We have already covered the electrical conduction system of the heart, and this forms the foundation for analyzing the PQRST EKG wave. In order to understand a normal EKG rhythm strip, you must first understand how the heart generates electrical impulses through the muscle. So if you haven’t read that material, watched the teaching tutorial, and passed the quiz on the electrical conduction of the heart, I really recommend you do that before starting with this lesson.
When you are looking at a telemetry strip or EKG, you are seeing electrical impulses generated by your heart that are being transferred to electrodes (the sticky patches on your patient’s skin), which in turn displays that impulse on a screen for you to analyze. Before you can start analyzing heart rhythms, (atrial fibrillation, atrial flutter, ventricular tachycardia etc.) you must know the basics about the PQRST wave.
Here is what a basic PQRST EKG strip looks like:
Now let’s break each part of this strip down and talk about what each area represents. You always read the PQRST wave starting from left to right. Please take note of the study tips because these are common questions are exams.
P-wave: The first little “hump” or “bump” you see is known as the P-wave. Remember from the electrical conduction lecture, that the SA node is responsible for this.
Study tip: The P-wave represents ATRIAL DEPOLARIZATION (depolarization is a big, fancy word for CONTRACTION).
QRS Complex: The next area you see is a big spike. This spike is called the QRS complex. The bundle of His, bundle branches, and Purkinje fibers are responsible for this.
Study tip: The QRS complex represent VENTRICLE DEPOLARIZATION (contractions of the ventricles)
T-wave: After this spike, you will see a “bump” shortly after the complex. This “bump” is called the t-wave and is caused by the ventricles relaxing. The ventricles are so large that when they contract (depolarize) the form a large electrical impulse that presents the QRS complex. Therefore, (because they are so large) when they relax (repolarize) they form a small electrical impulse that presents as the t-wave.
Study tip: What area of PQRST EKG reading represents ventricle repolarization? T-wave
U-wave: This is not very common, but I wanted to show it to you and mention it. The u-wave sometimes is seen after the t-wave. This is thought to be caused by the relaxation of the Purkinje fibers.
PR Interval & ST Segment:
PR -interval: As noted on the diagram above, the PR-interval starts at atrial contraction (remember atrial contraction is represented by the P-wave) and ends at the beginning of ventricle depolarization. So in other words, it starts at the P-wave and ends at the beginning of the QRS complex.
ST segment: This segment starts at the J-point. The J-point is where you start to see an upward stroke after the S wave. The segment ends at the beginning of the T-wave. The ST-segment represents when the ventricles are relaxing, also called repolarizing.
Now test your knowledge on how well you grasp the material by taking this quiz. If you would like more explanations or are a visual learner, I suggest you check out this teaching tutorial.