Hi. I’m Mark from ACLS Certification Institute. In today’s video series, we’re going to talk about interpreting and recognizing heart blocks on your ECG tracing.
First, let’s take a look at a regular cardiac complex, starting with the P wave. P waves should be rounded and upright, and a P wave denotes atrial depolarization or atrial contraction. Next, it returns to the isoelectric line, flat line, and that’s the area where the conduction has gone through the atrium and now it’s to the AV node. The AV node is going to pause the conduction for just a moment, allow for atrial contraction, before it sends it on through the ventricles, before it lets that impulse go on. When we’re talking about heart blocks, we’re talking about the relationship between the P waves and the QRS, the relationship between the atrial chambers and the ventricular chambers. Blocks are a delay in conduction at the AV node. Now, what’s a normal PRI? What’s a normal P-QRS interval? A normal PRI is between 0.12 and 0.20 seconds. If the PRI or PR interval is longer than that then we could call that a first-degree heart block.
Woman: “This is the sound of trouble. The kind that caresses lives even as it steals them away. It delicately unravels the fabric of entire towns like Corinth, Pennsylvania. When the trouble comes, it will sound like this, and loving will never be the same again.”
Heart blocks are kind of like relationships. If you take a man and a woman and you look at the atriums and the ventricles, there’s a relationship there. In the heart, we have a relationship between the atrial chambers and the ventricular chambers. In real life, we have relationships between men and women. If we look at the relationship in a first-degree heart block, it is a couple that’s together. The man and woman are together, always together, but they’re slightly separated a little bit, almost like at the beginning of a relationship when you may not be actually, completely honest with them. You know, “What do you do for a living?” “I’m an astronaut.” They’re together, but there’s still that little separation. That’s really all a first-degree heart block is. To take a look at it, it almost looks like a normal sinus rhythm. A first-degree heart block only means that the PRI is longer than 0.20 seconds. You’ll have a P wave before each QRS, a QRS after each P wave, and it looks like a normal sinus rhythm except the PRI is longer than 0.20 seconds. That’s a first-degree heart block. Usually, they’re benign. The patient’s asymptomatic. We just want to keep a watch on it because there is some conduction delay at the AV node. It could be a precursor to something else down the road, but generally first-degree heart blocks are no big deal.
Let’s get into second-degree heart blocks. There are two types of second-degree heart blocks: type 1 and type 2. Let’s look at second-degree heart block, type 1. This is a couple that’s arguing all the time. They’re arguing. Second-degree, type 1, Wenckebach: They argue. They get a little further apart in their relationship. They argue some more. They get a little further away in the relationship. They argue some more. They get a little further away in their relationship. Finally, they go, “Forget it. I’m out of here,” and they break up and they leave and the QRS drops. One of them leaves. They wait around that night. They’re at a bar, the same bar they always go to. They see each other. He gives her a little wink. They get back together again. It was the wink that brought them back, the wink-back, the Wenckebach, second-degree, type 1. They argue. They get further apart. They argue. They get further apart. They argue. They get further apart. Finally, he leaves. He’s had enough. A wink ensues. They come back together. Second-degree, type 1, Wenckenbach. Again, we’re looking at the relationship between the P wave and the QRS. You’ll have a PR interval. The next PRI is going to be a little longer. The next PRI will be a little longer. In the next one, you’ll have a P wave but no QRS. The QRS drops off. Then it starts over again. The PRI will be short. The next PRI will be longer. The next one will be longer, until the QRS gets dropped. That’s a second-degree, type 1, Wenckebach.
In second-degree, type 2, the relationship there is here’s a couple that when they’re together, they’re together, but he keeps going out on her. “He” being the ventricles. When they’re together, there’s a relationship, a regular relationship, but he keeps going out on her. He keeps leaving. When they’re together, they’re together. Normal P and normal QRS, but he keeps leaving. Then he comes back and they’re together. That’s second-degree, type 2. Again, we’re looking at the relationship between the P waves and the QRS. The PR interval in second-degree, type 2, may be normal. It may be slightly longer than 0.20, but there’s definitely a P wave before each QRS and the PRI is fairly normal. What happens is you’ll have P wave, QRS, P wave, no QRS, P wave, no QRS. There’s a complete block there. You have a P wave and no QRS following it. When you’re looking at the ratios on a second-degree, type 2, start counting the P waves after the last QRS. After that last T wave, start counting the P waves: 1 P wave, 2 P wave, 3 P wave, conduction. We would call that 3:1 ratio. There were 3 P waves before a QRS complex. That’s a 3:1 ratio. If we had 2 P waves and then a QRS, that would be 2:1 ratio. Remember to start to count the P’s after the last T wave.
Finally, she’s had enough of him. She kicks his butt out. Third-degree heart block, completely divorced. In this case, she’s doing her thing and he’s doing his thing and there’s no relationship there at all, the same as a third-degree heart block. The atriums are firing off doing their thing. The ventricles are firing off doing their thing. They are divorced. There is no relationship between the two. When you look at the PR interval, there isn’t one. There’s no relationship between the P waves and the QRS. There’s no set relationship there, no pattern to it. However, the P waves, since they’re marching out independently and firing all by themselves, they will march out. If you take your caliper out and you take a look at your P waves, all your P waves will march out nice and even. All of your QRSs will march out nice and even. However, there’s no relationship between the two. Both atrial and ventricular chambers are now not talking to each other and they’re all firing independently, all by themselves.
“Alright, enough. Turn around. You, turn around. You, put your hands on her shoulders. You, put your hands on his shoulders. Now, start dancing. Dance! Start dancing. Start dancing. You think I’m playing? Start dancing. Look lovingly into her eyes. Whoa, creepy, 60% less. Keep dancing. You need to keep dancing until I tell you to stop dancing. Got it? Keep dancing.”
Now I have two people. They don’t even want to be together. They’re ignoring each other. Can I get them to work together? In fact, can I get them to dance together on a dance floor? You bet I can. How? I have a gun. I can force them. I can get gangster and make them work together. Can I force the atrial chambers and the ventricular chambers to work together? You bet. I’m going to get gangster with that. I’m going to grab my ‘Whack Master 3000,’ set it to pacing, and provide transcutaneous pacing. Force those chambers to work together.
When looking at all blocks, what we really need to focus on is the ventricular response. That’s what’s really important. When we’re pacing a third-degree heart block, it’s not because we want the atrial chambers and ventricular chambers to work together. We want to get that rate up. We want to get that ventricular rate up. Remember: cardiac output = stroke volume x heart rate. In a third-degree heart block, their heart rate may be 30, very low. We have to get that ventricular rate up. That’s why we’re pacing them. It’s not so much to have the atrial chambers and ventricular chambers work together, but it’s to get that ventricular rate up, get their heart rate up, and get their blood pressure up. If you have a patient with third-degree heart block, symptomatic, low blood pressure—transcutaneous pacing.
You may have a patient and you go look at the monitor and go, “Holy $@%!. They’re in a third-degree heart block! We have to do something!” Then you look at the patient, and you go, “How do you feel?!” The patient goes, “Fine. How are you?” No need to get crazy. We don’t have to do anything right now. Just like you, I’ve had patients who were in a complete heart block, who were asymptomatic and maintaining a blood pressure. Now, am I going to put the pacer pads on them and be ready? You betcha. Am I going to have two big IVs in and be prepared for things to go south? Oh, you betcha. But emergently, I don’t have to do anything. Why? Because we don’t treat rhythms. We treat patients who have rhythms.
Heart blocks, heart ache. I’m Mark for ACLS Certification Institute. Thank you for watching today’s video on heart blocks.