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.