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Pacemaker Anatomy

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Pacemaker Anatomy Powered By Docstoc
					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.   Stimulate cardiac depolarization
2.   Sense intrinsic cardiac function
3.   Respond to increased metabolic
     demand by providing rate responsive
     pacing
4.   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                     Unipolar
 Lead has both negative,    Negative (Cathode)
  (Cathode) distal and         electrode in contact
  positive, (Anode)            with heart
  proximal electrodes        Positive (Anode)
                               electrode: metal
 Separated by 1 cm            casing of pulse
 Larger diameter: more        generator
  prone to fracture          Prone to oversensing
 Compatible with ICD        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: +
                           Anode
  >20mm


                                         -
                                   Cathode
         Pacemaker Code
    I                II            III               IV              V
 Chamber         Chamber      Response        Programmable       Antitachy
  Paced           Sensed      to Sensing      Functions/Rate    Function(s)
                                                Modulation

V: Ventricle   V: Ventricle   T: Triggered P: Simple           P: Pace
                                              programmable
                                             M: Multi-
A: Atrium      A: Atrium      I: Inhibited                     S: Shock
                                                programmable

D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating     D: Dual (P+S)

O: None        O: None        O: None        R: Rate modulating O: None

S: Single      S: Single                     O: None
   (A or V)       (A or V)
Common Pacemakers
   VVI
     – Ventricular Pacing : Ventricular sensing; intrinsic
       QRS Inhibits pacer discharge
   VVIR
     – As above + has biosensor to provide Rate-
       responsiveness
   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         V-A            AV   V-A




  AP                        AP
        VP                       VP

  Rate = 60 bpm / 1000 ms
  A-A = 1000 ms
Four “Faces” of Dual Chamber
Pacing
    Atrial Pace, Ventricular Sense (AP/VS)

         AV         V-A    AV        V-A




       AP                  AP
            VS                  VS
 Rate = 60 ppm / 1000 ms
 A-A = 1000 ms
    Four “Faces” of Dual Chamber
    Pacing
   Atrial Sense, Ventricular Pace (AS/ VP)

                       AV        V-A      AV        V-A




                  AS                    AS
                            VP                 VP

      Rate (sinus driven) = 70 bpm / 857 ms
      A-A = 857 ms
    Four “Faces” of Dual Chamber
    Pacing
   Atrial Sense, Ventricular Sense (AS/VS)

                  AV      V-A            AV        V-A




                AS                      AS
                     VS                       VS
Rate (sinus driven) = 70 bpm / 857 ms
Spontaneous conduction at 150 ms
A-A = 857 ms
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 post-
  implant 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.   Failure to Output
2.   Failure to Capture
3.   Inappropriate sensing: under or over
4.   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

                          Scheduled pace
         Intrinsic beat      delivered
          not sensed




                                           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

                              ...though no
         Marker channel    activity is present
         shows intrinsic
            activity...




                                                 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 cut-
    off 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

				
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