1. Electrocardiography for Healthcare Professionals
Kathryn A. Booth
Thomas O’Brien
Chapter 10:
Pacemaker Rhythms and Bundle Branch Block

2. Learning Outcomes
10.1 Describe the various pacemaker rhythms Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment Summarize pacemaker complications relative to the ECG tracing Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.

3. 10.1 Introduction to Pacemaker Rhythms Key Terms
Atriobiventricular pacing
Atrioventricular sequential pacing
Electronic pacemaker
LO 10.1: Describe the various pacemaker rhythms.
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Atriobiventricular pacing: A sequential pacemaker stimulation of the atria and then both ventricles, rather than just the lower right ventricle.
Atrioventricular sequential pacing: A pacemaker stimulation of the atria and then the lower part of the right ventricle in a sequence that mimics the normal cardiac conduction system and allows for atrial kick.
Electronic pacemaker: A synthetic source of electrical current causing depolarization of the myocardium; artificial pacemakers are electronic.

4. 10.1 Electronic Pacemakers
Also known as artificial pacemakers
Deliver electrical impulse to myocardium, causing cells to depolarize
Mimic normal pacemaker of the heart
LO 10.1: Describe the various pacemaker rhythms.
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Because of the variety of pacemakers available on the market, you should always check in advance regarding the proper procedure for performing an ECG on a patient with a pacemaker.

5. 10.1 Electronic Pacemakers
Can pace atria, ventricles, or both
Sometimes temporary, but usually implanted under the skin
Fastest pacemaker controls the heartbeat, whether inherent or artificial
LO 10.1: Describe the various pacemaker rhythms.
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The function of a pacemaker is to stimulate a contraction.

6. 10.1 Types of Pacemakers Atrial pacing Ventricular pacing
Atrioventricular pacing
Atriobiventricular pacing
LO 10.1: Describe the various pacemaker rhythms.
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Atrial pacing is used alone when AV node and ventricular conduction are performing correctly.
Ventricular pacing is used to correct problems with the ventricular conduction system.
Atrioventricular pacing stimulates the atria and ventricles sequentially, mimicking the normal cardiac conduction system and allowing for an atrial kick.
Atriobiventricular pacing stimulates the atria and both ventricles, instead of just the lower right ventricle.

7. 10.1 Types of Pacemakers (Cont.)
LO 10.1: Describe the various pacemaker rhythms.
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This atrioventricular pacemaker has leads that go to both the right atrium and the lower right ventricle.
Atrioventricular Pacemaker

8. 10.1 Pacemaker Safety
Pacemaker’s electrical current is not dangerous to you or other people.
Skin does not conduct electricity.
Current cannot be transmitted to another person.
LO 10.1: Describe the various pacemaker rhythms.
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9. 10.1 Apply Your Knowledge
What is the advantage of atrioventricular pacing?
ANSWER: It mimics the normal cardiac conduction system and allows for atrial kick.
LO 10.1: Describe the various pacemaker rhythms.
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10. 10.2 Evaluating Pacemaker Function Key Terms
Atrioventricular delay
Electrical capture
Inherent rhythm
Mechanical capture
Pacing spike
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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Atrioventricular delay: The measurement from the atrial spike to the ventricular spike, or from the beginning of the P wave to the ventricular spike on a pacemaker tracing.
Electrical capture: Evidence on an ECG tracing, including the spacing of spikes and waveforms.
Inherent rhythm: The patient’s own heart rhythm.
Mechanical capture: The heart’s ability to respond to electrical impulses delivered by a natural or electronic pacemaker.
Pacing spike: A thin spike on the ECG tracing that results from the pacemaker stimulation impulse.

11. 10.2 Evaluating Pacemaker Function
Based on ECG tracings
Verifies pacemaker effectiveness
Determines presence of pulse with each captured beat
Electrical capture
Mechanical capture
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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Electrical capture refers to the evidence seen when viewing the cardiac tracing on the heart monitor or ECG machine.
Mechanical capture is the heart’s ability to respond to the electrical impulses generated by the pacemaker.

12. 10.2 Evaluating Pacemaker Function (cont.)
Electrical evidence on a heart monitor is not enough.
Heart may not be pumping well enough to sustain life.
Always remember to check the patient!
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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13. 10.2 Pacing Spike
Thin spike on ECG tracing indicating electrical current from pacemaker
Evidence of depolarization should appear after the spike, depending on type of pacing.
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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Pacemaker rhythms are distinguished by the conspicuous presence of a pacing spike prior to the waveform of the portion of the heart that is being paced.

14. 10.2 Types of Pacing Spikes Atrial Ventricular Atrioventricular
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.

15. 10.2 Chamber Depolarization
Atrial pacing spike
Followed by P wave indicating atrial depolarization
Ventricular pacing spike
Followed by wide QRS complex
Similar to LBBB
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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The left ventricle is larger than the right ventricle, so it takes longer to depolarize; this makes it look similar to the electrical activity in left bundle branch block (LBBB).

16. 10.2 Atrioventricular Delay
Similar to PR interval on normal rhythm tracing
Measured from atrial spike to ventricular spike
Normally programmed to second
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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17. 10.2 Atrioventricular Delay (cont.)
Patient with normal P wave and ventricular pacing
Measure from beginning of P wave to ventricular spike
Patient with atrial pacer and normal QRS
Measure from pacing spike to beginning of QRS
Measurement should be less than set atrioventricular delay time
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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18. 10.2 Seven Steps to Evaluating a Pacemaker ECG Tracing
Step 1: What are the rate and regularity of the paced rhythm?
Step 2: What are the rate and regularity of the intrinsic rhythm?
Step 3: Is the atrial lead sensing appropriate?
AV sequential pacemakers only
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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Step 1: The pacemaker spikes should be spaced at regular intervals. If the patient’s own rhythm becomes faster than the paced rhythm, irregularities may occur.
Step 2: The fastest pacemaker site sets the heart rate, so if the patient’s inherent/intrinsic rate is faster than the pacemaker rhythm, the intrinsic rhythm controls the heart rate.
Step 3: Determine whether each P wave is preceded by a pacing spike. Sometimes the patient’s SA node or an ectopic focus will generate an atrial contraction without a pacemaker spike.

19. 10.2 Seven Steps To Evaluating a Pacemaker ECG Tracing (Cont.)
Step 4: Is atrial capture present?
Atrial, AV sequential, and atriobiventricular pacemakers
Step 5: Is atrioventricular delay appropriate?
AV sequential and atriobiventricular pacemakers
Step 6: Is ventricular sensing appropriate?
Step 7: is ventricular capture present?
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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Step 4: Every atrial pacing spike should have a P wave after it. This indicates that the pacing impulse is causing the atrial cells to depolarize.
Step 5: Determine whether the actual atrioventricular delay interval is the same as the atrioventricular delay set on the pacemaker.
Step 6: Determine whether a wide QRS complex follows each ventricular pacing spike. If the patient’s own conduction system generates a normal P wave or QRS complex before the pacemaker sends a ventricular impulse, the pacemaker generator is inhibited , as evidenced by the absence of a ventricular spike.
Step 7: Every ventricular spike should have a wide QRS complex after it, indicating that the pacing spike produced ventricular depolarization.

20. 10.2 Apply Your Knowledge
What term refers to the ability of the heart muscle to respond to electrical stimulation and depolarize the myocardial tissue?
ANSWER: Mechanical capture
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.
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21. 10.3 Pacemaker Complications Key Terms
Loss of capture
Malfunctioning
Malsensing
Oversensing
Pacemaker competition
Triggered
Undersensing
LO 10.3: Summarize pacemaker complications relative to the ECG tracing.
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Loss of capture: The pacing activity continues to occur without evidence that the electrical activity has depolarized or captured the myocardium.
Malfunctioning: The pacemaker fails to send an electrical impulse to the myocardium.
Malsensing: The pacemaker does not recognize or sense the patient’s own inherent cardiac electrical activity.
Oversensing: The pacemaker senses electrical current from other muscle movements or electrical activity outside of the body as the electrical current in the patient’s heart.
Pacemaker competition: Pacemaker sends impulses to the patient’s heart during the relaxation/repolarization phase, competing with the patient’s own inherent activity; result of malsensing.
Triggered: Caused to occur; in this case, the electrical impulses are caused to occur because the pacemaker fails to detect the normal contractions.
Undersensing: The pacemaker is unable to detect any electrical activity and never turns off.

22. 10.3 Pacemaker Complications Relative to the ECG Tracing
Weak battery complications
Slow firing rates
Less effective sensing capabilities
Less than predetermined electrical current
Pacemaker generator complication
Sensing capability too low for pacemaker to see normal contractions
Electrical impulses triggered, not inhibited
LO 10.3: Summarize pacemaker complications relative to the ECG tracing.
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23. 10.3 Reasons for Pacemaker Complications
Malfunctioning – failure to pace
Malsensing – failure to sense
Loss of capture – failure to depolarize
Oversensing – perceiving sources other than the heart
Undersensing – unable to detect any electrical activity
LO 10.3: Summarize pacemaker complications relative to the ECG tracing.
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These complications can be detected on the ECG tracing, so it is important to recognize normal and abnormal pacemaker rhythms and the possible complications.

24. 10.3 Responsibility to Recognize Rhythms
Recognize normal pacemaker rhythms and possible complications
Be aware of differences in ECG waveforms
Presence of pacing spike
Chamber depolarization characteristics
Atrioventricular delay
LO 10.3: Summarize pacemaker complications relative to the ECG tracing.
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If you observe pacemaker complications, notify licensed personnel immediately for appropriate treatment and interventions.

25. 10.3 Apply Your Knowledge
What is your responsibility in caring for patients with pacemakers?
ANSWER: Recognizing normal pacemaker rhythms and possible complications
LO 10.3: Summarize pacemaker complications relative to the ECG tracing.
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26. 10.4 Introduction to Bundle Branch Block Dysrhythmias Key Term
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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Bundle branch block: Impulse is delayed or blocked within the bundle branches of the normal conduction pathway.

27. 10.4 Bundle Branch Block
Damage to bundle branch(es) causes block or delay.
Causes include cardiac disease, drugs, and other conditions
Current travels through good bundle only
Activates myocardial tissue only in that ventricle
Other ventricle receives impulse on cell-to-cell basis
Affected ventricle contracts slowly, with wide QRS
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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Conduction through the ventricle that has a blocked bundle branch is slow because each cell will not contract until the cell next to it delivers the impulse. This causes the ventricle to take longer to contract.

28. 10.4 Characteristics of Bundle Branch Blocks
Any rhythm with normally narrow QRS can have BBB
Sinus
Atrial
Junctional
Underlying rhythm has P wave and wide QRS complexes
Basic rhythm must always be determined
Also identify left or right BBB
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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The underlying rhythm usually originates above the ventricles.
Discovery of a wide QRS complex is the clue to further investigate for bundle branch block.

29. 10.4 Right Bundle Branch Block (RBBB)
Septum depolarizes normally
Left ventricle activated
Current travels to right ventricle
Cell-by-cell conduction
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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30. 10.4 Left Bundle Branch Block (LBBB)
Left conduction pathway is blocked
Conduction travels to right ventricle first
Current moves to left ventricle
Abnormal septum depolarization
Cell-by-cell conduction
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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31. 10.4 Branch Bundle Block Dysrhythmias: Criteria
Specific characteristics of left or right BBB identifiable in leads V1 to V6
Lead V1 used to distinguish LBBB and RBBB
Positive QRS = RBBB
Negative QRS = LBBB
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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32. 10.4 Branch Bundle Block Dysrhythmias: Criteria (Cont.)
May be regular or irregular
Depends on underlying rhythm
Rate: Atrial and ventricular rates depend on basic rhythm.
P wave morphology: Morphology, deflection, and coordination with QRS depend on basic rhythm.
PR interval: Within normal range of 0.12 to 0.20 second
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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Although the P wave morphology will vary, the P wave will always be present if the rhythm initiates above the ventricles.

33. 10.4 Branch Bundle Block Dysrhythmias: Criteria (Cont.)
QRS duration and morphology: 0.12 second or greater
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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The underlying rhythm shown here is normal sinus rhythm. Notice that the P waves are present, but the QRS complexes measure 0.14 second, indicating bundle branch block.

34. 10.4 Bundle Branch Blocks: What You Should Know
Patient exhibits normal effects of basic rhythm.
Widening of QRS complex must be reported to a licensed practitioner immediately.
Bundle branch block is not considered life-threatening.
Condition can deteriorate to complete heart block.
May require pacemaker or emergency cardiac care.
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.
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If the current becomes completely blocked in both bundle branches, this is considered a complete heart block.

35. 10.4 Apply Your Knowledge
Describe the appearance of the QRS complexes in bundle branch block.
ANSWER: Wide QRS complexes with a 0.12 second or greater duration
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.

36. Chapter Summary
Electronic or artificial pacemakers deliver an electrical impulse to the myocardium, causing cells to depolarize.
Atria, ventricles, or both can be paced.
Atrial pacing spikes, ventricular pacing spikes, or both may be visible on the ECG, depending on the type of pacing.
Evaluating pacemaker function includes seven steps, although not all steps are required for every type of pacemaker.
LO 10.1: Describe the various pacemaker rhythms.
LO 10.2: Identify pacemaker rhythms using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.

37. Chapter Summary (Cont.)
Pacemaker complications relative to the ECG include malfunctioning, malsensing, loss of capture, oversensing, and undersensing.
Bundle branch blocks prevent current from traveling to one or both ventricles.
Left bundle branch block can be distinguished from right bundle branch block by viewing lead V1.
LO 10.3: Summarize pacemaker complications relative to the ECG tracing.
LO 10.4: Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient.