RR Interval in ECG [Micro Lecture]

In this micro-lecture APC Hon. Snr. Lecturer Sam Willis discusses R-R interval when interpreting ECG read-outs.

In today’s micro-lecture we’re going to talk about the R-R interval.

In my previous lectures, we’ve talked about all the things you can see on here including the voltage, time, the P-wave, the QRS complex, the PR-interval, the QRS, and the J point, and the ST-segment. Now it’s time to talk about the R-R interval.

Now as you can see, R-wave is here, it’s this form. When the conduction system has moved down the track as per the last session that we had, you’ll notice that this line continuously goes up until it gets to the peak which is called the R wave.

Now, the distance between two R waves is called the R-R interval, and I’m sure there’s a pirate joke in there somewhere. Now, the R-R interval can be used for a number of reasons. The primary two reasons are to, number one, calculate heart rates and, number two, to determine if the heart rate is regular or not.

As we’ve talked about before, the heart rate should be like this. The distance and the time between each contraction should be the same, if it’s not it’s called irregular.

There’s two types of irregular heart pattern, there’s regularly irregular where even though it’s regular irregular there’s still a pattern there. Then there’s of course irregularly irregular where there’s no pattern whatsoever, there’s just absolutely no pattern.

Now, the R-R interval helps you to see that. Now of course the R-R interval is just one way to help you determine if it’s irregular.

The other way is to actually feel on the radial pulse itself. Of course, we always say treat the patient, not the machine so when you look at the pattern what you need to do is you need to get at least a 10 second strip of ECG to have a look at the number of R-R intervals.

If you’re only looking at one or two, you may not necessarily see if the heart rate is irregular or not.

Now if you’re trying to calculate the heart rate using the R-R interval, there’s a number of ways you can do it.

Now my preferred way, and you are going to need to get your phone out and take the calculator out, is to type into your calculator 300 divided by, then the amount of large squares there are in between each R-R interval. On this image, you can see that there’s one.

So when we say large square we’re talking five by five small squares, one, two, three, four, five.

Here, this is a large square so if 300 divided by one large square, two large square, three large square, and there’s also a little bit in between so probably .5. If you were to do 300 divided by 3.5 you’d quite easily get the heart rate.

Okay, so that’s a micro-lecture on the R-R interval. My name’s Sam Willis and I look forward to speaking to you again in the next session.

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