ECG of Atrial Premature Beats

00:01 So let's start with the simplest atrial arrhythmias. These are single atrial premature beats.

00:07 You can have 1-3 of these beats sometimes in a row. They originate in the atrium.

00:13 They are extra beats therefore they're called premature atrial beats and they are often preceded by an abnormally appearing P wave but sometimes you can't see the abnormally appearing P wave.

00:26 It doesn't appear in the lead or the rhythm strip you're looking at.

00:30 So here is an example of atrial premature beats. Let's look at the first complex.

00:37 We don't see the P wave there. So, let's look at the second QRS.

00:42 There's a normal T wave then you have a normal P wave in the third beat and the T wave And, oh my goodness, look at that. There's a beat that occurs much too early.

00:53 Now if you look at the T wave there, you'll note and compare it to the previous T wave, you'll notice it's different.

01:00 Why? Because there's an abnormal P wave added into that T wave.

01:05 So, compare it to the T wave of the second beat. The T wave from the second beat is a normal T wave and the T wave of the third beat is a combination of the T wave plus the abnormal P wave from the premature beat.

01:18 Now if we look at the fifth beat, that's normal.

01:21 Normal P, normal QRS, normal -- not normal T. An abnormal T cuz again, it's the combination of the T wave and the premature beat and you see the premature beat.

01:31 Each of these two premature beats are marked with a green arrow and you can see in subsequently, this rhythm continues. Normal beat, premature beat.

01:40 Normal beat, premature beat. Normal beat, premature beat.

01:42 And in each case, the T wave before the premature beat is abnormal cuz it's the combination of a normal T wave and an abnormal P wave.

01:51 And that's pointed out here. The second hump on the T wave corresponds to the P wave from the atrial premature beat and it's partially hidden or combined within the T wave.

02:02 The QRS of the atrial premature beat is slightly widened because there's a little bit of intraventricular delay caused by the abnormal arrival of the premature beat's electrical impulse.

02:15 In other words, the system hasn't totally reset itself so you can have a slightly abnormal QRS but it's still narrow but not quite as narrow as the normal beat.

02:25 And that's probably because the whole system below the AV node hasn't had the chance to totally reset itself so you get a little tiny amount of block there but still narrow QRS.