Third Degree Heart Block ECG Interpretation


Description Part 1

  • Third Degree Heart Block is also known as “Complete Heart Block”.
  • This name more accurately describes the electrical event or problem occurring within the heart.
  • As a result of disease or tissue death, there is a blockage preventing electrical impulses within the atria from entering the ventricular conduction system.
  • The outcome of 3rd degree heart block ECG are two independently functioning pacemakers within the heart (typically one is supraventricular, the other is ventricular).
  • Essentially, the atria and ventricles are electrically separated (dissociated) from one another.

Description Part 2

  • What will be seen are regularly occurring P waves and QRS complexes, but at two distinctly different rates.
  • The QRS complexes may occur as a result of impulses coming from the His bundle or the Purkinje network.
  • Morphology and rate will often provide clues regarding the locus of ventricular impulse stimulation. A more narrow appearing QRS with a rate greater than 40 generally would indicate the impulse formation is coming from the His bundle. A wide, bizarre QRS with a rate of 40 or less indicates the impulses are originating in the Purkinje network.
  • Complete heart block presents with Regular P to P and R to R intervals and a variable P-R interval.
third degree heart block ecg image 110

ECG Practice Strip

third degree av block ecg image 111

Analyze this tracing using the five steps of rhythm analysis.

Show Answer
  • Rhythm: Atria and Ventricles - Regular
  • Rate: Atria – 94, Ventricles - 34
  • P Wave: Upright (some buried)
  • PR interval: Variable
  • QRS: 0.14 sec
  • Interpretation: Third Degree (Complete) Heart Block





Authors and Sources

Authors and Reviewers


Sources

  • Electrocardiography for Healthcare Professionals, 6th Edition Kathryn Booth and Thomas O'Brien
    ISBN10: 1265013470, ISBN13: 9781265013479
    McGraw Hill, 2023
  • Rapid Interpretation of EKG's, Sixth Edition
    Dale Dublin
    Cover Publishing Company
  • EKG Reference Guide
    EKG.Academy
  • 12 Lead EKG for Nurses: Simple Steps to Interpret Rhythms, Arrhythmias, Blocks, Hypertrophy, Infarcts, & Cardiac Drugs
    Aaron Reed
    Create Space Independent Publishing
  • Heart Sounds and Murmurs: A Practical Guide with Audio CD-ROM 3rd Edition
    Elsevier-Health Sciences Division
    Barbara A. Erickson, PhD, RN, CCRN
  • The Virtual Cardiac Patient: A Multimedia Guide to Heart Sounds, Murmurs, EKG Jonathan Keroes, David Lieberman
    Publisher: Lippincott Williams & Wilkin)
    ISBN-10: 0781784425; ISBN-13: 978-0781784429
  • Project Semilla, UCLA Emergency Medicine, EKG Training Breena R. Taira, MD, MPH
  • ECG Reference Guide
    PracticalClinicalSkills.com






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