Second degree heart block Type 2, which is also called Mobitz II or Hay, is a disease of the electrical conduction system of the heart. Second-degree AV block (Type 2) is almost always a disease of the distal conduction system located in the ventricular portion of the myocardium.
This rhythm can be recognized by the following characteristics:
- non-conducted p-waves (electrical impulse conducts through the AV node but complete conduction through the ventricles is blocked, thus no QRS)
- P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
- fixed PR interval
- The QRS complex will likely be wide
Click here to see why.
The QRS on an ECG will most likely be wide because the block occurs in the His bundle or bundle branches and conduction through the ventricles is slowed. This slowing of conduction appears as a wide QRS complex on the ECG.
Second-degree heart block type 2 is usually caused by structural damage to the conduction system of the heart. Causes of the structural damage to the conduction system include the following:
Causes:
- Myocardial infarction that damages the conduction system
- Idiopathic fibrosis
- Cardiac surgery
- Infections and inflammatory conditions
- Hyperkalemia
- Autoimmune diseases affecting the heart
Second-degree AV block (Type 2) should be treated with immediate transcutaneous pacing or transvenous pacing because there is risk that electrical impulses will not be able to reach the ventricles and produce ventricular contraction.
Second-degree AV block (Type 2) is clinically significant because this rhythm can rapidly progress to complete heart block.
Atropine may be attempted if immediate TCP is not available or time is needed to initiate TCP. Atropine should not be relied upon and in the case of myocardial ischemia it should be avoided.
Below is a short video which will help you quickly identify second-degree heart block type 2 on a monitor. Please allow several seconds for the video to load. (2.65 mb)
Click for next Rhythm Review:
Complete Heart Block (3rd Degree Block)
Top Questions Asked On This Page
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Q: The video says “sometimes has wide QRS.” What else would you see with 2nd-degree if the block is occurring in the bundled His? I have seen the portrayed rhythm many times and was not sure what it was.
A: For 2nd-degree block type II you will see:
non-conducted p-waves (electrical impulse conducts through the AV node, but complete conduction through the ventricles is blocked, thus no QRS)
P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
fixed PR interval -
Q: Having trouble differentiating between Mobitz II and third-degree block.
A: The main difference is this:
Mobitz II: There will be a P-wave with every QRS. There may not always be a QRS complex with every p-wave. The rate will usually be regular. Also, the PR interval will be regular.
3rd Degree Block: There may not be a p-wave with each QRS, and the PR interval will not be the same with each PQRS.
These videos may help you.
They are kind of hard to hear, but the content is good. -
Q: Your video says pace right away for 2nd degree? TCP should only take place if the patient is symptomatic or showing signs of inadequate perfusion? Correct?
A: Correct. If the patient is unstable which is defined as “showing signs of poor perfusion.”
Jillian says
This is easier to understand than even Rapid Interpretation of EKG’s by Dale Dubin, MD.
Phil r moran says
Hey Jeff ,
Your video says pace right away for 2nd degree ? TCP should only take place if the patient is symptomatic or showing signs of poor perfusion ? Correct ? Love your program has been a real asset for me ! Thanks so much , Phil
Jeff with admin. says
Correct. If the patient is unstable which is basically defined as “showing signs of poor perfusion .
Kind regards, Jeff
nancybomber says
I really LIKE the music, it helps me learn!
Ina says
I learned the difference between the two blocks as the second degree block type II the p waves and the qrs waves that are there are married
In The third degree block the p waves and qrs are divorced (they do not stay together.)
Ronnie says
Light bulb went off with your explanation of second degree type II and third degree blocks
P(when present) and QRS married in type II and divorced in Third degree. Brilliant
dinniehp says
Thank you for the wonderful learning tool!
Jeff with admin. says
Thanks for the complement 🙂 I’m so glad that the site is helpful for you.
Kind regards, Jeff
sg says
I have been symptomatic for 3 years. My kidneys are starting to fail.
I know this rhythm needs paced.
I know this leads to 3rd degree block.
I have an issue with the fact that I have tattoos seems to be more important to the cardio doc than my life.
Video is great. I’m 2:1 ratio.
Thank you
Carolyn says
That sounds pretty serious. Why don’t you go to a different doctor about it?
dpelto says
sure you’re not talking about trigeminy?
Pearly says
I just love the music. So many different styles of learning on one page!! I also love the comments after. And Jeff from admin always signing of with, KINd regards!!! So pleasant. Great site!!
dianne1984 says
Great review. I depart a bit from ACLS recs on advanced HB: atropine is likely to increase the atrial rate and, with infrahisian block, can actually decrease the ventricular response. Isoproteronol increases the escape (or ventricular rhythm).
From an EPdoc
MCKINNEY says
The video by michelekunz was a big help.thx
cirvine says
Having trouble differentiating between Mobitz II and third degree block.
Jeff with admin. says
The main difference is this:
Mobitz II: There will be a p-wave with every QRS. There may not always be a QRS complex with every p-wave. The rate will usually be regular. Also, the PR interval will be regular.
3rd Degree Block: There may not be a p-wave with each QRS. And the PR interval will not be the same with each PQRS.
These videos may help you.
They are kind of hard to hear but the content is good.
Kind regards,
Jeff
Dorothy Hondros says
Thank you Jeff for the most comprehensive ACLS review that I have yet to see! You have made this nervous ICU nurse much more confident!
Barbara says
3rd Degree, the top and the bottom parts of the heart are doing their own thing and “don’t talk to each other” and beat at their own rate, p’s are usually regular and QRS is regular, but usually at a slow ventricular rate.
2nd Degree, the parties involved talk to each other most of the time, but not always.
amyj1979 says
It was put to me like this: a third degree heart block has no rhyme or reason to the p wave. They just pop up where they want to. No real relation to the QRS. Mobitz, however, the p wave is with a QRS, there just may be some QRS complexes missing. That helped me to understand 🙂
ptrimble says
Excellent explanation — I believe that was what I learned at my first ACLS certification. Thank you!
aseel hanna says
very good explanation for type 2 2nd degree heart block
savvygirl says
Jeff-
The video says “sometimes has widw QRS”. What else would you see with second degree if the block is occurring in the bundled His? I have seen the portrayed rhythm many times and was not sure what it was. Thank You for the methods you use to teach these concepts. Blocks have always been my problem area.
Stacie
Jeff with admin. says
For 2nd degree block type II you will see:
Kind regards,
Jeff
Lisa says
this is finally making sense, showing the simulated rhythms makes it clear
Marina LaPalma says
thank you for the clear information
Marmotess says
I love the content and the music! Even my children are learning over my shoulder. Great site!! Thanks!!