Pacemakers and AICD’s - Chapter 10
Objectives:
 State the indications for temporary and permanent pacing modalities
 Discuss the components of the various pacing systems
 Identify normal and abnormal pacemaker function on a rhythm strip
 Discuss significant hemodynamic consequences of abnormal pacemaker function
 Discuss the clinical management of patients with pacemakers
 Describe the care considerations in a patient with an implantable cardio-defibrillator
Pacemaker
 An artificial device that electrically stimulates the myocardium to depolarize, which begins a
contraction
 Temporary or permanent
Indications for Pacing – Page 256
 Symptomatic bradyarrhythmias
 Drug Toxicity
 Moderate to Severe Heart Failure
 Support cardiac output after cardiac surgery, or high risk cardiac catheterization
Components of a Pacing System – Page 256
 Pulse generator
 Pacing Leads
Components of Pacing System Page 256-260
 Pulse generator
o Houses the battery that creates electrical stimulus to maintain a specified rate
o Contains controls: electrical output(mA), rate, sensitivity (mV), mode
o Power source
Pulse Generator
 Temporary transvenous or epicardial
Pulse Generator – Page260 Figure 10-6
 Permanent pulse generator
Basic Components of the Temporary Pulse Generator – Page 260 Figure 10-5
 On-Off control
 Mode Dial
o Fixed rate or asynchronous
o Demand or synchronous pacing
Basic Components of the Temporary Pulse Generator – Page 260 Figure 10-5
 Rate control o Sets number of beats/minute
o Usually set at 60-80 bpm to ensure adequate cardiac output
 mA or Output Dial
o Regulates the amount of energy ( in mA) delivered to the distal electrode.
o Ranges from 0.1 to 20 mA
 Sensitivity
o Regulates pacemaker’s ability to detect heart’s intrinsic electrical activity
o 1 mV is maximum sensitivity (will see a complex that is very small in size)
o 20 mV is asynchronous (will not sense any intrinsic electrical activity)
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Components of a Pacing System – Page 257 Figure 10-1, Page 260 Figure 10-6
 Pacing catheter (lead or electrode)
o Transmits the patient’s rhythm to pulse generator
o Transmits electrical stimulus between generator and chamber paced
Transcutaneous Leads Page 258-259
 Noninvasive procedure where two large pacing pads are placed on the anterior and posterior
chest
 Pacing pads are attached to a pacing cable, which is then connected to a defibrillator/monitor
 ECG leads are also attached to the patient
 Initiate when drug therapy has been ineffective in increasing cardiac output
 Requires a higher current output (mA)
 May cause chest wall pain and skin burns
 Effective when meaningful contractile activity is present only
Transvenous Pacemakers – Page 260 Figure 10-5
 The pacing electrode is advanced through a vein into the RA, RV, or both
 Inserted into the RA for atrial pacing
 Inserted into the RV for ventricular pacing
 May be unipolar or bipolar leads
Epicardial Pacing – Page 259
 Electrodes are attached to the epicardial surface of the heart
 Atrial and/or ventricular wires
Permanent Pacemaker
Modes of Pacemaker Function – Page 256
 Asynchronous (Fixed)
o Initiate impulses at a set rate regardless of patient’s intrinsic rate
o Used when no intrinsic heart rate
o Set at 20 mV on sensitivity dial
 Synchronous (Demand)
o Senses intrinsic rhythm and inhibits discharge when intrinsic heart rate adequate –
synchronized with the patient’s own heart activity
Permanent Pacemaker Identification Codes – Page 261-262
 First letter = chamber paced
 Second letter = chamber sensed
 Third letter = response mode
 Fourth letter = programmable functions
 Fifth letter = antitachycardia functions
Chamber Paced
 Single-chamber:
o Sense and pace either the atrium or ventricle
 Dual-chamber:
o Sense and pace both the atrium and the ventricle
Response to Sensing
 Triggered
o Ventricular pacing is triggered by sensing of an atrial event
 Inhibited
o Sensing of a spontaneous ventricular depolarization inhibits ventricular pacing
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Two common pacemakers:
 VVI
o Ventricle paced
o Ventricle sensed
o Pacing inhibited in response to a sensed beat
 DDD
o Both atrium and ventricle paced
o Both atrium and ventricle sensed
o Ventricle triggered in response to an atrial beat and inhibited in response to a ventricular
beat
Advantage of Dual Chamber
 Restores AV synchronous sequence of the heart (atrial kick)
 Reduces incidence of atrial fibrillation
Pacemaker Terminology - Page 262
 Ventricular capture
o Ventricle has responded to a pacing stimulus
o Stimulus artifact (pacing spike) followed by a wide QRS (depolarization of the right
ventricle)
Pacemaker Terms – Page 263-264 Figure 10-9
 Native Beat (Intrinsic beat)
o Produced by patient’s own electrical conduction system
 Fusion Beat
o Pacemaker fires at same time that the patient’s normal electrical impulse has activated
the ventricles
o Fusion beats are normal and appear as a blend of the two beats
Pacemaker Terms – Page 263
 Automatic Interval
o Heart rate at which pacemaker is set
o Measured from one pacing spike to the next consecutive pacing spike
 Escape Interval
o Interval between intrinsic beat and next paced beat
o Should be same as automatic interval
Paced Rhythm – Page 265 Figure 10-12
 Pacemaker Rhythm
o Occurs when the heart’s rhythm is completely pacemaker induced
o No intrinsic patient beats are seen
Ventricular Paced Rhythm
 Characteristics/Criteria:
o Rhythm: Atrial – none Ventricular: Regular
o Rate: Automatic interval (spike to spike)
o P Waves: none PRI: none present
o QRS: wide and bizarre as a ventricular originated beat
o QT: Normal for rate
Pacemaker Malfunctions
 Failure to pace (fire)
o Pacemaker fails to deliver the pacing stimulus
o No pacing artifact even though the patient needs pacing
o May result in hypotension, bradycardia
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Pacemaker Malfunctions Page 266 Figure 10-14
 Failure to capture
o Failure of the heart to respond (depolarize) following a pacing stimulus
o Reflected as pacing spike that occurs on time, not followed by a QRS complex
o May cause bradycardia, hypotension, fatigue
 Causes
o MA output is too low
o Lead dislodgement
o Catheter tip in infarcted tissue
o Fractured lead wire
o Electrolyte imbalances
o Faulty connections
 Interventions
o Increase mA till consistent capture is is achieved
o Place patient on left side
o Physician may need to reposition pacing catheter
o Correct electrolytes
Undersensing – Page 266 Figure 10-15
 Occurs when the pulse generator does not sense the patient’s intrinsic beats
 Reflected on ECG by a pacing spike that occurs earlier than it should after a native or paced beat
 May cause palpitations, skipped beats, VT/VF
 Causes:
o Pacing catheter out of place or lying in infarcted tissue
o Sensitivity set too low
o Pacemaker set on asynchronous (fixed rate) mode
 Interventions
o Increase sensitivity
o Place patient on left side
Pacemaker Malfunctions – Page 267
 Oversensing
o Inappropriate sensing of extraneous electrical signals leading to triggering or inhibiting
stimulus output – may be sensing tall P or T wave by mistake
o Causes pauses on ECG
o Pacemaker paces at a slower rate than set
o No paced beats
Clinical Management
 Patient/Family Teaching
 Always check the effect of pacer malfunction on patient’s hemodynamic status
 A 12-lead ECG should be done to assess pacemaker malfunction
 Wear gloves when handling wires from the temporary or epicardial pacer to reduce incidence of
microshock
Clinical Management – Temporary Transvenous Pacing
 Assess that all connections from the lead connections to the bridging cable to the pulse generator
are secure
 Insulate metal tips of lead wires when they are not in use with a finger cot. Keep negative and
positive ends separated
 Maintain asepsis at all insertion sites
 Keep dressings dry
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Biventricular Pacing
 CRT: Cardiac Resynchronization Therapy
 Paces both of the heart’s ventricles
 Used to coordinate heart’s 4 chambers to pump more effectively
Implantable Cardioverter-Defibrillator (ICD)
 An implanted electronic device used in treatment of life-threatening tachydysrhythmias
 Generator is placed in subcutaneous tissue, usually in pectoral region
ICD System Components
 Can
 Leads
 Programmer
 Software
ICD System Functions
 Reliably sense cardiac signals in all rhythms
(VT, VF, SR, AF, …)
 Detect VF, VT, reject SR, SVT
 Shock or Anti-Tachy pace for VF or VT as appropriate
 Pace as needed for bradyarrhythmias
 Store diagnostic data
o Episode data
o System function data
ICD System
 Continuously monitors and analyzes a patient’s rhythm
 Initiates low-voltage electrical impulse (0.1 – 0.5 joules) when heart rate becomes very fast (more
than 160 – 180)
 Contains sensing electrodes to recognize dysrhythmias
 Contains defibrillation electrodes that are in contact with the heart
 Contains pacing leads
Indications for ICD
 Cardiac arrest caused by VF/VT
 Spontaneous sustained VT not responsive to drug therapy
 Hemodynamic compromising VT/VF induced during an electrophysiology study
 Atrial fibrillation (tachydysrhythmia)
THERAPIES
 Bradycardia pacing
 Antitachycardia pacing
 Cardioversion
 Defibrillation
THERAPIES
Tachyarrhythmia
Shock Therapy
•
•
Cardioversion:
Synchronous Electrical Shock
Defibrillation:
Asynchronous Electrical Shock
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Clinical Management
 Monitor for complications
 Avoid MRI, TENS, lithotripsy, electrocautery, welders, transformers
 If defibrillating or cardioverting, place paddles and/or electrodes about two inches away from
device
 Provide patient education
Quick Quiz
When a VVI pacemaker senses intrinsic ventricular activity, it responds by:
1. Inhibiting its pacing
2. Triggering its pacing
3. Doing nothing
Failure to capture is represented on the ECG as:
1. No pacemaker activity
2. Spikes occurring where they shouldn’t
3. A spike without a complex
In a synchronous pacemaker, failure to sense is characterized on the ECG by:
1. Lack of a pacemaker spike
2. A pacemaker spike in the presence of native (intrinsic) activity
3. A pacemaker spike without evidence of cardiac stimulation
CHECKPOINT !!
Analyze the following rhythm strips for appropriate pacemaker function:
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Page 271 Strip 10-5
Page 274 Strip 10-13
Page 275 Strip 10-16
Page 275 Strip 10-17
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