Pacemakers and AICD

1
PacemakersandAICDs
2
Pacemaker Basics

• Provides electrical stimuli to cause cardiac
  contraction when intrinsic cardiac activity is
  inappropriately slow or absent
• Sense intrinsic cardiac electric potentials

3
ICD Basics

• Designed to treat a cardiac tachydysrythmia
• Performs cardioversion/defibrillation
• Ventricular rate exceeds programmed cut-off rate
• ATP (antitachycardia pacing)
• Overdrive pacing in an attempt to terminate
  ventricular tachycardias
• Some have pacemaker function (combo devices)

4
(No Transcript)
5
Pacemaker and ICD Basics

• Pulse Generators
• Placed subcutaneously or submuscularly
• Connected to leads
• Battery
• Most commonly lithium-iodide type
• Life span 5 to 8 years
• Output voltage decreases gradually
• Makes sudden battery failure unlikely

6
Pacemaker and ICD Basics

• Asynchronous
• Fixed rate
• Impulse produced at a set rate
• No relation to patients intrinsic cardiac
  activity
• Susceptible to Torsades if impulse coincides with
  t wave

7
Pacemaker and ICD Basics

• Synchronous
• Demand mode
• Sensing circuit searches for intrinsic
  depolarization potential
• If absent, a pacing response is generated
• Can mimic intrinsic electrical activity pattern
  of the heart

8
Pacemaker Nomenclature
I II III IV V
Chamber Paced Chamber Sensed Response to Sensing Rate Modulation, Programmability Anti-tachycardia Features
AAtrium AAtrium TTriggered PSimple PPacing
VVentricle VVentricle IInhibited MMulti-programmable SShock
DDual DDual DDual RRate Adaptive DDual
ONone ONone ONone CCommunicating
ONone
9
Examples

• VVI
• Paces ventricle
• Senses ventricle
• Inhibited by a sensed ventricular event

10
Pacing Nomenclature Examples

• AAT
• Paces atria
• Senses atria
• Triggers generator to fire if atria sensed
• DDD
• Paces atria and ventricle
• Senses atria and ventricle
• Atrial triggered and ventricular inhibited
• EKG 2 spikes

11
DDD
Atrial Spike
Ventricular Spike
12
Pacemaker Lead System

• Endocardial leads placed via central access
• Placed in right ventricle and/or atria
• Fixed to the endocardium via screws or tines
• Experimental pacing systems
• 2 atrial leads (minimize afib)
• Biventricular pacing

13
(No Transcript)
14
(No Transcript)
15
Magnet Inhibition

• Closes an internal reed switch
• Causes sensing to be inhibited
• Temporarily turns pacemaker into asynchronous
  mode (set rate)
• Does NOT turn pacemaker off
• Rate can confer info regarding battery life
• Distinct rates for BOL, ERI, EOL

16
Pacemaker Indications

• Absolute indications
• Sick sinus syndrome
• Symptomatic sinus bradycardia
• Tachy-brady syndrome
• Afib with slow ventricular response
• 3rd degree heart block
• Chronotropic incompetence
• Inability to increase heart rate to match
  exercise
• Prolonged QT syndrome

17
Pacemaker Indications

• 3rd Degree heart block

18
Pacemaker Indications

• Relative indications
• Cardiomyopathy
• Dilated
• Hypertrophic
• Severe refractory neurocardiogenic syncope
• Paroxysmal atrial fibrillation

19
ICD Indications

• Generally
• Used in cases where there was a previous cardiac
  arrest
• Or, patients with undetermined origin or
  continued VT or VF despite medical interventions

20
Pacemaker Complications

• EKG abnormalities due to
• Failure to output
• Failure to capture
• Sensing abnormalities
• Operative failures

21
Pacemaker Failure to Output

• Definition
• No pacing spike present despite indication to
  pace
• Etiology
• Battery failure, lead fracture, break in lead
  insulation, oversensing, poor lead connection,
  cross-talk
• Atrial output is sensed by ventricular lead

22
Pacemaker Failure to Capture

• Definition
• Pacing spike is not followed by either an atrial
  or ventricular complex
• Etiology
• Lead fracture or dislodgement, break in lead
  insulation, elevated pacing threshold, MI at lead
  tip, drugs, metabolic abnormalities, cardiac
  perforation, poor lead connection

23
Pacemaker Sensing Abnormalities

• Oversensing
• Senses noncardiac electrical activity and is
  inhibited from correctly pacing
• Etiology
• Muscular activity (diaphragm or pecs), EMI, cell
  phone held within 10cm of pulse generator
• Undersensing
• Incorrectly misses intrinsic depolarization and
  paces
• Etiology
• Poor lead positioning, lead dislodgement, magnet
  application, low battery states, MI

24
Pacemaker Operative Failures

• Due to pacemaker placement
• Pneumothorax
• Pericarditis
• Perforated atrium or ventricle
• Dislodgement of leads
• Infection or erosion of pacemaker pocket
• Infective endocarditis (rare)
• Venous thrombosis

25
Pacemaker Complications

• Pacemaker syndrome
• Patient feels worse after pacemaker placement
• Presents with progressive worsening of CHF
  symptoms
• Due to loss of atrioventricular synchrony,
  pathway now reversed and ventricular origin of
  beat

26
ICD Complications

• Similar to pacemaker complications
• Operative failures
• Same as pacemakers
• Sensing and pacing failures
• Inappropriate cardioversion
• Ineffective cardioversion/defibrillation
• Device deactivation

27
ICD Sensing failures

• Similar to pacmakers
• Oversensing
• Undersensing
• Appropriate failure to treat
• Programmed cut off at 180 bpm
• If V Tach occurs at 160 bpms, appropriately fails
  to cardiovert

28
ICD Inappropriate Cardioversion

• Most frequent complications
• Provokes pain and anxiety in pts
• Consider when
• Pt is in afib
• With ventricular response gt programmed cut off
• Received multiple shocks in rapid succession
• Etiology
• Afib, T-wave oversensing, lead fracture,
  insulation breakage, MRI, EMI

29
ICD Inappropriate Cardioversion

• Treatment
• Magnet over ICD inhibits further shocks
• Does NOT inhibit bradycardiac pacing
• Note
• Some older devices produce beep with each QRS
• If left on for gt30 seconds, ICD disabled and
  continous beep
• To reactivate, lift off magnet and then replace
  for gt 30 seconds, beep will return with each QRS

30
ICD Failure to Deliver Cardioversion

• Etiology
• Failure to sense, lead fracture, EMI, inadvertent
  ICD deactivation
• Management
• External defibrillation and cardioversion
• Do not withhold therapy for fear of damaging ICD
• If pts internal defibrillator activates during
  chest compressions, you may feel a mild shock (no
  reports of deaths related to this)
• Antidysrhymthic medications

31
ICD Ineffective Cardioversion

• Etiology
• Inadequate energy output
• Rise in the defibrillation threshold
• MI at the lead site
• Lead fracture
• Insulation breakage
• Pre-programmed set of therapies per dysrythmia
• Manufacturer specific
• Once number of attempts reached, will not deliver
  further shocks until new episode is declared

32
Electromagnetic Interference

• Can interfere with function of pacemaker or ICD
• Device misinterprets the EMI causing
• Rate alteration
• Sensing abnormalities
• Asynchronous pacing
• Noise reversion
• Reprogramming

33
Electromagnetic Interference

• Examples
• Metal detectors
• Cell phones
• High voltage power lines
• Some home appliances (microwave)

34
Electromagnetic Interference

• Intensity of electromagnetic field decreases
  inversely with the square of the distance from
  the source
• Newer pacemakers and ICDs are being built with
  increased internal shielding