Paramedics Course – Part 4 – ECG QRS Complex

ECG Lecture Part 4 – QRS Complex

Micro Lecture by the Australian Paramedical College

In this micro-lecture APC Hon. Snr. Lecturer Sam Willis talk about QRS complex, which actually represents ventricular contraction.


[button open_new_tab=”true” color=”accent-color” hover_text_color_override=”#fff” size=”jumbo” url=”” text=”CONTACT US TO LEARN MORE OR ENROL” color_override=””]

Electrocardiogram – QRS Complex – Interpretation Lecture Part 4


In today’s micro lecture, we’re going to talk about the QRS complex.

Now, in previous micro lectures on ECG’s, we’ve talked about the axes of time and voltage. We’ve talked about the P wave, the PR interval, very briefly touched on the QRS complex, and the T wave.

Now, the QRS complex, as you know, actually represents ventricular contraction. So remember, in the atria at the top, the ventricles at the bottom. So, when you look at the ECG screen, and you see a QRS complex, if there’s a heartbeat, you can palpate a heartbeat somewhere, then you know that the patient has got ventricular contraction.

Even if they haven’t got peripheral heartbeats, haven’t got a peripheral pulse, but they’re conscious and talking, you know that there’s a heartbeat. You know that the ventricles are contracting.

And I say that because there are cardiac arrest rhythms known as pulseless electrical activity, where you feel for a pulse and there isn’t a pulse, and they’re in cardiac arrest. So, that’s just something for you to think about for future lectures.

What you notice on this QRS complex, now the first thing is the Q wave is a negative deflection. Negative meaning it goes below this line. Anything below it is negative, and anything above it is positive.

Not everybody has a Q wave, by the way. But for the purposes of this lecture, there is this thing called a Q wave.

Then this next line is an R wave, and then it comes back and then it goes deeper below the Q wave, and that’s the S wave.

Now, what you also need to remember is there’s this thing called a QRS duration. If you notice that each of these small square is 0.04 seconds in time, then you can see that it’s approximately one box in here. So, this QRS duration is actually about 0.04.

Now, that’s a pretty small duration, and it does depend on where you measure it from. But according to this duration, anything 0.08, 0.10 is okay. So, I mean, that’s absolutely fine, and you would always treat your patient and not the machine. So if your patient has this ECG and they’ve got some kind of symptoms, either it’s not caused by the heart, or there’s something else, maybe this very short QRS duration is affecting them somehow. Highly unlikely, though.

That’s the other thing. So, if it’s bigger than 0.10, in other words more than two and half small squares … because that’s 0.04, 0.08, so to get that up to 10, you’ve got a half a square. So if it’s more than two and half small squares, that’s not good. That’s actually a type of block. In other words, it’s taking the signal of the heart too long to move from one part to the next in the lower part of the ventricular system, and there’s something there blocking it.

When we look at the QRS system, not only are we looking to make sure all the components are there, we’re also looking at this QRS complex in terms of its duration. Yes, we are also looking at the voltage, in other words, the higher the voltage, the more electricity there are.

And the final thing we’re looking at is this part here called the J point. Now, the J point is something we’re going to talk about in another lecture, because it really does relate to your stemmers and your non stemmers.

Then finally, just one thing to mention is, notice how it’s nice and straight. You don’t have what we call RSRs here. It’s just a nice, straight line up and a nice, straight line down. And that’s what we’d typically call a normal QRS complex.

Okay, I hope you’ve enjoyed this micro lecture. My name’s Sam Willis (APC Hon. Snr. Lecturer) and I will talk to you again shortly.

[button open_new_tab=”true” color=”accent-color” hover_text_color_override=”#fff” size=”jumbo” url=”” text=”CONTACT US TO LEARN MORE OR ENROL” color_override=””]

ECG Interpretation Lecture Part 4 – QRS Complex

What is your career journey?

To discover how you can become a fully qualified Ambulance Paramedic or Basic/Advanced Life Support Medic, complete a personalised paramedical career development plan.