Copyright

Electrocardiogram (ECG): Definition & Wave Types

Electrocardiogram (ECG): Definition & Wave Types
Coming up next: Arrhythmia of the Heart: Terms, Definition & ECG Detection

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:06 Intrinsic Conduction System
  • 0:36 Electrocardiogram (ECG)
  • 1:49 P Wave
  • 2:30 QRS Wave
  • 4:00 T Wave
  • 4:46 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Do you know how problems in the heart are detected? In this lesson, you will learn how to read an electrocardiogram (ECG) and discover what is happening in the heart during the P, QRS, and T waves.

Intrinsic Conduction System

Your heart is a very unique muscle because it has the ability to create electrical impulses on its own without any outside influences. This ability is thanks to the built-in regulating system called the intrinsic conduction system. We previously learned that the electrical impulse begins at the pacemaker of your heart, which we call the SA node. Then the impulse travels through the atria to the AV node, and then down through the ventricles, causing the heart to beat in a rhythmic and predictable way.

Electrocardiogram (ECG)

When this electrical impulse passes through your heart, electrical currents are created that spread through your body and reach the surface of your skin. Now, you don't feel these impulses, but they can be picked up and graphed as an electrocardiogram or ECG, which is simply a recording of the flow of the electrical current through the heart. This is a common test used to detect problems in the heart. You've probably seen one if you've ever watched a television drama based in a hospital, because when one of your favorite characters 'flatlined,' that meant that the ECG was no longer detecting an electrical charge, and you heard that familiar flatline 'beeeeep' of the ECG monitor.

Electrodes placed on the chest read the electrical currents produced by the heart
how ECG is performed

An ECG is performed by placing electrodes on the skin overlying the heart. As the electrical impulse moves from the atria, which are the top two chambers, to the ventricles down below, the voltage measurement between the electrodes varies, and this produces a graph of how your heart is performing. This provides the person running the test with valuable information based on the intensity of the heart's contractions and the time intervals between those contractions.

P Wave

In a normal ECG, there's three distinct waves. Together these waves represent one heartbeat. Looked at separately, the waves tell us what's happening in the heart at a certain time. The first wave is called the P wave. You can see from this picture that it's a relatively small wave. It represents the depolarization of the atria. What does that mean? Well, we remember that depolarization is defined as the change in the cell's membrane potential to a more positive state. It's this change that generates the electrical impulse that starts the heart's contraction. So we can associate the P wave of an ECG with the contraction of the atria.

QRS Wave

If we move along the graph of the ECG, we see a small dip followed by a large spike and another dip. This series is usually considered together, and it's called the QRS wave. You'll notice that this puts the waves in alphabetical order. The QRS wave is sometimes called the QRS complex, and it represents the depolarization of the ventricles. This quickly leads to the contraction of the ventricles and ejection of blood out of the heart and into the large arteries exiting the heart.

The QRS Wave is the largest spike on the ECG graph and is associated with ventricle contraction
QRS Wave

So if we think about this further, because the QRS wave is associated with the contraction of the ventricles, then we see that it's also associated with the beginning of systole, because systole is the phase of the cardiac cycle where the ventricles contract. We remember that the contraction of the ventricles causes the AV valves to close, and this causes the first heart sound, 'lub.' So the first heart sound is also associated with the QRS wave.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support