Heart Blocks

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.

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.

Analyze this tracing using the five steps of rhythm analysis.

Show Answer

Authors and 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