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How to Read an EKG in Three Easy Steps

Taking the mystery out of EKG interpretation

Here are a few simple things you need to know before we get started:

1. ST-elevation indicates the patient has actual injury to the myocardium.


2. You have to have at least 1 mm ST-elevation in 2 consecutive leads to suggest the patient is patient is having an MI.


3. The heart is in the left chest and sits a little sideways. The very bottom of the heart or apex is pointing toward the left. The most inferior aspect of the heart is actually the right ventricle, and when you apply electrodes (leads) to a patient, one lead is placed on the patient's right arm (the actual electrode you place on the patient's right arm reads RA). The other electrodes: LA goes on the patient's left arm (usually on the left deltoid or nearby on the left upper chest), the electrode labeled LL goes on the left leg (to keep things simple, in EMS, we usually place the LL lead on the patient's lower left abdomen, it's just easier to get to this spot than to actually get to the patient's leg), the lead labeled RL, goes to the right leg (or right lower abdomen) and the chest leads (V1, V2, V3, V4, V5, V6) go on the patient's chest. V1 sits in the 4th intercostal space, just to the right of the sternum, V2 sits in the 4th intercostal space on the left edge of the sternum, etc, etc.

OK, with this understood, let's read an EKG. If you have an EKG nearby, grab it. It may be helpful as you read on.

When you pick up an EKG, you have to know by memory the different groups of leads. The Inferior leads, Anterior leads, and the Lateral leads.

The Inferior Leads (II, III, aVF). When looking at the actual EKG, the inferior leads appear in the lower left corner of the EKG paper. The Inferior leads monitor the electrical activity in the inferior or lower aspect of the heart. This happens to be the right side of the heart.

The Anterior Leads (V1, V2, V3, V4) look at the anterior aspect of the heart. When you place these leads on a person's chest, these leads are literally on the front of the patient's chest. That's why they are called the anterior leads. This is not brain surgery here. The Anterior leads monitor and look for any disturbances (ST-elevation) that may be going on in the anterior aspect of the heart. If you have ST-elevation in 2 or more of these leads, the patient is probably having an anterior wall MI. Memorize these leads.

The Lateral leads (V5, V6, I, aVL). These leads look at and monitor the electrical activity of the lateral or left side of the heart. Think about it; when you apply the chest leads (V1, V2, V3, V4, V5, V6) to the patient's chest, leads V5 and V6 are on the lateral aspect of the patient's chest. The best way to remember what leads are the lateral leads (sort of a pneumonic) is: V5 and V6 are on the lateral wall of the patient's chest (that makes them lateral leads), aVL (the L in aVL is for lateral), and lead I (a roman numeral one) looks like a lower case L. So the next time someone asks you what are the lateral leads, tell them V5, V6, aVL and I.

Commit this to memory. You have to know, by heart, so to speak, which leads are the Inferior leads, the Anterior leads and the Lateral leads.

Now that you know which leads are which, reading an EKG is a snap!

Be systematic! Follow the 3 steps below every time you pick up an EKG.

Step One: Look at lead II. Do not look at the other leads yet! What is the overall rate and rhythm in lead II. Read lead II like you'd read any other rhythm strip. Look at lead II and only lead II. What is the rate and rhythm?

Step Two: Now look at the Inferior leads (II, III, aVF) and only the Inferior leads. They appear in the left, lower hand corner of the EKG. Is there ST-elevation in these leads? Now look at the Anterior leads (V1, V2, V3, V4). Is there ST-elevation in these leads? Now look at the Lateral leads (V5, V6, aVL and I). Is there ST-elevation in these leads?

Special Note: Posterior wall MI's are fairly common yet they do not have leads dedicated just for them. If you see St-depression in the Anterior leads you are probably looking at a posterior wall MI. More about posterior wall MI's in future postings.

Step Three: The final interpretation. If you have ST-elevation (at least 1 mm in at least 2 consecutive leads) in the Inferior leads, the patient is probably having an inferior wall MI. If there is ST-elevation in the Anterior leads, they are probably having an anterior wall MI. If they have ST-elevation in the Lateral leads they are probably having a lateral wall MI.

The patient may have ST-elevation in two or more groups of leads. For example: A patient that has ST-elevation in leads: II, aVF, V5 and V6, is having an inferior-lateral wall MI. This is a common scenario. A patient with ST-elevation in leads: V2, V3, V4, V5, and aVF is having an anterior-lateral wall MI. Another common scenario. Many times, the patient is only having St-elevation in one group of leads. For example: II, III and aVF. This too is a common scenario (an inferior wall MI).

That's it! You know how to read an EKG. So the next time you see an EKG, follow the steps above: Read lead II, get the rate and rhythm, then look at the Inferior, Anterior and Lateral leads, one group at a time.

Put your blinders on. Avoid looking at all of the leads, all of the goofy scribbles that fill the page. Focus on lead II, then the Inferior leads, then the Anterior leads then the Lateral leads, one group at a time.

And don't be afraid to read it out loud. In fact, step out of the crowd and read it out loud. "We have normal sinus rhythm at a rate of 70 with ST-elevation in leads II, III and aVF. The patient is having an inferior wall MI."

When you see St-elevation, call the receiving ED ASAP! They need to mobilize their resources and be ready for you when you hit the door. Give them a heads up.

Memorize your leads if you don't already know them. You'll be able to accurately and effectively read any EKG if you follow the steps in this lesson. There are many nuances in EKG interpretation yet everything you need to know to identify an MI (STEMI) in the field is listed above.

Next time, we'll talk about: How to identify a right-sided MI and why high doses of nitroglycerin are avoided in these cases.