ is intended for use in combination with a Medtronic implantable pacemaker with Remote Assistant diagnostic capabilities.

CONTRAINDICATIONS

Medtronic pacemakers are contraindicated for the following applications:

       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.

       Medtronic.Kappa 400 Series pacemakers are contraindicated for use with epicardial leads and with abdominal implantation.

WARNINGS/PRECAUTIONS

Pacemaker patients should avoid sources of magnetic resonance imaging, diathermy, high sources of radiation, electrosurgical cautery, external defibrillation, lithotripsy, and radiofrequency ablation to avoid electrical reset of the device, inappropriate sensing and/or therapy.

9462

Operation of the Model 9462 Remote Assistant™ Cardiac Monitor near sources of electromagnetic interference, such as cellular phones, computer monitors, etc. may adversely affect the performance of this device.

See the appropriate technical manual for detailed information regarding indications, contraindications, warnings, and precautions.

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

Medtronic Leads

For Indications, Contraindications, Warnings, and Precautions for Medtronic Leads, please refer to the appropriate Leads Technical Manual or call your local Medtronic Representative.

Caution: Federal law restricts this device to sale by or on the order of a Physician.

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.

Continued inContinued in

Basic Pacing ConceptsBasic Pacing ConceptsPart IIIPart III