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Pacemakers and Internal Cardiac Defibrillators

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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

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

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