It is important to have a good structure for analysing and subsequently reporting an ECG.
When reporting an ECG, you should use the same structured approach every time. This is particularly important when first learning about ECGs. A structured approach allows you to systematically assess the ECG in order and not forget any key elements. Once you improve, you’ll start to develop pattern recognition for classic ECG features.
We propose the following structure for analysing and reporting an ECG:
This structure uses all the elements we have encountered in our previous ECG notes.
Always confirm the correct details on an ECG before attempting interpretation.
It is essential that the patients name, hospital number and date of birth appear on the ECG. This should be appear alongside the date and time of the ECG.
Often, patients will require serial ECGs to look for any dynamic changes. Therefore, it is essential to be able to tell the order in which ECGs were completed.
Rate is defined as the number of times the heart beats per minute.
The heart rate is usually automatically printed at the top of the ECG. However, get familiar with calculating the rate yourself. This is particularly important for exams on ECGs (you won’t have the handy metrics at the top!).
Rhythm refers to the part of the heart that is controlling the initiation of electrical activity.
To determine the rhythm of the heart initially look for any P waves.
If P waves are present and there is a 1:1 relationship with each QRS complex, it is sinus rhythm. If P waves are absent or do not fully correspond with each QRS complex, ask yourself further questions.
All of these questions will help you determine whether there is an ectopic beat, escape rhythm, heart block (and other bradyarrhythmias), supraventricular tachyarrhythmias or ventricular tachyarrhythmia.
The cardiac axis should be determined by analysis of the limb leads I, II & III.
Cardiac axis can normal, left axis deviated or right axis deviated. To assess this, look at the positive or negative deflections of the QRS complexes in limb leads I, II & III.
Determine the normal conduction intervals and the morphology of P waves and QRS complexes.
When assessing P waves, consider:
When assessing Q waves, consider:
When assessing the QRS complexes, consider:
Assess the ST segments in each of the leads and look for patterns.
The pattern and morphology of ST elevation or ST depression will help you determine the underlying cause.
When assessing ST changes, consider:
T waves may be flat, inverted, bifid or peaked.
When assessing T waves look for any changes in the normal T wave shape and the distribution of the T wave changes. T wave inversion may be a normal variant in some patients. New T wave changes is always pathological. Important to compare with old ECGs (if possible).
When assessing T waves, consider:
Calculation of the QT interval is required to determine the corrected QT interval.
Calculate the QT interval and then the corrected QT interval (QTc = QT / √RR.).
When assessing the QTc, consider
Report a summary of all the major findings with a conclusion as to the working diagnosis.
“This is an ECG of Miss Ellen Pages, hospital number 8972529, date of birth 12/01/1973. The ECG was taken on 06/06/2020. The heart rate is 80 beats per minute and it appears to be in sinus rhythm. The cardiac axis is normal. P waves are present with normal morphology. There are no pathological Q waves and the QRS complexes appear normal and narrow. There are no ST segment changes. There is evidence of T wave inversion in leads aVR, V1-V2 and lead III. The QT interval is 420 ms and the corrected QT interval is 430 ms.”
In conclusion, this ECG shows sinus rhythm with T wave inversion in leads aVR, V1-V2 and III, which are likely normal variants”
Here are two ECG examples putting our structured approach into practice.
NOTE: left axis deviation indicates left anterior hemiblock due to a block in the anterior fascicle of the left bundle branch
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