 Hello, welcome to Erythmia Part 2. This section focuses on tachycardic rhythms. If you have not done so already, please watch Part 1 on bradycardia. If this is your first few months of clerkship, you might want to review the basic discussion on tachycardia before reviewing this segment. Tachycardia is defined as heart rate greater than 100 beats per minute. On a standard rate rhythm strip, it means that the cure-as complexes are closer together than three large squares. We will first discuss how tachycardia occurs and then go through a few tachycardic rhythms. There are two different mechanisms of tachycardia, enhanced automaticity and re-entry tachycardia. Enhanced automaticity occurs when the depolarization of pacemaker cells is increased. Re-entry tachycardia happens when there are two distinct pathways for impulse conduction, something like this. So let's say this is pathway number one, from here to here. And this was pathway number two, from here ending at exactly the same spot. What happens with impulses is that they can go down one pathway and decides to go up through the other pathway. Or vice versa, creating a circuit loop. And every time this circuit goes around the loop, this activates the more distal conduction pathway, creating activation of the ventricles. Re-entry tachycardia can involve large areas of myocardium, or small areas like inside a node. Now let's look at an approach to tachycardic rhythms. The two key pieces are whether the rhythm is regular or irregular, whether the cure-as is narrow or wide. Regular rhythm suggests that a single impulse focus causes the tachycardia. It also usually happens in re-entry tachycardia as well. Irregular rhythm can result from premature beats, either from the atrium or the ventricles, multiple foci, variable blocks, or disorganized electrical activity. Let's look at this ECG, this is regular or irregular. Sometimes when the heart rate is really high, the irregularity is subtle. However, if you map out the individual cure-as complexes on a piece of paper, you see that this rhythm is irregular. Next, narrow versus wide cure-as complex. When the ventricle depolarization occurs from the normal conduction system as shown here in blue, the cure-as complex is narrow. Activation partially outside the normal pathway or from a blocked normal pathway will result in a wide cure-as complex. This includes ectopic foci, premature ventricular activation, accessory pathway, and for blocked conduction system things like bundle branch blocks. Now, let us look at the various tachycardic rhythms. We will start from the essay node and work our way down. First up is sinus tachycardia. The rate is usually 100 to 140 per minute. This is from an enhanced sinus node automaticity. The sinus nodes simply create faster impulses. Is this regular? Yes. Is this narrow? Yes. You can also clearly see P-waves that's where the impulses are generated from. Now we're going to move on to the atrium itself. This is atrio tachycardia. The cure-as is irregular. It is narrow. This is also known as multifocal atrio tachycardia, or MAT. What happens here is that there are different pace-making foci in the atrium that contribute to different-looking P-waves. If you look at lead 2 here, the arrows are showing there are at least 3 to 4 different-looking P-waves since each different P-wave are coming from a different foci in the atrium. Since there are different foci, the cure-as is not exactly regular. We're still staying in the atrium and this is atrial fibrillation. The impulses originate from the chaotic depolarization of the atrium. Is the cure-as regular? No. Is it narrow? Yes. You can differentiate atrial fibrillation from MAT from before since there will be no P-waves. Depending on how fast the AV node is conducting the depolarization from the atrium, the rate for atrial fibrillation varies. You may remember that in the bradycardia video, we talk about atrial fibrillation having a slow ventricular response rate, leading to rate that's less than 60. We've seen this before too in the bradycardia video. This is atrial flutter. Atrial flutter is a specific re-entry atrial tachycardia, producing these large flutter waves giving rise to the baseline sol-tooth pattern. This rate, as we talked about before, will be at 300. The rate and whether the cure-as complex is regular or not is dependent upon how much the AV node blocks the impulse. Let's say the AV node blocks every other flutter wave. It will produce this rhythm strip. You can see here every other flutter wave contributes to a cure-as complex. This is what we call a two-to-one block as in two flutter wave, one cure-as complex. Because the base rate is 300, this rate will be squarely at 150. By the same token, if we have a fixed three-to-one block, this is the strip that will be on the ECG. And now the rate will be squarely at 100. However, sometimes, as you can see on this rhythm strip, the AV block is variable. Sometimes it let every third impulse through, sometimes every fourth even in here. So you can have either regular or irregular cure-as complexes. It will always be narrow. Next, we talk about the AV node. We will be discussing a specific tachycardia that has to do with a re-entry tachycardia within the AV node. As we talked about before, a re-entry circuit means that there are two different pathways. Every time a impulse go through, it will then go up the other pathway and causing a circuit loop. And every time this happens, it will trigger more impulse downstream. AV node re-entry tachycardia is usually triggered by a premature atrial complex. This is what it will look like on an ECG strip. The rate is fast. It can be anywhere between 150 to 250. The cure-as complexes are regular and narrow. This contributes to one of the most common reasons patients might present with paroxysmal superventricular tachycardia or PSVT. Now, the next two rhythms is not something we see very often, but we should discuss it for a completeness sake. This is AV re-entry tachycardia. So the re-entry tachycardia has something to do with the AV node, but is not inside the AV node. What happened is that there is an accessory pathway outside the AV node. And here it will be this guy. This is just like a re-entry tachycardia that we talked about before. The impulse choose to go down the original pathway or the normal pathway is seen here. But it goes out through the accessory pathway. This is the most common type of AVRT or AV re-entry tachycardia. The technical term is called orthodromic. You notice that the regular rhythm goes down the normal conduction pathway here. And therefore the cure-as complexes will be narrow on the ECG. This is what AVRT that's orthodromic look like on a 12-litre ECG. This looks remarkably like the AV NRT and sometimes it's impossible to tell the difference between the two. You can see that it's fast. The cure-as complexes are regular and they're narrow. This is a second form, a much less common form of AV re-entry tachycardia. The circuit loop is still being formed by the accessory pathway and the normal conduction system. So accessory pathways here, conduction system is here. However, in this instance the impulse decides to go down the accessory pathway this way. And it conducts retrograde-ly through the normal conduction system. You remember that at any point if the ventricles are being depolarized secondary to impulses that does not occur inside the normal conduction system, the cure-as then becomes wide. And therefore in this instance of AV re-entry tachycardia, since the activation is through here, the cure-as complexes will be wide. It will be regular since this circuit loop just goes around and around in circle producing a regular tachycardia. And this is what the 12-litre ECG looks like, very different from what we looked at before. Cure-as complexes are regular but they are wide. And as we will see in the next few slides, this looks exactly like ventricular tachycardia. Since this is a very rare form that we encounter in patients, if you see a 12-litre ECG like this, you'll want to assume the patient has ventricular tachycardia instead of the very rare AV re-entry tachycardia. Remember one thing we talked about before is even if the conduction is not outside the conduction system, but if there are some sort of blockages then the cure-as will appear wide. Therefore if you have a normal narrow cure-as complex, if you happen to have a bundle brand block downstream, it will look wide on your 12-litre ECG. So now we're going to move further down into the his bundles and the ventricles. You might remember this rhythm that we saw in the brachycardia video. This is an accelerated idioventricular rhythm. This is generated from the his bundle or the ventricles. There are no P-ways. The cure-as is regular. Depending on where the impulses are being generated from, they can be narrow if it's closer to the AV node or wide if it's closer to the ventricles. What about this rhythm? The cure-as complexes are wide and regular. This is ventricular tachycardia. Anytime you see a wide and regular rhythm that's also fast, you want to think ventricular tachycardia first. It is wide because the impulses occur at a focus in the ventricles. This would be what the focus for the ventricular tachycardia might look like. What about this rhythm? It's wide. It's mostly regular. This is torsats. This is a specific type of ventricular tachycardia in which the arrhythmia has a cycling pattern of alternating up and down and amplitude. You can see the cure-as complexes going bigger and smaller. This occurs with a prolonged QT interval. What about this rhythm? This rhythm has wide cure-as complex. It's irregular and there seems to be no organization. This is VF, a ventricular fibrillation. In the heart, there are multiple little foci trying to create ventricular contraction but it's completely disorganized. The myocardium will not generate effective contraction with this rhythm. This is a rapidly fatal rhythm unless it's being stopped quickly. Let's see if you can fill in the blanks here. You might want to pause here and then check your answers once you're done. What would give you a regular and narrow cure-as complexes? It includes sinus tach, AVNRT, AVRT, the orthodromic or the most common form, and atrial flutter at a fixed block rate. What about irregular and narrow? They include MAT or multi-focal atrial tachycardia, atrial fibrillation, and atrial flutter with a variable block. Let's see if you can fill in the blanks for the rhythms that will give you regular and wide cure-as complex and irregular and wide cure-as complex. You can pause here and then check your answers once you're done. For regular and wide, the ones that we really want you to think about is ventricular tachycardia. It can also be accelerated idioventricular rhythm. It can also be the rare form of AVRT that goes backwards, so the antidromic form. But again, we want you to think v-tach first. How about irregular and wide? They include torsods and ventricular fibrillation. Also remember that we said that a narrow rhythm, if downstream there is a bundle branch block that can also make the cure-as complexes look wide and therefore, if you have a narrow and regular rhythm, if you add a bundle branch block, it will look like a regular and wide cure-as complex. And if you have a narrow and irregular rhythm, you add a bundle branch block, it will look wide and irregular. In this segment, we reviewed a lot of different tachycardic rhythms. We hope you find this useful. Thank you for watching.