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Vectors, Axis and Cardiology
Cardiology - the study of the heart, I truly enjoy learning and studying the heart, how it works and why it works that way. I had the privilege of teaching a paramedic class today and going over the vectors and axis information for them. I am not strong in this area and tried to do the best I could as well as provide some online resources for them to look at. Then I got the dreaded question, "what good will this do for me when I am working with a patient?" I tried to make the point that it has to do with conduction pathways and determining where the impulse is coming from, but I know that it was not an effective answer.
Does anyone have a better answer that I can use and some resources that I can use myself and provide to the students on these subjects? Thank you for any help you can give.
Dave
Views: 215
Replies to This Discussion
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Permalink Reply by Life Saver on -
honestly... i would like an answer too
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Permalink Reply by Tom Bouthillet on -
That's a fair question, Dave M.
I'm reminded of what Jeff Beeson, DO, LP said in a breakout session at EMS Today 2009. "The eyes cannot see that which the mind does not know." Without a proper understanding of axis and vectors you cannot really "see" a 12-lead ECG. Once you fully understand axis and vector it gives you a vocabulary that allows you can take ECG interpretation to the next level.
It doesn't help that this topic is poorly taught at all levels.
Here are some examples where understanding the heart's axis and vectors has helped me make wise decisions on actual emergency calls.
The most common causes of left axis deviation are left anterior fascicular block and Q-waves from inferior MI. So when I see a left axis deviation it prompts me to consider these conditions. Many times I have caught subtle inferior STEMIs because the axis was slightly to the left and it prompted me to look at lead aVL for subtle reciprocal changes.
A paced rhythm with a pacing lead in the apex of the right ventricle typically shows LBBB morphology in lead V1 and left axis deviation. So this prompts me to double-check for a pacemaker pocket on the patient's chest and consider that the rhythm may be paced before I decide the patient is showing frequent PVCs or a run of slow VT.
Conversely, it would be very unusual for LBBB or paced rhythm to show LBBB moprhology in lead V1 with a right axis deviation. That in turn further supports the dx of VT in a patient who happens to have a pacemaker. That helped me identify a run of VT at a rate of 140 when others called it a "runaway pacemaker."
A pulmonary disease pattern may pull the axis to the right. It may also cause right atrial enlargement. In addition many congenital heart defects cause right ventricular hypertrophy with an associated right ventricular strain pattern. So when you see right axis deviation, tall R-waves in lead V1, and T-wave inversion in the right precordial leads, you know it's consistent with the patient's history and not "anterior ischemia" requiring NTG. There is a young woman with a congenital heart defect in my jurisdiction who has received MONA for her anxiety attacks more than once because of her abnormal ECG.
Q-waves from high lateral MI pulls the axis to the right. Left posterior fascicular block is rare as an isolated finding, but that also pulls the axis to the right.
Combine left anterior fascicular block (left axis deviation) or left posterior fascicular block (right axis deviation) with RBBB morphology in lead V1 and it's referred to as a "bifascicular pattern" which is the key to understanding wide complex tachycardias, IMHO.
An extreme right axis deviation (or right superior axis depending on what terminology you prefer) might suggest incorrect lead placement, electrolyte derangement, or help you rule-in a ventricular rhythm. I can't discuss this topic without mentioning that failure to "rule-in" VT based on QRS morphology does not "rule-out" VT. Brugada and Wellens' criteria are not well understood, IMHO, and have led far too many health care providers of all stripes to call a wide complex rhythm "SVT with aberrancy" when it was not warranted which can lead to clinical misadventure.
I could give other examples, but the point is that you cannot develop a "trained eye" or a nuanced understanding of the 12-lead ECG if you don't have tools to describe what you see. I was explaining the concept of appropriately discordant T-waves with bundle branch block to someone the other day and it would have been extremely difficult if he didn't understand the concept of a terminal deflection.
If you want a dramatic illustration of this point, teach a 12-lead ECG class and at the beginning of the class ask the students to take out a blank piece of paper and draw a picture of a normal 12-lead ECG. If you don't understand "normal" how can you possibly hope to identify "abnormal"?
So I would suggest that anyone who asks "why do we need to know that?" that it's no different from considering a Mallampati score when evaluating a patient's airway anatomy. You're looking at the big picture and you're seeing it. Therefore you retain more and you learn more with each patient encounter.
I've been collecting ECGs for 15 years, and I'm still amazed at what I can "see" now in ECGs that I collected 10 or 15 years ago. It scares me, actually, because I wonder how I was able to treat some of these patients without knowing what I know now, but experience is funny like that.
I hope this supplies at least a partial answer. Learning to read a 12-lead ECG is like learning a foreign language. If you only want to learn how to find the bathroom or order a beer, you can learn what you need to know in a couple of days. If you want to learn how to sing the national anthem and make the locals cry it takes a little longer.
Tom
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Permalink Reply by James Ownbey on -
Tom,
Can you recommend any good 12 lead ecg books or websites . It seems every source I look at only wants to discuss st elevation and depression. I am looking for something that goes more into it. Do you have any recommendations
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Permalink Reply by James Ownbey on
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While I cant possibly give as great of a answer as tom did I will give you my feelings on it.
It drives me up the wall that some Medics and EMT’s will go out of there way to justify not learning something. EMS is full of knowledge that we cant fix but we can recognize therefore it guides our treatment. A more complete understanding of a condition will help us with pts that don’t fit perfectly into a algorithm and a understanding will sometimes point to a more appropriate treatment plan.
Exp: CVA, we don’t do a damn thing to fix a CVA yet we spend precious EMS class time learning to recognize it. Since we don’t treat it does that mean we should not need to learn about it. of course not, recognition is in its own way our treatment of it. We can give early alerts speeding up hospital treatments, we know not to treat the bradycardia or the htn . We know to expect airway compromise. And we know that time is brain matter. Again we don’t actually treat the CVA but yet we still need to be able to recognize it.
Long story short I would explain that better a and p knowledge leads to better decision making.
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Permalink Reply by Dave M on -
I am glad that I was sitting down when I read your reply Tom, I'm pretty sure there would have been a head rush and possibly a syncopal episode if I wasn't:)
The really frightening part is that I actually understood much of what you were talking about. The way to better understand something really is to teach it! What I need now is something that I can put my hands on that will give an in depth explanation with corresponding rhythm strips or illustrations for comparison and study. I know of a couple of books out there but would be interested in your recommendations as well.
When I tried to answer the question I went back to one of the mantras I had for the duration of the class. I tried to impress on the students that it is extremely important to figure out where the pacemaker for the rhythm is in the heart. From this they will be guided to an interpretation of the rhythm. To do this I gave them some basic question to ask and answer for every rhythm that they see. (is it regular/irregular, what is the rate, are there P waves, etc.) This seemed to work very well for them to be able to look at a rhythm and make an interpretation, but when I added the vector and Axis information it just seemed to confuse them.
In this context, a paramedic student just learning about the basic rhythms and starting to get an understanding of them, how deep should we go into the vectors and axis information? I know that I have been a medic for years and am just now gaining an understanding of it. Are we not doing more to confuse the new medic than helping them?
Sorry for the ramble, but I am still working over that answer in my head so that I can give a better answer in the next class that I teach.
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Permalink Reply by David Baumrind on -
James,
not too long ago, i was in your same position... i have been studying for months and months now, and it is quite an undertaking to become skilled at ECG interpretation--I still have quite far to go... I think the issue really is not so much that it is overlooked, but rather the time needed to integrate it into a curriculum is extensive. it will take much more than several "classes" to become skilled. And once you start down that path, you will realize the sheer volume of information needed to learn for a comprehensive understanding of ECG interpretation. Now, i fully believe in this process and it's value, and will continue to learn as much as i can, as long as it takes. Tom's analogy that this is akin to learning a foreign language is accurate... ask yourself, if you were going to pick up a language to learn, how much studies would be necessary to converse with someone in that language? Oh yeah, and you have 2 minutes to do it, under pressure, and the future treatment of the patient depends on it...
i believe that 12 Lead interpretation in the prehospital arena is still in it's infancy, and will be addressed much more going forward...
having said all that, I would recommend the following websites and books to start, and i'm sure Tom will add to the list..
ems12lead.com (authored by Tom... excellent site!)
ecg-experts.blogspot.com (co-authored by Tom and others)
"12 Lead ECG...The Art of Interpretation" by Garcia and Holtz
"The 12- Lead ECG In Acute Coronary Syndromes" by Tim Phalen/Barbara Aehlert
Hope these help!
-David
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Permalink Reply by Robyn richter on -
In the cardiology class I help teach, we talk about vectors and axis from the beginning. Once that groundwork is laid, it makes it easy to talk about why some of the rhythms look the way they do, particularly junctional rhythms and why P waves are inverted. As for axis, it is useful for the reasons previously mentioned. We also teach about the z axis (precordial leads) to help explain what to expect in normal R wave progression. Finally, the axis may be "normal", but if you are doing serial 12 leads and the axis is changing, that is a sign that something is going on that might not be good.
Tomas Garcia's textbook on 12 lead interpretation is a terrific tool.
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Permalink Reply by Tom Bouthillet on
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I'll second Garcia and Holtz 12 Lead ECG: The Art of Interpretation. I also own a copy of Chou's Electrocardiography in Clinical Practice for reference.
When I started the Prehospital 12-Lead ECG blog the very first thing I did was write a 6-part tutorial on axis determination.
Axis Determination - Part I
Axis Determination - Part II
Axis Determination - Part III
Axis Determination - Part IV
Axis Determination - Part V
Axis Determination - Part VI
My favorite ECG website is Dr. Smith's ECG Blog.
Tom
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Permalink Reply by Daved van Stralen on -
Dave, you have great answers here for the cardiac part and the way you asked tells me that area will be well-served by you. May I take a different angle on your question and respond to "why do I need to learn this?"
It has been my experience that some students ask this question because they are trying out their new independence and newly developed powers to reason. They want to spar with you to strengthen their reasoning abilities. These discussions can advance their powers to think for the rest of their life. I find these students keep in touch with me and I take the question as a complement.
Some are naïve to the hazards in the field and have made their judgments from the safe environment they live in. Others are naïve to where their reasoning leads. If it is an individual, I meet after the lecture but if there are too many I believe it is important enough for 15 minutes of lecture time. This can be a serious stumbling block to passing them for work in a dangerous environment.
First, I agree with them. Then I proceed to show how they can take care of a patient without knowing this material. They usually see it is more work and they never gain the feeling of safety. I may present a patient and ask what they will do to evaluate and manage. They must justify their answers without using the forbidden material. Then we discuss how we evaluate how intelligent someone is. Worldwide it is through use of language (not yours, theirs; they judge you by how you use their language). Can they use the language of healthcare fluently? If not, your students will have a more difficult time gaining respect.
For the stubborn I ask for their reason not to study the topic. Next, I ask them to list what they do believe is important. Once I have the list we can discuss what their reasons are for including things. The reasons must be consistent. Usually they are not and this uncovers a bias which we can then discuss.
The one group I have never heard of a solution for is the one who believes that they are right and will only look for evidence that confirms that. This is cognitive dissonance and seems to get worse with time.
This happens in medical school, residency, with respiratory care practitioners, nurses, and physicians.
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Permalink Reply by RICHARD PAYNE on
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i would have to write a book here to explain axis. the best book i have seen so far is Bob Page's 12 lead book. it explains that and other stuff very well. he also has a class at some ems conferences.
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