Second degree AV block |


  1. rathmagg says

    I’m not sure what is meant by “The main identifying characteristic is that the atrial rhythm is regular.” I see that the ventricular rhythm is reg except for the dropped QRS. The p waves are reg, but the distance between p waves clearly is not. Am I missing something?
    Thanks for all the work you’ve put into this.

    • Jeff with admin. says

      Atrial rhythm = atrial contraction = p-waves.

      The p-waves are regularly spaced. (5 large squares between each p-wave).

      2nd degree block type 1’s primary characteristics are the atrial rhythm (p-waves) is regular with equidistantly spaced P-waves and a progressively longer PR interval. At the end of the progressively longer PR interval series, you will see a dropped QRS complex and then the process starts over.
      I hope that helps.

      Kind regards, Jeff

  2. says

    A poem I recall, to help us remember:

    “Long, longer, longer- Drop-
    Mobitz 1 or Wenckebach!”

  3. aba says

    Hi Jeff,
    I’m new to this. can you please explain the difference between Mobitz I and II. All I see is dropped QRS in both!

    • Jeff with admin. says

      With Mobitz I, the PR interval will get longer and longer and then there will be a p-wave with no QRS.

      Mobitz II, the PR interval will be the same, but there will be p-waves without any QRS complexes.

      That is the easiest way to tell the difference. Look at this page and the page below a couple of times and make sure to watch the videos at the bottom of each page. It will get easier as you learn to recognize the PR interval.

      2nd Degree Block Type 2

      Kind regards,

      • Blonde4fun says

        While I know the definition of Type 2 HB and 3 Degree HB, it is still difficult for me to actually recognize (especially if the monitor is moving the rhythm strip across the screen). Any suggestions of quick recognition would be appreciated. Love your site. So helpful!

      • Jeff with admin. says

        These can be tricky blocks to recognize. Here is what will do the trick. For a month do this: Each day you work, look at 2 different examples of each rhythm that you want to be able to recognize. Go through the entire interpretation process for each rhythm. You might have to spend 5 or 10 minutes per day. After a month you should be able to quickly recognize each. In this case, practice does really make perfect.

        Kind regards,

      • Erika says

        I always remembered this way:

        “P’s short-longer-longer-drop then you have a Wenkebach” (and its a PATTERN that repeats)

        “If some P’s dont get through, then you have a Mobitz II”

        “If P’s & Q’s dont agree, then you have a 3rd degree” (CHB)

      • bisabelh says

        Why isnt type1 significant for ACLS but type 2 is? I understand that the dropped QRS could lead to complete block, but if type 1 is also missing the complex…


      • Jeff with admin. says

        Type 1 Mobitz I is typically caused by a reversible conduction block at the level of the AV node.
        Malfunctioning AV node cells tend to progressively fatigue until they fail to conduct an impulse. The AV node cells then recover and the process typically begins again.
        While Mobitz I is typically caused by a functional suppression of AV conduction with reversible causes (i.e. drugs, reversible ischemia), Mobitz II (Type II) is more likely to be due to structural damage to the conducting system (i.e. infarction, fibrosis, necrosis) which is more likely to degrade to complete failure in conduction and the resulting Third Degree Block (complete block).
        Hope that helps.
        Kind regards,

  4. gerry says

    thanks for the link on Heart Blocks. I am just beginning my review of the material for ACLS and am reviewing general information first to be able to put the specifics of ACLS in context. This brief link is worth a look

  5. says

    Great info. Great for ACLS and just for overall cardiac knowledge. In regards to blocks, hat is a Bundle Branch Block then? Does it fall in one of these types of categories that you have mentioned?

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