 Welcome to EM Ottawa whiteboard video. In this segment, we will discuss the various types of tachycardia and how to interpret these rhythms. Tachycardia is defined as heart rate greater than 100 per minute. On a regular, paced rhythm strip, it means that the QRS complexes would be closer together than three large squares. There are a few classifications to define the types of tachycardia. One, whether the QRS is narrow or wide. Two, whether the rhythm is regular or irregular. And three, whether there are p waves. First, we will look at how to determine whether the QRS is narrow or wide. A narrow QRS is a QRS complex that means from the beginning of Q to the end of S that are narrower than 0.1 seconds or two and a half small boxes. Therefore, you can see in the top rhythm strip that a QRS is narrow. Where else in the bottom rhythm strip, you can see that there is a wide QRS because the QRS complexes are wider than 0.1 seconds or two and a half boxes. Next, regular versus irregular. This refers to whether there is a fixed distance between the QRS complexes. Most of the time, it is pretty obvious whether the rhythm is irregular or regular. However, when the heart rate is quite high, sometimes the irregularity is subtle and it might be best done by mapping out the individual QRS complexes by a piece of paper. If you look at the 12-lead ECG shown on this slide, at first glance it might look like the rhythm is regular. However, if you map out the individual QRS complexes, you can see that this is not a regular rhythm. Third, are there P-waves? P-waves, as you know, denote sinus activity. Any sinus rhythm should have P-waves. Sometimes, if the rhythm is very fast, they are hard to see. Most of the time, you should be able to see P-waves in front of the QRS complexes, as shown on this rhythm strip. Now, we will discuss the various tachycardic rhythms with the above classifications in mind. These would be narrow or wide QRS complexes, whether the rhythm is regular or not, and whether there are P-waves. The first one is sinus tachycardia. Sinus tachycardia usually has a rate from 100 to 140. Since the impulse really comes from a fast-acting sinus node, it will be narrow, it should be regular, and you should also see P-waves. Next is atrial fibrillation. In atrial fibrillation, the impulses do not come from the sinus node. Rather, it comes from different foci in the atrium. Therefore, there should be no P-waves. And depending on the conduction of these foci down the AV node, atrial fibrillation is irregular. It is still narrow because it is above the AV node. Atrial flutter is quite similar to atrial fibrillation. The only difference is that in atrial flutter, the impulses are generated from the atrium at a fixed rate of 300. As the same as atrial fibrillation, because the impulses do not generate from the SA node, there will be no P-waves. These 300-minute impulses are going to try to transmit through the AV node. Again, because it is higher than the AV node, the QRS is narrow. The AV node usually is unable to transmit 300 per minute. And therefore, it may block every second impulse and only transmit 150 a minute. Or it may block every second and third impulse and only transmit at 100 a minute. You can see on this rhythm strip, the baseline has this wavering sawtooth pattern in here. And each sawtooth wave means one impulse trying to be generated from the atrium. Every QRS complex is only possible if the AV node lets that impulse through. And therefore, if the block is consistent at a certain ratio, whether it's every second or every third beat that comes through, that might be regular. However, in this rhythm strip, you can see that there are various different ratio of blocks that the AV node does in here. So for example, in the beginning of the rhythm strip, you can see that the QRS only happens every third of the sawtooth wave. And then here, on this speed, the AV node only let every fourth beat comes through. And therefore, it could also be irregular if there are multiple levels of block in atrial flutter. In superventricular tachycardia or SVT, the impulses are generated above the AV node. And as you can guess, it should be narrow. We usually refer SVT to a type of reentry tachycardia. There are different kinds of reentry circuits that produce this kind of tachycardia. One often seeing one is a reentry tachycardia that involves the AV node. In AVNOTO reentry tachycardia, a reentry circuit has formed within the AV node. Every time the reentry circuit goes around the AV node, it stimulates it. And as the circuit keeps going around in circles, up in here, impulses are being transmitted down. And that's what's called a reentry tachycardia, which manifests itself as an SVT. On a rhythm strip, an SVT will be narrow and regular. In certain forms of reentry tachycardia, you might be able to see P waves. However, because the heart rate is often so high, about 160 to 180, they're fairly hard to see. Next, we will talk about wide complex tachycardia. These are rhythms generated from the ventricles. The first one is ventricular tachycardia or VTAC. This rhythm is a tachycardia that comes from the ventricles. Since it comes from the ventricles, the cures complexes are wide. They will be regular. And since it does not come from the SA node, there will be no P waves. Ventricular fibrillation is the next rhythm that's generated from the ventricles. The difference between this and the last rhythm we looked at is that even though the ventricles are generating a rhythm, it is a fairly uncoordinated rhythm. The ventricles do not contract together as a whole. Instead, it fibrillates from different parts. Or it quivers. On the rhythm strip, the complexes will be wide. They will be irregular because of this quivering or fibrillation. And there will be no P waves. One point to note, clinically, the patient is usually unable to generate enough cardiac output from this quivering of the ventricles to generate a pulse in this rhythm. To summarize, we talk about how to approach tachycardic rhythms when you see patients. We talked about the three classifications. One, whether the cures complexes are narrow or wide. Two, whether the rhythm is irregular or regular. And three, whether there are P waves available. These classifications will allow you to identify tachycardic rhythms when you're seeing your patients.