5 Tips To Improve Your 12-Lead ECG Reading Skills
This weeks' topic comes from one of our listeners Kris who asks about tips for reading 12-lead ECGs quickly in the field when caring for a sick patient.
As most paramedics already know, rapid 12-lead ECG interpretation is a skill that takes a long time and lots of practice to become good at. In this episode I share with the 5 Step approach I use every time I read an ECG that makes the process simpler, faster, and more accurate.
Tips Shared in This Episode
Tip #1 - Read A Lot Of 12-Leads
Tip #2 - Know What a Normal 12-Lead Looks Like
Tip #3 - Develop A System For Reading a 12-Lead and Follow it Every Time
Tip #4 - Put Your Findings Into Context
Tip #5 - Follow Up With The Cardiologist
Tip #1 - Read A Lot of 12-leads
Fact #1 about reading ECG’s - The only way to get really good at reading ECG’s is to read them often.
The more ECG's you see, whether their totally normal or not, the better you'll become at reading ECGs.
With skill comes speed!
Just like everything else we do in this job, the better you master the skill the faster you'll become.
Fact #2 about reading ECG’s - Flights is not a great place to learn ecg’s. The number of 12-leads we read is far less than what street medics or nurses in the hospital have access to. So it's up to you to seek out opportunities for looking at ECG's
One more thing...., in flights we often know what we’re looking for which tends to jade our thinking when we first pick up an ECG. If at all possible, even if you've already been told what's going on with a patient by a doc, try to look at every ECG with a fresh set of eyes.
Tip #2 - Know What a Normal ECG Looks Like
It may sound trivial, but before you can start reading abnormal 12-leads it’s essential to know what a normal 12-lead looks like and what proper lead placement looks like so you can recognize when something's out of place.
Proper lead placement
Limb Leads must be on the limbs. Doesn't matter where, just make sure their on the limbs for a true diagnostic 12-lead.
Precordial (chest) leads
PRI - 0.12-0.20
QRS - 0.04-0.12
QT/QTc - <440 (men)/<460 (women)
Proper QRS orientation
Upright except in aVR
Negative in V1-V2
Negative or Isoelectric in V3 (point of transition)
Positive in V4-6
SA node 60-80
AV node 40-60
TIP #3 - Have a systematic process for reading ECG’s, and follow it every time.
Figure out a system for evaluating each part that works for you, and use it every time regardless of the patient.
Also, understand that there’s a lot of overlap between steps when reading an ECG, and the significance of a finding in one step may vary based on findings in another step.
Also, keep in mind that the steps below are my way of reading an ECG, but by no means is the only way.
Use this process as a guide to get you started, but be willing to change it up if the flow doesn’t seem to work for you.
The best way to read an ECG is the way that works best for you.
Step 1: Skim the ECG
I like to start by giving the ECG a quick skim looking for anything overtly abnormal. I liken it to looking at the cover of a book and reading the synopsis. It helps me mentally prepare to analyze the ECG in more detail, and ensure I don’t miss something that may require immediate attention like…
Complete heart block
If you see something that’s abnormal, quickly decide
Is this life threatening - treat
Is this not life threatening - continue
Don’t know if this is life threatening?
Is the patient stable or unstable
Stable - move on and follow up
Unstable - Immediately seek consultation
Step 2: Analyze Rate, Rhythm, Width
Rate, Rhythm, and Width are best assess looking at the 10 second strip that prints below most ECG’s
Is the rate faster than 100 or slower than 60?
Is the rhythm regular or irregular?
Are the QRS complexes narrow or wide?
Most monitors will accurately determine the rate and QRS width and print it out with the ECG strip (top left corner.)
Two more ways to determine the rate is by taking the number of complexes displayed on the 10 second strip and multiplying it by 6,
or use the R-to-R method, counting the number of large blocks between R-waves.
1 small box = 0.04s
1 large box = 0.2s
There are 60 seconds in a minutes so 60seconds / 0.2s (that's the amount of time one large box represents) = 300 so if the R-R wave are 1 large box apart then the heart rate is 300.
Here's how the pattern goes
1 box | 2 boxes | 3 boxes | 4 boxes | 5 boxes | 6 boxes | 7 boxes | 8 boxes
300 150 100 70 60 50 43 38
If your ECG doesn’t print a 10 second, single lead, strip below the ECG consider looking at the basic rhythm strip.
If neither of these are available, just make sure you’re comparing complexes from the same column when evaluating whether the rhythm is regular or irregular.
Most monitors obtain the ECG over a 10 second period, capturing 4 x 2.5 second snapshots of the heart's electrical activity. Each color coded column below represents a separate 2.5 second period of time.
Put a different way, Leads I, II, and III are captured at the same time, followed by lead aVR, aFL, and aFV, followed by V1-V3, and finally V4-V6.
So if you happen to not have the 10 second rhythm strip shown at the bottom of the below ECG, just make sure when you compare complexes that your looking at complexes from the same column, otherwise you may erroneously end up thinking the rhythm is irregular.
Lastly, take a quick look at the QRS complexes. Do they appear narrow or wide?
I don’t worry about determining what the exact QRS duration is right now, I’m just trying to get a general feel for what I might see as I dig into the ECG more.
Now take a bit closer look at the ECG and begin analyzing its individual parts, but remember that everything we see on the ECG is connected to everything else in one way or aother.
Step 3: Evaluate the Intervals / Morphology
Now is when I start looking at the specific parts of the ECG, starting with the P-wave and working my way across, looking for patterns that would indicate a problem. This is where it’s important to know what a normal ECG looks like.
Are they present in a 1:1 ratio with each QRS?
Do the precede the QRS?
Do they all look the same?
Are they proper morphology
Peaked = RAE >2.5mm and peaked
M shaped = LAE
Is the PRI within normal parameters? (0.12-0.20)
Remember, the PRI will change depending on the heart rate, as will the QT.
Shortened PRI can indicate…
Accessory pathway like WPW, or an alternative supraventricular origin.
<110ms (0.04 - 0.11 or <3 small boxes)
>120ms (>.12 or 3 small boxes)
Compare this with the deflection in V1 to determine BBB
This is important to recognize early because it will alter your interpretation of axis and ST-T wave changes
Look at J-point
Is the direction of the QRS deflection normal for each lead?
Upright in all chest leads except aVR, and in V4-6
Normal in V1-V2
Normal R wave transition occurs between V3 and V4
QT is the measurement from the beginning of the Q wave to the end of the T wave and changes with heart rate. Because of this variation in QT due to heart rate, clinicians should use the QTc, or corrected QT, to assess the QT interval.
Prolonged if >440 in men / >460 in women
>500 = risk for TdP
Should be < ½ the preceding R-R
Do you see anything extra that you don’t see in most ECG’s
J-wave (Osborne Wave)
De Winter’s T-wave
Step 4: Determine Axis
There are two primary ways to determine axis.
Look at Lead I, II and III
Read the QRS or R axis printed on the strip.
Typical causes of Right Axis Deviation
Left posterior fascicular block
Normal finding in children
Typical causes of LAD
Left Anterior fascicular block
Left ventricular hypertrophy
Left bundle branch block
Typical causes of Extreme Right Axis Deviation
Step 5: Look for Blocks
Look for Left and Right BBB
Look for Hemiblocks
Left Anterior Hemiblock
Pathological Left Axis
Small Q waves with tall R waves in leads I and aVL
Small R waves with deep S waves in leads II, III, aVF
QRS narrow or wide
Small think bundle of cardiac cells
Single Blood Supply from LAD
Left Posterior Hemiblock
Right Axis Deviation
Small R waves with deep S waves in leads I and aVL
Small Q waves with tall R waves in leads II, III and aVF
QRS narrow or wide
Larger/Thicker bundle of cardiac cells
Two arteries supply blood
LPHB far less common and much more critical
A bifascicular Block is anytime there are 2 out of the 3 FASCICLES of the bundle brand network blocked.
Right BBB + left anterior hemiblock
Right BBB + left posterior hemiblock
Complete Left BBB
Patients are at risk for developing Complete Heart Block
Look for AV Blocks
Anytime you say the word "block" when reading an ECG counts towards the patients risk stratification for complete heart block and hemodynamic collapse.
Example - Right Bundle Branch Block + Left Anterior fascicular block + 1st Degree AV Block
The problem here is both the AV node has been damages plus the Purkinje Fibers have been damaged too.
Step 6: Evaluate the ST segment & T-wave
Remember, the ST segment represents the time from Ventricular Depolarization until complete Repolarization
Measured from the J-point (where the QRS “turns” towards the T-wave.
Could be infarct or not.
Think back to the previous section. Is there LBBB? The delayed depolarization of left ventricle “drags” the ST segment up.
Must use Sgarbossa criteria to assess for STEMI in the presence of LBBB
It could also be Benign Early Repolarization or Pericarditis.
If you do see ST Elevation
Are there reciprical changes?
Where do you see changes?
Are the leads contiguous?
Does the patient have ACS symptoms?
Does the pattern make sense?
Could be ischemia or maybe not.
Sometimes ST depression indicates posterior elevation, and sometimes it’s ischemia, and sometimes is may be associated with proximal LAD occlusion with De Winter's T-wave
Wellens’ Type 1
Deeply Inverted in V2-V3
Can be normal in children
Benign Early Repolarization
Flat / Rounded
Size relative to QRS
>⅔ the R-wave = abnormal
Remember, if there is a depolarization abnormality there will be a repolarization abnormality too.
Tip #4 - Ask yourself, “Does this make sense?”
Make sure that what you see on the ECG makes sense given the clinical presentation of the patient.
Tip #5 - Follow up with the Cardiologists
Follow up with the cardiologist who cared for your patient, especially if the patient goes to the cath lab.
Or even better, see if you can accompany the patient to the cath lab.
This way you can compare your diagnosis to what the Cardiologists actually finds, and you can ask where you may have been wrong in your reading the the ECG.
Other Great Resources
Here's a blog post from Dr. Grauer, ECG Guru and host of the ECG Interpretation Blog, sharing his Systematic Approach to ECG Interpretation
Here's a post by Tom Bouthillet, Paramedic, ECG Master, and Founder of EMS12Lead.com sharing his 6 Step Method for 12-Lead ECG Interpretation
Want more, here are 30 practices ECG's, with diagnosis from Jones and Barttlet
A special thanks Kris for her question this week.
If you have a question you'd like featured on the podcast, head on over to AskFlightCrit.com, or use the tool at the bottom of this post, and drop me a message.
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Fly Safe, and Live Well!