1. Pacemakers and AICD’s

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)

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 NomenclatureI II
III IV V
Chamber Paced
Chamber Sensed
Response to Sensing
Rate Modulation, Programmability
Anti-tachycardia Features
A=Atrium
T=Triggered
P=Simple
P=Pacing
V=Ventricle
I=Inhibited
M=Multi-programmable
S=Shock
D=Dual
R=Rate Adaptive
O=None
C=Communicating

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

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
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 Appropriate failure to treat
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 > 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 >30 seconds, ICD disabled and continous beep
To reactivate, lift off magnet and then replace for > 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 pt’s 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