Tiny Tips: STEMI? Don’t forget your PAILS!

In Medical Concepts, Tiny Tips by Thomas WinterLeave a Comment

Reading ECGs is a bread and butter emergency medicine skill. At busy centres a triage nurse may hand you tens of them to glance at per shift. It can be a mindless, monotonous task, but your brain needs to know where to look.

So, when you identify legitimate ST elevation and you are concerned about a STEMI, where are those reciprocal changes found again?

Think of PAILS!

This mnemonic identifies that ST segment elevation in a group of leads most commonly creates reciprocal changes in the leads that are represented by the next letter of the mnemonic. For example, Posterior STEMI often causes ST depression in Anterior leads, and so forth.

What is the double arrow under the L for? Although the PAILS mnemonic is floating around the FOAMed world, it doesn’t make perfect sense as Lateral ST elevation more commonly causes inferior rather than septal reciprocal changes.​1​ The double arrow is something novel that I have added to remind you that L is the exception to the rule, hence the following:

Posterior – anterior reciprocal changes

Anterior – inferior reciprocal changes

Inferior – lateral reciprocal changes

Lateral <-> inferior or septal reciprocal changes

Septal – posterior reciprocal changes

This post was reviewed by Brent Thoma and copyedited by Pouria Rezapour.


  1. 1.
    Burns E. Lateral STEMI. Life in the Fast Lane. Published 2019.

Reviewing with the Staff

Over a few years of practice, ECG patterns like the ones described in STEMI\'s above become quite recognizable. However, they are not necessarily intuitive which is why I think this mnemonic is quite useful for junior learners as a way to easily remember where to look for those reciprocal changes! I recommend that enterprising medical students take this concept a step further by answering the questions: 1) Why do reciprocal changes occur where they do? Which coronary artery is likely to be involved with each of the patterns?

Dr. Brent Thoma
Assistant Professor, University of Saskatchewan, Department of Emergency Medicine

Thomas Winter

Dr. Thomas Winter is an emergency medicine resident at the University of Manitoba with an interest in simulation, trauma, and patient safety.

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