Paramedics Course – ECG Times

ECG Times

Micro-lecture by the Australian Paramedical College


In today’s micro-lecture, Australian Paramedical College Hon. Snr. Lecturer Sam Willis talks about the ECG strip timings.

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ECG Times

Hey there. How are you doing? Today we’re going to talk about the ECG strip timings. Now, the times on an ECG strip are extremely important for a number of reasons.

Now, first and foremost, as you can see on this ECG strip, the bottom axis is represented by time. The other axis is voltage, meaning the amount of electrical energy that’s occurring, so it’s a measurement of the voltage.

Now, as you can see with the voltage, every one small square horizontally is 0.1 millivolts. And that’s clearly listed on there.

Now, generally speaking, we don’t tend to put a massive amount of time into calculating how many millivolts there are. Generally speaking, it’s either normal, small or big. Of course, that’s different when you go through the advanced ECG courses.

But what you do need to know a little bit about, are the timings. In other words, how long it takes for an electrical signal to be represented and printed onto the piece of paper.

Now, as you can see the bottom axis, the horizontal axis is time. And as you can also see here, every one small square is represented by the time of 0.04 of a second. So that’s really, really fast. And sometimes it’s quite difficult to get your head around. So it’s not an easy concept by any stretch of the imagination.

Try and understand that this line here, also called the isoelectric line, the amount of time it takes to get from one end of the line to this small box, to the other, is 0.04 of a second.

Also, try and understand that this line does represent the electrical activity inside the heart. And now what you’re doing is you’re building up a picture. So you’re taking this massively complex subject, and you’re breaking it down into its smallest pieces.

Also, notice how you’ve got these small squares here, which are the smallest building blocks of the ECG, but if you put five of them together, one, two, three, four, five, they make up this bigger square. So five down here and five up there, they make up the bigger square, five by five. Now, this is important, particularly when you’re going to be calculating heart rates.

Now, we’ve already said that it takes 0.04 of a second for the signal to get from here to here. In other words, if you’re reading a signal, if you’re trying to take a … imagine you being in a police car, and you’re seeing how fast it takes a car to go past, and it’s giving you that reading of 0.04 seconds, so it’s really fast.

Also understand that if you times it by five, so you’ve got one, two, three, four, five, you’ve 0.2 seconds, for five of them when you add them together.

Now the reason we need to know this is because as you can see here, you’ve got all these things called intervals. So of course, this PR interval from the beginning of the P to the beginning of the negative Q wave, shouldn’t be more than five small squares. And that’s called the PR interval. So it shouldn’t be more than 0.20 seconds. And therefore, five small squares is your upper limit.

So again, we’ve taken this hugely complex thing, we’ve broken it down into its smaller points. And now we can see that one small square is 0.04 of a second, remember the speed of a car passing by.

If you’re following that car still over a longer period, it should take 0.2 seconds to get across five. And if you apply those principles to the actual ECG, every single one of these things, P wave, Q, R, S, and T wave, they’ve all got their normal limits in terms of time, and they’re all listed here.

So I hope you’ve enjoyed this micro-lecture.  There’s always more to read about the ECG, which is why I find it so fascinating, and I hope you’ve enjoyed this micro lecture.


For more information about courses and becoming a Medic / Paramedic or any other professional in the pre-hospital emergency health care sector Contact the Australian Paramedical College today:

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