My EKG, Web of the Electrocardiogram Logo

How to Read and Report an Electrocardiogram

How to read an Electrocardiogram

Image courtesy of stockimages /

We do not have to insist on the importance of reading an electrocardiogram correctly. Therefore, we try to give you the tools that allow you to correctly interpret an EKG.

In this article we will focus on the steps to follow for the correct analysis of the electrocardiogram.

We must remind you that the EKG must be evaluated as a whole, where each of the electrocardiogram leads must be analyzed as a whole.

The results obtained must be analyzed with the patient's clinic, his or her history and with the results of other diagnostic tests.

How to Read an Electrocardiogram

The first step is to make sure the electrocardiogram is correctly performed.

Determine if the paper speed and amplitude values are normal. In a standard EKG, the speed is 25 mm/s and the amplitude 1 mV by 10 mm (read EKG paper).

For that, we must check the speed at which the paper moves and the amplitude values–on a standard EKG, speed is 25 mm per second and the amplitude value, 1 mV per 10 mm (read EKG paper).

Check that all 12 leads are correctly recorded and that the EKG does not have too many artifacts that make reading difficult.

If the reading is difficult or the electrocardiogram has errors, it should be repeated if possible.

Assuming the electrocardiogram is well done, we start our reading, always following the same sequence so we do not miss anything:

Heart Rate

The first step is to determine the heart rate. We must at least know if we are dealing with a tachycardia, a bradycardia or a normal heart rate. This will allow us to move on to the next step.

In the article how to calculate the heart rate we explain how to calculate it, and even provide you with a heart rate calculator to make your job easier.

Heart Rhythm

The next step is to determine if the QRS complexes are rhythmic. How to know, simple, observe if the R-R intervals (distance between two QRS) are similar. If in doubt, make sure by using a compass or a ruler.

Then you must determine whether the electrocardiogram is in sinus rhythm. To do this, you must determine whether each cardiac cycle has a P wave generated by the sinus node always followed by a QRS complex (read sinus rhythm).

If these conditions are met, we can say that the electrocardiogram is rhythmic and it has a sinus rhythm (read heart rhythm analysis).

PR Interval

The PR interval (normal between 0.12 s and 0.20 s) should be measured from the beginning of the P wave to the beginning of the QRS complex.

A prolongation of the PR interval allows the diagnosis of a first degree AV block. A short PR interval allows the diagnosis of Wolff-Parkinson-White syndrome (read PR interval).

QT Interval

The QT interval should be measured from the beginning of the QRS complex to the end of the T wave.

The QT interval varies depending on the heart rate, so its value should be corrected according to the heart rate. The corrected QT interval or QTc is normal between 350 ms and 440 ms (read QT interval).

Heart Axis

It is one of the most hardest steps in EKG analysis. A safe and quick method to know if it is normal is to determine if the QRS complex of leads I and aVF is positive (read how to calculate heart axis).

ST-Segment Abnormalities

Now it's time to look at the ST-segment. That dreaded line that warns us of the presence of ischemic heart disease.

The ST-segment is the line between the end of the QRS complex and the beginning of the T wave. It must be isoelectric, to be sure if it has a depression or an elevation it must be compared with the PR segment or, in case of doubt, with the TP segment (between the T wave of the previous beat and the P wave of the analyzed beat) (read ST segment abnormalities).

Check all Waves and Intervals:

To finish the analysis, each waves and intervals of the electrocardiogram that we have not previously evaluated must be assessed.

For example, evaluate the presence of a bundle branch block, alterations of the P wave, pathological Q waves, or alterations of the T wave (read abnormal waves and intervals).

How to Report an Electrocardiogram

By following these steps you will be able to read an EKG. But all the data obtained has to be organized to report the electrocardiogram. For example:

Electrocardiogram in sinus rhythm, with heart rate of 80 bpm. Normal PR and QT intervals, normal axis at 45º , without ST-segment abnormalities or other waves and intervals.

This is a full report. But if you want to report an EKG with more detail, you could expand on each wave, segment and interval. For example:

ECG in sinus rhythm, with heart rate of 80 bpm. Positive P wave in all leads except aVR, followed by narrow QRS complex, with normal QRS axis of 45º. Normal PR interval of 0.15 s. Normal QTc interval of 400 ms. Isoelectric ST-segment without significant abnormalities, positive T wave in all leads except aVR. No presence of pathological Q wave.

We hope we have been able to help you read an EKG. For further details on determining heart rate, click "next".

previous | next

If you Like it... Share it.