Medical Education Fundamentals of Pacing Therapy · Device Function Impedance Electrical Terms and...

Medical Education

4 71 Ohm’s Law EnergyDisclaimer

5 82 Device Function SensingObjectives

StimulationThreshold

6 93 Overview Questions

Fundamentals of Pacing Therapy

Electrical Terms and Concepts

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Stimulation Threshold

Energy

Sensing

Questions

This presentation is provided with the understanding that the slide content must not be altered in any manner as the content is subject to FDA regulations.

This presentation is to be used in conjunction with other resource material including the applicable Boston Scientific device physician’s manual and any implant accessories instructions for use.

This presentation is not intended to replace implant training.

Proper surgical procedures and techniques are the responsibilities of the medical professional.

If this presentation is not used in its entirety, the following information must be included:

• Appropriate Indications

• Contraindications

• Warnings

• Precautions and Adverse Events

Medical Education

Objectives

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Define basic electrical terms

Explain how these terms relate to device function

Discuss the relationship between voltage, current, and resistance

Define stimulation threshold and factors affecting it

Explain pacemaker sensing and factors affecting it

When we complete this program you will be able to:

Medical Education

Overview

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Ohm’s Law• Voltage

• Current

• Impedance

Energy

Sensing• Slew Rate

Electrical Terms and Concepts:

Medical Education

Ohm’s Law

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Ohm’s Law: V = I x R

Describes the relationship between voltage, current, resistance: V = I x R; I = V/R; R = V/I

Voltage The electrical force that makes current move through a conductor – measured in volts (V)

Impedance The total opposition presented to the flow of current by an electrical circuit or device –measured in ohms (R)

Current The transfer of electrical charge (electrons) through a cross-section of a conductor –measured in amperes (I)

Medical Education

Ohm’s Law

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

The force or “push” that causes electrons to move through a circuit

Measured in volts

Represented by the letter “V”

Often referred to as amplitude

Voltage:

Medical Education

Ohm’s Law

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Current:

The flow of electrons in a completed circuit

Measured in mA (milliamps)

Represented by the letter “I”

Medical Education

Ohm’s Law

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Impedance:

The opposition to current flow

Measured in ohms

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

Often referred to as resistance

Medical Education

Ohm’s LawCan Be Used to Find Current

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Example 1:

Voltage = 5 V

Impedance = 500 Ω

What will the current be?

I = V/R 5 V ÷ 500 Ω = 0.010 Amperes x 1000 = 10 mA

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Example 2:

Voltage = 2.5 V

Impedance = 500 Ω

I = V/R 2.5 V ÷ 500 Ω = 0.005 Amperes 0.005 x 1000 = 5 mA

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Example 3:

Voltage = 5 V

Impedance = 250 Ω

I = V/R 5 V ÷ 250 Ω = 0.020 Amperes 0.020 x 1000 = 20 mA

Medical Education

Ohm’s LawElectrical Analogy

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Voltage = Current x Resistance

“Normal” Resistance

“Low” Resistance

“High” Resistance

“Normal”Current

“High”Current

“Low”Current

Current is similar to the flow of water

Voltage is analogous to water pressure

Resistance can be compared to resistance to flow

Medical Education

Device FunctionInsulation Break

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Current is Escaping:

Decreased Resistance

Increased Current Drain

Increased Energy Usage

Medical Education

Device FunctionLead Fracture

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Current Cannot Reach Heart:

Increased Resistance

Decreased Current Drain

Decreased Energy Usage

Medical Education

Device FunctionHigh Impedance Leads

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Reducing Electrode Size:

Increases impedance

Decreases current drain

Increases longevity

Smaller current drainLarger current drain

Medical Education

Device FunctionImpedance

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

High Impedance

Decreases battery current drain, increases longevity

Low Impedance

Increases battery current drain, decreases longevity

Medical Education

Device FunctionConstant Voltage Pacemakers

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

V = IR

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Definition:

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

Medical Education

Stimulation ThresholdPulse Amplitude

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

The voltage delivered by the electrical pacingstimulus (volts)

Amplitude

Pacing Pulse

Medical Education

Stimulation ThresholdPulse Width

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Pacing Pulse

Pulse Width

Duration of the electrical pacing pulse (milliseconds)

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Amplitude (V) + Pulse Width (ms) = Output

Lowest Output that Captures Outside of Refractory = Threshold

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Why Measure?

Assure proper lead placement

Determine safety margin

Medical Education

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Affected by:

Lead Maturation

Lead Technology

Medications

Lead Location

Medical Education

Stimulation ThresholdLead Maturation

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Chronic Electrode:

Excitable Tissue

Non-Excitable Fibrotic Tissue

Virtual Electrode

Electrode

Medical Education

Stimulation ThresholdsEffect of Steroid

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Pulse Width = 0.5 msec

Implant Time (Weeks)

Non-steroid

Steroid/IROX Electrode

0 1 2 4 5 7 8 9 10 11 12

S. Furman, D. Hayes, D Holmes; “A Practice of Cardiac Pacing” 2nd Revision, 1989; p.36

Medical Education

Stimulation ThresholdStrength Duration Curve

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Capture

Noncapture

1.0Pulse Width (ms)

Pulse Amplitude

Medical Education

Stimulation ThresholdStrength Duration Curve

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions Pulse Width (ms)

Voltage StimulationThreshold (Volts)

0.5 1.0 1.5 2.0 2.5 3.0

Medical Education

Energy

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

V2 TE =

E = Energy

V = Voltage

T = Time

R = Resistance

Medical Education

Energy

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

2x Voltage = 4x Energy

2x Pulse Width = 2x Energy

Medical Education

Energy

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

5.02 (.50ms)25 µJ

Medical Education

Energy

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

2.52 (.50ms)6.25 µJ

Medical Education

Energy

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

5.02 (.25ms)12.5 µJ

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Definition:

Sensing is the ability of the pacemaker to “see” when an intrinsic depolarization is occurring

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Accurate sensing requires filtering out extraneous signals

Unwanted signals include:

T-waves

Far-field events

Myopotentials

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Electrophysiological properties of the myocardium

Characteristics of the electrode

Lead placement

Sensing amplifiers of the pacemaker

Lead polarity

Lead integrity

Sensing may be affected by:

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Review of Sensitivity:

*programmed sensitivity

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Programming a higher setting decreases the sensitivity of the device – fewer signals are sensed

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Programming a lower setting increases the sensitivity of the device – more signals are sensed

Medical Education

Sensing

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Slew Rate:

∆ V / Time = Slew Rate

Medical Education

Questions

Disclaimer

Objectives

Overview

Ohm’s Law

Device Function

Energy

Sensing

Questions

Medical Education Fundamentals of Pacing Therapy · Device Function Impedance Electrical Terms and...

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