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ECG Basics: Normal 12-Lead ECG

Dawn's picture
Wed, 08/07/2013 - 13:14 -- Dawn

Up until now, we have posted basic rhythm strips in this area of the ECG Guru for those of you who are teachers of beginning students.  Today, we offer a "normal" 12-Lead ECG for those desiring to introduce students to the 12-Lead format.  It is always best to become familiar with normal before venturing into the realm of "abnormal".  Encourage your students to find what they know to be normal, then add to their knowledge.  Examples of findings which are within normal limits are:  rate, rhythm, P wave morphology, QRS morphology, intervals, axis, R wave progression, ST segments, and T wave direction. 

While advanced practitioners can almost always find something that is not "normal", we must remember that that can be said about almost any human body.  This ECG was taken from a healthy volunteer with no medical complaints.

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Comments's picture

     The ECG presented represents a normal 12-lead ECG obtained from a healthy volunteer with no medical complaints. As per Dawn - those who teach ECG interpretation can encourage systematic assessment of the parameters of Rate - Rhythm - Intervals - Axis - Chamber Enlargement - and QRST Changes.

The point to emphasize is that ECG interpretation should always consist of 2 Steps.

  • Step 1 = Descriptive Analysis = Simply describing what one sees without any processing of information. In this tracing - there is normal sinus rhythm at ~80/minute; normal intervals (PR/QRS/QT) - at normal axis (~ +50 degrees) - No chamber enlargement - and very small lateral q waves (in leads I,aVL,V4,V5,V6); normal transition (between leads V2-to-V3) with normal ST-T waves.
  • Step 2 = Clinical Impression = Given the above Descriptive Analysis in this young healthy and asymptomatic subject - this is a normal ECG. Small septal q waves are commonly seen as a normal finding in one or more of the lateral leads.
For those interested - CLICK HERE for a pdf on brief review of the Systematic Approach to 12-Lead ECG Interpretation. 

BEYOND-the-CORE: Did you notice that there is PR segment depression? This is best seen in each of the inferior leads, where the baseline right after the P wave is lower than the baseline just before the P wave. This may also be present in leads V4,V5 - and there seems to be a slight hint of PR elevation in aVR.

  • If teaching a basic group - I would NOT even mention this PR segment depression !!!
  • If teaching more advanced providers - I would mention it, to keep them on their toes.
  • PR segment depressiondoes have a clinical use. It is a supportive finding in the ECG diagnosis of acute pericarditis. That said - this tracing provides an excellent example of how PR depression is NOT a specific finding - since on occasion it will be seen in normal subjects who do not manifest any ST elevation and who certainly do not have acute pericarditis. Given the setting of this tracing - the PR depression seen should be interpreted as a normal finding.

For more on Pericarditis - CLICK HERE.

Ken Grauer, MD   [email protected] 

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