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Normal 12-Lead ECG

Sun, 08/16/2015 - 10:13 -- Dawn

This ECG is nearly completely normal.  We say "nearly" because there are VERY subtle changes which may or may not be chronic.  Unfortunately, we know nothing about this patient's history or circumstances except age, gender, and race, and the fact that she was an Emergency Department patient.  If she presented with chest pain, the ECG might be viewed completely differently than if she presented with a fever.

So, first, let's look at what is within NORMAL range.  Most of these characteristics will be readily seen by your BASIC LEVEL students.  The rate and intervals are within normal ranges.  The rhythm is normal sinus rhythm.  There is good R wave progression in the precordial leads.  That is, V1 is primarily negatively-deflected and V6 is positive, with Leads V2 through V5 gradually becoming more and more positive.  The frontal plane axis is within normal range - Leads I and II are positive.  This would be a suitable ECG to use when introducing beginning students to the 12-lead ECG.

As for what is NOT NORMAL, there are several subtle characteristics.  First, the P waves are slightly tall and have a pointed appearance.  The P wave in V1 is biphasic.  This can represent P PULMONALE, a sign of right atrial strain.  This is often seen with pulmonary disease.  One might also expect to see a shift of the frontal plane axis to the right if there is right ventricular hypertrophy as a result of increased strain on the right heart, but here we see a subtle shift to the left.  The axis is still within normal limits, but at 17 degrees, it is closer to the left than the right.

The ST segments here are not perfect.  One could argue that there is VERY slight elevation in Leads I and aVL, and the shape of the ST in V1 is coved upward.   Lead III's ST segment is flat, and the T wave is inverted.  Without clinical corelation, it is impossible to determine the importance of these changes.  It is a good discussion to have with your more advanced students.

As said, it would be MUCH easier to ascribe meaning to these changes if we knew something of the patient's chief complaint, symptoms, and history.

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Comments

Jerry W. Jones MD FACEP's picture

Dawn...

Thanks for posting ECGs that are helpful to those who are just starting to learn about ECGs. Even in my advanced classes I begin with "normal" ECGs. Throughout my residency in internal medicine, I was never up at 3 am wondering if an ECG was ABnormal... I was always trying to decide if a finding was really NORMAL instead.

Here are a few of my thoughts...

A biphasic P wave in V1 is basically the norm. Even when there is only a monophasic deflection, it's usually because the other half of the biphasic deflection is isoelectric.

In my advanced courses we always begin with a normal tracing and I have all the participants measure the R-R intervals with ECG calipers to demonstrate that there is often considerable variation in the rhythm and that there is very rarely a perfectly regular sinus rhythm (and when there is - it's only for a few moments!). This comes in handy occasionally in deciding whether a tachycardia is sinus or not.

I often find that beginners have the impression that the R waves in the precordial leads increase in size from V1 through V6 - and that should never be the case in a "normal" ECG. Typically the tallest R wave peaks at V4 or V5. Because the V6 electrode is the furthest of all the regular precordial leads from the surface of the heart, it actually diminishes in amplitude. When the R wave in V6 is the tallest across the precordium, it means that the heart has enlarged enough to extend its surface a lot closer to the V6 electrode. That alone is a very good indication of cardiac enlargement.

One other thing I would really emphasize to a newbie is that the ST segment should rise gently into the upslope of the T wave and that there should never be a perceptible angle indicating where the ST ends and the T wave begins - it should be smooth and without a discernible margin. And the T wave should always be asymmetrical - NOT symmetrical. However, when the downslope of the T wave returns to the baseline it CAN create a noticeable angle.

I hope some of these comments help those of your readers who are just beginning to read ECGs.

Thanks again...

Jerry W. Jones MD FACEP FAAEM
https://www.medicusofhouston.com

ekgpress@mac.com's picture

Thank you Dr. Jones for your insightful comments. As you emphasize — an essential step in learning to recognize the "abnormal" — is complete appreciation of what constitutes "normal". Our comments "crossed" (as I had written mine thoughts prior to seeing your comment) — but hopefully the consistency of our remarks serves to emphasize "normality" that much more. THANKS again for taking the time to contribute to the ECG Guru!

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

ekgpress@mac.com's picture
 
The question of what is a “normal” vs “abnormal” ECG can at times be a challenging one. As implied in Dawn’s comment — much more important than the label of “normal” vs “abnormal” — is clinical correlation with the case at hand. One seeks to determine whether there is or is not anything to be concerned about. Although there are subtle findings in this tracing that we can comment on — there is little of concern.
 
Systematically — I would interpret this tracing as follows: The rhythm is sinus at ~85/minute. Intervals and the axis are within normal limits. There is RAA (Right Atrial Abnormality) — as seen by the presence of a tall (≥2.5 mm), peaked and pointed P wave in one or more of the inferior leads. The reason I favor use of the term, “RAA” (Abnormality) instead of RAE (Enlargement) — is that the presence of a pointed inferior P wave does not necessarily mean there is anatomic enlargement of one or the other atria. Instead, there are other reasons for such P wave morphology, including body habitus variation and intra-atrial conduction defects. So the isolated finding of “RAA” in an otherwise asymptomatic patient without reason for having severe pulmonary disease is not something that requires investigation. If and when clarification of atrial dimensions is desired — then an Echocardiogram would be the optimal noninvasive way to assess for atrial abnormalities. (For review on ECG Diagnosis of Atrial Abnormalities — Please see my ECG Blog #75).
  • NOTE: The slight terminal negative component to the P wave in lead V1 in this tracing is not abnormal (as the P wave in V1 may normally be positive, negative, or biphasic). Sometimes the presence of terminal negativity to the P wave in lead V1 is a clue to abnormal lead placement (1 or 2 interspaces too high) — and this might be the case, given a somewhat taller-than-expected initial R wave in both leads V1 and V2. That said — none of these findings (ie, the tiny negative component to the P wave in V1; the somewhat taller-than-expected initial R waves in V1,V2) are that unusual as to warrant investigation.
Q-R-S-T Changes: There are narrow Q waves in leads I and aVL. Transition occurs normally (ie, between V2-to-V3 here) — and there are the minimal ST-T wave abnormalities that Dawn mentioned (flat ST segment in lead III; minimal J-point upward concavity ST elevation in leads I, aVL, V1,V2).
  • The Q waves in leads I and aVL are most probably normal septal Q waves. Even though the Q in aVL looks a bit deeper than is usually seen, these Q waves are narrow and do not suggest prior infarction given the absence of other supportive findings on this tracing. The slight upward concavity ST elevation in the leads mentioned is consistent with a normal repolarization variant. There are no reciprocal changes. The ST segment flattening in lead III is not abnormal as an isolated finding, especially given the predominantly negative QRS complex in this lead (See my ECG Blog #79 for full discussion on which leads may normal manifest isolated Q waves and/or T inversion).
BOTTOM LINE: My final interpretation would be sinus rhythm at 85/minute. Small septal q waves. RAA. Slight J-point ST elevation consistent with a repolarization variant. No acute changes. Suggest clinical correlation (with implication that nothing need be done for an asymptomatic, otherwise healthy adult with this ECG).
 

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

Submitted by Dawn on

I have spent my teaching career emphasizing the importance of "fluency", which comes only from being very familiar with what "normal" looks like.  I am still learning, myself, and really appreciate the well-written comments that both Dr. Jones and Dr. Grauer have contributed above.  If you are an instructor, those comments above will be a great help to you.  So many instructors immediately dive right into the "abnormal" findings on ECG because they feel it is more interesting.  Meanwhile, the students are struggling to visualize the abnormal in the context of what it should have looked like.

Beginners and experienced ECG interpreters alike - spend some time becoming familiar with all the variations of "normal".  You won't regret the time spent.

Thanks again, Drs. Grauer and Jones!

 

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