Second Degree Heart Block- Type 2

Second-Degree (AV) Heart Block (Type 2)

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.

2nd Degree Block Type 2
This rhythm can be recognized by the following characteristics:

  1. non-conducted p-waves (electrical impulse conducts through the AV node but complete conduction through the ventricles is blocked, thus no QRS)
  2. P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
  3. fixed PR interval
  4. The QRS complex will likely be wide click here to see why»

Second-degree AV block (Type 2) is clinically significant for ACLS because this rhythm can rapidly progress to complete heart block

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.

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 AV block type 2 on a monitor. Please allow several seconds for the video to load.

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 slowedPowered by Hackadelic Sliding Notes 1.6.5


  1. tecintron says

    Hi Jeff!
    I am a new nurse and I am curious as to why the QRS points are pointing downward (probably a stupid question).

    The music reminds me of Mission Impossible!! I love it!

    • says

      This is a good question. In the video, the QRS complexes are “pointing down” (negatively deflected) because this rhythm is being observed from a lead in which the electricity is moving away from the lead being observed. There are 12 leads that can be read on an ECG and some of them are normally negatively deflected.

      Basically, if the lead that you are looking is negatively deflected the electricity is moving away from the lead. If the lead that you are looking at is positively deflected the electricity is moving toward the lead.

      This stuff can get a bit technical and is way beyond basic ACLS. If you would like understand more about ECG axis and 12 lead interpretation, here is a ECG axis.

      Here is a link to a Normal 12 lead wavesof that all of the normal leads look like.

      For the beginner, the lead that is the “easiest” and most common to look at is Lead II, but all of the rhythms that are learned in ACLS can be easily interpreted no matter what lead you are looking at.

      Kind regards,

  2. brendabikes says

    2nd recert next month. 2nd time using your site. Thank you so much. My only suggestion would be to make the images larger (the defib monitor) as well as some of the writing. I find myself squinting and sitting close to the computer.

    • says

      I’m so glad that you have found the site helpful. The videos found on the ACLS rhythm interpretation section of the knowledge base were created using software that was formatted for standard definition. They are in the process of being edited to improve the screen quality. They will eventually (within the next 6 months) be the same improved quality as found in the megacode series videos and the rapid rhythm ID videos.

      Kind regards,

  3. vicki says

    In all the heart blocks is seems to me that the p to p interval is consistent. Or in old school terminology they “walk off’.This is not mentioned regarding Mobitz type 2, am I correct or incorrect?

  4. Jbailey777 says

    Hi Jeff,
    It says in the red box above “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.” But on page 166 in the manual, it says in bold that “Atropine Sulfate will not be effective for infranodal (Mobitz type II) block.”
    So regardless if you don’t have immediate access to TCP, don’t try Atropine?
    What do you think?

    • says

      Atropine may be used and can be effective with any type of sinus bradycardia. It can be effective and should be attempted if possible. With Mobitz II and 3rd degree block at worst, it won’t work. It won’t hurt to try.
      If there is a possibility of ischemia then atropine should be used with caution because it can worsen ischemia.
      Atropine can be effective for increase heart rate and can improve symptoms that are being caused by the low heart rate. I would use atropine if time and the situation permits.

      Kind regards,

    • says

      If you are having this problem on all of the videos, you may need to update your flash player. You can find out how to do that here: Video Help
      If you can see some of the videos then this problem is most likely related to the WiFi getting hung up. The easiest way to solve the problem is to restart your computer. You may also want to reset your WiFi router if the computer restart does not solve the problem.

      All of the videos do seem to be working fine of the server side.

      Kind regards,

  5. says

    Is the reason for atropine being avoided in cardiac ischemia due to the fact you want to keep oxygen demand low for the heart? And if thats the case but your patient is still unstable after nitro and other interventions what is the best option?

    • says

      Correct. Atropine with increase the heart rate significantly and could potentially worsen ischemia. Your best option in this situation would be to use TCP and pace at as low a heart rate as possible that will minimize symptoms while you get the patient to PCI.

      Kind regards,

  6. Gretzel Mae Deang says

    hello.. i would likely to know the difference between mobitz2 type1 and mobitz2 type2 in an ecg example? thank u

    • says

      “In the 2010 up date it said initial treatment of bradycardia is Atropine.”

      On page 111 of the AHA Provider Manual it states:
      “Atropine administration should not delay the implementation of external pacing for patients with poor perfusion.”
      Also on page 111 it states:
      “Do not rely on atropine in Mobitz Type II and also 3rd degree block or in patients with third-degree AV block with a new wide QRS complex.”
      The above would be the main reason for skipping over the atropine and going straight to TCP if it is ready for use.

      Kind regards,

  7. 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

  8. 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.)

    • 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

  9. 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

  10. 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!!

  11. 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

    • 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,

      • 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!

      • 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!

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