 Hi, welcome to Nursing School Explained. This is part 3 of the playlist EKG interpretation and goes over the basics of normal intervals of the EKG as well as rules to memorize. If you haven't already done so, I highly recommend watching my other videos about basic electrophysiology as well as the video on how to read the EKG paper and determine the heart rate. Here is a quick review of the EKG paper. So every bigger line up here represents three seconds. And so two of those will give us the six second strip that we usually get when we look in at a telemetry strip. Each small box over here represents 0.2 seconds, which over on the right again is this box right here. And then each smaller box out of this 0.2 is one fifth, which gives us the 0.04 seconds. And these are very important to remember because then we'll know how to measure the different intervals that we've been looking at over here. Next we'll look at normal intervals and waveforms. These are things that you will have to memorize in order to be able to interpret dysrhythmias or really any kind of EKG rhythm. First of all, we'll be looking at the isoelectric line, which is this line that all of the waves should come back to. So it starts right here, goes across and see every time the waves either come above or below the isoelectric line every time they return back to this line, which is normal. Secondly, our PR interval or PRI, the normal length of it is 0.12 to 0.2 seconds, which are three to five small boxes. So this would basically be one, two, three small boxes would be the minimum to five boxes right here. So the PRI should not be longer than five boxes right here. And the PRI represents atrial depolarization. And the shorter the PRI is, the faster the hardware typically is. Now if the PRI is abnormal, meaning less than 0.12, or more than 0.20 seconds, that means that there is some sort of a problem going on. Now if we look at our heart and the four chambers and remember the PRI looks at atrial depolarization. So here we have our SA node and then we have the AV node. And the PRI basically measures the time it takes for the impulse to travel through the atria from the SA to the AV node. Now if it's abnormal, if it's shorter, that means that we can have some ectopic irritated cardiac cell. Remember that every cardiac cell has the ability to initiate an impulse. And if it gets irritated or excitable, it can start firing. So now if we have an impulse that starts down here, an X to P that starts down here, the time it takes for that to reach the AV node is going to be less than the 1.2 seconds. So that means there's an ectopic impulse or an irritated cardiac cell that is closer to the AV than the SA node. Now if the impulse takes longer than the 0 to 0 seconds, again we have our four heart chambers here and our SA and AV node. So now if this impulse here is just slow, it's less than 0.2 seconds, that means that there is some point or some part of a conduction delay in the atria. So something happened to the conduction system here that is delaying this impulse to come through at the expected time of 0.12 to 0.20 seconds. Now the QRS complex is down here, there it is, and represents ventricular depolarization and it's supposed to be less than 0.12 or less than three boxes. In this case we can look at it one, two, three boxes, so in this case it would be 0.08 which is normal because I know it's less than the 0.12. Going back here looking at the PRI we can count that so we can count one box, two boxes that are here three, four and five boxes which I know is the 0.20 so that's normal. And the QRS complex represents ventricular depolarization like I've already mentioned and then again if it is abnormal, meaning that it's now greater than the 0.2, that means that there's some sort of a stimulus coming from the purkinje fibers just firing all over the heart and taking longer than we would expect the ventricles to discharge and that's when we'd get into ventricular dysrhythmias that can become dangerous. The next segment we'll look at is the ST segment as I discussed on the previous slide and we always have to look at the isoelectric line and the J point that we also saw on the previous picture. So here the ST segment always comes back to this isoelectric line and one box here one small box represents on the vertical axis one millimeter as you can see over here. Now if it is one millimeter above or below the isoelectric line as we can see in this example over here so the dotted line here is the isoelectric line but this ST segment is way above the isoelectric line so that is ST elevation and ST elevation means that there is either myocardial injury or infarction and you've probably heard of a STEMI meaning ST elevation myocardial infarction and that is not a good thing to happen to a patient because they are having a heart attack right there in front of you. So if you see ST elevation in a patient with complain of chest pain, shortness of breath, dizziness, it could be anything like that it's a heart attack happening right there in front of you so you need to act accordingly. Now not looking at ST elevation but the other option that we have here is ST depression so again the dotted line here is the isoelectric line now this time the ST segment is depressed it doesn't come back to the isoelectric line and ST depression usually means ischemia and ischemia usually is the precursor to infarction so if you have a patient who was admitted let's say for chest pain or coronary artery disease or angina or any of these diagnosis and now you see ST depression on their rhythm strip you want to make sure that that patient is okay because eventually the ischemia will lead to injury or infarction and then of course that can be a bad outcome for our patient. Now next we'll look at the T wave so the T wave usually goes into the same direction as the QRS complex you can see this on the first example right here so this is our T wave and the QRS is upright and in this case the T wave also goes horizontally up. Now an abnormal T wave would be a T wave that goes the opposite direction of the QRS so this would look something like this here we have the QRS and then the T wave kind of is inverted looks like that this would be our T wave and that usually also means that there's ischemia going on now there can be a peaked and a tall Q wave which would mean that it would be much higher than this one over here for example so this would be peaked and it would kind of look like this and a peaked T wave means ischemia I'm sorry means hyperkalemia so that's what we a lot of times can see in patients who are on dialysis who might have missed their treatment and now they are ill for some reason and peaked T waves think hyperkalemia danger and then again the QT interval represents the entire ventricular activity like we already discussed so here are some rules and this is very important if you memorize these rules and apply them the same way each time you look at an EK rhythm strip you will be just fine you won't have too much trouble with this EKG strip so very important over here so the first rule is we want to look at the hard rate we want to look at the number of QRS complexes in a six second period multiplied by 10 to get our 60 second or one minute hard rate I explained that in the previous video about the termination of hard rate then we want to look into the rhythm or regularity by measuring the P to P interval or R to R interval and they typically both work the same but the R wave is just a little bit easier to measure because it's higher in amplitude and therefore can be easier distinguished and you can use calipers or just the simple piece of paper and I explained that in the previous video about EKG paper and determination of hard rate now number three is the P wave so remember P wave represents atrial depolarization is the P wave upright so does it go up in amplitude is there one P wave for every QRS complex but if there's no P wave that usually means that the impulse comes from the AV node so for some reason the SA node has had some injury or has got knocked out for some reason the AV node takes over and remember the AV nodes intrinsic hard rate is only about 40 to 60 beats per minute so if we don't have a P wave we know that the atria are not involved in this in this conduction so that means that something else is going on here and again we'll look further into that when we look at the different this with me as and then number four is looking at the intervals we just discussed PRI needs to be between 0.12 and 0.2 seconds and the QRS needs to be less than one point so the QRS needs to be less than 0.12 seconds so next we'll apply this so remember number one determination of the hard rate we're going to look at the QRS complexes one two three four five six seven and this is a six second rhythm strip with the we know this by looking at the taller lines here six seconds so seven QRS is in this on a six second strip we multiply that by 10 seven by 10 our hard rate is 70 beats per minute then we look at the rhythm or regularity and you can again either do this by measuring the calipers or lining this piece of paper up here and marking the R to our interval and then just moving that paper over and seeing if that still lines up and again I explain it in the previous video then we'll look at the P wave so are the P waves upright and is there one for every QRS so let's look at this so these P waves here they are upright they go they have a positive amplitude they go up all of them we look at every single one of them on this rhythm strip great and then secondly is there one for every QRS so here we have a P and the QRS a P and the QRS a P and the QRS and so forth so all these look nice and normal so that means that yes over here we are doing well and then we're looking at the PRI and the QRS and this can sometimes be a little bit daunting depending on where we look at the boxes and remember you can also use the calipers to measure that the other option is to find a PRI and the QRS that kind of start at the box that's easy to look at so in this case let's find one so this would be the last one here I would say is an easy one to look at because you see the P wave starts right here at the sticker line so now what I can do is I can measure these boxes remember from the beginning of the P to the beginning of the R wave so now I look at the small boxes one two three four five small boxes so the PRI five small boxes is 0.20 seconds so I know that that is normal perfect and then lastly I'll look at my QRS segment and again I find a place where the QRS maybe starts at a line so I like this complex here because it helps me when I look at the box it starts right here so this middle QRS complex it starts right here and then I look at the boxes so this is like one two maybe like two boxes or one and a half boxes which would be about 0.8 seconds I know it needs to be less than 0.12 and so this is normal so my analysis of this rhythm strip by applying these four principles here is this is a normal sinus rhythm and these four things looking at hard rate, rhythm, P wave, is it upright one for every QRS and at the intervals by memorizing what they're supposed to be if I applied it every single time I won't have too much trouble with EKG interpretation. Here are some credits and references for other EKG rhythms and then please also watch the other videos in my EKG interpretation playlist about basic electrophysiology and the basics of EKG paper and determination of heart rate as well as upcoming videos about sinus rhythms, atrial rhythms, atrial ventricular blocks and ventricular dysrhythmias. I hope you enjoyed this video and it helped to clarify EKG interpretation please share subscribe leave me comments and I'll see you again soon thanks for watching Nursing School Explained.