Dawn's picture
Submitted by Dawn on Sat, 05/25/2013 - 13:12

Today's basic rhythm strip illustrates second-degree AV block, Type II.  Even though there is fine baseline artifact present, it is easy to measure the P-to-P interval, and your students will be able to see that every third P wave falls in the T wave.  The PR intervals are constant and the atrial rate is about 110/min.  The ventricular rate results from a 3:1 conduction ratio, and is less than 30/min.  For your students who have learned about bundle branch block, this strip shows a right bundle branch block, which is very common in second-degree Type II blocks, as they usually represent "intermittent tri-fascicular block" - that is, two of the three fascicles in the bundle branches are blocked, and one is intermittently blocked.  Other combinations of complete block and intermittent block are possible, resulting in intermittent failure of conduction.  This strip can start a lively classroom discussion about treatment of bradycardias.  See comments below for discussion of terminology, second-degree AVB and high-grade AVB.  This strip can be used as a good example of high-grade AVB. 

Related Terms: 
Second-degree AV block Type II
ECG Basics
Rhythm strip
AV Block
High-grade AV Block
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Dave Richley's picture

Submitted by Dave Richley on Mon, 05/27/2013 - 01:43

Some authors would describe this as an example of high grade (or advanced) AV block, a sub-category of 2nd degree block. Although there is no universally agreed definition of high grade block, two that I have seen are where there are more blocked than conducted P waves and where there two consecutive blocked P waves. This strip satisfies both definitions. In the hierarchy of AV block, high grade block is generally considered worse than type two 2:1 block but not as bad as complete block.

 

 

Dave R

Submitted by VinceD on Sun, 05/26/2013 - 10:50

I might also add that you actually cannot determine the type of AV block, I or II, since no two consecutive P-waves are conducted to prove or disprove Wenkebach phenomenon. The presence of a BBB suggests type II, but is not determinant of it, so I'm left calling it "high-grade AV block, undetermined type."

Vince D
http://www.medialapproach.com

Dawn's picture

Submitted by Dawn on Mon, 05/27/2013 - 00:22

I definitely agree with you, Dave, that the conduction ratio is 3:1, and I am editing the description of the strip accordingly.  I apparently forgot how to count, momentarily!  And, I do agree with the definition of "high-grade AV block", and also that it is very difficult to determine if there is a Wenckebach mechanism when two beats are not consecutively conducted.  However, most very basic students in my area are not taught this definition - they are just taught Type I and Type II. The concepts of "high-grade" and "2:1 AVB" come later.  It is very difficult for me to decide exactly how much to put in the description, since I am trying to reach out to the teachers of beginner students, and I think I fell short this time.  Thanks, Dave and Vince (two actual Gurus) for helping me out.

Dawn Altman, Admin

Dave Richley's picture

Submitted by Dave Richley on Mon, 05/27/2013 - 01:45

Dawn - I've edited my comment now that you have edited your description!

Dave R

Dawn's picture

Submitted by Dawn on Mon, 05/27/2013 - 10:22

The ECG Guru was always intended to be a forum for teachers, and we are happy when students stop by, too.  But it is input from educators like you that make the ECG Guru what it is.  Thanks so much!

 

Dawn Altman, Admin

Submitted by VinceD on Tue, 05/28/2013 - 16:09

Thanks for the quick reply, and I agree that teaching AV blocks is actually a lot more difficult than more instructors like to present it - I know I haven't figured out a great approach yet either (hence why I'm only an informal 'teacher' :-) . Frequently cited ECG teaching hero Amal Mattu even slips up on this topic, and as chance would have it, did so on this very topic just this week. http://youtu.be/D2O9q3Gj5H0

Keep up the great posts! If I didn't like what you're doing or find it useful I wouldn't be taking the time to read and comment, so I'm glad you know we're only trying to be supportive and constructive.

Vince D
http://www.medialapproach.com

ekgpress@mac.com's picture

Submitted by [email protected] on Tue, 05/12/2015 - 17:39

Apologies for my late entry into this basic but discussion-fostering short rhythm strip. I'd like to add a few thoughts to comments provided by Dawn, Vince & Dave.

This rhythm strip is short. For the beginner - it is fine to show it as preparation for an ACLS course or in basic teaching of AV block - but for the more advanced interpreter - more information (a longer rhythm strip) is needed ...
  • There appears to be at least near-regularity of the P-P - and the QRS does appear to be widened - but I think it worthwhile to point out that with this degree of baseline artifact - it is difficult to be certain of conclusions. I am not completely certain the QRS is widened from this single lead ....  And while diagnosis of RBBB is possible (if not probable) - at a minimum, one should see a right and left-sided lead before safely postulating this (ie, V1/MCL-1 and I, V6, or MCL-6). The skinny negative deflection arising shortly after the upright 5mm complex in this lead II is not that much deeper or wider than many of the artifact spikes I see in this erratic baseline ....
  • I realize beginners are often taught to distinguish between just 2 types of 2nd degree AV block - which are Mobitz I and Mobitz II. That said - I feel that is imparting incorrect information. I've taught for years in my most basic AV block talks to even beginner providers the need to add a 3rd type of 2nd degree AV block = 2:1 AV block, in which because you never see 2 conducted beats in a row you simply can NOT TELL if the disorder represents Mobitz I or Mobitz II. That is what we have here ....
  • I agree with the above comments re this being a case of "high-grade" AV block - since it is "worse" than just 2:1 AV block - but it is definitely not complete AV block (because the PR interval preceding QRS complexes is constant). I think it best in this case to just describe in words what one has which is: "2nd degree AV block with 3:1 AV conduction and a ventricular rate of ~ 40/minute".
  • For beginning students - we can NOT tell if this is Mobitz I or Mobitz II - since we never see 2 QRS complexes conducting in a row. Calling it, "high-grade 2nd degree AV block with a ventricular rate of ~ 40/minute" is a basic description that accurately reflects what we see. The KEY concept - is the likely need for a pacemaker, depending on the clinical situation.
  • It is important to realize that 2nd degree AV block, Mobitz Type I (= AV Wenckebach) CAN present with this picture. You can drop 2 beats in a row with Mobitz I .....  The QRS could be wide from preexisting BBB if this is Mobitz I - and then again, I'm still not prepared to definitively call the QRS wide with this abbreviated lead II artifact-laden strip .... I think the QRS is probably wide, and I think it is probably RBBB - but no way to be certain from the snapshot that I see here ...
  • The atrial rate is relatively fast (a bit over 100/minute). It is VERY possible that other recent strips on this patient showed a "lesser degree" of AV block when the atrial rate was slower. Perhaps this strip was obtained after atropine was given - which paradoxically sped up the atrial rate and reduced the number of impulses able to penetrate the diseased AV node. We just don't know ..... 
So - LOTS to potentially talk about depending on one's teaching situation about this simple short rhythm strip ....

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

Dawn's picture

Submitted by Dawn on Thu, 05/30/2013 - 11:05

Thanks, all.  I love all the interaction, that's what the ECG Guru is for.  AV blocks ARE difficult to teach.  I have taught classes for people desiring to be monitor techs.  In my local community, many of these speak English as a second language and have minimal science education.  They would not even be able to comprehend the discussions in these posts.    I have also taught many hundreds of paramedics.  In my community, they are also firefighters.  Sadly, most of them have little interest in ECG as an interesting topic, they just want to know enough to follow their protocols.  There are some very notable exceptions, of course.  I am always seeking to reach and slightly extend the level of my students.  I am trying to provide something on the ECG Guru for teachers who teach these types of students, as well as for those who teach more advanced students.  It is important for the students to have the MOST basic information, and for the teachers to understand the topic BEYOND the level they are teaching.   Thanks for helping me provide all this for teachers everywhere.

One more comment on the Type I / Type II discussion.  Granted, two conducted P waves in a row are necessary to know for sure whether you are dealing with Type I or Type II, but when there is a non-conducted P wave far out in the open, not near a refractory period, Type II is strongly implied.  I feel confident that the above strip is not an AV node block of Wenckebach type.  Just me ....

Thanks again to those of you who take the time to post here.  There are almost 12,000 visitors a month to the ECG Guru.  Even though very few of you post comments, I know people out there are reading what you write.

Dawn Altman, Admin

Dave Richley's picture

Submitted by Dave Richley on Fri, 05/31/2013 - 00:29

I think this discussion has raised some very interesting points about how to teach AV block. I know that I find it difficult. The dilemma I have is between oversimplifying and making it easy to understand, but knowing that students will inevitably come across examples that they can't interpret, and trying to teach in depth but knowing that many students will get confused. In my experience AV block causes more confusion than any other ECG topic. I haven't resolved this one but I do have an aversion to excessive oversimplification. I think it is important to try to teach the mechanisms at work in AV block, rather than just pattern recognition, but ultimately I suspect that true understanding only emerges when students have to work through many examples and try to work out for themselves what is happening, helped where necessary, of course, by the teacher. This all takes time - I know of no short-cuts!

 

Dave R

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