March 21, 2017

How To Read An Electrocardiogram (EKG/ECG)

How To Read An Electrocardiogram (EKG/ECG)
Dawn Gray By: Dawn Gray

Regular, irregular, fast, slow, wide, narrow, stable, unstable. Does looking at a 12-lead EKG put your own heart into a lethal rhythm? Nurses are usually the first ones to read that “hot off the press” EKG tracing. How do you know when you need to act immediately or can wait for expert consultation? Here are seven tips to help you gain confidence in interpreting what you see.

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1. Assess your patient.

This must come first! There are many clues you can learn when obtaining the EKG that will help you analyze and act on what you see.

  • Is the patient’s skin warm and dry, or is it damp and clammy?
  • How is their color?
  • Are they having chest pain?
  • Can you palpate peripheral pulses?
  • Is your patient talking to you or are they struggling to catch their breath?

Put these facts together to determine stable or unstable rhythm. Looking at a sheet of paper with a tracing on it does not provide enough information. A heart rate of 38 can be normal in an athlete. But it also can require an immediate pacemaker insertion if accompanied by chest pain, shortness of breath, and an EKG interpretation of third degree heart block.


2. Know your normals.

Don’t sweat all the complex details when you are first beginning to read and interpret EKGs. A normal heart rhythm contains a P wave, a QRS, and a T wave. Knowing the normal amplitude, deflection, and duration of each component is essential to accurate rhythm and EKG interpretation.


Normal 12-Lead EKG/ECG Values

Wave/Interval Values
P Wave Amplitude: 2-3 mm high
Deflection: + in I, II, AVF, V2-V6
Duration: 0.06 - 0.12 sec
PR Interval Duration: 0.012 - 0.20 sec
QRS Complex Amplitude: 5-30 mm high
Deflection: + in I, II, III, AVL, AVF, V4-V6
Duration: 0.06 - 0.10 sec
ST Segment Duration: 0.08 - 0.12 sec
T Wave Amplitude: 0.5 mm in limb leads
Deflection: I, II, V3-V6
Duration: 0.1 - 0.25 sec
QT Interval Duration: 0.36 - 0.44 sec

Leads and Heart View

Lead Heart View
Inferior II, III, AVF
Lateral I, AVL, V5, V6
Septal V1, V2
Anterior V2, V3, V4
Anterolateral I, AVL, V3, V4, V5, V6

The twelve leads show the electrical current through the heart from different planes.  Think of each lead as a different snapshot of the heart you are trying to interpret.  

There are six limb (I, II, III, AVR, AVL, AVF) leads and six precordial (V1-V6) leads.  The limb leads look at the heart from a vertical perspective;  the V leads show a horizontal perspective.  

Keeping this in mind will help you to interpret what you are seeing and identify which areas of the heart may be “hurting” or have damage.  

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3. Use a systematic approach.

Approach your analysis to a 12 lead EKG the same way every time. 

First, determine whether your rhythm is regular or irregular; you can use calipers if you have them or use a simple piece of paper and track your P waves and QRS complexes with a pencil mark and see if they march along or have gaps. 

After determining this, next decide if your rhythm is fast or slow (more on this in the next section).  

Lastly, examine the ST segments for any elevation or depression; again, you can use a sheet of paper to help you evaluate this.  If you can tell elevation or depression without the help of paper, be prepared to act and inform the provider immediately. 

4. Determine your heart rate.

Look at the EKG to see if the rate is regular and how fast the heart is beating; both are important for rhythm interpretation. The pace at which a rhythm is conducting can help determine the stability of the rhythm.  A stable rhythm often correlates with a stable patient.  Slow or fast can be “good” or “bad” depending on the patient presentation and corresponding rhythm.  

Rate is usually determined by which electrical circuit is “conducting” the heart.  Rhythms conducted above the atria are usually above 60 and tend to be abnormal when the rate is fast (atrial flutter, atrial fibrillation, supraventricular tachycardia).  Rhythms conducted below the atria are slower and tend to be unstable when the rate is irregular (heart blocks). 

Another comment about rate: know what medications your patient is taking. Many heart medications have beta-adrenergic effects which correlate to slower heart rates (beta blockers).     

5. Identify lethal rhythms.

When evaluating lethal rhythms on a 12 lead EKG, it is important to remember the rhythm alone can be lethal as well as what the EKG is showing you in terms of heart function.  

A rhythm that does not perfuse well can lead to impending heart failure quickly if not addressed.  

Rhythms that commonly lead to negative outcomes are: 

  • Mobitz Type II
  • Third Degree Heart Block
  • Ventricular Tachycardia
  • Idioventricular Rhythms

When it comes to heart function, the view (lead) you are looking at will determine which part of the heart you are trying to interpret. This is especially important when analyzing ST segment abnormalities. The location of the infarct determines what treatment should be used to improve oxygenation to the heart to minimize damage.  

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6. Access your resources.

There are many awesome resources available for review, as well as practice EKG tracings to perfect your skills.  

The more familiar you are with different rhythms, the easier interpretation becomes.  Don’t forget your colleagues are great resources as well; let them know you are working on your 12 lead EKG interpretation skills and ask them to save interesting tracings for your review.  

A favorite EKG interpretation resource is ECG Interpretation Made Incredibly Easy, a book that is also available as a free download on

I also really like websites that let you practice rhythm strips and EKG interpretation for free like

7. Look at your patient.

Yes, this is a repeat, but it is an important repetition. Lead placement is critical to accurate interpretation.  The most stable looking rhythm can be lethal if it doesn’t match what your patient is telling you.  Trust your gut; nurses have great intuition skills—don’t be afraid to ask questions and seek more information when you feel something isn’t right. 

Carry This Card On Your Badge For Help.

We like this EKG Ruler Vertical Badge ID Card Pocket Reference Guide ECG and many of our nurse friends do, too! It includes an overview of EKGs, basic terminology, and an EKG ruler.

This section includes affiliate links. 

Jobs Requiring EKG/ECG Proficiency

EKG/ECG proficiency is required for many nursing jobs.  Telemetry, cardiac, and stepdown units all require some level of proficiency.  These jobs are also in high-demand. See 1,260 open nursing positions requiring EKG proficiency now.

Or perhaps you are ready to take the next step in your nursing career through an RN to BSN or RN to MSN program. Use our search tool to find the right program in your area.

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Dawn Gray, RN has been a nurse since 1987 and has spent the majority of her career in critical care and emergency department settings. She contributed several chapters to Fast Facts for the Triage Nurse, published in 2015 by Springer Publishing. Dawn loves facing a challenging shift and problem-solving difficult situations, and helping other nurses to improve quality outcomes in patient care.

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