Modified Chest Leads

[TheLocalMedic]

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.

 

[DrankTheKoolaid]

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

 

[KellyBracket]

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.

 

[Aprz]

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.

 

[NomadicMedic]

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"?

 

[Akulahawk]

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?

 

[NomadicMedic]

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

 

[KellyBracket]

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.

 

[Brandon O]

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.

 

[jwk]

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.

 

[TomB]

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.

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.

 

[KellyBracket]

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.

 

[MagicTyler]

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.

 

[Christopher]

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.

 

[Veneficus]

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.

 

[Christopher]

(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)

 

[Brandon O]

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?

 

[emtdansby]

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.

 

[TomB]

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.

 

[Jon]

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