Transcript Pacemaker Anatomy

Pacemakers and Internal Cardiac
Defibrillators
Mark Wahba
Resident Rounds
September 11, 2003
See:
Brady’s, Blocks, & Pacers
Moritz Haager
1 hr rounds
July 17, 2002
Brief History
First described in 1952
 Introduced into clinical practice in 1960
 First endocardial defibrillators in 1980
 1991 in USA 1 million people had
permanent pacemakers

Outline








Indications
Basics, Pacemaker Components and Code
Complications of Implantation
Pacemaker Malfunction
Management
Disposition
ICD
Guest
Basically:
Device that provides electrical stimulation to
cause cardiac contraction when intrinsic
cardiac electrical activity is slow or absent

http://www.emedicine.com/emerg/topic805.htm
Pacemaker Functions
1.
2.
3.
4.
Stimulate cardiac depolarization
Sense intrinsic cardiac function
Respond to increased metabolic
demand by providing rate responsive
pacing
Provide diagnostic information stored
by the pacemaker
Indications for Pacer

30 AVB and any of:
–
–
–
–
–
Symptomatic bradycardia
Asystole >3 sec or vent escape <40bpm
Post-AVN ablation
Post-op and not expected to improve
Neuromuscular disease
20 AVB + symptomatic bradycardia
 Chronic bi-/trifasicular block w/ intermittent 30 AVB or 20 AVB
Type II
 Post-MI and any of:

– Persistent 20 AVB or 30 AVB
– Transient 20 AVB or 30 AVB and BBB


SAN dysfunction + symptomatic brady’s (e.g. SSS)
Recurrent syncope due to carotid sinus stimulation
Pacemaker Components and
Anatomy
Pacemaker Components
Pulse Generator
 Electronic
Circuitry
 Lead System

Pulse Generator
Subcutaneous or submuscular
 Lithium battery
 4-10 years lifespan
 long life and gradual decrease in power
 sudden pulse generator failure is an
unlikely cause of pacemaker
malfunction

Electronic Circuitry
Sensing circuit
 Timing circuit
 Output circuit

Lead System
Bipolar
 Lead has both negative,
(Cathode) distal and
positive, (Anode)
proximal electrodes
 Separated by 1 cm
 Larger diameter: more
prone to fracture
 Compatible with ICD
Unipolar
 Negative (Cathode)
electrode in contact
with heart
 Positive (Anode)
electrode: metal
casing of pulse
generator
 Prone to oversensing
 Not compatible with
ICD
Difference on an ECG? Bipolar

current travels only
a short distance
between electrodes
 small pacing spike:
<5mm
+
Anode
Cathode
Difference on an ECG? Unipolar

current travels a
longer distance
between electrodes
 larger pacing spike: +
>20mm
Anode
Cathode
Pacemaker Code
I
Chamber
Paced
II
Chamber
Sensed
III
Response
to Sensing
IV
Programmable
Functions/Rate
Modulation
V: Ventricle
V: Ventricle
T: Triggered P: Simple
programmable
A: Atrium
A: Atrium
I: Inhibited
M: Multiprogrammable
D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating
O: None
O: None
S: Single
S: Single
(A or V)
(A or V)
O: None
V
Antitachy
Function(s)
P: Pace
S: Shock
D: Dual (P+S)
R: Rate modulating O: None
O: None
Common Pacemakers




VVI
– Ventricular Pacing : Ventricular sensing; intrinsic
QRS Inhibits pacer discharge
VVIR
– As above + has biosensor to provide Rateresponsiveness
DDD
– Paces + Senses both atrium + ventricle, intrinsic
cardiac activity inhibits pacer d/c, no activity:
trigger d/c
DDDR
– As above but adds rate responsiveness to allow
for exercise
Rate Responsive Pacing

When the need for oxygenated blood increases,
the pacemaker ensures that the heart rate
increases to provide additional cardiac output
Adjusting Heart Rate to Activity
Normal Heart Rate
Rate Responsive Pacing
Fixed-Rate Pacing
Daily Activities
Determining type of pacemaker




Wallet card: 5
letter code
CXR: code visible
Single lead in
ventricle: VVI
Separate leads
DDD or DVI
Single Chamber

VVI - lead lies in
right ventricle
 Independent of atrial
activity
 Use in AV
conduction disease
Paced Rhythm Recognition
VVI / 60
Dual Chamber




Typically in pts with
nonfibrillating atria and
intact AV conduction
Native P, paced P,
native QRS, paced
QRS
ECG may be
interpreted as
malfunction when none
is present
May have fusion beats
Four “Faces” of Dual Chamber
Pacing

Atrial Pace, Ventricular Pace (AP/VP)
AV
AP
V-A
VP
Rate = 60 bpm / 1000 ms
A-A = 1000 ms
AV
AP
VP
V-A
Four “Faces” of Dual Chamber
Pacing

Atrial Pace, Ventricular Sense (AP/VS)
AV
AP
V-A
VS
Rate = 60 ppm / 1000 ms
A-A = 1000 ms
AV
AP
VS
V-A
Four “Faces” of Dual Chamber
Pacing

Atrial Sense, Ventricular Pace (AS/ VP)
AV
AS
V-A
VP
V-A
AV
AS
Rate (sinus driven) = 70 bpm / 857 ms
A-A = 857 ms
VP
Four “Faces” of Dual Chamber
Pacing

Atrial Sense, Ventricular Sense (AS/VS)
AV
AS
V-A
VS
Rate (sinus driven) = 70 bpm / 857 ms
Spontaneous conduction at 150 ms
A-A = 857 ms
AV
AS
V-A
VS
Pacemaker Interventions

Magnet application
– No universal function of magnet
– Model-specific magnet, some activate reed
switch  asynchronous pacing at pre-set
rate

Interrogation / Programming
– Model-specific pacemaker programmer
can non-invasively obtain data on function
and reset parameters
Magnet Application
Complications of Pacemaker
Implantation
Complications of Pacemaker
Implantation
Venous access
 Infection
 Thrombophelbitis
 Pacemaker Syndrome

Venous Access
Bleeding
 Pneumo / hemothorax
 Air embolism

Infection
2% for wound and ‘pocket’ infection
 1% for bacteremia with sepsis
 S. aureus and S. epidermidis
 If bacteremic: start Vancomycin, remove
system, TV pacemaker and IV abx for
4-6 weeks, new system

Thrombophlebitis
Incidence 30-50%
 1/3 have complete venous obstruction
 b/c of collateralization only 0.5-3.5%
devp symptoms
 Swelling, pain, venous engorgement
 Heparin, lifetime warfarin

Pacemaker Syndrome

Presents w/ worsening of original Sx postimplant of single chamber pacer
 AV asynchrony retrograde VA conduction
 atrial contraction against closed MV + TV
 jugular venous distention + atrial dilation 
sx of CHF and reflex vasodepressor effects
 Dx of exclusion
 Tx w/ dual chamber pacer
Pacemaker Malfunction
4 broad categories
1.
2.
3.
4.
Failure to Output
Failure to Capture
Inappropriate sensing: under or over
Inappropriate pacemaker rate
Failure to Output
absence of pacemaker spikes despite indication
to pace
 dead battery
 fracture of pacemaker lead
 disconnection of lead from pulse generator
unit
 Oversensing
 Cross-talk: atrial output sensed by vent lead
No Output

Pacemaker artifacts do not appear on
the ECG; rate is less than the lower rate
Pacing output delivered; no
evidence of pacing spike is seen
Failure to capture
spikes not followed by a stimulus-induced
complex
 change in endocardium: ischemia,
infarction, hyperkalemia, class III
antiarrhythmics (amiodarone,
bertylium)
A: failure to capture atria in DDD
Inappropriate sensing:
Undersensing
Pacemaker incorrectly misses an intrinsic
deoplarization  paces despite intrinsic
activity
 Appearance of pacemaker spikes occurring
earlier than the programmed rate:
“overpacing”
 may or may not be followed by paced
complex: depends on timing with respect to
refractory period
 AMI, progressive fibrosis, lead displacement,
fracture, poor contact with endocardium
Undersensing

Pacemaker does not “see” the intrinsic
beat, and therefore does not respond
appropriately
Intrinsic beat
not sensed
Scheduled pace
delivered
VVI / 60
Undersensing

An intrinsic depolarization that is
present, yet not seen or sensed by the
pacemaker
P-wave
not sensed
Atrial Undersensing
Inappropriate sensing:
Oversensing
Detection of electrical activity not of cardiac
origin  inhibition of pacing activity
 “underpacing”
 pectoralis major: myopotentials
oversensed
 Electrocautery
 MRI: alters pacemaker circuitry and results
in fixed-rate or asynchronous pacing
 Cellular phone: pacemaker inhibition,
asynchronous pacing
Oversensing
Marker channel
shows intrinsic
activity...
...though no
activity is present
VVI / 60

An electrical signal other than the
intended P or R wave is detected
Inappropriate Pacemaker Rate

Rare reentrant tachycardia seen w/ dual
chamber pacers
 Premature atrial or vent contraction 
sensed by atrial lead  triggers vent
contraction  retrograde VA conduction 
sensed by atrial lead  triggers vent
contraction  etc etc etc
 Tx: Magnet application: fixed rate, terminates
tachyarrthymia,
 reprogram to decrease atrial sensing
Causes of Pacemaker
Malfunction




Circuitry or power source of pulse
generator
Pacemaker leads
Interface between pacing electrode
and myocardium
Environmental factors interfering with
normal function
Pulse Generator

Loose connections
– Similar to lead fracture
– Intermittent failure to sense or pace

Migration
– Dissects along pectoral fascial plane
– Failure to pace

Twiddlers syndrome
– Manipulation  lead dislodgement
Twiddler’s Syndrome
Twiddler’s Syndrome
Leads

Dislodgement or fracture (anytime)
– Incidence 2-3%
– Failure to sense or pace
– Dx w/ CXR, lead impedance

Insulation breaks
– Current leaks  failure to capture
– Dx w/ measuring lead impedance (low)
Cardiac Perforation
Early or late
 Usually well tolerated

– Asymptomatic  inc’d pacing threshold,
hiccups
– Dx: P/E (hiccups, pericardial friction rub),
CXR, Echo
Environmental Factors
Interfering with Sensing
• MRI
• Electrocautery
• Arc welding
• Lithotripsy
• Cell phones
• Microwaves
• Mypotentials from muscle
Management
Management: History
Most complications and malfunctions
occur within first few weeks or months
 pacemaker identification card
 Syncope, near syncope, orthostatic
dizziness, lightheaded, dyspnea,
palpitations
 Pacemaker syndrome: diagnosis of
exclusion

Management: Physical Exam
Fever: think pacemaker infection
 Cannon “a” waves: AV asynchrony
 Bibasilar crackles if CHF
 Pericardial friction rub if perforation of
RV

Management: adjuncts
CXR: determine tip position
 ECG

Potential Problems Identifiable on an
ECG Can Generally Be Assigned to
Five Categories:
Failure to output
 Failure to capture
 Undersensing
 Oversensing
 Pseudomalfunction

Pseudomalfunction: Hysteresis

Allows a lower rate between sensed
events to occur; paced rate is higher
Lower Rate 70 ppm
Hysteresis Rate 50 ppm
Management: ACLS
Drug and Defibrillate as per ACLS
guidelines
 However keep paddles >10cm from
pulse generator
 May transcutaneously pace
 Transvenous pacing may be inhibited
by venous thrombosis: may need
flouroscopic guidance

AMI + Pacers
Difficult Dx; most sensitive indicator is
ST-T wave changes on serial ECG
 If clinical presentation strongly
suggestive then should treat as AMI
 Coarse VF may inhibit pacer
(oversensing)
 Successful resuscitation may lead to
failure to capture (catecholamines,
ischemia)

Disposition
Disposition

Admit
– Pacemaker infections /unexplained fever or WBC
– Myocardial perforation
– Lead # or dislodgement
– Wound dehiscence / extrusion or erosion
– Failure to pace, sense, or capture
– Ipsilateral venous thrombosis
– Unexplained syncope
– Twiddlers syndrome
Disposition

Potentially fixable in ED w/ help
– Pacemaker syndrome
– Pacemaker-mediated tachycardia
– Cross-talk
– Oversensing
– Diaphragmatic pacing
– Myopotential inhibitors
Internal Cardiac Defibrillators
Internal Cardiac Defibrillators





Device to treat tachydysrhythmias
If ICD senses a vent rate > programmed cutoff rate of the ICD  device performs
cardioversion/defibrillation
All ICDs are also vent pacemakers
Required shock is approximately <15 Joules
Similar problems with implantation as
pacemakers
Indications for ICD

Cardiac arrest from VF or VT not due to
reversible etiology
 Spontaneous sustained VT
 Syncope NYD + inducible symptomatic VF or
VT in setting of poor drug tolerance or
efficacy
 Non-sustained VF or VT + CAD, prior MI, LV
dysfunction and inducible VF or VT not
responding to Class I antiarrhythmic Tx
ICD Malfunction
Inappropriate Cardioversion
 Ineffective Cardioversion
 Failure to Deliver Cardioversion

Inappropriate Cardioversion

Most frequently associated problem
 Sensing malfunction: SVT sensed as VT
 Shocks for nonsustained VT
 T waves detected as QRS complex and
interpreted as  HR

h/r Could be  incidence of VT, VF (hypoK,
hypoMg, ischemia +/- infarction)
Ineffective Cardioversion
Inadequate energy output
 Rise in defibrillation threshold 
antiarrhythmics
 MI at lead site
 Lead fracture
 Dislodgement of leads

Failure to Deliver Cardioversion
Failure to sense
 Lead fracture
 Electromagnetic interference
 Inadvertent deactivation

ACLS Interventions
ICD may not prevent sudden cardiac
death
 Same approach as with pacemakers
 Person performing CPR may feel a mild
shock if ICD discharges during
compressions
 Can deactivate device with magnet
during resuscitation efforts

Disposition
“in almost all instances, admission to a
monitored setting with extended
telemetric observation will be
necessary”
 Rosen’s

Thanks to:
Calgary Health Region Pacemaker nurses
 Karen and Sandra
References








Brady et al. 1998. EM Clinics NA. 16(2): 361-388
Xie et al. 1998. Em Clinics NA. 16(2): 419-462
Shah et al. 1998 EM Clinics NA. 16(2): 463-487
Harrigan and Brady. 2000. EMR 21(19): 205-216
Rosen
American College of Cardiology ECG of the Month Feb 2001:
http://www.acc.org/education/online/ecg_month/0201/Feb01_02.htm
Pacemaker and Automatic Internal Cardiac Defibrillator, Weinberger et.
al http://www.emedicine.com/emerg/topic805.htm
CorePace presentation 99912 by Medtronic Inc. 2000 available from
Pacmaker Nurses at Foothills Hospital, www.medtronic.com
Pacemaker and Defibrillator Clinics
-Open Mon.-Fri. 0800-1600 hrs.
 -Electrophysiology for ICD’s 41248
 -Pacemaker Clinic 41188
 -On call pager #0569

ECG analysis
Building on routine ECG
interpretation skills

Low Rate
– Pacemakers not programmed below 50
BPM
– ICD’s often low rate of 40 BPM
Assess atrial rhythm

P waves and rate
Atrial sensing
 Any atrial pacing
 Atrial capture

Assess Ventricular Rhythm
QRS rate and morphology
 Relation to atrial rhythm
 Ventricular pacing
 Ventricular capture

Upper Rate

Pacemakers do not prevent intrinsic heart rate from going too
fast

Pacing therapy and Drug therapy is required to suppress rapid
rhythms like atrial fibrillation

Mode switching devices recognize fast atrial rhythms and
automatically switch to a non-tracking mode

Some pacemakers Medtronic AT501 have anti-tachycardia
therapies to treat Atrial Flutter but they cannot terminate atrial
fibrillation
Defibrillators

Most often ICD patient are not paced

VT/VF detection and treatment with
pacing or shock is their primary purpose

Event memory to analyze rhythm
detected and treated.
PM and ICD Pts in ER

-Direction of Medical Director is that
Cardiology should be consulted.

-Cardiologist to initiate calling in On-Call
Pacemaker Clinic nurse to assess
device function and diagnostics.
Complete assessment in ER

Assess symptoms

ECG Look for Pacing and sensing, Atrial/Ventricular

Obtain patients device info from card or old chart if
possible
Medications and compliance

Surgical Complications

Incision issues: Infected pacemaker site
presents risk for endocarditis

Needs to be brought to Pacemaker or ICD
clinic attention

Cardiac perforation/Tamponade
– Early Post implant
– New or unusual symptoms of sharp,
stabbing chest pain.
– Worse with deep breath
– Usual cause is atrial perforation or tear
–
PACE, Vol. 25, No.5 Post Pacemaker Implant Pericarditis: Incidence and Outcomes
with Active Fixation Leads. Soori Kivakumaran, M. E. Irwin, S. S. Gulamhusein
Management in ER

Echocardiogram
– Look for blood in pericardium
– CV surgery consult
– Don’t anticoagulate
Less than appropriate reasons we
are called..
Don’t need to bother Cardiologist
 Will call Cardiology after device assessed
 Pt in ER with angina, not appropriate to
assess device at that time
 We do follow patients with devices on a
routine basis so they don’t need to be
checked just because they have a device.

Magnets and devices

No universal response to magnet
application with cardiac devices.
Pacemaker Clinic

FMC Monday to Friday 0800-1600

Phone 944-1188
EP Clinic

ICD patient issues

Monday to Friday 0800-1600 hrs

Phone 944-1248
Nurse on Call

CHR pager

Please consult Cardiology

Medical Director: Dr. A. M. Gillis
– Electrophysiology