Heart Block Poem: 1st, 2nd, 3rd Degree Types and ECG Rhythm Explained
Video: Heart blocks made easy using a poem to explain the different types of AV blocks and their ECG (EKG) rhythms! Example rhythm strips included. Great for nursing, USMLE, and medical learners!
Save Time with a Video!
Save time by watching the video first, then supplement it with the lecture below!
Click below to view the EZmed video library. Subscribe to stay in the loop!
Become a Member!
Instant Access to All PDF Lectures, Study Guides, and Flashcards!
Instant access to a members-only page of ALL the flashcards, study guides, and PDF lectures. Cancel anytime.
Download the Lecture!
Download your own copy of the lecture below! Learn heart blocks in minutes! Poem INCLUDED!
AV Heart Blocks: Types & Definition
Atrioventricular (AV) heart blocks occur when the electrical transmission from the atria to the ventricles is interrupted, either partially or completely.
There are 3 main types of AV heart blocks: first-degree, second-degree, and third-degree.
Second-degree heart blocks can be divided into 2 different types, but more on that later!
In this lecture, AV heart blocks are made easy with a poem to remember the different types of blocks along with their associated EKG (ECG) rhythms.
You will also be given example EKG rhythm strips for each type of heart block.
Let’s get started!
Cardiac Conduction System
In order to better understand AV heart blocks, let’s briefly review the cardiac conduction system.
In a normal functioning heart, the SA node spontaneously produces action potentials (electrical impulses) that ultimately become the heart rate.
The action potential generated by the SA node travels through the atria and depolarizes the cardiac myocytes (muscle cells) of each atrium.
Atrial contraction occurs as a result.
Next, the action potential must travel from the atria to the ventricles, and does so by passing through the AV node, bundle of His, right and left bundle branches, and Purkinje fibers.
As the action potential travels through this part of the conduction system, it causes ventricular depolarization and ventricular contraction to occur.
For a simple step-by-step guide on the conduction system of the heart using the image below, make sure to check out the following EZmed video and lecture for more information!
Conduction System of the Heart: The Electrical Pathway
For a simple discussion on cardiac action potentials, view the EZmed video and lecture below - filled with lots of memory tricks!
Cardiac Action Potentials Made Easy: Summit, Plummet, Climb, Continue
Cardiac conduction system of the heart: SA node, AV node, bundle of His, bundle branches, Purkinje fibers
AV Heart Block Definition
An AV heart block is present when there is disruption of electrical transmission from the atria to the ventricles, either delayed or completely blocked.
AV heart block definition: Interruption of electrical transmission from the atria to the ventricles
Heart Block Poem
As mentioned above, there are 3 main types of AV heart blocks: first-degree, second-degree, and third-degree.
Second-degree heart blocks can be divided into 2 different types: Mobitz I (Wenckebach) and Mobitz II.
As we walk through the different types of heart blocks, you can use the following poem to remember each one and their associated EKG findings!
Heart Block Poem
If the R is far from the P, then it must be a First Degree
If PR gets longer then a QRS drop, then it must be a Type I Wenckebach
If PR stays normal and QRS quits, then it must be a Type II Mobitz
If P and QRS beat independently, then it must be a complete Third Degree
Heart block poem to remember the different types and their associated EKG rhythm.
Heart Block Trick
While the above poem is useful, it can be challenging to memorize it all.
So let’s condense it down to a few simple words.
Remembering the below catchphrase for each heart block will help you on exams and throughout your career.
First Degree = Far away P
Wenckebach = Longer then Drop
Second Degree = Drop Randomly
Third Degree = Beat Independently
This is much simpler to memorize, and it concisely describes the EKG findings for each type of heart block.
Of note, the “Wenckebach” in the above catchphrase refers to a second-degree Mobitz type I, whereas the “second-degree” above refers to a second-degree Mobitz type II.
We will discuss each type of heart block next!
Heart block poem (short-version) to remember the different types and their associated EKG rhythm.
1st Degree AV Heart Block
Let’s now walk through each AV heart block starting with a first-degree.
Catchphrase: First-Degree = Far away P
Poem: If the R is far from the P, then it must be a first degree
Both the catchphrase and poem refer to the prolonged PR interval seen in a first-degree heart block.
For a quick refresher on the different EKG intervals and waveforms, make sure to check out the EZmed video and lecture below!
EKG Waves Made Easy: Step-By-Step Guide
In a first-degree heart block, the PR interval is prolonged to greater than 0.20 seconds (200 msec).
Remember the P wave on an EKG represents atrial depolarization and the QRS complex represents ventricular depolarization.
Therefore, the PR interval represents the time it takes for the electrical impulse to travel from the atria (P wave - atrial depolarization) to the ventricles (QRS complex - ventricular depolarization).
The PR interval in a first-degree heart block is prolonged, which means the electrical conduction from the atria to the ventricles is delayed.
The delay usually occurs in the AV node.
Despite the prolonged PR interval, every P wave is still followed by a QRS complex - there are no dropped or skipped beats.
This means every action potential (electrical impulse) is still being transmitted from the atria to the ventricles, however the conduction through the AV node is slowed which creates the prolonged PR interval.
This differentiates a first-degree heart block from a second-degree and third-degree heart block.
For second and third-degree heart blocks, a QRS complex is not always present after each P wave. This means not every electrical impulse is conducted from the atria to the ventricles - more on this below!
First-degree heart block: Prolonged PR interval
2nd Degree AV Heart Block
There are 2 different types of second-degree heart blocks: Mobitz I (Wenckebach) and Mobitz II.
You can remember Wenckebach is a Mobitz type I because we “wink with 1 eye”.
Second-degree heart block types: Mobitz I (Wenckebach) and Mobitz II
Mobitz Type I (Wenckebach)
Let’s start with a second-degree Mobitz type I heart block, also referred to as a Wenckebach phenomenon.
Catchphrase: Wenckebach = Longer then Drop
Poem: If PR gets longer then a QRS drop, then it must be a type I Wenckebach
Both the catchphrase and poem refer to a PR interval that progressively lengthens with each beat until there is a QRS drop.
This means the conduction from the atria to the ventricles is progressively slowed with each beat (prolonged PR interval), until the atrial impulse is not conducted to the ventricles (dropped QRS complex).
Conduction is then resumed after the dropped beat, and the sequence of events is repeated.
Most Mobitz I blocks occur at the AV node, with some occurring at the bundle of His or bundle branches.
Mobitz Type I (Wenckebach): PR interval progressively lengthens then a QRS drop
Mobitz Type II
Moving on to a second-degree Mobitz type II heart block, we can use the following catchphrase and poem.
Catchphrase: Second-Degree = Drop Randomly
Poem: If PR stays normal and QRS quits, then it must be a type II Mobitz
The “second-degree” in the above catchphrase refers to a Mobitz type II.
Remember Wenckebach (Mobitz I) is a type of second-degree heart block as well.
Both the catchphrase and poem refer to a PR interval that remains constant with each beat, and then the QRS complex intermittently drops.
This means each electrical impulse is conducted at a constant rate from the atria to the ventricles (constant PR interval), but then the atrial impulse is blocked intermittently and does not conduct to the ventricles (causing a dropped QRS complex).
Mobitz type II blocks typically occur below the AV node (infranodal) in the bundle of His or bundle branches.
Mobitz Type II: Constant PR interval with intermittent QRS drop
3rd Degree AV Heart Block
The final type of heart block is a third-degree, also referred to as a complete heart block. (First and second-degrees are partial blocks).
Catchphrase: Third-Degree = Beat Independently
Poem: If P and QRS beat independently, then it must be a complete third degree
Both the catchphrase and poem refer to a rhythm in which there is no relationship between the P waves and QRS complexes.
This means the signal between the atria and ventricles is completely blocked, and there is no electrical communication between the atria and ventricles as a result.
Therefore, the atria and ventricles are forced to generate their own action potentials as shown below.
Cardiac function is maintained through a junctional escape rhythm in the ventricles.
The junctional escape rhythm allows for the ventricles to depolarize and contract without receiving an electrical impulse from the atria.
Third-degree heart block: No relationship between P waves (blue arrows) and QRS complexes (red arrows). The electrical signal is completely blocked between the atria and ventricles.
Before You Go….
Save yourself time, improve your studying, and help your career! Make sure to sign up for FREE to the EZmed blog down below, and don’t miss out on weekly updates on future medical and science topics made easy!
A weekly notification is sent right to your inbox filled with new blog posts, new videos, and exam prep!
Enjoy the post? Leave a comment down below!
Feedback or suggestions for future topics? Reach out using the contact button!
Thank you for using EZmed!
Make Your Learning Experience Even Easier!
Perform well in class, ace your exams, and keep up with your medical knowledge throughout your career using the following EZmed platforms:
YouTube Channel: EZmed - Animations and videos that simplify medicine and science
Instagram: @ezmedlearning - High yield exam content
Pinterest: ezmedlearning - Easy illustrations and flashcards