Moving beyond the 'standard' 12-lead ECG
There's more to a diagnostic ECG than just 12-leads, and there's more to a 12-lead than just ST-Elevation
Acquiring a 12-lead ECG has become the standard practice for paramedics when encountering a variety of patient presentations. Aside from the basics of assessing a rhythm strip for the purpose of rhythm identification, your 12-lead gets you into the realm of diagnostic information and actual rhythm interpretation.
In many EMS systems, 12-lead acquisition has even become a standard part of basic life support patient assessment. After all, a printed ECG simply represents a moment in time; who’s to say it won’t be different in ten minutes, or two hours? Acquiring an immediate ECG can serve as a baseline for subsequent print-outs and continued patient care.
Aside from lead-II and V1, there are 10 additional views that can give you a greater picture of the “workhorse” of the heart: the left ventricle. Recognizing lateral, inferior, septal and anterior infarction is a necessity as a paramedic.
What is often forgotten is what’s beyond the 12-lead.
Bundle Branch Blocks
Looking at V1, viewing the angle of deflection before the J-point can help you determine which bundle branch is blocked. In a wide-complex rhythm, upward deflection before the J-point indicates a right bundle branch block, while downward deflection indicates the left.
This information can be helpful because STEMI (ST-Elevation Myocardial Infarction) evaluation can be skewed in the presence of a left bundle branch block. Utilizing additional helping points, like Sgarbossa’s Criteria, can aid you in interpreting through this.
The acute or new onset of a left bundle branch block can also be an indicator of ischemic activity. In the presence of acute coronary syndrome findings, any ECG changes should be questioned.
Axis deviation and hemi-blocks are often overlooked in many ECG curriculums. Utilizing leads-I, II and III on a 12-lead print-out can quickly help you determine this. For starters, leads-I, II and III are typically positive deflecting. When one or more are noted as negative deflecting, or they’re noted as negative in certain patterns, then a hemi-block could be suspected.
Hemi-blocks, or hemi-fascicular blocks, are electrical conduction pathway abnormalities involving one of the two branches off the left bundle branch. One fascicle moves toward the anterior, while the other goes toward the posterior.
Where this is clinically relevant is the fact that anterior hemi-blocks make patients four times more likely to arrest when they also have acute coronary syndrome findings, and can also hide proximal left anterior descending (LAD) coronary artery occlusion. In terms of the posterior hemi-fascicle, ECG patterns indicating this type of blockage often come with very high mortality values with patients experiencing an AMI. It can also indicate serious occlusion problems involving two different coronary arteries .
A regular, wide-complex rhythm with a rate above 150 certainly sounds like ventricular tachycardia (VT) on the surface … but is it really VT?
Utilizing a 12-lead ECG can help you interpret the difference between true VT and another tachycardia with some sort of aberrancy, like a bundle branch block.
With your limb leads properly in place, an upright aVR could be an indicator of VT in this situation. Or, a positive deflecting V1 or negative deflecting V6 could also sway your decision toward VT. Precordial lead concordance or poor R-wave progression in the same leads can also lead you toward VT… which is something that a standard 3-lead rhythm strip can’t do.
Of course, if your tachycardic patient is unstable, then a 12-lead is about the fifth thing on your mind at the time. But, if they’re presenting in stable condition and you’re debating between different antidysrhythmic medications, then a 12-lead is exactly the tool that you’re looking for to help you out.
Most ambulances don’t have point-of-care (POC) lab assessment monitors available to detect electrolyte imbalances, but they do have a 12-lead monitor.
QRS-complex widening, peaked T-waves and a prolonged QTc-interval can all lead you into the direction of hyperkalemia, hypocalcemia and other electrolyte abnormalities.
Overdoses on medications, like tricyclic antidepressants, can have ECG changes that present in the form of a widening QRS-complex. A side effect of some sedative or tranquilizing medications can also present with a prolonged QTc-interval. Understanding each of these findings is our clinical responsibility.
If we administer a medication, then we have to know what to expect from it. If we carry an antidote, then we need to be able to pick out the signs and symptoms of the overdose. Your 12-lead ECG may hold the answers to your questions.
15- and 18-lead ECGs
While there are some advantages to obtaining a 12-lead ECG, there are also some limitations.
Since the lateral, inferior, septal and anterior portions of the heart focus primarily on the left ventricle, what about the right side?
Obtaining your 12-lead ECG and then simply moving three of your precordial leads around will allow you to look at a total of 15 different leads. Moving all six precordial leads around will increase your view from 12 to 18. Both options increase your “camera angle” to include both the right side and posterior aspect of the heart.
Many people wonder about reciprocal changes, or may consider flipping an ECG print-out over. Reciprocal changes indicate opposite side changes, and simply flipping your ECG over will create a reciprocal image. Neither of these, arguably, are diagnostic or conclusive.
Instead, move your patches around and get the real image, not just a transposed one. This little bit of extra work (and $1.50 worth of patches), will give you a comprehensive view of the patient’s heart. In fact, I would encourage you to obtain a 15- or 18-lead-ECG whenever you see ST-changes on your 12-lead print-out. After all, if you’re worried about a heart attack, wouldn’t you want to accurately rule it in out?
The 12-lead ECG is just the beginning
Moving beyond your “standard” 12-lead is more than just a best clinical practice … it’s becoming our standard of practice.
When the patient is in our care, it’s our responsibility to provide a quality assessment that focuses on comprehensive patient care. Relying on a 3-lead rhythm strip doesn’t accomplish that, and settling for a 12-lead ECG only suffices. Upgrading to a 15- or 18-lead ECG is where EMS is progressing for the future. Moving beyond what we consider a standard today will help us become more progressive moving into tomorrow.
1. Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ