When you are learning EKG heart rhythms, you must be familiar with the differences between each heart block. In nursing school, I had difficultly at first figuring out the differences between each AV heart block, but now it is second nature to me. Whether you are in nursing school, a new nurse, seasoned nurse needing to brush-up on this material, or another type of healthcare professional learning heart blocks, this article will help refresh you on the important things you need to know about AV heart blocks.
In this article, I am going to cover the following heart blocks:
- AV 1st Degree
- 2nd Degree Type 1, also called Wenckeback, Mobitz I
- 2nd Degree Type 2, also called Mobitz II
- 3rd Degree which is known as a Complete Heart Block
Video Teaching Tutorial on Heart Blocks
After you read this article, I highly recommend you watch my teaching tutorial on these heart blocks to further help you understand the material. Then, take the EKG Heart Block Quiz to test your knowledge on what you have learned.
1st Degree AV Heart Block
The picture above will help illustrate to you what I am talking about. The big thing you need to take away from this rhythm is that it looks normal (like normal sinus rhythm) BUT it has a secret. Note the PR interval on the strip. It is much longer than a normal PR interval. A normal PR interval is 0.12-0.20 and here the PR interval is greater than 0.20. If you don’t know how to measure a PR interval see this article and video.
In addition, this is what will be present with a 1st Degree AV Heart Block:
- Regular P-waves and R-waves
- P-wave always accompanying the QRS complex
- QRS complex will measure normal
- PR INTERVAL WILL BE PROLONGED
2ND Degree Type 1 | Wenckebach | Mobitz I
This rhythm is so easy to remember once you figure out its “hallmark”. Note the PR interval on the EKG strip. See how the PR interval are progressively lengthening and then all of a sudden a QRS complex is missing and then the pattern starts all over? This is the key in understanding a Wenckebach.
This rhythm is CYCLIC and will always present with progressively lengthen PR intervals until a QRS complex disappears and then it will repeat itself. You will also have the following with this rhythm:
- P-waves & R-wave will be IRREGULAR
- PR intervals ABNORMAL
- Missing QRS complex
- CYCLIC
2nd Degree Type 2 | Mobitz II
Many people like to confuse this rhythm with a Wenckebach and third degree. However, there are some major differences. One being the rhythm is not cyclic, it does NOT have a pattern. Second, its QRS complexes will be IRREGULAR and this is the opposite for a 3rd degree heart block. Third, it can have NORMAL PR Intervals, where a 3rd degree heart block does not contain any PR Intervals.
Notice the strip above: The p-waves are nice and regular while there are some missing QRS complexes which makes the R-wave irregular. In addition, there is no pattern of lengthening p-waves. So, the things to take away from this rhythm are the following:
- P-waves will be regular, however R-waves will NOT
- PR interval will measure normal (most of the time)
- NO Pattern
- Missing QRS Complexes after p-waves randomly
3rd Degree Heart Block (Complete Heart Block)
Out of all the heart blocks for a patient, this is the worst one. It requires major interventions. In this rhythm, the atriums and ventricles are NOT beating together and are working independently of each other. Therefore, the important “hallmarks” to take away from this rhythm is the following:
- P-waves will be Regular AND R-waves will be Regular
- P-wave will not accompany QRS complexes and vice versus, hence no relationship between the atriums and ventricles
- You can’t measure a PR interval because the atriums and ventricles are independent
Quiz on Heart Blocks
Now test your knowledge on heart blocks and don’t forget to watch the teaching tutorial above!