The Leads Less Traveled
Improvising in the absence of pre-hospital 12-lead EKGs
When I was a brand new medic, I was given an EKG pocket reference called The Leads Less Traveled. The book was a small, spiral bound compendium of non-traditional EKG lead placements, written by a nurse/medic and fellow Louisiana boy named Rick McCrory. Through that book, I learned a number of ways to make my old LifePak 5 stand up and do tricks in the days when pre-hospital 12-lead EKGs were still a fanciful dream for most EMS systems.
I was recently reminded of that book while polishing an old, outdated lecture I'd been asked to deliver to a state EMS conference. Apparently, there are still significant rural swaths of this country whose EMS systems do not have the ability to perform 12-lead EKGs.
So, on that note, I'd like to point out a few of the Leads Less Traveled, and some of them might even prove useful to those of you with 12-lead machines.
Modified Chest Leads are roughly analogous to the precordial leads in a traditional 12-lead EKG. To obtain them with your three- or four-lead monitor, set the monitor to display Lead III, and move the left leg electrode to mimic the placement of the precordial leads: MCL1 in the fourth ICS, right sternal border; MCL2 in the fourth ICS, left sternal border; MCL4 in the fifth ICS, mid-clavicular line; MCL6 in the fifth ICS, midaxillary line; MCL3 midway between MCL2 and MCL4; and MCL5 midway between MCL4 and MCL6.
If you're using a Medtronic/Physio Control monitor, you'll have to turn off the bandwidth filter on your monitor first. Press and hold the PRINT button for 10 seconds until "DIAG" mode appears on the screen, and what prints out will be a true, diagnostic quality tracing.
V4R, the right-sided chest lead, can reveal ST segment changes that unmask a right ventricular myocardial infarction. RVI is present in 30-50 percent of inferior wall myocardial infarctions. Many of these patients are highly dependent upon preload to maintain cardiac output, and administration of vasodilators like nitroglycerine may cause a precipitous drop in BP.
You should get a V4R tracing in any patient with suspicious ST changes in inferior leads (II, III and AVF), and obtaining one is as simple as moving your V4 (or MCL4) lead to the right 5th ICS, mid-clavicular line. If you see ST changes there, be careful with the nitro.
The three most common paramedic copouts are, "I was up against a valve," "he had a really anterior glottis," and "looks like atrial fib to me." To avoid overusing the latter of those excuses, I suggest using the S5 Lead.
S5 highlights atrial activity, thus making it a valuable tool in differentiating atrial fibrillation with RVR from atrial flutter, or even to just identify P waves that would otherwise be obscured by artifact.
To use the S5 Lead, set your monitor display for Lead I, and move the right arm electrode to the manubrium. Move the left arm electrode to the fifth ICS, right sternal border. Left leg electrode goes to the right lower costal margin. This lead configuration should emphasize any P waves that are present.
I hope you find these non-traditional lead placements useful, and remember, if ever someone suggests that you try the Modified Scrotal Lead, they're pulling your leg.
Don't tell the next guy, though. It's still a funny joke.
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