# Modified Chest Leads



## TheLocalMedic (Mar 26, 2013)

So, although 12-lead is the standard of care for virtually everywhere now, I work for a company operating in a fairly rural/wilderness area that has yet to get with the program and get us anything more advanced than a simple three lead monitor.  The nearest STEMI receiving facility from my station is roughly 90 miles away, and often calls originate in remote areas that are difficult to access (even by air due to thick forests).  My unit generally runs 5-7 calls per 24 hr shift, most of which are pretty legitimate as most woodsy folks here are pretty independent and don't call for us unless it's really necessary.  

I've been getting an uptick in cardiac calls lately, several of which were later revealed to be STEMIs.  Because we lack 12-lead capabilities, I have resorted to trying out modified chest lead placements to get different views of the heart.  Two weeks ago I had a patient with pretty classic cardiac symptoms.  Leads I, II and III all looked okay-ish with a little ST depression, but MCL 1, 2, 3 and 4 showed various degrees of ST elevation.  I used this to presumptively declare a STEMI in the field, and due to extended transport time (30 mins to the tiny local ED) called for a helicopter to transport the patient to the STEMI facility in the next county.  

The local ED doc lit me up later, saying that modified leads are inconclusive at best, and that I would have done better to have grounded the guy in, at which time they could have treated him and flown him later should the need arise.  He went further to say that what I had done was a waste of resources and that if I had made base contact he would have told me not to fly the guy out.  

So, I guess my question is: has anyone out there used modified chest lead placement, and does anyone know how different these views are from a standard 12-lead?

Also, I have no idea if the guy was actually having a real STEMI or not and couldn't get an update from the receiving hospital, so I'm not sure of the ultimate outcome.


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## DrankTheKoolaid (Mar 26, 2013)

Switch your monitor to lead 3, Cycle red Lead through V1 -  V6 position and there ya have it Ghetto 12 lead and even better you can run a standard 15 lead in the same fashion and run leads v4r and v8 and v9


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## KellyBracket (Mar 27, 2013)

The problem is that your monitor/defib is not set up to appropriately display STE/STD, or other *morphologic* changes. It is reading certain frequencies of electrical input, those that give you an accurate reading of *intervals*; QRS duration, QTc, etc.. There are electrical filters designed to eliminate artifact so you can see the heart rate, QRS interval, etc., despite being in a moving vehicle with a moving patient.

When you get a true 12-lead ECG, switching from "monitor" mode to 12-lead acquisition, the machine removes those filters. This is why it's so hard to get a clean ECG! It also means you are getting an accurate view of the electrical activity, injury currents, etc.

This is a very common mistake - *you can't use the monitor mode to check for STEMI*. It's just the wrong tool, and can lead you into some bad mistakes, e.g. thinking there's no STE on the monitor leads, so there's no point in doing a full 12-lead.

(If anyone can explain the physics of this more clearly, be my guest!)

Now, you _can_ use the MCLs to check for, say, occult atrial activity, checking MCL1 for tiny p-waves. 

It's too bad you aren't given the tools to do your job, especially since you have the drive to do more. But you also have to know the limits of the tools you do have.


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## Aprz (Mar 27, 2013)

I don't know if all monitors allow this, but I've read that you can switch to diagnostic mode on Life Packs by holding the print/record button. I think if you're looking at all 12-leads in diagnostic mode, it's fine.

Like the ST elevation you saw in MCL1-4, did you look at MCL5 and MCL6 also to see if it met voltage criteria for LVH?

I think that's a problem with 12-leads in general. People only look for ST elevation. Nothing else.


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## NomadicMedic (Mar 27, 2013)

Aprz said:


> I think that's a problem with 12-leads in general. People only look for ST elevation. Nothing else.



Not all people. In my case, not most people. 

Try to avoid these generalizations. Perhaps you meant to write, "in my limited experience, I find the people I've interacted with only seem to look for ST elevation when interpreting a 12 lead"?


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## Akulahawk (Mar 27, 2013)

You would have to put the monitor in diagnostic mode, and even then it's only going to approximate the V-leads. Why? The MCL leads aren't unipolar. They use discrete positive and negative leads. On the other hand, with MCL leads, you can reposition those leads around to pick up those P waves more specifically. Lewis Lead anyone?


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## NomadicMedic (Mar 27, 2013)

Yep. The S5 lead. I learned that little trick from my preceptor in paramedic school. I haven't used it since, but nice to have in my bag o' tricks


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## KellyBracket (Mar 27, 2013)

Whenever I try to explain this crucial point about monitor versus 12-lead quality, I end up waving my hands in the air, saying stuff like "You know, frequencies..." I don't have much of an electrical background, so I copied the information from the relevant *Wikipedia article*.




> Modern ECG monitors offer multiple filters for signal processing. The most common settings are *monitor mode* and *diagnostic mode*.
> 
> In *monitor* mode, the *low-frequency filter* (also called the high-pass filter because signals above the threshold are allowed to pass) is set at either *0.5* Hz or* 1* Hz and the *high-frequency filter* (also called the low-pass filter because signals below the threshold are allowed to pass) is set at *40* Hz. This limits artifacts for routine cardiac rhythm monitoring. The high-pass filter helps reduce wandering baseline and the low-pass filter helps reduce 50- or 60-Hz power line noise (the power line network frequency differs between 50 and 60 Hz in different countries).
> 
> In *diagnostic* mode, the high-pass filter is set at *0.05* Hz, which allows accurate ST segments to be recorded. The low-pass filter is set to *40, 100*, or *150* Hz. Consequently, the monitor mode ECG display is more filtered than diagnostic mode, because its passband is narrower.



If you take a look at the bottom left corner of ECGs, it will note the filter settings. So if the settings are, for example, *1 - 40 Hz*, it's in monitor mode, and while you can't evaluate the ST segments properly, you can sure diagnose AF or Mobitz II.

Also, since *Christopher* hasn't stopped by yet, I'll plug his great explanation of lead S5 (the "Lewis lead"), found on the EMCRIT podcast *The Lewis Lead and a course in ECGs with Christopher Watford*

Edit: *Akulahawk* - great point! I have to keep that in mind.
*Aprz* - I did this in the past with the LP-10. It was tough because it cycled through the 12-leads sequentially, but it didn't label them. Also, you have to cut them out to organize them yourself. Still, it was exciting to have a "real" ECG in the rig.


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## Brandon O (Mar 27, 2013)

KellyBracket said:


> This is a very common mistake - *you can't use the monitor mode to check for STEMI*. It's just the wrong tool, and can lead you into some bad mistakes, e.g. thinking there's no STE on the monitor leads, so there's no point in doing a full 12-lead.
> 
> (If anyone can explain the physics of this more clearly, be my guest!)



It doesn't really make any sense unless you look at exactly how the filtering algorithms normalize out artifact (and even then it doesn't make much sense unless you're an engineer), but it's important to understand that the filter not only smooths out jaggies, as a result of how it does so it literally tends to cause ST elevation. It's not obvious why, but it does.

So no matter how closely you look at a monitor-mode strip, you really cannot trust your ST segments. Although as someone noted, you can usually switch to diagnostic filters without actually adding any leads, if you know what button to push.


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## jwk (Mar 27, 2013)

Corky said:


> Switch your monitor to lead 3, Cycle red Lead through V1 -  V6 position and there ya have it Ghetto 12 lead and even better you can run a standard 15 lead in the same fashion and run leads v4r and v8 and v9



This is basically how old manual EKG machines used to work.  The V-lead was a single lead and had a little suction cup on it.  After recording the limb leads, you took the suction cup electrode and stuck it to the patient's skin at the V1 location - ran 6-10 seconds of a strip, moved it to V2, and on down the line to V6.  Of course then you would actually have to interpret the 10 foot long strip you were presented with, because a single sheet with all 12 leads and computerized interpretation didn't come along for another 20 years.

It sucks to be old.


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## TomB (Mar 27, 2013)

TheLocalMedic said:


> So, although 12-lead is the standard of care for virtually everywhere now, I work for a company operating in a fairly rural/wilderness area that has yet to get with the program and get us anything more advanced than a simple three lead monitor.  The nearest STEMI receiving facility from my station is roughly 90 miles away, and often calls originate in remote areas that are difficult to access (even by air due to thick forests).  My unit generally runs 5-7 calls per 24 hr shift, most of which are pretty legitimate as most woodsy folks here are pretty independent and don't call for us unless it's really necessary.
> 
> I've been getting an uptick in cardiac calls lately, several of which were later revealed to be STEMIs.  Because we lack 12-lead capabilities, I have resorted to trying out modified chest lead placements to get different views of the heart.  Two weeks ago I had a patient with pretty classic cardiac symptoms.  Leads I, II and III all looked okay-ish with a little ST depression, but MCL 1, 2, 3 and 4 showed various degrees of ST elevation.  I used this to presumptively declare a STEMI in the field, and due to extended transport time (30 mins to the tiny local ED) called for a helicopter to transport the patient to the STEMI facility in the next county.
> 
> ...




So what it a STEMI? It sucks when you're not given the tools to do your job as well as you'd like to.


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## KellyBracket (Mar 27, 2013)

TomB said:


> So what it a STEMI? It sucks when you're not given the tools to do your job as well as you'd like to.



America's health-care "system;" the medic has the education and the motivation, and even has a helicopter available, but *not* a 12-lead capable machine. Even one of *jwk*'s hand-me-downs.


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## MagicTyler (Mar 27, 2013)

If my monitor broke, and was in the same situation, I would have called a helio as well. Chest pain of suspected cardiac origin, cannot r/o STEMI, my transport time is 30 min to non cardiac hospital... Seems like a helio was justified to me.


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## Christopher (Mar 27, 2013)

TheLocalMedic said:


> So, I guess my question is: has anyone out there used modified chest lead placement, and does anyone know how different these views are from a standard 12-lead?



If you're in monitor mode, as many have pointed out, you will not have an accurate look at the ST-segments by a long shot.

Filters on your monitor are like a sieve. They are made such that unwanted bits fall through the screen and the stuff you care about stays on top.

ST-segments are largely affected by the *High Pass* filter. The confusing part is it is the first/smaller number given. Typically 0.5 to 1 Hz. A high pass filter lets things through that are _higher_.

Change Hz to Square Inch and go back to the sieve analogy:

The bits which make up the ST-segments are like fine grains of sand. If you want to catch sand in a sieve, you've got to use a smaller screen. So, we would go down to maybe 0.05 Square Inches in the screen; or in reality go to 0.05 Hz on the high pass.

Put another way: you _sweat the small stuff when you "diagnose"_, so you need a _smaller high pass filter_.

(The only problem with this is you end up with lots of other crap, which you usually don't care about when you're "monitoring".)

Most cardiac monitors have a means of triggering Diagnostic filtering. It would help if you let us know what brand.


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## Veneficus (Mar 27, 2013)

jwk said:


> This is basically how old manual EKG machines used to work.  The V-lead was a single lead and had a little suction cup on it.  After recording the limb leads, you took the suction cup electrode and stuck it to the patient's skin at the V1 location - ran 6-10 seconds of a strip, moved it to V2, and on down the line to V6.  Of course then you would actually have to interpret the 10 foot long strip you were presented with, because a single sheet with all 12 leads and computerized interpretation didn't come along for another 20 years.
> 
> It sucks to be old.



You laugh, but the modern 12 leads here are set up with those suction cups because it is far cheaper to make the nurse clean them then it is to keep buying disposable pads.


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## Christopher (Mar 27, 2013)

KellyBracket said:


> (If anyone can explain the physics of this more clearly, be my guest!)



Well, the components that make up the ST-segment are low frequency. Components that make up the QRS-complex are high frequency. If you look at the slopes of an action potential curve when each are occurring it makes sense (maybe).

As an aside, while reviewing my filtering comments I found this amazing illustration in an article on ECG acquisition. If I had an HP 9825 in 1983 I'd be pretty stoked too!






(just kidding, I would have rolled around or something...still _in utero_ in May '83)


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## Brandon O (Mar 27, 2013)

Christopher said:


> As an aside, while reviewing my filtering comments I found this amazing illustration in an article on ECG acquisition. If I had an HP 9825 in 1983 I'd be pretty stoked too!



Is that you doing a fist pump in the illustration?


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## emtdansby (Mar 29, 2013)

Really the best thing you can do for your pt is to treat them just like you treat any chest pain/cardiac pt. I understand the need for 12-lead to make a transport decision, but knowing if it's a true STEMI or not shouldn't change your treatment. So, treat for chest pain(ASA, Nitro, Morphine and O2), transport tithe closest facility and let them take it from there.
Now, I agree that 12-lead is a must for all EMS services, especially those in rural areas. Bring this concern to your employer and medical director. Hopefully one of them will listen to reason.


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## TomB (Mar 30, 2013)

emtdansby said:


> Really the best thing you can do for your pt is to treat them just like you treat any chest pain/cardiac pt. I understand the need for 12-lead to make a transport decision, but knowing if it's a true STEMI or not shouldn't change your treatment. So, treat for chest pain(ASA, Nitro, Morphine and O2), transport tithe closest facility and let them take it from there.
> Now, I agree that 12-lead is a must for all EMS services, especially those in rural areas. Bring this concern to your employer and medical director. Hopefully one of them will listen to reason.



STEMI patients are not "just like any chest pain or cardiac patient" and that's the point. Things like triaging to the most appropriate medical facility or preactivating the cardiac cath lab are ultimately our most important interventions.


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## Jon (Mar 30, 2013)

Wow. The amount of knowledge dropped in this thread really geeks me out. Thanks, Dr. Brackett, Christopher, and Tom for explaining it so well!


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## kindofafireguy (Mar 30, 2013)

emtdansby said:


> Really the best thing you can do for your pt is to treat them just like you treat any chest pain/cardiac pt. I understand the need for 12-lead to make a transport decision, but knowing if it's a true STEMI or not shouldn't change your treatment.



Actually, it can change your course of treatment. One example I can think of would be inferior STEMI, where you can dangerously drop preload through use of vasodilators (although you should always follow your protocol).

But to think that you should treat it the same as any other is dangerous. The old adage "No call is routine" comes to mind. When you start treating things the same, you run the risk of rote treatment and missing something critical.

Just my $0.02 though.


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## Brandon O (Mar 30, 2013)

More to the point, perhaps, STEMI care epitomizes the concept that EMS's most important role is triage, transport to the appropriate destination, and mobilization of needed resources. It may or may not be terribly important whether you crack open the nitro or morphine, but if you say "it's not just chest pain, it's a STEMI," bring them to the right place promptly, and activate the cath lab fast, you may get them reperfused (thrombolysis or preferably angioplasty) hours earlier. And yes, that may save their life.

Exciting stuff? I dunno. Do you want to save lives?


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## kindofafireguy (Mar 30, 2013)

Brandon Oto said:


> More to the point, perhaps, STEMI care epitomizes the concept that EMS's most important role is triage, transport to the appropriate destination, and mobilization of needed resources. It may or may not be terribly important whether you crack open the nitro or morphine, but if you say "it's not just chest pain, it's a STEMI," bring them to the right place promptly, and activate the cath lab fast, you may get them reperfused (thrombolysis or preferably angioplasty) hours earlier. And yes, that may save their life.
> 
> Exciting stuff? I dunno. Do you want to save lives?



Actually, it's the whole premise of EMS. EMS revolves ultimately around transport of the patient to the appropriate definitive care, with appropriate being the key word.

My point was simply that the 12-lead itself could change your treatment plan, but that was more of a specific point than a general concept.

I'm agreeing with you Oto, by the way. For some strange reason my post sounds wrong when I reread it. I hate the interwebz.


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## Brandon O (Mar 30, 2013)

kindofafireguy said:


> Actually, it's the whole premise of EMS. EMS revolves ultimately around transport of the patient to the appropriate definitive care, with appropriate being the key word.
> 
> My point was simply that the 12-lead itself could change your treatment plan, but that was more of a specific point than a general concept.



Agreed all around. And it does sometimes seem like you have to demonstrate to medics how certain elements of the 12-lead can directly affect their interventions before they appreciate their importance. (Me, I think that transport IS an intervention, but not everybody is impressed by that idea...)


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## kindofafireguy (Mar 30, 2013)

I like to point out to people that ultimately, the basics of EMS are the most critical parts of the system. 

Patient assessment and triage, followed by timely and proper transport are ultimately what save patients. Doctors save patients, EMS just makes sure they get to the right ones (in theory).

We are the band-aid on life's ills, not the saviors.


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## KellyBracket (Mar 31, 2013)

kindofafireguy said:


> ... Doctors save patients, EMS just makes sure they get to the right ones (in theory).
> 
> We are the band-aid on life's ills, not the saviors.



We're _all_ band-aids, and that's only if we're good at what we do. EMT-B, ED doc, ICU doc - we're all working to "cure sometimes, to relieve often, to comfort always."


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## abckidsmom (Mar 31, 2013)

KellyBracket said:


> We're _all_ band-aids, and that's only if we're good at what we do. EMT-B, ED doc, ICU doc - we're all working to "cure sometimes, to relieve often, to comfort always."



Quoted for truth.


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## TheLocalMedic (Apr 3, 2013)

*Update*

All right, so I totally just ran into the guy that was my patient in this post.  Turns out he's a groundskeeper at one of the local retirement communities.  I asked about what happened after he was flown out, and he said he "was really having a heart attack" and says that he had a stent placed that same day.  He also says he feels great now, even though he if being forced to eat healthier.  

So it sounds like he definitely benefited from being flown.


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## emtdansby (Apr 3, 2013)

Everyone has made many good points to my previous comment. It's very true, knowing where the STEMI is located can change the course of treatment. Perhaps my statement was too simple. What I was trying to say, with the OP's current situation, all he can really do is treat "suspected" STEMI's (ie chest pain with tale tell S/Sx) with appropriate chest pain protocol. He has no way to know for certain if it's truly a STEMI, hence the "suspected". As for the transport decision, with his current situation, transporting to the closet facility would be most appropriate, there they can obtain a 12-lead and start other treatments that would be needed. Once again, I will suggest he speak to his medical director about his concerns with the lack of 12-lead capabilities in the field.


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