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# EKG Interpretation, part 5: Sinus Rhythms

July 07, 2020

#### Full Transcript

In this video, we will go over the different sinus rhythms. We'll be going over normal sinus rhythm, sinus bradycardia, sinus tachycardia, as well as something called sinus arrhythmia. Here in this strip, we have normal sinus rhythm. So let's go through our different steps in interpretation. If we look at the rhythm, we can see that it is regular. So we would get our calipers out, measure from R wave to R wave and from P wave to P wave, and we can see that it's totally regular. So then we would use the small box method to calculate the heart rate. So in between these R waves, we have 25 small boxes. So if we take 1,500 divided by 25, we get 60 beats per minute. We can see that all the P waves are nice and upright and uniform in appearance. There's one P wave for each QRS complex. And if we measure our PR interval here, then we will see that it is within the range of three to five small boxes high and that the QRS complex is nice and narrow; it is under three boxes wide. So this is how we know we have normal sinus rhythm because, if you recall from our last video, the key characteristics of a normal sinus rhythm includes P waves that are upright and uniform in appearance, and there's always a P wave followed by a QRS complex. So this is normal sinus rhythm. We wish all our patients had this, for sure. Okay, we are looking at a sinus bradycardia strip. We can see that the heart rhythm is regular. If we get our calipers out and measure the distance between R waves, those would be consistent across the strip. Same thing with the distance between P waves. Those will also be consistent across the strip. Because we're dealing with a regular rhythm, we can calculate the heart rate using the small-box method. So if we count the number of small boxes between the R waves-- let's count them here. So 5, 10, 15, 20, 25, 30, 35, 40, 45 small boxes. So 1,500 divided by 45 equals approximately 33 beats per minute. So that is definitely on the slow side. If we look at the other components of this EKG strip, we can see that our P waves are nice and upright, smooth, and consistent in appearance. Our PR interval is of normal duration. Our QRS complex is nice and narrow, and we have a QRS complex for each P wave across the strip. So it is a sinus rhythm, but because the heart rate is under 60 beats per minute, it is sinus bradycardia, okay? In terms of interventions for sinus bradycardia. If the patient is asymptomatic, then often interventions are not required. However, if the patient is symptomatic, then we can treat that with medications such as atropine or with a pacemaker.

Okay, this is a sinus tachycardia strip. If we look at the rhythm, we see that it is regular. Again, we're measuring the R to R distance using our calipers, and it will be consistent across the strip, as well as our P wave to P wave distance, which will also be consistent across the strip. Because it's a regular rhythm, we can use the small-box method to calculate the heart rate. So if we count the number of small boxes between R waves-- I've got 1 here plus 10 here, so that's 11, 12, 13, so about 13 small boxes between R waves. So 1,500 divided by 13 is about 115 beats per minute, which is a little on the fast side. Other components of the strip are normal. So our P waves are nice and upright. Our PR interval is normal. Our QRS complex is nice and narrow. And we have a QRS complex for every P wave. So this is also a sinus rhythm, but because the heart rate is over 100, it is sinus tachycardia. So when a patient has sinus tachycardia, it is usually due to some underlying cause that we need to figure out. It could be something like a fever, hypotension, pain, anxiety as well as several other reasons. So, really, interventions are focused on determining the underlying cause and addressing that cause.

The strip you're looking at now is sinus arrhythmia, and it is the last of the sinus rhythms that we will cover in this video. So you can see from looking at this that the heart rhythm is irregular. So if you get your calipers out and measure the distance between the R waves, you can see that the distance between this R wave and that R wave is not the same as between these two R waves. It gets quite a bit longer. So we are dealing with an irregular rhythm. And because it's irregular, we will need to use the 6-second strip method to determine the heart rate. So this strip you're looking at is 6 seconds in duration because we have 30 big boxes. So if I count the number of QRS complexes in 6 seconds, I have 1, 2, 3, 4, 5, 6. So 6 times 10 is 60, so the heart rate is approximately 60 beats per minute.

If we look at the other components here on the EKG waveform, the P waves are nice and upright and smooth in appearance. The PR duration, PR interval looks good in terms of it being in the expected duration. Our QRS complexes are nice and narrow. We have a QRS complex for each P wave. The only thing that's different is that we have this irregularity. So this irregularity is caused when the heart rate increases slightly with inspiration and decreases slightly with expiration. So it is a very common finding in children and usually disappears with age, and it's not a cause for concern. So it is an abnormality, but it is, like I said, not a cause for concern, and no interventions are necessary.

So that wraps up our sinus rhythms, and in my next video, we will start in on atrial rhythms. Thanks so much for watching!

###### Cathy Parkes

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