Electrocardiography for Healthcare Professionals Kathryn A. Booth Thomas O Brien Chapter 10: Pacemaker Rhythms and Bundle Branch Block
Learning Outcomes 10.1 Describe the various pacemaker rhythms. 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. 10.3 Summarize pacemaker complications relative to the ECG tracing. 10.4 Identify bundle branch block using the criteria for classification, and explain how the rhythm occurs and may affect the patient. 2
10.1 Introduction to Pacemaker Rhythms Key Terms Atriobiventricular pacing Atrioventricular sequential pacing Electronic pacemaker
10.1 Electronic Pacemakers Also known as artificial pacemakers Deliver electrical impulse to myocardium, causing cells to depolarize Mimic normal pacemaker of the heart 4
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 5
10.1 Types of Pacemakers Atrial pacing Ventricular pacing Atrioventricular pacing Atriobiventricular pacing 6
10.1 Types of Pacemakers (Cont.) Atrioventricular Pacemaker 7
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. 8
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. 9
10.2 Evaluating Pacemaker Function Key Terms Atrioventricular delay Electrical capture Inherent rhythm Mechanical capture Pacing spike
10.2 Evaluating Pacemaker Function Based on ECG tracings Verifies pacemaker effectiveness Determines presence of pulse with each captured beat Electrical capture Mechanical capture 11
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! 12
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. 13
10.2 Types of Pacing Spikes Atrial Ventricular Atrioventricular 14
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 15
10.2 Atrioventricular Delay Similar to PR interval on normal rhythm tracing Measured from atrial spike to ventricular spike Normally programmed to 0.12-0.20 second 16
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 17
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 18
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? 19
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 20
10.3 Pacemaker Complications Key Terms Loss of capture Malfunctioning Malsensing Pacemaker competition Triggered Undersensing Oversensing
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 22
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 23
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 24
10.3 Apply Your Knowledge What is your responsibility in caring for patients with pacemakers? ANSWER: Recognizing normal pacemaker rhythms and possible complications 25
10.4 Introduction to Bundle Branch Block Dysrhythmias Key Term Bundle branch block
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 27
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 28
10.4 Right Bundle Branch Block (RBBB) Septum depolarizes normally Left ventricle activated Current travels to right ventricle Cell-by-cell conduction 29
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 30
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 31
10.4 Branch Bundle Block Dysrhythmias: Criteria (Cont.) Rhythm 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 32
10.4 Branch Bundle Block Dysrhythmias: Criteria (Cont.) QRS duration and morphology: 0.12 second or greater 33
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. 34
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 35
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. 36
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. 37