How to interpret Heart Blocks on ECG

 So today, we are going to talk about the easiest way to interpret your heart blocks but before we start, if you haven't it already, I highly recommend that you guys watch our EKG interpretation video. That video contains important concepts about EKG and the conduction system of the heart that will hopefully make today's topic easier to understand. If you're ready, I'm ready, let's get going. Hello guys. This is how you're going to interpret your heart blocks. First and foremost, what causes heart blocks? In heart blocks, the problem lies within the conduction system of the heart. The block may be found between the SA node and the AV node or the problem can be found between the AV node and the Bundle of His, all the way to the Purkinje fibers. Common causes of heart blocks are scarring of the cardiac cells due to aging, heart attacks, valve infections caused by endocarditis, and some medications such as Digoxin. Whatever the cause is, do know that they affect the conduction system of the heart and they cause your EKG to change. There are four types of heart blocks and we're going to talk about them one by one and we're going to emphasize specific characteristics about them. First up, first degree heart block. In your first degree heart block, there is a partial block between your SA node and your AV node. It is partial because even though there's a block here, the impulse still goes through all the way to the Purkinje fibers. There is a delay somewhere here, but it still goes all the way. In our EKG, this will cause a consistent prolonged PRI or PR interval. Note the word consistent. And just a review, our normal PR interval is between 0.12 to 0.20 seconds. So first degree heart block will look something like this. Sometimes, just by looking at your PRI, you can tell that the PRI is prolonged but the best way to know if your PRI is prolonged is when you measure it. So for this EKG, there are a one two three four five six seven eight nine small boxes times 0.04 seconds, your PRI for this EKG strip is 0.36 seconds. That is pretty long. Our normal is only up to 0.20 seconds. If you measure your other PRI, they are consistently long, the same measurements. That is your first degree heart block, consistently prolonged PRI. Next up, would be our second-degree heart block type 1. This is also known as your "Wenckebach". In your second-degree heart block type 1, there is a progressive block between your SA node and your AV node. And I emphasized the word progressive. So it starts with a normal conduction right here because there is no block, then eventually there would be a partial block that will occur, then the block becomes more prominent, and eventually there would be a complete block between your SA node and your AV node. In your EKG, you will have a progressively prolongation of your PRI and a drop in your QRS. Your key words here are progressively long PRI and your QRS will drop. So we begin with a normal PRI because initially, there is no block present. But then, when the partial block takes place, the PRI gets longer; there would be a delay from the conduction from the SA node all the way to the Purkinje fibers. As the block continues to progress, the PRI gets even longer. Eventually, when the complete block takes place, the QRS drops. So as you can see, there's a P wave here, there is no QRS complex. Then the cycle begins again. So this is your second-degree heart block type 1. You can remember this type with the term, "long, long, drop". This means that the PRI progressively goes longer then the QRS drops. So "long, long, drop". Next up would be your second-degree heart block type 2. This is also known as your "Mobitz II". In this heart block, there is an intermittent block between your SA node and the AV node. Note the solid line, this means the block is complete not partial but complete. As a result, the EKG will show drops in your QRS complex. Your word here is "drops". So let us take a look. As you can see, when there is no block yet, you will start with a normal EKG rhythm. However, once the block takes place, the QRS drops. As you can see, there's a P wave, there's no QRS complex. See, there's a drop here and there's a drop there. There's P wave, T wave, and your P wave again. This is your second-degree heart block type 2. And the way you're going to remember this is "normal, normal, drop". This refers to the normal PRI's before your QRS drops. Next up would be your third-degree heart block. This is also known as your complete heart block. Complete heart block takes place between the atria and the ventricles, meaning your atria will contract independently with your ventricles. What this will do to your EKG is that your P waves will have no correlation with your QRS complex. This is what it is going to look like in your EKG. You have P waves that march, meaning, they will have the same distance. There, there and there, there's a P wave here but it's covered by the QRS complex. Also, you will have QRS complex that will march as well, the same distance, however, there is no correlation between your P waves and your QRS complexes. P waves occur because the atria are contracting and your QRS occur because your ventricles are contracting but they are independent with one another. This is your third degree heart block. And the way you're going to remember this, is that your P waves march and your QRS complexes march but there is no correlation. Another hint that you will have when it comes to third degree heart blocks is that most are super bradycardic. So if you see a super bradycardia rhythm, look at the P's and the QRS complexes, march them. No correlation? That is third degree heart block. As a review, first degree heart block would be consistent prolongation of your PRI. Second-degree heart block type 1 would be "long, long, drop" where your PRI gets longer and longer and then your QRS drops. second-degree heart block type 2 would be "normal, normal, drop" where PRI would stay normal until the block takes place, then the QRS complex drops. Your third degree heart block, your P waves and QRS march but there would be no correlation. Plus usually, they're super bradycardic. That's it. Alright guys, I hope this video helps. And if you haven't already, hit the like and subscribe button. By doing this, our video will go straight to you. Until next time, MINT, signing out.