Broad complex tachycardias

Broad complex tachycardias are potentially life-threatening. Every clinician taking care of cardiac patients should be able to diagnose them.

Franz Wiesbauer, MD MPH
Franz Wiesbauer, MD MPH
17th Jun 2016 • 5m read
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Broad complex tachycardias are potentially life-threatening. Every clinician taking care of cardiac patients should be able to diagnose them. In this video, you will learn the essential basics relating to broad complex tachycardias. Plus, there will be some hands-on nuggets of wisdom that you’ll be able to apply immediately during your next night on call.

Video Transcript

[00:00:00] After having ruled out the rhythms at a glance, which are so typical that you should be able to recognize them immediately. We should now continue evaluation of rhythm problems in a more systematic way. One feature of a rhythm strip, that is a real eye-catcher, is when the heart runs in a rapid manner, something that we call tachycardia.

[00:00:30] The word tachycardia consists of two different Greek components. The first is tachys, which means fast. And the second one is cardia, which means heart. Tachycardias can come in various different forms. Let's look at some of them. Here are a couple of examples. This is fast, this is fast too, and what these two tachycardias have in common is the fact that

[00:01:00] they're rapid and regular. Well, every tachycardia is rapid, right? But not everyone is regular. What do I mean by regular? Regular means that the distance between the QRS complexes is constant. This is the same distance as this one, the same as this one, and the same as this one and the same holds true for the tachycardia below. This distance is the same as this one, as this one, as this one, and it goes on like that. Now here's a slightly different case.

[00:01:30] This tachycardia is rapid and irregular. You see that the distance between the QRS complexes varies. So, this is different than this one, and this one, then this one, then this one. So, really no two distances are the same. We're going to deal with rapid and irregular tachycardias a little later, so let's just forget about them for now. Rapid and regular tachycardias can come in two different forms. One is a broad complex

[00:02:00] tachycardia and the other one is a narrow complex tachycardia. Let's check it out. So, here, the distance from the beginning of the QRS complex to the end of the QRS complex is 0.12 seconds and as we already know, that's too broad. In the example below, the distance from the beginning to the end of the QRS complex is 0.06 seconds, so this is a narrow complex tachycardia. Let's check out what causes a QRS complex to be narrow or broad.

[00:02:30] In order to understand that, we need to review the cardiac conduction system and how impulses are transmitted inside the heart. Let's recap this is the AV node. This is the bundle of His. This is the right bundle branch and this is the left bundle branch, with the left anterior fascicle and the left posterior fascicle. When the impulses are generated in the atria and are conducted into the ventricles through the AV node, the bundle of His and the bundle branches,

[00:03:00] the ECG will look like this. Ventricular depolarization happens fast and, therefore, the QRS complex is narrow. Let's look at a slightly different example. If the impulse takes its origin in the atria, enters the ventricles through the AV node but it finds one of the bundle branches blocked, as in this example, the QRS complex will show a bundle branch block morphology

[00:03:30] and will, therefore, be broadened. It will be 0.12 seconds in duration or longer. This example shows a right bundle branch block and what the ECG would look like in V1. If you're still a bit confused why the QRS complex is narrow over here but broad over here, then think about it like this. Imagine someone filling up a pool. In the first instance, here's a friend available with another second hose, so filling up the pool will be much faster. In the second

[00:04:00] instance, he only has one hose available, so filling up the pool will be much slower. Similarly, the polarization of the ventricles will also be much quicker, if you have two conduction pathways, the left and the right bundle branches available. However, if you only have one host or one bundle branch, such as in bundle branch block, the duration of ventricular depolarization or in other words, the QRS duration will be much longer. If the impulse is generated within

[00:04:30] the ventricles, as in this example, then it has to travel to the rest of the ventricle through tissue that's usually not well suited for conduction. So, in this case, depolarization of the entire ventricle will also take longer than normal and the cure complex will be broadened. This is an example of how such an impulse could look like in V1. So, there are two types of broad complex tachycardias. In the first one, a pathologic focus, somewhere in

[00:05:00] the atria, has started to fire at a very fast rate overdriving the sinus rate progressing to the ventricles, but finding one of the bundle branches blocked. So, we'll see a bundle branch block pattern. This is called atrial tachycardia with aberrant conduction. In the second, the pathologic pacemaker focus is situated somewhere in the ventricles and depolarizes the heart, in the way just described. This type of tachycardia

[00:05:30] is called ventricular tachycardia. And how can you discriminate between those two different broad complex tachycardias? Well, first of all, if a broad complex tachycardia has Ps in front of the QRS complexes, as in this case, it's probably atrial tachycardia with aberrant conduction. If there's no P wave in front of the curious complex then the patient probably has ventricular tachycardia. Sometimes, you might even find P waves independent

[00:06:00] of the QRS, coming in at the slow rate of the undisturbed sinus impulse. But for this, you need a very sharp eye. We'll teach you a couple of tricks on how you can do it in a later chapter. For you, it's important to know that atrial tachycardia, with aberrant conduction, is usually not a life-threatening condition. On the other hand, ventricular tachycardia can be life-threatening and in most cases, you have to take action immediately. So, it's really important to check

[00:06:30] how the patient is doing clinically. Is the patient in cardiac arrest? Is he hemodynamically stable? How's the blood pressure doing? So, I can't stress enough how important it is to be on the lookout when you have a patient who has a broad complex tachycardia. You have to check the patient clinically. If you're sure that the patient has atrial tachycardia, with aberrant conduction, you can be sure that it's probably not a life-threatening condition. On the other hand, if the patient has ventricular tachycardia

[00:07:00] then you have to be really, really cautious. These ventricular tachycardias often hit hearts already jeopardized by extensive disease or previous infarctions, hence, the situation may become very unstable or life-threatening really, really quickly. Apart from the fact that we've just covered, there are a couple of other clues that can also give you hints about the underlying etiology of a broad complex tachycardia, not just QRS morphology, for example.

[00:07:30] Certain QRS morphologies are typical of atrial tachycardia, with aberration, while other morphologies are typical ventricular tachycardias. More about these morphologies in the black belt section. But now, it's time to practice. In the following exercises, you should determine the patient's heart rate, whether the rhythm is regular or irregular, whether the QRS is widened or narrow. If you think that you can already make a rhythm diagnosis,

[00:08:00] please go ahead and do so.