fundamentals of cardiac devices

8/13/2019 Fundamentals of Cardiac Devices

1/86

1

Welcome

Chris Stamper

Technical Field Engineer


2/86

2

The Fundamentals of Cardiac DevicesModule 2


3/86

3

Objectives

After completing this introduction to Cardiac Devices, you ill!e a!le to"

# $dentify the various cardiac device systems

#$dentify the !asic indications for implantation for eachdevice

# %ecogni&e each device type on a chest '(ray


4/86

)

Cardiac Devices

# Designed to"* %estore or maintain a rhythm and rate sufficient to meet

meta!olic needs

* +rovide diagnostic information a!out

# Device operation

# The patient


5/86

Cardiac Devices

# +acema-ers or $mplanta!le +ulse .enerators /$+.0* +rovide a rate to support meta!olic needs

* +rovide various diagnostics

* Single and dual cham!er

*A!out 1( years longevity

* Some of the neer pacema-ers include therapies hich

pace(terminate AT4AF


6/86

5

Cardiac Devices

# $mplanta!le Cardioverter Defi!rillators /$CDs0* %estore sinus rhythm in the presence of tachycardia

# Defi!rillate

# Cardiovert

# Anti(Tachy +ace /AT+0

* +rovide a rate to support meta!olic needs

# $ncludes single or dual cham!er pacing

* +rovide various diagnostics

*A!out 5(6 years longevity

* There are also devices designed to terminate AF via

cardioversion4AT+ in addition to standard $CD therapies


7/86

7

Cardiac Devices

# Cardiac %esynchroni&ation Therapy /C%T0* $+. ith C%T, or an $+. 8 $CD ith C%T

* %estore ventricular synchrony

# 9ses a specially designed lead placed usually on the posterior(lateral

all of the :; via the Coronary Sinus circulation

# :; epicardial lead placement is an option

# +rovides %; and :; synchronous pacing

* May restore rhythms in presence of lethal tachycardia

# C%T pacing 8$CD /


8/86

1

Cardiac Devices

# $mplanta!le :oop%ecorders /$:%0

* +rovides rate(!ased monitoring

# Fast rates

# Slo rates

* +rovides E.M during patient

triggered events


9/86

6

IndicationsPacemakers

# The A


10/86

IndicationsDefibrillators

# +rimary vs Secondary +revention for SCA* +rimary

# +atients ho have e'perienced a previous SCA or ventricular arrhythmia

# Studies such as A;$D, C$DS2, CAS


11/86

IndicationsDefibrillators (cont.)

Bell defined !y


12/862

IndicationsDefibrillators (cont.)

# $CD Class $ %ecommendation

# +atients at least ) days post(M$

# :;EF 3 * )

# =


13/863

IndicationsCardiac Resynchronization hera!y

# =


14/86)

Indications"oo! Recorders

# Transient, infreLuent !ut recurrent syncope


15/86

Reco#nizin# $ystemsPacemakers

Dual Cham!er +acema-er

%; :ead at the Ape'

%A :ead in Appendage


16/865

Reco#nizin# $ystemsICD or %i#h Po&er

%ight Atrial :ead

Appro'imate position outlined

%ight ;entricular :ead

Bith %; and S;C coils


17/867

Reco#nizin# $ystemsCR "o&'Po&er

%ight Atrial :ead

:eft ;entricular :ead

+laced on the surface of the

:; via the Coronary Sinus



18/861

Reco#nizin# $ystemsCR %i#h'Po&er

%ight Atrial :ead

:eft ;entricular :ead

+laced on the surface of the

:; via the Coronary Sinus


=ote the 2 high voltage defi!

coils

Surface EC. leads


19/866

Pacin# hera!y

#Senses underlying heart rate* Delivers lo energy electrical

pulses hen rate falls !elo

programmed limit

# :o energy pulses capture and

depolari&e the heart musclecausing it to contract

* Dual Cham!er $+.s provide

A(; synchrony


20/862

# Atrium and ;entricle

* Sensing

* +acing

# ;entricle

* Antitachycardia pacing /AT+0

ICD Pacin# hera!y

Atrial :ead

;entricular :ead


21/862

%i#h'olta#e hera!y

Cardioversion and

Defi!rillation are delivered in

!iphasic avesFor e'ample" First, from the S;C

coil and the Can to the %; coil,

and then reverse

The device must detect * charge

* confirm * and deliver the shoc-

Fast, accurate detection, and fast

charge times are critical


22/8622

ICD hera!y

Brady and

Anti-Tachypacing (ATP)

# The $CD lead is

designed to carry !oth

high voltage and

pacing therapies

* >rady

* AT+

* Cardioversion

* Defi!rillation


23/86


24/862)

Im!lant vol*tion

+acema-ersesterday

# First $mplants in early 65s

# Single Cham!er, non

programma!le

# A!out 2 year longevity

# A!out 2 cc

# A!dominal implants, sternotomy

for epicardial leads


25/862

Im!lant vol*tion

+acema-ersToday

# +ectoral implants

# 5(7 F transvenous lead

placement

* Hutpatient4overnight stay

# J 3 cc

# 1( years longevity

# Dual cham!er, multi(

programma!le

# Advanced diagnostics and

trending information


26/8625

Im!lant vol*tion

$CD +ast" N(2 years ago $CDs

# %eLuired maGor surgery

* A!dominal implants

* Median sternotomy to suturedefi! patches on heart

* :ength of hospital stay I ee-

# =onprogramma!le

#


27/8627

Im!lant vol*tion

$CDs Today

# Similar to a pacema-er implant

# Transvenous, single incision

* +ectoral implant

* Hvernight stay

# :ocal anesthesia, conscious

sedation

# +rogramma!le therapy options

# Single, dual and triple cham!er

/C%T0

# 9p to 6 years longevity

# A!out 3 cc

# I N, implants4year


28/8621

$tat*s Check

# .iven the folloing patient

* 57 H male patient, had an anterior M$ 2 years ago

* EF 2

* loc-er0

* C4H

# Severe shortness of !reath at rest, fatigue, una!le to perform AD:, vertigo, rare

syncope


29/86

26

$tat*s Check

# +atientPs EC."

=S%

%ate 71

:>>

Bhat device

system /if

any0 is the

patient li-ely

to getKClic- for Anser


30/86

3

$tat*s Check

# Could this !e the previous

patientPs chest '(rayK

* $s it C%TK

* $s it


31/86

3

$tat*s Check

# Consider the folloing patient* Elderly female patient

* Medical history includes

# E'(smo-er * Luit years ago

# Mild e'ertional angina

* Cardiac cath shos mild disease right coronary artery

# 3 adult children

*Medications# =itroglycerine +%= # Aspirin 1 mg 4day

* C4H

# Fatigue, una!le to perform normal activities


32/86

32

$tat*s Check

# +atientPs stress test indicates"

* Stopped after ) minutes for fatigue

* EC. immediately after stress test" Clic- for Anser

:i-ely a pacema-er, as the patient has chronotropic

incompetence * her heart rate does not increase ith e'ercise

Bhat device

system ould you

recommendK

=S%, %ate 7


33/86

3333

+asic Conce!ts,lectricity andPacemakers

-od*le


34/86

3)3)

Objectives

9pon completion you ill !e a!le to"# Descri!e the relationship !eteen voltage, current, and

resistance

# Descri!e the clinical significance of alterations in voltage,

current, and resistance


35/86

33

Characteristics of an electrical circ*it/Incl*din# a !acemaker circ*it

# ;oltage# Current

# $mpedance


36/86

35

olta#e

# ;oltage is the force, or ?push,@ that causes electrons tomove through a circuit

# $n a pacing system, voltage is"

* Measured in volts /;0

* %epresented !y the letter ?;@

* +rovided !y the pacema-er !attery

* Hften referred to as amplitude or pulse amplitude


37/86

37

C*rrent

# The flo of electrons in a completed circuit# $n a pacing system, current is"

* Measured in milliamps /mA0

* %epresented !y the letter ?$@

* Determined !y the amount of electrons that move through a circuit


38/86

31

Im!edance

# The opposition to current flo# $n a pacing system, impedance is"

* Measured in ohms /)

* %epresented !y the letter ?%@

* The measurement of the sum of all resistance to the flo of current


39/86

36

olta#e0 C*rrent0 and Im!edance are Interde!endent

# The interrelationship of the three components is analogousto the flo of ater through a hose

* ;oltage represents the force ith hich

* Current /ater0 is delivered through

*A hose, here each component represents the total impedance"

# The no&&le, representing the electrode

# The tu!ing, representing the lead ire

lt C t d I d


40/86

))

olta#e0 C*rrent0 and Im!edanceReca!

# ;oltage" The force moving the current /;0* $n pacema-ers it is a function of the !attery chemistry

# Current" The actual continuing volume of flo of electricity /$0

* This flo of electrons causes the myocardial cells to depolari&e /to

?!eat@0

# $mpedance" The sum of all resistance to current flo /% or

or sometimes )

* $mpedance is a function of the characteristics of the conductor /ire0,the electrode /tip0, and the myocardium

lt d C t 1l


41/86

)

olta#e and C*rrent 1lo&lectrical 2nalo#ies

Spigot /voltage0 turned up, lots of

ater flos /high current drain0

Spigot /voltage0 turned lo, little flo

/lo current drain0

Bater pressure in system

is analogous to voltage *

providing the force to

move the current

R i t d C t 1l


42/86

)2

Resistance and C*rrent 1lo&lectrical 2nalo#ies

# =ormal resistance* friction caused !y the hose and no&&le

More ater discharges, !ut is all of it going to

the no&&leK

#


43/86

)3

Ohm3s "a&

# Descri!es the relationship

!eteen voltage, current,

and resistance

#; Q $ %

# $ Q ; 4 %

# % Q ; 4 $

II

R

I

R

I

R

I Q

Q

Q


44/86

))

Ohm3s la& tells *s/

$f the impedance remains constant, and the voltagedecreases, the current decreases

2 $f the voltage is constant, and the impedance decreases,

the current increases

So BhatK


45/86

))

$tat*s Check

# Start ith"

* ;oltage Q ;

* $mpedance Q

* Current Q mA

# Solve for Current /$0"

* $ Q ;4%

* $ Q ; U Q Amps

* Current is mA

# %educe the voltage to 2 ;

* ;oltage Q ;

* $mpedance Q

* Current Q K

# $s the current increased4

decreased or unchangedK

* $ Q ;4%

* ; Q 2 ; U Q

Amps or mA

# he c*rrent is red*ced

Bhat happens to current if the voltage is reduced !ut the

impedance is unchangedK


46/86

)5)5

$tat*s Check

# Start ith"

* ;oltage Q ;

* $mpedance Q

* Current Q mA

# Solve for Current /$0"

* $ Q ;4%

* $ Q ; U Q Amps

* Current is mA

# %educe impedance to 2

* ;oltage Q ;

* $mpedance Q 2

* Current Q K

# $s the current increased4

decreased or unchangedK

* $ Q ;4%

* ; Q 2 ; U 2 Q

2 Amps or 2 mA

# he c*rrent is increased

Bhat happens to current if the impedance is reduced

!ut the voltage is unchangedK


47/86

)7)7

Other terms

#Cathode" A negativelycharged electrode

* For e'ample, the electrode on

the tip of a pacing lead

# Anode" A positivelycharged electrode

* E'amples"

# The ?ring@ electrode on a !ipolar lead

# The $+. case on a unipolar system

* More on this later /see"

+acema-er >asics0

2node

Cathode

+attery +asics


48/86

)1)1

+attery +asics$o &here does the c*rrent come from4

#A !attery produces electricity as a result of a chemicalreaction $n its simplest form, a !attery consists of"

*A negative electrode /anode0

*An electrolyte, /hich conducts ions0

*A separator, /also an ion conductor0 and

*A positive electrode /cathode0

=egative terminal

Anode

Separator

Cathode

+ositive terminal


49/86

)6)6

2!!lyin# lectrical Conce!ts toPacemakers

-od*le 5


50/86

Objectives

# 9pon completion you ill !e a!le to"* %ecogni&e a high impedance condition

* %ecogni&e a lo impedance condition

* %ecogni&e capture threshold

* Determine hich sensitivity value is more

/or less0 sensitive


51/86

lectrical Information

# Bhy is this electrical information relevantK

# A pacema-er is implanted to"

* +rovide a heart rate to meet meta!olic needs

# $n order to pace the heart, it must capturethe myocardium

# $n order to pace the heart, it must -no hen to pace, ie, it must !e a!le to

sense

# A pacema-er reLuires an intact electrical circuit

Ohm3s "a&


52/86

2

Ohm s "a&Relevance to Pacemaker Patients

#


53/86

33

e ect o ead e o a ce o

-yocardial Ca!t*re

Bhat ould you e'pect to happen if a lead as partially

fracturedK

# $mpedance /or %esistance0 ould rise

# Current ould decrease and !attery energy conserved

( !ut (

Could you guarantee that enough current /$0 can flo

through this fractured lead so that each time the

pacema-er fired the myocardium ould !eatK

%i#h Im!edance Conditions


54/86

)

Lead wire fracture

Increased resistance

%i#h Im!edance Conditions2 1ract*red Cond*ctor

# A fractured ire can cause

$mpedance values to rise

* Current flo from the !attery

may !e too lo to !e effective

# $mpedance values maye'ceed 3,

Hther reason for high

impedance" :ead not seated

properly in pacema-er header


55/86

"ead Im!edance al*es Chan#e as a Res*lt of/

# Bire fractures

# $nsulation !rea-s

Typically, normal impedance reading values range from 3to ,

* Some leads are high impedance !y design These leads ill

normally sho impedance reading values greater than , ohms

# Medtronic


56/86

5

"o& Im!edance Conditions

# $nsulation !rea-s e'pose the

lead ire to the folloing* >ody fluids, hich have a lo

resistance, or

* Another lead ire /in a !ipolar

lead0

# $nsulation !rea- that e'poses a

conductor causes the folloing

* $mpedance values to fall

* Current to drain through the

insulation !rea- into the !ody, or

into the other ire

* +otential for loss of capture

* More rapid !attery depletion

Current ill follo the path of

:EAST resistance


57/86

7

Ca!t*re hreshold

# The minimum electrical stimulus needed to consistently capture the

heart outside of the heartPs on refractory period

;entricular pacema-er 5 ppm

Capture Non-Capture


58/86

1

ffect of "ead Desi#n on Ca!t*re

# :ead maturation

* Fi!rotic ?capsule@ develops around the electrode folloing lead

implantation

* May gradually raise threshold

* 9sually no measura!le effect on impedance


59/86

6

$teroid l*tin# "eads

# Steroid eluting leads

reduce the inflammatory

process

* E'hi!it little to no acute

stimulation threshold pea-ing

* :eads maintain lo chronic

thresholds

Silicone ru!!er plugcontaining steroid

Tines for

sta!lefi'ation

+orous, platini&ed tip

for steroid elution


60/86

5

ffect of $teroid on $tim*lation hresholds

+ulse Bidth Q msec

$mplant Time /Bee-s0

Te'tured Metal Electrode

Smooth Metal Electrode

Steroid(Eluting Electrode

2

;olts

References/ +acing %eference .uide, >a--en Education Center, 66, 9C665)7aE= Cardiac +acing,2nd Edition, Edited !y Wenneth A Ellen!ogen 665


61/86

5

-yocardial Ca!t*re

# Capture is a function of"

*Amplitudethe strength of the impulse e'pressed in volts

# The amplitude of the impulse must !e large enough to cause depolari&ation /ie, to ?capture@

the heart0

# The amplitude of the impulse must !e sufficient to provide an appropriate pacing safety

margin

* +ulse idththe duration of the current flo e'pressed in

milliseconds

# The pulse idth must !e long enough for depolari&ation to disperse to the surrounding tissue

Com!arison


62/86

52

Com!arison6.7 olt 2m!lit*de at Different P*lse Widths

Amplitude

;

2 ms ms ms


63/86

53

he $tren#th'D*ration C*rve

# The strength(duration

curve illustrates the

relationship of

amplitude and pulse

idth

*Any com!ination of

pulse idth and voltage,

on or a!ove the curve,

ill result in capture

+ulse Bidth

.67

8.7

8.6

9.7

.96

;olts

7.6 8.7 8.6

Capture

=o Capture

%heo!ase

Chrona'ie


64/86

5)

D*ration

P*lse Width (ms)

Clinical :tility of the $tren#th'D*ration C*rve

# >y accurately determining

capture threshold, e canassure adeLuate safety margins

!ecause"

* Thresholds may differ in acute or

chronic pacing systems

* Thresholds fluctuate slightly daily

* Thresholds can change due to

meta!olic conditions or

medications

7.6 8.7 8.6

.67

8.7

8.6

9.7

.96$tim

*lationhresh

old(olts)

+rogrammed Hutput


65/86

5

Pro#rammin# O*t!*ts

# +rimary goal" Ensure patient safety and appropriate device

performance

# Secondary goal" E'tend the service life of the !attery

* Typically program amplitude to J 2 ;, !ut alays maintain

adeLuate safety margins# A common output value might !e 2 ; at ) ms

*Amplitude values greater than the cell capacity of the pacema-er

!attery /usually a!out 21 ;0 reLuire a voltage multiplier, resulting in

mar-edly decreased !attery longevity


66/86

5555

Pacemaker $ensin#

# %efers to the a!ility of the pacema-er to ?see@ signals

* E'pressed in millivolts /m;0

# The millivolts /m;0 refers to the si&e of the signal the

pacema-er is a!le to ?see@

m; signal

2 m; signal

$ensitivity


67/86

57

yhe al*e Pro#rammed into the IP;

ime

6.7 m

9.6 m

8.96 m

$ensitivity


68/86

51

Time

m;

2 m;

2 m;

m; sensitivity

At this value the pacema-er ill not

see the 3 m; signal


$ensitivity


69/86

56


At this value, the pacema-er can see !oth the 3 m; and the

3 m; signal So, is ?more sensitive@ !etter, !ecause the

pacema-er sees smaller signalsK

2 m; Sensitivity

Time

m;

2 m;

2 m

>ut hat

a!out thisK


70/86

7

$ensin# 2m!lifiers


71/86

7

$ensin# 2cc*racy

# Affected !y"

* +acema-er circuit /lead0 integrity

# $nsulation !rea-

# Bire fracture

* The characteristics of the electrode

* Electrode placement ithin the heart

* The sensing amplifiers of the pacema-er

* :ead polarity /unipolar vs !ipolar0

* The electrophysiological properties of the myocardium

* EM$ * Electromagnetic $nterference

"ead Cond*ctor Coil Inte#rity


72/86

72

2ffect on $ensin#

# 9ndersensing occurs hen the cardiac signal is una!le to

get !ac- to the pacema-er

* $ntrinsic signals cannot cross the ire fracture

# Hversensing occurs hen the severed ends of the ire

intermittently ma-e contact* Creates signals interpreted !y the pacema-er as +( or %(aves

"ead Ins*lation Inte#rity


73/86

73

2ffect on $ensin#

# 9ndersensing occurs hen inner and outer conductor coils

are in continuous contact

* Signals from intrinsic !eats are reduced at the sense amplifier, and

amplitude no longer meets the programmed sensing value

# Hversensing occurs hen inner and outer conductor coilsma-e intermittent contact

* Signals are incorrectly interpreted as +( or %(aves

: i l P k


74/86

7)

:ni!olar Pacemaker

#Bhere is the sensing circuitK

_

Cathode

Anode

:ead tip to canThis can produce a large potential

difference /signal0 !ecause the cathode

and anode are far apart

Clic- for Anser

+i l P k


75/86

7

+i!olar Pacemaker

# Bhere is the sensing

circuitK

Anode and

Cathode

Clic- for Anser

:ead tip to ring on the lead

This usually produces a smaller potential

difference due to the short inter(electrode

distance#>ut, electrical signals from outside the

heart /such as myopotentials0 are less

li-ely to !e sensed


76/86

t d ; di t


77/86

7777

ectors and ;radients

Sense

The ave of depolari&ation produced !y

normal conduction creates a gradient

across the cathode and anode This

changing polarity creates the signal

Hnce this signal e'ceeds the

programmed sensitivity * it is

sensed !y the device

Clic- for More

2 m;

Ch i th t


78/86

7171

Chan#in# the ector

Sense

2 m;

A +;C occurs, hich is conducted

a!normally Since the vector relative

to the lead has changed, hat effect

might this have on sensingK

Clic- for More

$n this case, the ave of

depolari&ation stri-es the anode and

cathode almost simultaneously This

ill create a smaller gradient and

thus, a smaller signal

P*ttin# It 2ll o#ether


79/86

7676


# Appropriate output programming can improve device longevity

* >ut, do not compromise patient safetyX# :ead design can improve device longevity via

* Steroid eluting leads

# Can help -eep chronic pacing thresholds lo !y reducing inflammation and scarring

*atteries, circuit !oards, capacitors, etc, specificto needs, can lead to

improved efficiencies and loered static current drain

*


80/86

11


# +acema-er :ongevity is"

*A function of programmed parameters /rate, output, time pacing0

*A function of useful !attery capacity

*A function of

# Static current drain

# Circuit efficiency

# Hutput $mpedance

# The loer the programmed sensitivity the MH%E sensitive

the device

* :ead integrity also affects sensing

$tat*s Check


81/86

11

$tat*s Check

# Determine the threshold amplitude

Capture threshold Q loest value ith consist capture

This is at 2 ;

Clic- for Anser

2 ; ;7 ; ;

$tat*s Check


82/86

1212

$tat*s Check

H%

Clic- for Anser

+acema-er A is a!le to ?see@ signals as small as m; Thus, it is

more sensitive

+rogrammed

Sensitivity m;

+acema-er

A

+rogrammed

Sensitivity 2 m;

+acema-er

>

# Bhich of these pacema-ers is more sensitiveK

$tat*s Check


83/86

1313

$tat*s Check

# A pacema-er lead must fle' and move as the heart !eats

Hn average, ho many times does a heart !eat in yearK

Clic- for Anser

3 M$::$H= times $t is not a simple tas- to design a

lead that is small, relia!le, and lasts a lifetime

$tat*s Check


84/86

1)1)

$tat*s Check

Clic- for Anser

:ead Fracture"

#


85/86

11

What &o*ld yo* e=!ect4

# Bhich value is out of rangeK

# Bhat could have caused thisK

+acema-er $nterrogation %eport

Mode" DDD%

:oer" %ate 5 ppm

9T%" 3 ppm

9S%" 3 ppm

Atrial :ead $mpedance" )7 Hhms

;entricular :ead $mpedance" 6 Hhms

$nsulation failure

Clic- for Anser


86/86

hank >o*

fundamentals of cardiac devices

Documents