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ECG Interpretation Made Easy - How to Read ECG

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Are you ready to get started learning about ECG’s and interpreting the electrocardiogram? If so, then you’re in luck, because that is what this EKG study guide is all about.

As a Respiratory Therapist, depending on where you work, you will most likely have to perform EKG’s on the job. That is why it’s important for you to learn the ins and outs of electrocardiograms, the procedure, and how to interpret the results. 

The good news it — this study guide can help you do just that. Also note: this information correlates well well Egan’s Chapter 17 on Interpreting the Electrocardiogram, so you can use it to prepare for your exams. Are you ready to get started?

ECG Interpretation

What is an EKG Test?

An electrocardiogram is a noninvasive test that is used to measure the underlying heart conditions of a patient by measuring the electrical activity of the heart.

It is often abbreviated as either an EKG or an ECG. These two abbreviations can be used interchangeably.

How is an EKG Measured?

EKG’s are measured with a device called an Oscilloscope. It is a monitor that provides a continuous visual image of heart activity and generally only displays a single Lead (normally Lead II).

They can also be measured with a Holter Monitor, which is a portable version of the electrocardiograph that is used to detect cardiac arrhythmias. It is worn underneath the clothes, usually for a 24-48 hour period.

It is mainly used to detect ECG abnormalities that may occur over an extended period
of time.

Electrophysiology of the Heart

  1. The SA Node, also called the pacemaker, generates an electrical impulse.
  2. The wave of depolarization goes through the atria which causes a contraction. (P wave)
  3. The impulse is received by the AV node and then there is a short delay. (P-R interval)
  4. Then, the stimulus moves through the bundle of His, then the left and right bundle branches, then to the purkinje fibers. This produces ventricular depolarization and contraction occurs. (QRS complex)
  5. Then there is a short delay (S-T segment) and then the heart repolarizes (T wave).

What is the EKG Axis?

The EKG Axis measures the net direction of the electrical activity through the heart during a contraction.

Just remember, the impulse moves down and to the left. (Starts in the SA node/right atrium and moves towards the left ventricle.

A myocardial infarction (heart attack) most often occurs in the left ventricle. This would cause the axis to shift to the right because the electrical activity decreases on the left, RAD or right axis deviation.

EKG Leads and Electrodes


These are placed on the skin on the arms and legs (limb leads) and chest (precordial leads) to conduct a readable electric current.


They display the movement of electricity from one electrode to another.

Chest Electrodes

The 6 chest electrodes allow for a 3D projection of the heart. They are as follows:

  • V1 – 4th intercostal space on the right side of the sternum
  • V2 – 4th intercostal space on the left side of the sternum
  • V3 – Between V2 and V4 on the left side
  • V4 – 5th intercostal space on the left mid-clavicular line
  • V5 – Between V4 and V6 on the left side
  • V6 – 5th intercostal space on the mid-axillary line

Final Thoughts

So there you have it! That wraps up our study guide on EKG’s and interpreting the electrocardiogram. I truly hope that this information was helpful for you and I hope you can use it to ace your exams in RT school. Not only that — I hope the information sticks with you throughout your career as a Respiratory Therapist.

Thank you so much for reading and as always, breathe easy my friend. 

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