Components of Pacing Leads:Design and Performance Factors

Pacing Lead Activity

• 70 bpm

• 100,000 beats / day

• 37,000,000 beats / year

Pacing Lead Components

Objectives

• Be awareness of how leads play a critical role inthe reliability of a pacing system -- A lead is not“just a wire”.

• Demonstrate an understanding of design and technology that influence potential performance and reliability of a lead -- All leads are not created equal.

• Demonstrate an understanding of lead assembly process

Conductor Tip Electrode Insulation Connector Pin

Pacing Lead Components• Conductor

• Connector Pin

• Insulation

• Electrode

• Lead Assembly

Conductor

• Purpose– Deliver electrical impulses from IPG to electrode

– Return sensed intracardiac signals to IPG

Conductor

Conductor -- Types

• Types

– Unifilar

– Multifilar

– Cable

Conductor -- Construction

• Unipolar Construction

Conductor -- Unipolar Construction

• Unipolar lead– 1 pacing conductor– IPG case (“can”)

for sensing

Conductor -- Unipolar Construction

• Unipolar Lead Characteristics– Larger pacing spikes on EKG– Small diameter lead body– Less rigid lead body– More susceptible to oversensing– May produce muscle and nerve stimulation

Conductor -- Construction

• Bipolar Construction– Co-axial

– Co-radialOuter insulation

Tip electrode coilIndifferent electrode coil

Integral insulation

Tip electrode coil

Indifferent electrode coil

Conductor -- Construction

• Bipolar Construction– Parallel Coils

– Coil / Cables

Conductor -- Bipolar Construction

• Bipolar– 1 pacing conductor– 1 sensing conductor

Conductor -- Bipolar Construction

• Bipolar Lead Characteristics– Larger diameter lead body– Tend to be stiffer– Less susceptible to oversensing– Unipolar programmable– Less likely to produce muscle and nerve

stimulation

Conductor -- Material

• Typical Conductor Materials– MP35N (nickel alloy)– MP35N silver cored

Connector

• Purpose– Connects lead to IPG, and provides a conduit to:

• Deliver current from IPG to lead • Return sensed cardiac signals to IPG

Connector

Connector -- IS-1 Standard

• IS-1 Standard Connectors

• Sizes Prior to IS-1 Standard– 3.2 mm low-profile connectors– 5/6 mm connectors

Insulation

• Purpose:– Contain electrical current– Prevent corrosion

Insulation

Insulation -- Properties

• Properties of Insulation Materials– Tensile strength– Elongation– Tear strength– Abrasion– Compression set– Crush (cyclic compression)– Creep

Insulation -- Type

• Insulation Types– Silicone– Polyurethane– Fluoropolymers (PTFE, ETFE)

Insulation -- Type

• Silicone– Advantages• Inert• Biocompatible• Biostable

Insulation -- Type

• Silicone– Disadvantages• High friction coefficient (sticky)• Handling damage• Size (for some types of silicone)

Insulation -- Type

• Polyurethane

– Advantages

• Biocompatible

• High tear strength

• Low friction coefficient

• Less fibrotic

• Small lead diameter

Insulation -- Type

• Polyurethane Disadvantages

Environmental Stress Cracking (ESC) Crazing or cracking of the polyurethane due to

exposure to the in-vivo environment and internal material stresses

Metal Ion Oxidation (MIO) Oxidative degradation of the polyurethane

insulation

Insulation -- Small Size

New Insulation Materials Facilitate the Benefits of Smaller Lead Diameters• Smaller introducer size• Easier insertion/passage through smaller

veins• More flexible lead bodies• Two leads through one introducer• Less intrusive

Electrodes

• Purpose

– Deliver a stimulus to myocardium– Detect (sense) intracardiac signals

Tip Electrode Ring Electrode

Electrodes

• Optimal Performance Factors– Low, Stable Thresholds– High Pacing Impedance– Low Source Impedance– Good Sensing

Electrodes

• Characteristics and Design Factors that Impact Electrical Performance– Fixation mechanism

– Polarity

– Surface material

– Size

– Surface structure

– Steroid elution

Electrodes -- Fixation Mechanism

• Passive Fixation Mechanism – Endocardial

– Tined – Finned

– Canted/curved

Electrodes -- Fixation Mechanism

• Passive Fixation Applications – Endocardial– Trabeculated ventricle– Atrial appendage present– Traditional pacing sites

Electrodes – Fixation Mechanism

• Active Fixation Mechanism – Endocardial

– Fixed screw

– Extendible/retractable

Electrodes -- Fixation Mechanism

• Active Fixation Applications -- Endocardial

– Smooth ventricular walls– Atrial appendage is missing/malformed– Alternate pacing site

Electrodes -- Fixation/Visualization

Fluoroscopic Visual Quality of Passive Fixation Leads

CapSure® CapSure SP® Novus CapSure Z® Novus

Electrodes -- Fixation/Visualization

Fluoroscopic Visual Quality of Active Fixation Leads

SureFixCapSureFix®

Extended Retracted Fixed Screw

space

Electrodes -- Fixation Mechanism

• Fixation Mechanism –

Myocardial / Epicardial

– Stab-in

– Screw-in

– Suture-on

Electrodes -- Polarity

• Characteristics and Design Factors that Impact Electrical Performance– Fixation mechanism

– Polarity

– Surface material

– Size

– Surface structure

– Steroid elution

Electrodes -- Surface Material

• Characteristics and Design Factors that ImpactElectrical Performance– Fixation mechanism

– Polarity

– Surface material

– Size

– Surface structure

– Steroid elution

Electrodes -- Surface Material

• Surface Material– Polished platinum

– Activated carbon

– Platinized metal

Electrodes -- Surface Material

• Surface Material Characteristics– Corrosion Resistant– Biocompatible– Reduced Polarization

Electrodes -- Size

• Characteristics and Design Factors that Impact

Electrical Performance– Fixation mechanism

– Polarity

– Surface material

– Size

– Surface structure

– Steroid elution

Electrodes -- Size

• Reducing Electrode Size

– Increases Impedance

– Reduces Current Drain

– Increases Longevity

Electrodes -- Size/Impedance

Pac

ing

Impe

danc

e (O

hms)

0

500

1000

1500

0 1 2 3 4 5.5 6

Geometric Tip Electrode Surface Area (mm2)

Size = Impedance

Electrodes -- Size/Current Drain

• Reducing electrode size– Increased impedance– Lower outputs, reduces current drain– Increases longevity

Largercurrentdrain

Increasedimpedance at the

tip electrodeSmaller current

drain (less current doessame amount of work)

Electrodes -- Size/Longevity• Impact of Pacing Impedance on Longevity

TotalTotal Pulse Width 0.4 ms in both chambersPulse Width 0.4 ms in both chambersLeadLead A = 3.5 VA = 3.5 V A = 2.5 VA = 2.5 V A = 2.5 VA = 2.5 V

ImpedanceImpedance V = 3.5 VV = 3.5 V V = 2.5 VV = 2.5 V V = 1.5 VV = 1.5 V

500 6.3 Yr 7.7 Yr 8.1 Yr

600 6.6 Yr 8.0 Yr 8.3 Yr

1000 7.7 Yr 8.6 Yr 8.8 Yr

1200 8.0 Yr 8.8 Yr 9.0 Yr

100% pacing at 60 ppm

Medtronic.KappaMedtronic.Kappa™ ™ DR Model KDR701DR Model KDR701

Electrodes -- Size/Polarization

• Reducing Electrode Size– Increases polarization

Electrodes -- Size/Polarization

Current Current Tissue

- +-

++

+++ -+

-

-++++ +--

Polarization Layering Effect

Electrodes -- Surface Structure

• Characteristics and Design Factors that ImpactElectrical Performance– Fixation mechanism

– Polarity

– Surface material

– Size

– Surface structure

– Steroid elution

Electrodes -- Surface Structure

• Porous Electrode Surface

CapSure® 8.0 mm2

Porous Electrode

CapSure® SP Novus5.8 mm2 Platinized Porous Electrode

CapSure® Z Novus1.2 mm2 Platinized Porous Electrode

15KV x2500 12.0V Medt

Electrodes -- Surface Structure

• Benefits of a Porous Electrode Surface– Reduces Polarization– Improves Sensing– Promotes Tissue In-Growth

Electrodes -- Size and Surface Structure

Increased Porosity Smaller Size

Longevity Increases!

Reduces polarization

Increases electrode tissue impedance

Decreased current drain

Electrodes -- Steroid Elution

• Characteristics and Design Factors that ImpactElectrical PerformanceFixation mechanismPolaritySurface materialSizeSurface structureSteroid elution

Electrodes -- Steroid Elution

Tines forStable Fixation

Silicone Rubber PlugContaining Steroid

Porous, Platinized Tipfor Steroid Elution

• Type - Steroid in matrix

Electrodes – Steroid Elution

IMPLANT CHRONIC(8 weeks or longer)

ExcitableCardiacTissue

Non-ExcitableFibroticTissue

ExcitableCardiacTissue

Electrodes -- Steroid Elution

Benefits of Steroid Elution

• Excellent Electrode-tissue Biocompatibility:– Fewer and less active inflammatory cells

– Less fibrotic development

• Improved Electrode Performance:– No significant threshold peaking nor chronic

threshold increases

– Improved consistent sensing characteristics

Electrodes -- Steroid Elution• Effect of Steroid on Stimulation Thresholds

Pulse Width = 0.5 msecImplant Time (Weeks)

Textured Metal Electrode

Smooth Metal Electrode

0

1

2

3

4

5

Steroid-Eluting Electrode

0 1 2 3 4 5 6 7 8 9 10 11 12

Vol

ts

Electrodes -- Steroid Elution

• Steroid Enhances Sensing– Steroid elution stabilizes electrode sensing performance

– Improved r-wave sensing: + 5-10 mV

– Improved p-wave sensing: + 0.5-1.0 mV

– Stable, acute atrial sensing

– Clinical benefits

• Less postoperative atrial sensing loss

• Can use higher atrial sensitivities

Electrode -- Summary

Design Factors that Impact Lead Electrical Performance

• Fixation Mechanism• Polarity• Surface Material• Size• Surface Structure• Steroid Elution

Lead Summary

• Lead environment is hostile • Leads are complex• Lead performance

Conductor Tip Electrode Insulation Connector Pin