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Basic Pacing Concepts Part II. Electrical Concepts. Every Electrical Pacing Circuit Has the Following Characteristics:. 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

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Basic Pacing Concepts Part II

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every electrical pacing circuit has the following characteristics
Every Electrical Pacing Circuit Has the Following Characteristics:
  • Voltage
  • Current
  • Impedance
  • 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
  • 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
  • The opposition to current flow
  • In a pacing system, impedance is:
    • Measured in ohms
    • Represented by the letter “R” (W for numerical values)
    • The measurement of the sum of all resistance to the flow of current
voltage current and impedance are interdependent
Voltage, Current, and Impedance Are 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 flow
Voltage and Current Flow

Spigot (voltage) turned up(high current drain)

Spigot (voltage) turned low(low current drain)

resistance and current flow
Resistance and Current Flow

“Normal” resistance

“Low” resistance

High current flow

“High” resistance

Low current flow

ohm s law is a fundamental principle of pacing that




Ohm’s Law is a Fundamental Principle of Pacing That:
  • Describes the relationship between voltage, current, and resistance

V = I X R

I = V / R

R = V / I


when using ohm s law you will find that
When Using Ohm’s Law You Will Find That:
  • 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
ohm s law can be used to find amounts of current passing through pacemaker circuitry
Ohm’s Law Can Be Used to Find Amounts of Current Passing Through Pacemaker Circuitry

If: Voltage = 5 V

Impedance = 500 W

What will the current be?

I = V/R

I = 5 V ÷ 500 W = 0.010 Amperes

0.010 x 1000 = 10 mA

in this example the voltage is halved
In This Example, the Voltage is Halved

If: Voltage = 2.5 V

Impedance = 500 W

Current = ?

I = V/R

V = 2.5 V ÷ 500 W = 0.005 Amperes

0.005 x 1000= 5 mA

in this example the impedance is reduced by half
In This Example, the Impedance is Reduced By Half

If: Voltage = 5 V

Impedance = 250 W

Current = ?

I = V/R

I = 5 V ÷ 250 W = 0.020 Amperes

0.020 x 1000 = 20 mA

impedance changes affect pacemaker function and battery longevity
Impedance Changes Affect Pacemaker Function 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 W
    • 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 can cause impedance values to fall
An Insulation Break Around the Lead Wire Can 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 W

Insulation break

Decreased resistance

a wire fracture within the insulating sheath may cause impedance values to rise
A Wire Fracture Within the Insulating Sheath May 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 W

Lead wire fracture

Increased resistance

stimulation process










Time (Milliseconds)

Stimulation Process

Phase 1

Phase 2

Phase 0

Transmembrane Potential


Phase 3


Phase 4

stimulation threshold
Stimulation Threshold
  • The minimum electrical stimulus needed to consistently capture the heart outside of the heart’s refractory period



VVI / 60

amplitude is the amount of voltage delivered to the heart by the pacemaker
Amplitude is the Amount of Voltage Delivered 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 of the pacing pulse
Pulse Width Is the Time (Duration) of 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

1.0 ms

0.5 ms

0.25 ms

the strength duration curve






The 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

Stimulation Threshold (Volts)






Pulse Width (ms)

clinical usefulness of the strength duration curve
Clinical Usefulness of the Strength-Duration Curve
  • Adequate safety margins must be achieved due to:
    • Acute or chronic pacing system
    • Daily fluctuations in threshold



Stimulation Threshold (Volts)









Pulse Width (ms)

after patient safety the second most important goal in programming is to extend battery life
After Patient Safety, the Second Most Important Goal in 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
factors that affect battery longevity include
Factors That Affect Battery Longevity Include:
  • Lead impedance
  • Amplitude and pulse width setting
  • Percentage paced vs. intrinsic events
  • Rate responsive modes programmed “ON”
lead maturation process
Lead Maturation Process
  • Fibrotic “capsule” develops around the electrode following lead implantation
steroid eluting leads
Steroid 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 tip

for steroid elution

Silicone rubber plugcontaining steroid

Tines forstablefixation

lead maturation process32



Smooth Metal Electrode



Textured Metal Electrode



Steroid-Eluting Electrode












Implant Time (Weeks)

Lead Maturation Process
  • Effect of Steroid on Stimulation Thresholds




Pulse Width = 0.5 msec


General Medtronic Pacemaker Disclaimer


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.


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


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.


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.


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.


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.