Third Degree Heart Block ECG

ECG Strip

Third Degree Heart Block Rhythm Strip Features

Rate: Characterized by Atrial rate usually normal and faster than ventricular rate
Rhythm: Regular, but atrial and ventricular rhythms are independent
P Wave: Normal shape and size, may appear within QRS complexes
PR Interval: Absent: the atria and ventricles beat independently.
QRS: Normal, but wide if junctional escape focus
Complete heart block presents with Regular P to P and R to R intervals and a variable P-R interval.
In third degree heart block, none of the SA node impulses reach the ventricles. The ventricles will typically compensate by their own pacemaking, known as an escape rhythm. Thus, the atria and ventricles will beat independently and this can be observed on the ECG. The P waves (atrial beating) and QRS complex (ventricles) are unrelated in time. The PR interval will be variable.
External Source:

Return to ECG Reference Guide Index

Authors and Sources

Authors and Reviewers

ECG heart rhythm modules: Thomas O'Brien.
ECG monitor simulation developer: Steve Collmann
12 Lead Course: Dr. Michael Mazzini, MD.
Spanish language ECG: Breena R. Taira, MD, MPH
Medical review: Dr. Jonathan Keroes, MD
Medical review: Dr. Pedro Azevedo, MD, Cardiology
Last Update: 11/8/2021

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