 Hi, welcome to Nursing School Explained and this video on EKG interpretation that focuses on sinus rhythms. If you haven't already done so, I highly recommend watching my previous videos in this EKG series called Basic Electrophysiology and then EKG Interpretation Basics where I go into explaining the different types of EKG paper and the determination of the heart rate as well as the normal intervals and rules to memorize so that you know what rules to apply when it comes to interpreting all the different dysrhythmias that there are. But for today, let's look at sinus rhythms. So remember whenever there's sinus in the terminology, that means that the impulse originates from the SA which is the Sinoatrial node. So that's pretty self-explanatory and then remember from the previous videos that the SA node has an intrinsic heart rate of 60 to 100. And as you can see in this table here, the normal sinus rhythm has a normal heart rate of 60 to 100 which would be the normal intrinsic beat of the SA node, the internal pacemaker. Now whenever we talk about measuring a patient's even just a regular pulse, we talk about a normal pulse which is usually 60 to 100 and then bradycardia when it's slower than 60 or tachycardia when it's greater than 100. And this all here applies to sinus rhythms as well. Looking at normal sinus rhythm. So the rules that we always have to apply are these four. Looking at the rate, the rhythm regularity, the P waves, are they upright and is there one for every QRS? And then the intervals knowing that the PRI needs to be 0.12 to 0.20 and the QRS complex needs to be less than 0.12 which is less than three boxes. So let's start by applying this here. So this is a six second rhythm strips. So determining the heart rate, I'm going to count the number of QRS complexes. One, two, three, four, five, six, seven. So my rate is 70 and knowing that the sinus node will initiate an impulse between 60 to 100, I know that this is a normal heart rate. And then I look at the regularity and as you can see here, these QRSs look like they're spaced out pretty equally, but you could take your EKG paper and apply it and mark it with the different QRSs and then march it out to see if it's regular or you can use your calipers to do that as I describe in my other video. Now then we look at the P-waves. So P-waves are right here in front of the QRS complex. Are they upright? Yes, all these P-waves are nice and upright. And is there one P-wave for every QRS? Well, certainly there is one P, one QRS, one P, one QRS. And I can march that out for the entire rhythm strip. So that all applies. And then my intervals knowing the normals, I now determine that my PRI is 0.16, which would be four boxes. And the easiest way to do this is to find a box where it starts at maybe a thicker line. So let's take this one right here, this second to last. So I would go right here and start counting from this box and then one, two, three, four. Because remember, it goes from the beginning of the P to the beginning of the QRS because it's the PRI interval. And so I have four boxes, which is the 0.16. So that's normal. And then the QRS needs to be less than 0.12. So then looking at here, I'm going to find again a QRS complex that maybe starts at a box that I can easily look at. So this one here I would take a look at. So it starts here at one, two, and then it kind of comes here. So it's maybe two boxes, which would be 0.08. And that is definitely less than 0.12, which is three boxes. And so that's normal. So normal sinus rhythm meets all these criteria. And this is a normal sinus rhythm that we are looking at here. Continuing on, sinus bradycardia. So now we know that bradycardia hard rate is less than 60 when the impulse comes from the sinus node. So in this case, you can already see that the QRS complexes or our beats here are much further spaced apart. I know again that this is a six second hard strip. So again, I'm counting my QRS 1234. I multiply that by 10, which gives me the hard rate of 40 beats per minute. The rhythm is pretty regular. Again, I can look at that manually or march it out with my EKG paper or my calipers. But in this case, it's regular. And then again, I look at my P waves. Are they upright? Well, certainly they look upright. Is there one for every QRS? Yes, there is one P wave in front of every QRS. And then I look again at my intervals. So in this case, I could look at maybe this first box right here. This is not a great example because you can't really see the small boxes too well. But if I start right here, I know that it doesn't go beyond the second thick line here. And knowing that the distance from one to the other thick lines here is the 0.20. And I know that my PRI needs to be less than that. I can already see that that applies. So it is five boxes. And then I look at my QRS. So the QRS, maybe let's look at this first one here as well. So it starts at the thicker line here and it goes to about only a third of the second line, so which would be probably about two boxes, which makes it less than three boxes. And so everything still applies. My rhythm is regular. The P wave is upright one for every QRS. The PRI and QRS complexes are within normal limits, but the hardware is slower. So it's less than 60. So I know that I have a sinus bradycardia, sinus because I know I have a P wave. So the impulse initiates from the SA node. Causes for sinus bradycardia can be physiological conditioning. A lot of endurance athletes will automatically have a lower heart rate at rest because they've conditioned their bodies to work much more efficiently during rest because of their vigorous cardiac conditioning. So that's very common. And then when we sleep, the heart rate also goes down because the metabolic demands go down. And then vomiting or anything that causes a vagal response. Remember the vagus nerve is in charge of the parasympathetic nervous system and that nervous system slows everything down. So when that vagus nerve is stimulated, it will stimulate the heart rate to be lower and therefore can cause sinus bradycardia. Certain medications can cause bradycardia, such as beta blockers, which is why we need to always assess the patient's heart rate before we administer these beta blockers. And anything that causes a decrease in heart rate and the decrease in cardiac output. So that pertains to preload, afterload, as well as contractility. And please look at my previous videos regarding that. Then we have inferior wall MIs. So if the inferior wall of that heart is not supplied with enough blood as happens in myocardial infarction, that means that the SA node might not get the blood supply that it needs to initiate the impulse at the normal rate and therefore their heart rate can slow down. SA node disease for the same reasons and then hypothyroidism because hypothyroidism will slow everything down, including the heart rate. Now typically interventions are not needed if the patient is asymptomatic. So if this is an endurance athlete that has a resting heart rate of 45, let's say, they don't need any interventions. They function just perfectly fine with that lower sinus bradycardia heart rate. But if the patient is asymptomatic, then treatments could include administering oxygen. So that would definitely be indicated in a patient who's suffering an MI or was suspected of suffering an MI. Atropine is a medication that a lot of times is given to bring up the heart rate, to speed up the heart rate, and IV fluids, et cetera, and anything that treats the underlying cause. So let's look at sinus tachycardia. We know tachycardia pertains to when the heart rate is greater than 100. In this case, we're looking at our rhythm strips and this is a six second rhythm strips. So I count my QRS complexes, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. Multiply that by 10, knowing the heart rate is 130, so that certainly applies. Looking at my rhythm and regularity by rule number two looks pretty regular. Again, I would march it out with my calipers or with my EKG paper method. Then I look at the P wave is the one for every QRS and is it upright while certainly looking at all the different P waves and QRS's that applies. Then again, I look at my intervals. So again, I find a one that maybe starts at a thicker line, which I'm going to pick this fourth one here. So I'm going to count the small boxes, 1, 2, 3, 4, which makes the PRI 0.16 seconds and then I'm looking at my QRS and I'm going to choose to start with this one right here because again, it starts at a thicker line and I can see it's 1, 2 boxes apart, which makes it 0.08 seconds, which certainly is less than the 0.12 and that's normal. So I know that the impulse is coming from the sinus node because all the P wave criteria are met, but it's tachycardic. So this is sinus tachycardia. Reasons for sinus tachycardia is anything that increases oxygen demand, such as fever, infection, pain and exercise. We can all relate to those. CHF can certainly make the hard work harder, therefore the heart rate goes up, anxiety or panic attacks will make the patient more worked up and therefore the heart rate will go up. Certain medications such as epinephrine, which is what it's supposed to be doing, right? It increases the adrenergic response. So think about patients who might have just got an EpiPen, for example, for an allergic reaction or receiving albuterol. Caffeine and nicotine can increase heart rate and certain illicit drugs such as cocaine and methamphetamines. And keep in mind that long-term abuse of cocaine and methamphetamines or anything that stimulates the heart into being tachycardic will eventually lead to congestive heart failure. Now interventions for sinus tachycardia treat the underlying cause. If there's fever, treat the fever, give the patients fluid, treat the infection and so forth. So there's a lot of different measures to be taken here. There's arrhythmia. So now arrhythmia should already let us know that something is irregular. So let's start with our rules. So in this case, we're going to start by counting again the QRSs, 1, 2, 3, 4, 5, times 10, make it with a heart rate of 50. And now you can already see this is pretty irregular. Now there is a gap between this QRS and this QRS. You can see that with the naked eye. But the beats look pretty normal. They all look pretty uniform. There is a P, there is a QRS, and there's a T-wave for every single one of these beats. But certainly we need to notice that it's irregular. And we can again use our calipers to march this out or use our EKG paper marching method to determine that. And then let's look at the P-waves. Are they upright? Well, yes they are. 1, 2, 3. Oh, this is not a P. This is the next P here and here and there. They're all there. There's a P-wave for every QRS. So that applies. And then we'll look at our boxes, at our intervals here. So the PRI looks like we might want to start looking at this first one here, which starts at this thicker line. So I can already see it goes from this to that next box. So I know that it's about 0.16 or 0.20, which is a normal PRI. And then I look at my QRS and I find again one that's easy to look at that starts at a thicker line. So in this case, I might choose to look at this first one again, which starts at this thicker line. And then I have one, two boxes, which makes it 0.08, so it's less than three boxes. So that's normal. So now I have theoretically a bradycardia, but when it's arrhythmia, you could really turn this a sinus brady arrhythmia. But that applies also with sinus rhythm, but it wouldn't be a normal sinus rhythm because it's not normal now that it's irregular. So sinus brady arrhythmia as evidenced by this gap here in this B. Now causes for sinus arrhythmia are usually benign. They are very common in children. So if you have small children or you're in a pediatric rotation, I encourage you to really listen to the patient's heart rate for four minutes to really see and hear actually hear that irregularity. And the heart rate increases usually with inspiration and decreases with exhalation. So just listen to the patient's heart rate and the breathing pattern at the same time, and then you can notice that. And that basically has to do with the changes in pressure in the thoracic cavity and the heart rate being a little bit irregular there. And interventions are usually not needed because the patient is usually asymptomatic and unaware that this is even happening. And then we have sinus pause, also known as sinus arrest. And that's pretty easy already determined by the terminology. So there's a pause from the sinus node, which would mean that the P wave is not there or the whole complex, the whole beat is delayed. And arrest basically means the same thing. It just means that it's a little bit longer lasting than a pause. So looking at our algorithm strip here, again, we'll count the QRSs, 1, 2, 3, 4, 5, 6, gives us a heart rate of 60. And then certainly we can see that this is irregular here already with the naked eye. We don't even have to break out the calipers of our EKG paper. Then we're looking at our P waves, their uprights. There's one for every QRS. So that applies. And then our intervals. So now let's look at that here in a little bit greater detail. So one that would be easy to look at I think would be this third one starting at the thicker line. So then I can already see that it lasts from this thick line to the next, the PRI from the P to the R. So I know that that's 0.20 seconds, which makes five little boxes. And then I look at the QRS that's easy to look at. That starts at a thicker line. So I would use probably this second to last one here. So it starts here and it goes one, two little boxes, which makes it less than 0.123 boxes. So I know now that it's sinus because the P wave is there originating in the SA node. It's certainly irregular, but it's not just an irregularity like we had previously in the sinus arrhythmia. There is certainly a pause here. So it's almost like we're missing a QRS and the P wave here, or maybe even two of those. So there's certainly something missing here. So there's a pause. So something has paused the SA node from initiating an impulse. Causes for sinus pauses and sinus arrests can be medications. Think about the juxtaposition or adenosine. Adenosine comes into play when we're talking about tripping for superoventricular tachycardia. We'll be discussing in a later video. Certainly MI, if the SA node takes an insult because of insufficient blood flow, coronary artery disease or CHF can cause sinus pauses and sinus arrests. And then always we want to treat the underlying cause of that. Here are some references. I highly recommend looking at this website here, Practical Clinical Skills. They have very good resources and practice strips for you that you can look at. And then certainly I encourage you to look at my basic videos, as well as the ones that come on atrial rhythms, AB blocks, and ventricular dysrhythmias. Thanks for watching Nursing School Explained in this video on sinus rhythms. Please subscribe, leave me a feedback, share this with your friends, and I'll see you next time. Thanks so much.