I was asked a question about using Lead III in the post below about 3rd degree Heart Block. While the strip says “III,” it is actually something called “S5,” which I neglected to label.

“S5” is done by putting the left leg (red) lead in the fifth intercostal space just to the right of the sternum and putting the left arm (black)lead just below the suprasternal notch. Then run “Lead III” on the monitor, which instead of giving you an inferior view from the left leg to the left arm now gives you a closeup of the right atrium.

I read about this lead in a great book called Taigman’s Advanced Cardiology. It is an excellent lead to let you get the clearest view possible of the p wave. I most often use it when I am trying to determine if a patient is in afib or not. I will have to look through my garage for some old strips I have, including one that shows an indistinguishable question afib rhythm that when placed in S5 then shows distinct p waves. I use this view in all heart block patients.


Several years ago before we had 12-leads, another medic taught me how to do modified 9-leads, which enabled you to closely mimic a 12-lead while still just using the old 3-lead Life Pack 10.

Just as in the S5 above, you do it by running Lead III on the monitor. In this case, you keep the left arm lead (black) on the left arm, and you then move the left leg lead (red) across the chest in each of the precordial positions. Instead of V1-V6, the leads are labeled MCL1-6. While many have heard of MCL1, I had never heard of MCL 2-6. The leads must be run at diagnostic frequency.

The day after the medic taught me this, I had a patient — a 32-year-old black male in excellent physical shape, complaining of chest pain. He was warm and dry, ambulatory with perfect vitals. 120/80. heart rate -64, Sat – 100% on room air. No medical history. His only complaint was chest pain. He said it hurt more when he moved.

I thought it was BS and had him walk to my stretcher which was just outside his front step. Fortunately I was working in the suburbs and not just right around the corner from the hospital. On the easy ride in, I decided to work him up. (He did at one point say it felt like someone was sitting on his chest).

He was in a normal sinus with normal STs. Still I gave him some aspirin and put in an IV lock. I decided then to fool around with the new leads I had been taught. I did the MCL4.

He had a massive ST elevation.

I wasn’t certain I was doing it right. At triage, I told the nurse, I had just learned how to do this and wasn’t certain I was doing it right, but this is what I got and I showed her the strip. I think he’s having an anterior MI, I said. She looked annoyed at me, but instead of the patient going to the waiting room where I believe she was planning to put him, he was assigned a room. We took him down to the room, got him onto the hospital’s bed, and then I went to write my run form.

As I walked back to the room to leave the form, the nurse came running out screaming that the patient had just coded. They shocked him, got him back, and then rushed him up to the cath lab, where he was found to have a 100% occlusion of the anterior lateral descending artery, also known as “The Widowmaker.”

I hate to think if I stuck with my original impression and he had been placed in the waiting roon, what might have happened.

After that I did modified 9-leads on all my chest pain patients. Where the Life Pack 10, which utilized Leads I, II, and III, only could view the inferior and lateral parts of the heart, using the MCL leads, you could see the anterior. Few calls have been more satisfying to me in my career than to be able to pick up an anterior MI with a Life Pack 10, using the modified chest leads.

(I made certain at the time to collect the hospital’s 12-lead and compare it to my 9-lead. In most cases, it matched up perfectly. I did have some cases, where there was a difference, but then only in MCL5 and 6.)

Of course, we then got Life Pack 12s which do full 12-leads and come with a computerized readout, which, while they can be wildly wrong (and we are cautioned not to use them), are often right and take some of the pride of accurate interpretation out of it. Is this really your interpreation or did you just read that the machine said ACUTE MI?

There are still some lessons that can be used from the old MCL leads. When pressed for time or if I just want a quick interpretation, I sometimes, run the modified leads MCL4 in the house instead of immediately doing a 12-lead.

Also, to check for a right-sided MI, instead of doing a full right-sided 12-lead, I may quickly move the left leg lead to what is called MCR4 (fourth intercostal space midclavicular on the right side) to take a quick peak to see if the right ventricle is involved. Again, these are read in Lead III on the monitor.

When I get a chance I will do the full 12-leads. If the initial test is positive, it at least tells me what is going on sooner and I can step up the pace of the call.

And as stated above I use the multi-leads for S5 to view the atrium when I want a clearer look at the p waves.

Two gurus behind these multi-leads are Mike Taigman and Bob Page, a popular lecturer on the EMS Conference circuit, who has many more great tips in his 12-lead classes. I haven’t read Page’s 12-Lead Book yet, but I have heard it is excellent.



  • Medic 61 says:

    “In this case, you keep the left arm lead (black) on the left arm, and you then move the left leg lead (black)…”Do you mean the red left leg lead? Also, do you know of anything that gives you a better look at t-waves?

  • PC says:

    Thanks, I corrected it.T waves, I don’t know of any better way of seeing them.

  • Gary says:

    We had the LP10 with 12 lead adapter. They were a pain in the butt to use, but they did give good tracings as long as you had the diagnostic mode running. If you suspect a RV Infarct, try moving V4 to the right side. You now have V4R and it’s very good at showing ST elevation on the right side. You just have to be sure to mark it as such on your print out. When we first started doing 12 leads, a lot of us were amazed at how much we had been missing and how many more STEMIs we were catching. Now, we do them almost as a routine procedure. You can also do a “6 lead” with just the four limb leads attached. Press the 12 lead button and just ignore the prompts about the chest leads. It will give you a good idea if there is something afoot that you should do a 12 lead to find.

  • Witness says:

    Holy crap, you’re like an EKG ninja or something.

  • Rogue Medic says:

    Maybe I should read the newer posts before commenting on the older ones, when I am catching up on my reading. 🙂