Introduction to Heart Block Rhythms

Overview

This page provides an introduction to Heart Block rhythms with links to our lessons and drills.

Heart block rhythms occur when the cardiac electric impulse is delayed or blocked within the AV node, bundle of His or the Purkinje system. Heart block rhythms are classified into categories including these:

  • First Degree Heart Block
  • Second Degree Heart Block Type I
  • Second Degree Heart Block Type II
  • Third Degree Heart Block
  • Bundle Branch Block

Heart Block Categories

First Degree Heart Block

First Degree Heart Block EKG tracing First degree heart block is actually a delay rather than a block. It is cause by a conduction delay at the AV node or bundle of His. This means than the PR Interval will be longer than normal (over 0.20 sec.).

Second Degree Heart Block Type I

Second Degree Heart Block Type I EKG tracing With second degree heart block, Type I, some impulses are blocked but not all. More P waves can be observed vs QRS Complexes on a tracing. Each successive impulse undergoes a longer delay. After 3 or 4 beats the next impulse is blocked. On an EKG tracing, PR Intervals will lengthen progressively with each beat until a QRS Complex is missing. After this blocked beat, the cycle of lengthening PR Intervals resumes. This heart block is also called a Wenckebach block.

Second Degree Heart Block Type II

Second Degree Heart Block Type II EKG tracing With Mobitz Type II blocks, the impulse is blocked in the bundle of His. Every few beats there will be a missing beat but the PR Interval will not lengthen.

Third Degree Heart Block

Third Degree Heart Block EKG tracing With this block, no atrial impulses are transmitted to the ventricles. As a result, the ventricles generate an escape impulse, which is independent of the atrial beat. In most cases the atria will beat at 60-100 bpm while the ventricles asynchronously beat at 30-45 bpm.

Bundle Branch Block

Bundle Branch Block EKG tracing With this conduction block, either the left or right bundle branch is blocked intermittently or fixed. The QRS complex is wider than normal (> 0.12 sec.). Using a 12 lead EKG, blocks in either the left or right bundle branch may be diagnosed.
Click To Begin Heart Blocks Training Module

Overview

Heart Block Dysrhythmias

Thomas E. O'Brien
AS CCT CRAT RMA

Learning Objectives

At the conclusion of this training module the reader will be able to:

  • Recall and apply the 5-steps of heart rhythm interpretation
  • Recognize the difference between regular and irregular rhythms
  • Recall the normal range for PR interval and QRS complex
  • Recognize the features and qualifying criteria for the following complexes and rhythms:
    • First Degree Heart Block
    • Second Degree (Mobitz) Heart Block Type I aka Wenckebach Phenomenon
    • Second Degree (Mobitz) Heart Block Type II
    • Third Degree Heart Block aka Complete Heart Block

Using This Presentation

how to use this presentation image

Heart Block Dysrhythmias

Introduction Part 1

  • The dysrhythmias in this category occur for a variety reasons. It may be congenital as is often the case in First Degree Heart Block. They may occur secondary to medications or the result of transient illness or disease which results in tissue death affecting a portion of the conduction system.
  • Each heart block has at least one distinctive feature making it unique when comparing them with other heart blocks and dysrhythmias in other categories.
  • We will focus on those “unique” features during this presentation.

Introduction Part 2

  • Sometimes organizing heart blocks can help you to separate one heart block from another.
  • On the next slide we have organized heart blocks by constant vs. variable P-R interval.

Heart Blocks Chart

heart block ecg image 101

First Degree Heart Block

Description

  • First Degree Heart Block will look like a typical sinus rhythm with one distinguishing feature.
  • The P-R interval will be constant throughout the tracing and measure greater than 0.20 seconds.
  • Rate, regularity, P wave morphology and QRS duration and morphology will be unaffected.
  • NOTE: The rate will be that of the underlying rhythm. If the rate is “normal”, it will be 60 – 100 bpm. If it is bradycardia, the rate will be less than 60 bpm.
  • First Degree Heart Block is the most common heart block.
  • People are born with it everyday. They will likely live a long and healthy life and die from some other malady.
  • Patients who develop a heart block during an MI bear close observation. This must be reported to the licensed healthcare practitioner immediately.

Example

Notice the following: the only abnormality when analyzing this tracing is the abnormal duration of the P-R interval.

heart block ecg image 102

Practice Strip

  • Analyze this tracing using the five steps of rhythm analysis.
  • Compare your answers with the answers on the next slide.

heart block ecg image 103

Answers

  • Rhythm: Regular
  • Rate: 68
  • P Wave: Upright
  • PR interval: 0.28 sec
  • QRS: 0.08 sec
  • Interpretation: First Degree Heart Block
heart block ecg image 10bb

Second Degree Heart Block Type I

Description

  • Also known as Wenckebach Phenomenon; this dysrhythmia is typically stable and often temporary with the patient remaining asymptomatic as long as the ventricular response remains within the “normal” range.
  • The unique feature (hallmark) of this dysrhythmia is the presence of a prolonging P-R interval from one cardiac complex to the next, until it reaches a point where the QRS complex is non-conducted ( blocked or more simply missing). Then the pattern starts over again.

Example

  • In this dysrhythmia, if the third QRS complex is dropped/blocked, then it will always be the third complex that is blocked before re-setting in a repetitious pattern.
  • It is important to note the following:
    • The P – P intervals are regular and the R to R intervals are irregular.
    • here are more P waves than QRS complexes. Report the rate of each separately.

heart block ecg image 104

Practice Strip

  • Analyze this tracing using the five steps of rhythm analysis.
  • Compare your answers with the answers on the next slide.

heart block ecg image 105

Answers

  • Rhythm: Atria – Regular, Ventricles - Irregular
  • Rate: Atria – 56, Ventricles - 40
  • P Wave: Upright
  • PR interval: Variable, progressive
  • QRS: 0.10 sec
  • Interpretation: Second Degree Heart Block Type I
heart block ecg image 105b

Second Degree Heart Block Type II

Description

  • The hallmark of this dysrhythmia is a constant P-R interval with missing QRS complexes.
  • This dysrhythmia may present in a couple of different ways.
    • A. QRS complexes occurring in a specific pattern in a ratio with the P waves. This is often referred to as 2:1 or 3:1 block depending upon the ratio of P waves to each QRS complex.
    • B. QRS complexes occur in a more unstable, unpredictable manner.
  • Either presentation requires immediate reporting due to its potential for conversion to Third Degree (Complete) Heart Block.
A.heart block ecg image 106
B.heart block ecg image 107

Practice Strip

  • Analyze this tracing using the five steps of rhythm analysis.
  • Compare your answers with the answers on the next slide.

heart block ecg image 108

Answers

  • Rhythm: Atria and Ventricles - Regular
  • Rate: Atria – 125, Ventricles - 41
  • P Wave: Upright
  • PR interval: 0.14 sec
  • QRS: 0.06
  • Interpretation: Second Degree Heart Block Type II, 3:1
heart block ecg image 108b

Practice Strip #2

  • Analyze this tracing using the five steps of rhythm analysis.
  • Compare your answers with the answers on the next slide.

heart block ecg image 109

Answers #2

  • Rhythm: A – Regular, V - Irregular
  • Rate: Atria – 68, Ventricles - 40
  • P Wave: Upright
  • PR interval: 0.16 sec
  • QRS: 0.08
  • Interpretation: Second Degree Heart Block Type II
heart block ecg image 109b

Third Degree Heart Block

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 this impediment 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.
heart block ecg image 110

Practice Strip

  • Analyze this tracing using the five steps of rhythm analysis.
  • Compare your answers with the answers on the next slide.

heart block ecg image 111

Answers

  • 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
heart block ecg image 111b

Test Questions 1-4

Question #1

When analyzing a rhythm strip, it qualifies as being regular when

A. the QT intervals are the same
B. the PR interval measures the same
C. the QRS complexes measures the same
D. the R - R intervals measure the same




Question #2

Which of the following steps is not one of the five-steps of rhythm analysis?

A. PR interval measurement
B. Rhythm regularity
C. QT Interval
D. QRS complex measurement




Question #3

Which of the following is considered normal range of the QRS complex?

A. 0.12 - 0.20 minutes
B. 0.06 - 0.10 minutes
C. 0.12 - 0.20 seconds
D. 0.06 - 0.10 seconds




Question #4

Which of the following is considered normal range of the PR interval?

A. 0.12 - 0.20 minutes
B. 0.06 - 0.10 minutes
C. 0.12 - 0.20 seconds
D. 0.06 - 0.10 seconds





Test Questions 5-9

Question #5

Which feature is most closely associated with First Degree Heart Block rhythm?

A. Wide & bizarre QRS complexes
B. PR interval measuring greater than 0.20 seconds
C. Pronged QT interval
D. Three or different shaped P waves




Question #6

Which feature is most closely associated with Second Degree Type I?

A. Repetitious pattern of prolonging P-R intervals with a missing QRS complex
B. P to P waves and QRS complex intervals are constant, but at two distinctly different rates
C. Prolonged P-R intervals without a missing QRS complex
D. Constant P-R intervals with missing QRS complexes




Question #7

Which feature is most closely associated with Complete Heart Block?

A. Repetitious pattern of prolonging P-R intervals with a missing QRS complex
B. P to P waves and QRS complex intervals are constant, but at two distinctly different rates
C. Prolonged P-R intervals without a missing QRS complex
D. Constant P-R intervals with missing QRS complexes




Question #8

Which feature is most closely associated with Second Degree Heart Block Type II?

A. Repetitious pattern of prolonging P-R intervals with a missing QRS complex
B. P to P waves and QRS complex intervals are constant, but at two distinctly different rates
C. Prolonged P-R intervals without a missing QRS complex
D. Constant P-R intervals with missing QRS complexes




Question #9

In Third Degree Heart Block, the tracing demonstrates a narrow, normal appearing QRS complex at a rate of 52. Which region of the heart is the likely locus of stimulation?

A. SA node
B. Bachmann’s bundle
C. Central fibrous body
D. Bundle of His
E. Purkinje network





Test Questions 10-11

Question #10

heart block quiz tracing 1

Select the heart rate most closely associated with this tracing.

A. 30
B. 47
C. 58
D. 75




Question #11

heart block quiz tracing 2

What is the most correct interpretation of this tracing?

A. First Degree Heart Block
B. Wenckebach phenomenon
C. . Second Degree Heart Block Type I
D. Second Degree Heart Block Type II
E. Third Degree Heart Block





Test Questions 12-14

Question #12

What would be the most proper description of the P-R interval in this tracing?

ekg heart block quiz tracing 12
A. Constant
B. Absent
C. Variable
D. Multifocal




Question #13

What is the most correct interpretation of this tracing (two answers are correct)?

ekg ventricular quiz tracing 12
A. First Degree Heart Block
B. Wenckebach phenomenon
C. Second Degree Heart Block Type I
D. Second Degree Heart Block Type II
E. Third Degree Heart Block




Question #14

Which term is most appropriately used to describe the R to R intervals in this tracing?

ekg ventricular quiz tracing 12
A. Absent
B. Regular
C. Multifocal
D. Irregular





Test Questions 15-18

Question #15

What would be the most proper description of the P to P intervals in this tracing?

ekg ventricular quiz tracing 15
A. Irregular
B. Absent
C. "f" waves
D. Regular




Question #16

Select the number that most closely represents the ventricular rate.

ekg ventricular quiz tracing 15
A. 40
B. 68
C. 88
D. 116




Question #17

Select the number that most closely represents the atrial rate.

ekg ventricular quiz tracing 15
A. 40
B. 68
C. 88
D. 116




Question #18

What is the most correct interpretation of this tracing?

ekg ventricular quiz tracing 15
A. First Degree Heart Block
B. Wenckebach phenomenon
C. Second Degree Heart Block Type I
D. Second Degree Heart Block Type II
E. Third Degree Heart Block





Test Questions 19-22

Question #19

. What would be the most proper description of the atrial and ventricular activity in this tracing?

ekg junctional quiz tracing 19
A. Irregular
B. Absent
C. Regular
D. Delta waves




Question #20

. Select the number that most closely represents the atrial rate.

ekg junctional quiz tracing 19
A. 75
B. 94
C. 34
D. 46




Question #21

Select the number that most closely represents the ventricular rate.

ekg junctional quiz tracing 19
A. 75
B. 94
C. 34
D. 46




Question #22

What is the most correct interpretation of this tracing?

ekg junctional quiz tracing 19
A. First Degree Heart Block
B. Wenckebach phenomenon
C. Second Degree Heart Block Type I
D. Second Degree Heart Block Type II
E. Third Degree Heart Block





EKG Self Test

EKG Rhythms Self Test

If you would like to tests the knowledge and skills learned in this module, use our EKG Rhythms Self Test. You can choose to focus this self-test on any of all of the following:

  • Sinus Mechanisms
  • Atrial Rhythms
  • Junctional Rhythms
  • Ventricular Rhythms
  • Atrioventricular Blocks
  • Pacemaker Rhythms

EKG Rhythm Tests »

Lessons and Drills

Heart Block Rhythms Training

We recommend starting with our heart block rhythms training module. This module focuses on the morphologic features and qualifying criteria of heart block rhythms.

Heart Block Rhythms

EKG Rhythm Tests

Hundreds heart rhythms in this practice test. Test can be tailored for specific learning needs.

EKG Rhythm Tests




External References

Wikipedia
Free Dictionary