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Third Degree Heart Block | Reference Guide

EKG Strip

ecg rhythm strip for reference guide

EKG 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.
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Authors and Reviewers

Authored by Thomas O'Brien
EKG tracings reviewed by Dr. Pedro Azevedo, MD, Cardiology
Medically reviewed by Dr. Jonathan Keroes, MD, Cardiology
Last Update: 11/8/2021


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