confused.. Non-conducted PAC vs Type II AV block?

  1. how do you know when it is a type 2 AV block and or just maybe it's multiple non-conducted PAC?

    or is Type 2 AV block basically having multiple non-conducted PAC?

    I read online, non-conducted PAC can be non-pathological but type 2 AV block can be pathological.. why is that?
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    Joined: Mar '09; Posts: 18


  3. by   ChaseZ
    A blocked, or non-conducted PAC is what the name implies... A premature atrial beat that is not conducted to the ventricles; P wave but no QRS. The key is the fact that it is early. So take your calipers and measure out the P-P interval then measure form the last normal p wave and look where the calipers land. Does the non conducted P wave come sooner than where your calipers land? If so then it is a blocked PAC. They commonly are buried in the preceding T wave so look closely for changes in T wave moroplogy. There may be an extra hump or taller peak. Now with Second degree type 2 there is not a premature beat, there is an intermittent failure of conduction to the ventricles. So same as before take your calipers, get the P-P and measure out from the last normal P. Is there a non conducted P wave exactly where your calipers land? That is second degree hesrt block. Slide your calipers from that non conducted P wave and they should land exactly on another P wave, this time with an associated QRS. This is what people refer to as "marching out". With a second degree type 1 (Wenckeback) there is no marching out of p waves. Each consecutive PR Interval increases until there is a non conducted p wave. Longer, longer, dropped then the cycle repeats. So fixed PRI for the beats preceding a dropped best is not Wenckeback, most likely a PAC or 2nd degree type 2. Hope that helps, I typed this on my IPad so sorry for the format and typos
  4. by   nooneelse
    ahh.. I get it now!! thanks so much ChaseZ!
  5. by   Bertpr8
    Everything that ChaseZ mentioned is on point. The only thing I should say is that on the 2nd degree Type I the P waves do march. They all come from the SA node, but the elongation of the PRI happened due to the delay on the AV node. I was trying to add an example, but I couldn't add it.
  6. by   MsBruiser
    Good question and good answer.
  7. by   Csizi
    What if the non-conducting P wave comes later than it should be? Like 8ms-10ms-6ms. Maybe a blocked atrial escape rythm that came late?
  8. by   2210485
    Quote from Csizi
    What if the non-conducting P wave comes later than it should be? Like 8ms-10ms-6ms. Maybe a blocked atrial escape rythm that came late?
    Well, of course 8- 10- 8ms would be virtually impossible to determine in a 12 lead or even an intracardiac electrogram. Even a diagnostic ep catheter has a margin of error and at least some degree of limitation.

    If however you see like.. 80ms, 100ms, 80 ms variations:

    It could be escape if the morphology (shape) of the wave is different. Possibly 2nd degree avb, sinus arrest with non conducting escape. That's a possibility.

    It could also be a disease superior to the AV Node and/or SSS. Conduction Disease can occur just about anywhere along the conduction pathway.

    Marching out the P waves as you did is a good plan. If you have a longer strip or a long term monitor watching for patterns in the P waves can help make sense of it sometimes.

    If you have a PAC or a pathway you can have concealed conduction creating the phenomenon as well. So gathering information about potential interactions between ectopics or abberency is always useful, as is a thorough understanding of patient history.

    Unfortunately with situations such as these theres just so many options that it's pretty difficult to develop a concise algorithm.

    Once you get the basics down and you've seen enough if these recordings to know what things look like:

    The only way to advanceg with this stuff, imo, is to stop thinking about EKG criteria, and a simple block of 3 components (pri, qrs, tu) and start thinking in terms of Anatomy and Physiology and electricity. Instead of seeing a P wave and associating it with 'atria' bear in mind that the atria can be futher subdivided into inconceivably small units and that each of those units plays a role in generating an ekg complex. Not sure if that helps or not, just my 2 cents on it.

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