03.01 Normal Sinus Rhythm

Hey guys, in this lesson we are going to talk about a normal sinus rhythm and the steps you need to learn to be able to identify it on an EKG. So let’s get started!

If yall refer back to the lesson about the electrical A&P of the heart, you will remember that the SA node initiates that electrical impulse then travels down AV node, then the bundle of His, then the right and left bundle branches and the purkinje fibers. So in a normal sinus rhythm the impulse is initiated by the sinoatrial node, this is the proper name for the SA node. This is actually where the term sinus rhythm comes from, because the electrical conduction originates in the sinoatrial node. So when the SA node stimulates the atria to contract and the ventricles to contract at rate of 60 to 100 beats per minute the PQRST waveforms are produced on an EKG. In the next slide I am going to show you guys how to interpret this normal sinus rhythm in 6 steps, and the cool thing about these 6 steps is that it will also help you identify all abnormal rhythms!

Ok so these steps are the easiest way to interpret a heart rhythm. So the first thing you need to look at is the regularity of the rhythm, is it regular or irregular. I’ll show you how to do that on the next slide. In the second step you need to look at the heart rate, is it between 60-100 beats per minute. In the third step you need to look at the P to QRS ratio, is it one to one, do we have one P wave followed by one QRS. In the fourth step, you need to figure out the PR interval, is it between 0.12-0.20 seconds and in the fifth step you need to look at the QRS complex, is it between 0.06-0.12 seconds. After you figure out steps 1 through 5 you should be able to identify the rhythm. You would need to remember the rules for each rhythm, we have provided you with resources and cheat sheets to help you remember the rules or characteristics of each rhythm, but we will go through those in these lessons as well! But for now, let’s go to the next slide so we can do each step and identify our rhythm!

So the first thing we need to do is determine if the rhythm is regular, in order to do that you need to look at the number of boxes in between the R waves. So from this R wave to this one we have about 21 small boxes, from this R to this one we have about 20 and from this one to this one we have about 23 small boxes. So for the most part, they are within 1-2 small boxes, and that is enough to call it a regular rhythm. If I were to have 20 boxes from this R wave to this one and 32 from this R wave to this R wave, that would be irregular, but in this strip, we are regular! Another way to determine if its regular or irregular would be to get a piece of paper and make a little mark where the top of the R wave is and move it down and march it out to see if these R waves match the R waves on the paper, this is an easier and quicker way to determine if the rhythm is regular or not. So let’s move on to step two, let’s look at the heart rate, if you remember from the calculating a heart rate lesson, we can find the number of small boxes from here to here which is 20. So we divide 1500 by 20 because this is the most accurate method and we would get 75 beats per minute and that is within the normal range. In the third step we need to look at the P to QRS ratio, do we have 1 P wave followed by 1 QRS, and we do! Every P wave on this strip is followed by a QRS. So in the fourth step we would measure the PR interval, we need to measure from the beginning of the P wave to the beginning of the QRS, it’s about 4 small boxes from here to here we have four, , so if you remember each small box is 0.04 seconds. So we would multiply 4 times 0.04 and get 0.16 seconds. So our PR interval is 4 small boxes which equals 0.16 seconds, which is also within the normal range. And in our fifth step we need to measure the QRS complex, so we start at the beginning of the Q wave to the end of the S wave. So in this QRS complex it is about one and a half boxes, here and also here. So we would multiply 1.5 by 0.04 and we get 0.06. So the QRS complex is 1.5 small boxes which equals 0.06 seconds, so again we are within the normal range. So the rhythm is regular, the heart rate is regular, our PR interval is 0.16 so that is regular as well. The P to QRS ratio is one to one, and the QRS complex is normal as well, these are the characteristics of a normal sinus rhythm! As we interpret other abnormal rhythms in the other lessons, you will see how these 6 steps will help you identify all of them!



So the biggest take away from this lesson is to remember the steps to identify a rhythm. Is it regular or irregular? What is the heart rate? Is it fast or slow? Do we have one P wave followed by one QRS, is the PR interval between 0.12-0.20 seconds, and is the QRS complex between 0.06-0.12 seconds. If all these things are normal on an EKG, the rhythm is a normal sinus rhythm. Whenever any of them become abnormal we have some type of arrhythmia and it is our job as nurses to identify them quickly so we can take action and prevent complications, an example would be a patient would have a stroke in an A-fib rhythm but we will talk about that in the Afib lesson! So the main nursing intervention for a normal sinus rhythm would be to just keep monitoring the patient as long as they remain stable.


So I hope you guys are excited to start identifying rhythms, make sure you check out all of the resources attached to this lesson and our cheat sheets so you can practice. And also make sure you look at all of the other lessons in this module so you can learn how to identify all abnormal rhythms. Now, go out and be your best self today! And, as always, happy nursing!