Bradycardia: Sinus Bradycardia and Heart Blocks

by Carlo Raj, MD

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    00:01 So with arrythmias, well we said there was two major categories. One was one in which it was conduction system diseases and then the vascular component. Now what we will first discuss would be the conduction system disease category first, and our first topic under this would be bradyarrhythmia.

    00:23 So what is brady? I told you earlier that if you find your beats per minute, which is normally 60 to 100 to be less than 60 and trust me you will know if your patient has decreased heart rate. Fifty is the actual technical definition of bradycardia. Bradycardia and what does that mean to you? It means that R wave, when you compare one R wave to another are further apart and earlier told you about "what sounds like a telephone number" which is your "300, 150, 100". So what exactly does that mean? Well when we look at that EKG, if there is one line separating an Rwave from each other, that is 300 beats per minute.

    01:17 What if there's two lines separating an Rwave? 150. Three lines, 100. You group those together 300, 150, 100. Just like a phone number, divide that into whatever numbers so that you can remember this easily. The other three numbers were 75, 60 and 50. So 50 brings you to six lines separating an R wave from one another, and that is 50 beats per minute. Welcome to bradycardia.

    01:52 And sinus means what to you? Sinoatrial wave representing the existence of a P wave.

    01:59 Is that clear? It can be seen in competitive athletes. It is perfectly normal and that you can expect. So if you take a look at the R waves that the upper deflection here and you find a number of lines in between them or you are in the realm of bradycardia. Now with a competitive athlete, just one more thing that I wish to bring to your attention.

    02:22 Apart from having a normal sinus bradycardia, you can also have a patient who is an athlete, that has a well trained and very efficient left ventricle. What are you referring to? I am referring to the fact that with your very efficient left ventricle that could be enlarged, by your proper cardiac output, you might hear what heart sound? Granted, S1 and S2. You have to right if the person is alive. But it is the S3 that I am really having you pay attention to. The S3 would be found in that patient and we have discussed that earlier. If symptomatic in older patients, well syncope is what you are worried about. So now let us go into our clinical manifestations. So could it be normal? Sure, competitive athletes, marathon runners well-conditioned individuals right. But you can also have symptomatic. If you have an older patient that has sinus bradycardia, that means perhaps this patient might not have enough cardiac output. There is not enough cardiac output, then the patient may be suffering from syncope. That is not very good. It is not a good feeling and treated with what? A permanent pacemaker, right. Now heart block is where we go next. So with sinus bradycardia, I gave you two differentials there. A competitive athlete and an older patient in which unfortunately there is a sinus brady and may require pacemaker, okay. But if it is a heart block, what does that mean to you? It is not that a conduction or an impulse is not traveling through at all. Are you with me? So the impulse will be traveling through, but it might be retarded. It might be delayed. At some point in time, when the heart block gets bad enough and it doesn't travel through it at all, guess what degree we are in now? A third-degree AV block, okay. Now the same concept was also used for LBBB and RBBB, where there is the bundle-branch block. You call that block, but the impulse is still traveling through, at a very slow rate. Let's talk about heart block. First degree, second degree, third degree. Under second degree, we will then get into Mobitz type 1 and Mobitz types 2 at least. Know that before you walk into any medical environment.

    04:51 Third degree, that is a complete heart block, okay. Obviously, I will have to talk about physio here and some of the fundamentals that we have already laid down for EKG. So what interval would you name this if I was to describe to you the impulse that's originated in an SA node making us way down to the AV node? What interval would you define that as being? PR interval, good. You tell me what the time is normal? 0.12 seconds to 0.2 seconds. Do you remember that? Good. So now you start having issues with a delayed impulse, what can you expect that PR interval to do? Good. Increase to be great than 0.2 that is what you are paying attention to, so far, so good. Now is that in every single case? No and you will see why.

    05:47 You will see conditions in which you won’t always find a PR interval, but still would be defined as being a type of heart block. You see what I am referring to. Now the second part of this so that it makes sense to you is say that you did have a third degree AV block okay. And if you did have a third degree AV block may be because of myocardial infarction there is no impulse that is being dictated by your SA node. Remember, the SA node is the conductor of the heart. It is the Zubin Mehta of your conduction of your symphony. And so therefore if the SA node loses control, how? With the third degree AV block, then who is controlling your ventricles? An ectopic foci. What does that mean? Every single part of the heart is its own pacemaker right. But you have to have a ring leader. That is an SA node and if that SA node loses the control of the conduction system of the heart, trust me the heart itself has an inherent ability of creating an ectopic foci, alright? Now that ectopic foci may still cause contraction of left ventricle or create electrical activity, but it does not look normal. You tell me, what is the ventricular depolarization represented as on your EKG? QRS complex. Are you picturing that? Now say that if it is an ectopic foci, the QRS complex looks bizarre. There is going to be no correlation between the P wave and the QRS complex. So these are things that you are want to lay down before even move forward with any of these so that when we get to the topic at hand, we will be able to go through efficiently.

    07:31 Okay. First degree AV block, what does that mean?

    About the Lecture

    The lecture Bradycardia: Sinus Bradycardia and Heart Blocks by Carlo Raj, MD is from the course Arrhythmias.

    Included Quiz Questions

    1. Six lines
    2. One line
    3. Four lines
    4. Two lines
    5. Three lines
    1. All of the above
    2. Increased cardiac output
    3. S3 heart sound
    4. Sinus bradycardia
    5. Left ventricular enlargement
    1. 250 milliseconds
    2. 0.12 seconds
    3. 0.15 seconds
    4. 200 milliseconds
    5. 0.2 seconds
    1. Syncope
    2. Dyspnea
    3. Hypertension
    4. Headache
    5. Chest pain

    Author of lecture Bradycardia: Sinus Bradycardia and Heart Blocks

     Carlo Raj, MD

    Carlo Raj, MD

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