Sinus Bradycardia

Hey guys, my name is Brad, and welcome to nursing.com. And in today’s video, what we’re going to be doing is we’re going to discuss sinus bradycardia. I’d like to discuss the physiology behind sinus bradycardia, as well as some signs and symptoms that you may see in a patient, how we may treat a patient with bradycardia, as well as how to identify this on an EKG strip? Let’s dive in. 

So whenever we’re taking a look at sinus bradycardia, sinus bradycardia is simply normal sinus rhythm, but with a slower heart rate. And typically what we’re looking at is a heart rate, less than 60 beats per minute. This is how we define bradycardia. Now it’s important to know that sinus bradycardia, just like normal sinus rhythm, is indeed a sinus rhythm because the impulse, the electrical impulse, actually begins in that SA node, in that sinoatrial node. So, therefore, we have a sinus rhythm, but again, the main differentiator between normal sinus rhythm and sinus bradycardia is that we have this slower heart rate. 

Now, what are some of the common causes of bradycardia? So some of the common causes of bradycardia include hypoglycemia. Hypoglycemia is actually associated with hypokalemia right, lower blood potassium levels, which results in bradycardia. Hypothyroidism is also something that can cause bradycardia, as well as hypothermia. I’d like for you to imagine that you are climbing Mount Everest and you are in an extremely cold environment. As you’re moving through an extremely cold environment, you’re going to slow down physically. Everything is going to slow down. Your metabolism is going to slow down, all of the cellular processes of your body, everything is going to slow down in an attempt to conserve energy. And as a result, one of the other things that will drop is heart rate. 

So what are some of the common assessment findings that we may see in patients experiencing bradycardia? Well, it’s important to remember that cardiac output equals stroke volume times heart rate (CO = SV X HR). Now, if that sounds a little bit fuzzy to you, make sure you check out our course on hemodynamics to bring further clarity. But, what we have here in a patient with bradycardia is we have a decreased heart rate, right? Again, remember less than 60 beats per minute. And if our heart rate is decreased, then it stands to reason, that’s going to decrease our cardiac output. If your cardiac output is decreased, the amount of blood that your left ventricle can eject per minute, then it stands to reason that’s going to cause a drop in your blood pressure. So what you’re going to see as a result, all of this, as a result of decreased heart rate, you’re going to see a drop in your blood pressure, dizziness, syncope, shortness of breath, cool and clammy skin, all a result of the bradycardia that the patient is experiencing. 

So what are some of the therapeutic managements that we may see for a patient experiencing bradycardia? Well, we could see a pharmacological option, something such as atropine, which is essentially a positive chronotrope. You may hear that terminology thrown around, but positive chronotrope basically just means it increases their heart rate. So if a patient’s bradycardic, you may see something like that you use.  You could also see something like transcutaneous pacing, which is essentially where you take a patient and you hook them up to the pads, right? The defibrillator pads that we would normally use during codes connected to the defibrillator, but instead of shocking the patient to try and correct an electrical abnormality in a code situation, for instance, instead, we’re actually going to use the defibrillator machine to pace them. We would set the defibrillator machine to a particular heart rate, something greater than 60 beats per minute, and this would actually deliver mechanical shock to the patient to mechanically increase their heart rate. Again, the overall idea of these treatment modalities is we need to increase the heart rate and, as usual with everything, is patient dependent. 

And so now we get to the point where we need to try and learn how to identify sinus bradycardia on a rhythm exam. Again, I highly encourage you, go check out how to solve a basic EKG strip here on nursing.com. If you’re not familiar with what these different types of waves are, as well as what a normal PR interval length or a normal QRS length is, for instance. 

So what are we going to see when we use the six step method to solve for sinus bradycardia? Well, we know that what we’re going to be looking at a heart rate, less than 60 beats per minute. Regularity, that R to R regularity. We will indeed see a normal R to R interval. One P for every QRS complex. Again, yes, we will see that. This is essentially normal sinus rhythm, but with a slower heart rate. Let’s remember, that’s what sinus bradycardia is. PR interval length, we will recall that the normal is 0.12 to 0.20 seconds. And that is indeed what we will see with sinus bradycardia. And then a normal QRS length is 0.06 to 0.12 seconds. And this is also what we will see in sinus bradycardia. Now let’s actually take a look at a practice, a practice exam question, and go from there. 

And so looking at sinus bradycardia, or should I say looking at an actual little strip here again, we’re going to implement this six step method to solve. Knowing that that six step is to solve. And the first thing that we’re going to do is we’re going to look at a heart rate, remembering that this here is a six second strip. So all we do is take our number of QRS complexes and multiply by 10. In this instance, we have 1, 2, 3, 4, 5 QRS complexes, times 10 equals a heart rate of 50 beats per minute (5 X 10 = 50). If we were going through an exam question that we had this, and this is the first thing on our six step method, and we see a heart rate less than 60 beats per minute, that should be queuing you off. Maybe what we’re dealing with is some kind of bradycardia. 

The second step is looking at the R to R interval. Again, you’re actually measuring the distance between each individual R wave looking to make sure that the distance is the same. And in sinus bradycardia, indeed it is.

 P to QRS ratio. Do we have one P wave for every QRS complex, P QRS, P QRS, P QRS all the way down. And indeed we do have one P wave for every QRS complex. 

Now that PR interval that we’re taking a look at, let’s go down here and we’ll take a look at this one, right? Let’s measure the number of little squares. We have 1, 2, 3, 4. Four squares of our PR interval. Remember one little individual square here is 0.04 seconds. And one larger square is 0.20 seconds. So we have 1, 2, 3, 4 little squares. 0.04 times four is going to equal 0.16 seconds (0.04 X 4 = 0.16), which is normal between 0.12 and 0.20. 

And then we’re gonna take a look at our QRS complex length in this example. We have, we’re going to count little squares. 1. 2.  Let’s try this one. 1, 2.  So 0.04 times two is 0.08 (0.04 X 2 = 0.08), which again is between 0.06 and 0.12. So we have a normal QRS complex length and using this information that we have, this six step method, while looking at the strip that we have, we know, without a doubt, that what we’re dealing with is sinus bradycardia. 

And so to summarize some of our key points surrounding sinus bradycardia, remember sinus bradycardia is essentially normal sinus rhythm, but with a slower heart rate, specifically a heart rate, less than 60 beats per minute. Recalling also, it’s a sinus rhythm because it originates in that sinoatrial node. This is going to be regular with a normal R to R interval, as well as being consistent with one P wave for every QRS complex. Our PR interval length in sinus bradycardia will indeed be normal 0.12 to 0.20 seconds. And our QRS complex lengths will also be normal in sinus bradycardia. 

Guys, I hope this video really helped you understand sinus bradycardia well. A lot of the things that we would see in the patient as well as treatment options, as well as how to identify it on an exam, as far as an EKG goes. Guys, go out there and be your best selves today. And as always, happy nursing.