Complete Heart Block Confusion

Here is part of the problem I see with getting people to understand heart blocks. The first thing that is noticed is sometimes what looks normal and comforting. We do not go looking for problems, even though in EMS, we are not supposed to be called for things that are not problems. We are setting ourselves up for making the problem worse. Here is the unmarked copy of Adam's Complete Heart Block ECG.

When I would show strips like this to people in ACLS (mostly nurses, some doctors, some respiratory, occasionally a paramedic), the first thing someone would comment on is the least important, most misleading part of the strip. The single instance of the normal looking PR interval. Some people see the normal PR interval and assume that all of the PR intervals are normal, just difficult to identify. This is the wrong approach.

This is one of the reasons I keep highlighting the importance of science in EMS.

What does science have to do with this?

The approach of science is to examine research with the attitude of trying to find where there are problems. Falsifiability. Science is about performing research, then publishing it with the expectation that others will look for the problems with the study. And not being mad at those who find flaws in the research. The critic is not the one who made a mistake. That does not mean that the critic would be able to do research as well as the researcher being criticized, but that has nothing to do with science.

Research is validated only when no significant problems can be found with the research.

So what does this have to do with EMS and ECG reading?

We too easily dismiss a patient's complaint as bogus, when we have not assessed the patient thoroughly enough. If you see the normal PR interval, have you identified this as a healthy rhythm?

Certainly not. We need to keep looking for problems until we have ruled out the potential problems. Many times that is impossible in EMS, but it does not stop some medics from dismissing a patient's complaint as bogus. This is not good medicine.

Here is the same ECG, but I have marked the normal PR interval on this blatant heart block with a circle. The three beats on top of each other are the same beat, just presented in different leads, so this is three instances of just one normal PR interval. I have also drawn a line over the changing PR intervals. Looks like a pattern.

The PR intervals over the ECG do seem to form a pattern. Longer, longer, longer, repeat. Has Adam missed, right after posting a music video on the topic, a Wenkebach block - a 2nd degree type 1 heart block?

There does seem to be the progressive lengthening of the PR interval. What about the dropped beats? In order to compare the R to R interval in a way that makes this a bit clearer, I copied each pair of beats, after the first pair, and placed the copies under the first pair of beats. I drew a line down the middle of each of the first 2 beats and tried to line up all of the others with those lines. Is there any lengthening of the R to R interval that would indicate a dropped beat?

Click on the image to make it bigger.

I don't see any significant difference. Without any dropped beats, this cannot be Wenkebach. Longer, longer, longer, repeat. Wenkebach is longer, longer, longer, dropped. The number of longers is not always three. It could be two, or four.

There is a slight variation in the R to R interval. A variation that is more than just my lack of cut and paste skill. Does this variation mean that these beats are not controlled by the ventricles? No.

The vagus nerve is often the culprit in heart rate variability. The vagus nerve is not supposed to connect to the ventricles. However vagal innervation is not the only reason for heart rate variability. Some patients also will have the vagus nerve attached to their ventricles.

This is a nice example of a Complete Heart Block. The terminology is something that cardiologists may not approve of, but I think this is adequate for EMS use. The understanding of the concept is much more important than the terminology.



Anonymous said...

That looks a bit like a dropped P wave in V1 right after the T wave. Also, can you really call this with such a short strip or a single 12 lead ? It seems to be borderline.

Adam Thompson, EMT-P said...

Has Adam missed, right after posting a music video on the topic, a Wenkebach block - a 2nd degree type 1 heart block?I have to admit that you had me going. I said "no, wait a second, no I couldn't of have, maybe I..aww okay, thought so" aloud.

The three beats on top of each other are the same beat, just presented in different leadsThanks for pointing this out. There are a lot of medics that don't understand this concept, or it was never taught to them. I was going to go over this in a future post along with the different angles of view based on which lead you are looking in.

Anonymous,It fits the criteria for a complete AV block. Given what we see, we have enough of a strip to see a pattern, if there is one; as RM pointed out. Some rhythms may be harder to determine given only a 12-lead.

I think a 6 second strip is most commonly used to interpret from. Probably because a common (not most adequate) way of determining the HR is to count the QRS complexes or R-R intervals in 6 seconds and multiply by 10.

Rogue Medic said...


I agree that there are plenty of dropped P waves. Adam listed a bunch of them in his ECG strips in Complete Heart Block.

I do not see this as borderline. So I do not know what you consider it to be borderline between - complete heart block and what?

There clearly are more P waves than QRS complexes, yet the R to R interval remains constant. I was pointing out the misleading appearance in two areas. The short, normal looking PR interval that I circled, which does not appear to be present elsewhere. An isolated normal PR interval does not make this a sinus rhythm. There are other P waves that do not generate ventricular contractions, so this is clearly some sort of heart block.

If you think it is borderline between Wenkebach and complete heart block, how do you explain more than one P wave not generating a ventricular contraction? Wenkebach only has one P wave not generating a ventricular contraction for every bunch of ventricular contractions. This seems to have several P waves that do not generate ventricular contractions for every P wave that does appear to generate a ventricular contraction.

The abundance of P waves that go nowhere seems to make it clear that this is a complete heart block. The P waves that appear to generate a ventricular conduction are just coincidentally close to the QRS complex. They provide nothing more substantial than the appearance of conduction.

This is similar to the anecdotal tales of successful treatments with alternative medicines that do not really work. Every now and then, spontaneous resolution of an illness will coincidentally occur just after the treatment. Spontaneous resolution of illnesses is not as uncommon as we expect, so we attribute meaning to this coincidence, when it is really nothing more than a coincidence.

The not uncommon spontaneous resolution comes right after some kind of attempt at treatment. This occasionally occurring sequence leads to belief in the alternative medicine treatments - even though research makes it clear that alternative medicine does not work.

Here you have plenty of evidence that none of the P waves are leading to QRS complexes. There is the appearance that one caused the next, but only because they are close together and the expected result comes after the expected cause. Coincidence.

There is no cause and effect that I can see. Adam came to the same conclusion, and he posted this a day before I responded with my post.

Look at all of the extra P waves. It does not matter where they are. The have no effect on the ventricular activity. This strip is long enough to make that clear to me. With a complete heart block, the important question is Where are the conducted beats? I don't see consistent evidence that they exist, do you?

Without evidence, we only have anecdote/coincidence/magic. This rhythm is not magic.

With a 12 lead it is difficult to look for any change in morphology as an indicator of the origin of beats, since only a couple appear in each lead. Consistent morphology is not necessary to figure out this rhythm.

If I am misinterpreting what you wrote, please provide some more detail of what you meant. Thank you.

Rogue Medic said...


This is a good strip for getting people to second guess themselves. Sometimes ambiguity is bad for explaining a concept, but here I saw it as an opportunity to clarify a concept. In a heart block with some conduction - Wenkebach (2nd degree type 1) and classic (second degree type 2) - there is some consistent evidence of conduction. This ECG only has the appearance of conduction, but there is nothing to differentiate that one beat from any of the others.

As I mentioned with the reference to alternative medicine, this is just the kind of coincidence that is to be expected. It is nothing more than coincidence, but it gives a different perspective on the ways we can mislead ourselves by not examining closely enough.

Anonymous said...

a-v dissociation?