1. Pacemakers and Internal Cardiac Defibrillators
Mark Wahba
Resident Rounds
September 11, 2003

2. See: Brady’s, Blocks, & Pacers
Moritz Haager
1 hr rounds
July 17, 2002

3. 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

4. Outline Indications Basics, Pacemaker Components and Code
Complications of Implantation
Pacemaker Malfunction
Management
Disposition
ICD
Guest

5. Basically:
Device that provides electrical stimulation to cause cardiac contraction when intrinsic cardiac electrical activity is slow or absent

6. Pacemaker Functions Stimulate cardiac depolarization
Sense intrinsic cardiac function
Respond to increased metabolic demand by providing rate responsive pacing
Provide diagnostic information stored by the pacemaker

7. 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
Class I recommendations From Rosen

8. Pacemaker Components and Anatomy

9. Pacemaker Components
Pulse Generator
Electronic Circuitry
Lead System

10. 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

11. Electronic Circuitry
Sensing circuit
Timing circuit
Output circuit

12. 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
Both are ONE wire. Don’t confuse bipolar and unipolar leads with single chamber and dual chamber pacemakers.
Unipolar prone to oversensing because Anode may pick up myopotenials from muscle or other extrinsic source

13. Difference on an ECG? Bipolar
current travels only a short distance between electrodes
small pacing spike: <5mm +
Anode -
Cathode

14. Difference on an ECG? Unipolar
current travels a longer distance between electrodes
larger pacing spike: >20mm +
Anode -
Cathode

15. Pacemaker Code P: Simple programmable V: Ventricle V: Ventricle
Chamber
Paced II
Sensed
III
Response
to Sensing IV
Programmable
Functions/Rate
Modulation V
Antitachy
Function(s)
P: Simple
programmable
V: Ventricle
V: Ventricle
T: Triggered
P: Pace
M: Multi-
programmable
A: Atrium
A: Atrium
I: Inhibited
S: Shock
D: Dual (A+V)
D: Dual (A+V)
D: Dual (T+I)
C: Communicating
D: Dual (P+S)
The first letter refers to the chamber(s) being paced
The second letter refers to the chamber(s) being sensed
The third letter refers to the pacemaker’s response to a sensed event:
T = Triggered D = Dual (inhibited and triggered*)
I = Inhibited O = No response
*In a single chamber mode, “triggered” means that when an intrinsic event is sensed, a pace is triggered immediately thereafter. In a dual chamber mode, “triggered” means that a sensed atrial event will initiate (trigger) an A-V delay.
The fourth letter denotes the pacemaker’s programmability and whether it is capable of rate response:
P = Simple Programmable (rate and/or output)
M = Multiprogrammable (rate, output, sensitivity, etc.)
C = Communicating (pacemaker can send/receive information to/from the programmer)
R = Rate Modulation
O = None
Note that this sequence is hierarchical. In other words, it is assumed that if a pacemaker has rate modulation capabilities, “R”, that it also can communicate, “C”.
The fifth letter represents the pacemaker’s antitachycardia functions:
P = Pace D = Dual (pace and shock available)
S = Shock O = None
You may want to test the audience by having them describe different pacing modes. More modes and ECG strips are found in Module 2.
O: None
O: None
O: None
R: Rate modulating
O: None
S: Single
(A or V)
S: Single
(A or V)
O: None

16. 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
Biosensors --- most are vibrations sensors that increase HR in proportion to activity sensed, but can also have pH, venous temp, resp rate, QT interval, stroke volume, O2 sat, RA pressure sensors less commonly.
Dual chamber pacing allows for atrial contribution to CO (up to 30% of CO)

17. 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
Piezoelectric crystal that detects mechanical signals produced by movement, mechanical signals translate into electrical signals that increase rate of the pacemaker
Daily Activities

18. Determining type of pacemaker
Wallet card: 5 letter code
CXR: code visible
Single lead in ventricle: VVI
Separate leads DDD or DVI

19. Single Chamber VVI - lead lies in right ventricle
Independent of atrial activity
Use in AV conduction disease

20. Paced Rhythm Recognition
VVI / 60

21. 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

22. Four “Faces” of Dual Chamber Pacing
Atrial Pace, Ventricular Pace (AP/VP) AV
V-A AV
V-A
Knowing the basic A-V and V-A intervals will help in understanding the four modes or “faces” of dual chamber pacing. In the first example, the pacemaker is pacing in both the atrium and the ventricle–most likely a patient with sinus node dysfunction and AV block. AP VP
Rate = 60 bpm / 1000 ms
A-A = 1000 ms

23. Four “Faces” of Dual Chamber Pacing
Atrial Pace, Ventricular Sense (AP/VS) AP VS
V-A AV
In this example, the atrium is being paced, but AV conduction is intact, so the ventricular output is inhibited by a sensed ventricular event.
Rate = 60 ppm / 1000 ms
A-A = 1000 ms

24. Four “Faces” of Dual Chamber Pacing
Atrial Sense, Ventricular Pace (AS/ VP)
V-A AV
In this example, the atrial rate is driving the ventricular rate–also called atrial tracking. This patient has adequate sinus node function with AV block. AS AS VP VP
Rate (sinus driven) = 70 bpm / 857 ms
A-A = 857 ms

25. Four “Faces” of Dual Chamber Pacing
Atrial Sense, Ventricular Sense (AS/VS)
V-A AV AS VS
In this example, the patient has adequate sinus node function and intact AV conduction, but may experience little to no increase in sinus rate with activity and/or AV block that occurs at increased rates. At appropriate rates, it is best to try and utilize the patient’s intrinsic rhythm when possible.
Rate (sinus driven) = 70 bpm / 857 ms
Spontaneous conduction at 150 ms
A-A = 857 ms

26. 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
Useful to test pacemaker function and battery life, especially if intrinsic HR > paced rate
Pre-set paced rate dec’s w/ dec’g battery life
Programmable functions include lower rate limit, upper rate limit, AV interval, energy output, refractory periods, blanking period (interval after d/c during which no signals are sensed), mode of function (e.g. A, V, or D), max atrial tracking rate (fastest atrial rate pacer will keep up with), vent pacing response, algorithm for tachycardia termination, sensing parameters

27. Magnet Application
demand ventricular pacer: a low pacemaker rate of 50 beats/min was programmed to preserve the patient's intrinsic sinus rhythm. Magnet application (arrows) causes fixed-rate pacing (extremely small pacing artifacts are visible in lead V3) at 100 beats/min. The rapid magnet-induced pacing rate (asterisks on the lead-V1 rhythm strip) prevents competition with the intrinsic rhythm. Note the P waves following the pacemaker-induced QRS complexes, indicating 1:1 ventricular-to-atrial conduction.

28. Complications of Pacemaker Implantation

29. Complications of Pacemaker Implantation
Venous access
Infection
Thrombophelbitis
Pacemaker Syndrome

30. Venous Access
Bleeding
Pneumo / hemothorax
Air embolism

31. 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

32. Thrombophlebitis Incidence 30-50% 1/3 have complete venous obstruction
b/c of collateralization only % devp symptoms
Swelling, pain, venous engorgement
Heparin, lifetime warfarin

33. 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
Present w/ presyncope, syncope, orthostatic dizziness, lightheadedness, fatigue, lethargy, CP, neck fullness, other non-specific complaints
Can get w/ dual chamber pacer if SA node rate > paced rate in pts w/ AV block

34. Figure A 12-lead ECG from a 63-year-old woman with recurrent syncope several months after implantation of a VVI pacemaker. The arrows show the retrograde P waves of 1:1 ventricular-to-atrial conduction that may be associated with a pacemaker syndrome.
Pacemaker syndrome

35. Pacemaker Malfunction

36. 4 broad categories Failure to Output Failure to Capture
Inappropriate sensing: under or over
Inappropriate pacemaker rate

37. 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
Cross-talk = oversensing of pacemaker generated electrical activity E.g. vent lead senses atrial pacing spike  misinterprets as vent contraction  inhibits pacer d/c  skipped beat  dizziness / syncope

38. CorePace Module 4: Troubleshooting
No Output
Pacemaker artifacts do not appear on the ECG; rate is less than the lower rate
When the pacemaker problem is no output, the marker channel shows pacing markers—AP or VP—although no artifact appears on the ECG.
No output is defined as the failure to pace. Impulses are generated from the IPG, but is not transferred to the lead.
Pacing output delivered; no evidence of pacing spike is seen

39. Failure to capture spikes not followed by a stimulus-induced complex
change in endocardium: ischemia, infarction, hyperkalemia, class III antiarrhythmics (amiodarone, bertylium)

40. Failure to sense or capture in VVI
Figure A 12-lead ECG with a lead-V1 rhythm strip from an 84-year-old man who returned to a pacemaker clinic with dizziness 11 years after implantation of a VVI pacemaker. Arrows show pacing artifacts continuing regularly (68/min) not sensing for the patient's intrinsic beats and not producing paced beats. The asterisks indicate the single incidence of ventricular capture by the pacemaker
Failure to sense or capture in VVI

41. A: failure to capture atria in DDD
Figure A 12-lead ECG with a lead-V1 rhythm strip from a 73-year-old man seen in a pacemaker clinic 6 months after implantation of a DDD pacemaker. During the pause after the VPB, minimum-rate pacing occurs (the first six arrows), but with failure of atrial capture. An asterisk and the last arrow indicate the single incidence of atrial capture by the pacemaker.
A: failure to capture atria in DDD

42. 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

43. Scheduled pace delivered Intrinsic beat not sensed
Undersensing
Pacemaker does not “see” the intrinsic beat, and therefore does not respond appropriately
Scheduled pace delivered
Intrinsic beat not sensed
VVI / 60

44. CorePace Module 4: Troubleshooting
Undersensing
An intrinsic depolarization that is present, yet not seen or sensed by the pacemaker
P-wave not sensed
An intrinsic depolarization occurs in the atrium, but this depolarization is not sensed by the pacemaker. Therefore, the pacemaker sends an inappropriate pacing pulse to that chamber. Undersensing can be thought of as “overpacing.”
In this example, an AAI pacemaker is programmed to inhibit the atrial pacing pulse when a P-wave is sensed. Because the P-wave was not sensed, the pacemaker delivered an atrial pulse. If a pacemaker is undersensing, you will not see appropriate atrial sense markers on the marker channel.
Atrial Undersensing

45. 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

46. Oversensing
VVI / 60
...though no activity is present
Marker channel shows intrinsic activity...
An electrical signal other than the intended P or R wave is detected
Oversensing will exhibit pauses in single chamber systems. In dual chamber systems, atrial oversensing may cause fast ventricular pacing without P waves preceding the paced ventricular events.

47. 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

48. 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

49. Pulse Generator Loose connections Migration Twiddlers syndrome
Similar to lead fracture
Intermittent failure to sense or pace
Migration
Dissects along pectoral fascial plane
Failure to pace
Twiddlers syndrome
Manipulation  lead dislodgement

50. Twiddler’s Syndrome

51. Twiddler’s Syndrome

52. Leads Dislodgement or fracture (anytime) Insulation breaks
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)
Fractures occur at sharp turns (pulse generator, entry into vein, in ventricle, most commonly occurring at the clavicle/first rib location
Measure lead impedance w/ pacemaker programmer
Insulation break like leaky garden hose

53. Cardiac Perforation Early or late Usually well tolerated
Asymptomatic  inc’d pacing threshold, hiccups
Dx: P/E (hiccups, pericardial friction rub), CXR, Echo

54. Environmental Factors Interfering with Sensing
MRI
Electrocautery
Arc welding
Lithotripsy
Cell phones
Microwaves
Mypotentials from muscle

55. Management

56. 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

57. Management: Physical Exam
Fever: think pacemaker infection
Cannon “a” waves: AV asynchrony
Bibasilar crackles if CHF
Pericardial friction rub if perforation of RV

58. Management: adjuncts
CXR: determine tip position
ECG

59. CorePace Module 4: Troubleshooting
Potential Problems Identifiable on an ECG Can Generally Be Assigned to Five Categories:
Failure to output
Failure to capture
Undersensing
Oversensing
Pseudomalfunction
The causes of undersensing, oversensing, noncapture, lack of output, and pseudomalfunctions vary. However, each of these anomalies compromises the pacemaker’s ability to supplement intrinsic conduction.

60. Pseudomalfunction: Hysteresis
CorePace Module 4: Troubleshooting
Pseudomalfunction: Hysteresis
Allows a lower rate between sensed events to occur; paced rate is higher
Hysteresis Rate 50 ppm
Lower Rate 70 ppm
Hysteresis provides the capability to maintain the patient’s intrinsic heart rhythm as long as possible, while providing back-up pacing if the intrinsic rhythm falls below the hysteresis rate. Because hysteresis exhibits longer intervals between sensed events, it may be perceived as oversensing.

61. 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
May defibrillate in AP direction

62. 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)

63. Disposition

64. 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

65. Disposition Potentially fixable in ED w/ help Pacemaker syndrome
Pacemaker-mediated tachycardia
Cross-talk
Oversensing
Diaphragmatic pacing
Myopotential inhibitors

66. Internal Cardiac Defibrillators

67. 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

68. 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

69. ICD Malfunction Inappropriate Cardioversion Ineffective Cardioversion
Failure to Deliver Cardioversion

70. 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)

71. Ineffective Cardioversion
Inadequate energy output
Rise in defibrillation threshold  antiarrhythmics
MI at lead site
Lead fracture
Dislodgement of leads

72. Failure to Deliver Cardioversion
Failure to sense
Lead fracture
Electromagnetic interference
Inadvertent deactivation

73. 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

74. Disposition
“in almost all instances, admission to a monitored setting with extended telemetric observation will be necessary”
Rosen’s

75. Thanks to:
Calgary Health Region Pacemaker nurses
Karen and Sandra

76. References Brady et al. 1998. EM Clinics NA. 16(2): 361-388
Xie et al Em Clinics NA. 16(2):
Shah et al EM Clinics NA. 16(2):
Harrigan and Brady EMR 21(19):
Rosen
American College of Cardiology ECG of the Month Feb 2001:
Pacemaker and Automatic Internal Cardiac Defibrillator, Weinberger et. al
CorePace presentation by Medtronic Inc available from Pacmaker Nurses at Foothills Hospital,

77. Pacemaker and Defibrillator Clinics
-Open Mon.-Fri hrs.
-Electrophysiology for ICD’s 41248
-Pacemaker Clinic 41188
-On call pager #0569

78. ECG analysis Building on routine ECG interpretation skills
Low Rate
Pacemakers not programmed below 50 BPM
ICD’s often low rate of 40 BPM

79. Assess atrial rhythm P waves and rate Atrial sensing Any atrial pacing
Atrial capture

80. Assess Ventricular Rhythm
QRS rate and morphology
Relation to atrial rhythm
Ventricular pacing
Ventricular capture

81. 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

82. 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.

83. -Direction of Medical Director is that Cardiology should be consulted.
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.

84. 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

85. Surgical Complications
Incision issues: Infected pacemaker site presents risk for endocarditis
Needs to be brought to Pacemaker or ICD clinic attention

86. 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

87. Echocardiogram Look for blood in pericardium CV surgery consult
Management in ER
Echocardiogram
Look for blood in pericardium
CV surgery consult
Don’t anticoagulate

88. 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.

89. Magnets and devices
No universal response to magnet application with cardiac devices.

90. Pacemaker Clinic
FMC Monday to Friday
Phone

91. EP Clinic ICD patient issues Monday to Friday 0800-1600 hrs
Phone

92. Nurse on Call CHR pager Please consult Cardiology
Medical Director: Dr. A. M. Gillis
Electrophysiology