How To Analyse an ECG Systematically

ECG rhythm analysis

What is it about ECGs that make us take one quick glance at it and want to hide it in the patient’s folder where it belongs? ECG interpretation does take practice and can sometimes be tricky, but being able to identify an ECG that is not normal doesn’t have to be tricky at all! All you need is a process that is followed each and every time in order to analyse an ECG systematically!

Step One: Know the presenting history of the patient

This is very important because everything is all about context. Patient history will give you a lot of information that you can draw from to help you analyse what is normal or abnormal for the patient.

Step Two: Analyse the rhythm using lead II

Your thought process should go something like this:

  1. Is my rate between 60 – 100 beats per minute?
  2. Is it regular?
  3. Is there a P wave and does it precede every QRS complex?
  4. Is the P wave upright and rounded?
  5. Is my PR interval less than or equal to 1 big ECG box (0.2 seconds)?
  6. Is my QRS complex less than or equal to 1/2 a big ECG box (0.1 seconds)?

If your answer to ALL of these questions is YES, then you have a normal sinus rhythm (yay)!

If your answer to ANY of these questions is NO, then you do not have a sinus rhythm and there may need to be a further investigation!

If you would like a more in-depth discussion about how to diagnose a cardiac rhythm, this article will help you out: How to Diagnose ANY Cardiac Rhythm Systematically

Step Three: Group anterior, inferior and lateral leads

It is important to look at the ECG based on the area of the heart it is focusing on. It makes sense that if there is an abnormal change in one anterior lead, for instance, some of the other anterior leads are likely to show a similar abnormal change due to proximity. Therefore, always look at one lead grouping in its entirety before moving on to the next lead grouping.

If you are unsure about which leads are which, this article will help you out: Demystifying the 12 Lead ECG!

Step Four: Analyse the rest of the waves, intervals, and segments according to lead groupings

Your thought process should go something like this:

  1. Is there a pathological Q wave?
  2. Is there ST elevation or ST depression?
  3. Is there T wave inversion?
  4. Is the QT interval more than half of the RR interval?

If your answer to ALL of these questions is NO, then your ECG is normal (yay, again)!

If your answer to ANY of these questions is YES, then you do not have a normal ECG and there may need to be a further investigation!

If you would like a more in-depth discussion about the relevance of pathological Q waves, ST elevation, ST depression and T wave inversion, this article will help you out: ST What?! Recognising Myocardial Ischaemic ECG Changes!

Step Five: Assess the QRS cardiac axis

If the cardiac axis is normal, then your ECG is normal (the biggest yay yet, because you can put away your ECG now)!

If the cardiac axis deviates away from normal, then you do not have a normal ECG and there may need to be a further investigation!

If you are unsure about how to calculate the cardiac axis, this article will help you out: Cardiac Axis Deviation

Step Six: Practice makes perfect! 

The more you practice, the quicker you’ll become at systematically analysing a 12 lead ECG. Once you train your brain to follow the same process and to recognise what is not normal, the above 5 steps won’t take you more than a minute! So next time you have an ECG in front of you, don’t turn the other way; remember these steps and give it a go! We all have to start somewhere…so why not give the ECG below a go?

normal sinus rhythm ecg

References

  • Wagner, G. S., & Strauss, D. G. (2014). Marriott’s practical electrocardiography (12th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.
  • Wesley, K. (2017). Huszar’s ECG and 12 lead interpretation (2nd ed.). Missouri: Elsevier.

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