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How to Read and Report an Electrocardiogram


How to read an Electrocardiogram

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Obviously, we don’t have to insist on the importance of correctly reading an Electrocardiogram (EKG or ECG). Therefore, we will try to give you tools to interpret and understand an EKG in an easier way.

In this article we will focus on the steps to follow to correctly read an Electrocardiogram.

We must remind you that a 12-Leads Electrocardiogram must be valued and analyzed as a whole.

Results must be compared to the patient clinical record, precedences and other diagnostic procedures, if needed.


How to Read an Electrocardiogram

The first thing to check for when reading an Electrocardiogram is if it is correctly performed.

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, 1mV per 10 mm (see EKG Paper), that all 12 Leads are present, and that the EKG doesn’t show too many artifacts which could make our reading difficult.

If that is not the case, the Electrocardiogram must be performed again, if possible.

Assuming the Electrocardiogram is well done, we start our reading, always following the same sequence so we don’t miss anything:

Heart Rate

Heart Rate must be determined on every Electrocardiogram, at least know if the EKG has a tachycardia, bradycardia or normal normal Heart Rate. This allows you to move to the next step.

We tell you how to calculate HR in the article Determining Heart Rate, and we even give you a Heart Rate calculator to make this task easier.

Heart Rhythm

Next thing to check is: Is the QRS complex rhythm regular or not? To know, we must see a similar distance between QRS complexes. When in doubt, use a compass or ruler.

Then we must determine whether the Electrocardiogram returns a report of Normal Sinus Rhythm. To do that, we must ascertain whether each cardiac cycle has a sinus P Wave (Read Normal Sinus Rhythm) always followed by a QRS complex.

If these two measurements meet the criteria, then we can say the EKG represents a Sinus Rhythm (Read Heart Rhythm).

PR Interval

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

Prolongation of the PR interval provides a diagnosis of First Degree AV Block. A short PR interval may be caused by a 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 heart rate, so to determine whether is normal or not it should undergo adequate rate correction. The corrected QT interval or QTc interval is normal between 350 ms and 454 ms (Read QT Interval).

Heart Axis

This is one of the hardest Electrocardiogram reading steps. We can quickly determine it is normal if leads I and aVF are positive (Read Heart Axis).

ST Segment Abnormalities

Now is the time to look at the ST segment, the scary line that warn us of coronary artery 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 find out if we are confronting a ST segment elevation/depression we must compare it to the PR segment or, when in doubt, to the TP segment, the one between the previous cycle’s T wave and the actual cycle’s P wave (Read ST Segment Abnormalities).

Check all waves and intervals:

To end our analysis we must check every ECG wave and interval not evaluated by now. For example: Bundle Branch Block, P wave or T wave abnormalities (Read Abnormal waves and intervals).


How to Report an Electrocardiogram

By following these steps you will be able to read an ECG. What remains is to organize all the data collected to report the electrocardiogram

Electrocardiogram rhythm in Sinus Rhythm, with Heart Rate 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 a thorough ECG report, you can provide more details on each wave, segment and interval:

ECG rhythm in Sinus Rhythm, with Heart Rate 80 bpm. Positive P wave in all leads except aVR, followed by narrow QRS with normal Cardiac Axis of 45º. Normal PR interval of 0.15 s. Corrected normal QT interval of 40 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 ECG. For further details on Determining Heart Rate, click Next.

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