Occasionally, we like to feature a normal ECG.  It is important to start with the characteristics of the  normal ECG when learning to recognize “abnormal”.  Of course, there are many variations in ECGs considered to be normal.  Once a student recognizes the features of the normal ECG, it becomes possible to recognize “abnormal” and then learn the clinical ramifications of the abnormalities. 

This strip includes a 12-lead ECG in standard format, as well as three rhythm strips in Leads V₁, II, and V₅. All six channels are run simultaneously, so it is easy to compare one heartbeat in multiple leads. 

NORMAL FEATURES

What are the features of this ECG that make it “normal”?  It is a combination of features the ECG has, and features it does NOT have.  Normal findings include:

*  Normal sinus rhythm.  The rhythm is regular, the rate is 80 bpm, and there is a P wave before every QRS complex.  The P waves all look alike in each lead, and they are upright in the inferior leads (II, III, and aVF).

*  The intervals are within normal limits.  The PR interval is about .16 sec. (160 ms), the QRS complexes are narrow, and the QT interval is about 320 ms.

*  The ST segments are not elevated or depressed.  The T waves are upright, except in Leads III and aVR. Negative T waves are normal in these leads.  The shape of the ST segments is concave upward, “smiling”.

*  The frontal plane axis is within normal limits.  It is slightly to the left of the center of normal, making Lead I taller than Lead II.  But, when Lead II is positive, the axis is normal.

It is always good to have a number of "normal" ECGs in your collection.  This particular ECG has only three channels, lacking the fourth channel that is usually used for a rhythm strip.   Some of your students might not work in settings where they have access to four-channel ECG machines. Often, paramedics in the field and medical personnel who use "crash carts" have ECG machines with narrow paper that run three channels at once.  They will print their rhythm strips on one sheet and the 12-lead on another.  This poses a slight handicap when evaluating complex rhythms, but is adequate for most emergency ECG screenings.

This ECG has a number of features that your students should recognize as normal.  The rate and intervals are within normal ranges.  The ST segments are neither elevated or depressed.  The axis of the frontal plane leads is normal, as is the R wave progression in the chest leads.  The T waves are upright, and the P waves are uniform and upright in the inferior leads.  The rhythm is sinus.  There is no appreciable artifact.

A good understanding of what is "normal" is vital for recognizing "abnormal".

A nice, normal ECG for your collection.  It always helps to have a normal ECG for your students to compare to the abnormal examples you show them.  It pays to teach the characteristics of "normal" to your students so that they might readily recognize "abnormal".  One could argue that the voltage in this ECG is rather low, but that can be explained by body habitus.  Whether you are teaching basic rhythm interpretation, axis determination, R wave progression, or intervals, this ECG can be of help to you.  Remember, if you are teaching students who have not yet learned 12-lead interpretation, the bottom line of a four-channel ECG is usually a rhythm strip - most often Lead II.  It is easy to download this image, then crop it using any photo management program to include only the rhythm strip.  At the ECG Guru, we use Irfanview for the Instructors' Collection ECGs.