Lets learn about the tachyarrhythmias. Sinus node (Sinus Tachycardia) is by far the most common cause of tachyarrhythmias in children.
Definition of TACHYARRHYTHMIAS
So, in children and infants who present with a high heart rate, it’s usually a normal response to an abnormal condition.
- Classically one might think of fever. Now, one caveat I’ll add to this is that it’s not actually the temperature that’s driving the heart rate; it’s the interleukins and other inflammatory markers that are causing the high heart rate. Both the fever and the heart rate go up at the same time, but the heart rate isn’t caused by the fever.
- Likewise, medications can certainly cause a sinus tachycardia. Any medications such as albuterol which we commonly use is a beta-agonist which will speed up the heart at the SA node.
- Fear – Kids are often afraid when they’re in the doctor’s office and we see this a lot and it’s important to be able to distinguish whether their heart rate is coming down when they’re in their calming moment or if it’s staying up.
- And likewise, pain often causes a high heart rate in children.
Alternatively, there can be some pathologic causes of high heart rate in children that we have to be aware of.
SVT or supraventricular tachycardia is generated above the AV node and usually below the SA node. It’s in the atria. So, let’s take a look at this.
- We can have atrial tachycardia. So, there are several different types of atrial tachycardia, one could be an intra-atrial re-entrant tachycardia. This is an area where a group of atrial cells are signalling to each other.
- Their signal is just going around and around and around very quickly because of aberrancy in that atrial muscle and that’s causing continuous fibrillation of the atria.
- If you were to open up the patient and look inside, their atria would look like a bag of worms undulating in there. And in this EKG you can see right here is a case of atrial fibrillation.
- If you look very carefully at that line, it’s sort of wiggling along like a little bag of worms.
- Now, if this is happening, that signal can get transduced through the AV node and the patient may result in having a tachycardic rhythm.
Another one is atrial flutter, which is similar to atrial fibrillation but in this case it’s a little bit slower and you can see these waves are a little bit more sinusoidal than you would see in the previous slide.
Another possibility is a re-entrant tachycardia. So, a reentrant tachycardia happens when the electrical signal comes down out of the heart out of the atria and comes back up and goes back up into the atrium and stimulates it again too early.
- This is Wolff-Parkinson-White syndrome. So, here we have a patient who has SVT or supraventricular tachycardia and they have a pathway where the electricity can go through down the ventricles and then back up through an accessory pathway up into the atria. If that starts going very, very fast, these patients can have sustained heart rates between 220 and 240, even higher.
- What’s key is there isn’t any variability to their heart rate. When you watch them on the monitor they’re at 226 and they’re staying there. In a child who has a tachycardia driven from the SA node, let’s say a really a high fever or severe dehydration, there’s gonna be some variability in that number.
- The other key thing is when you get an EKG, you’ll notice something that’s really important that you can see on this EKG right here called a delta wave. What’s happening in this case is the electrical signal from the ventricle is coming up into the atria in that accessory pathway and it’s pre-exciting the atrial fibers. In other words, it’s pre-excitation. This creates an earlier sweep to that QRS complex which makes a figure somewhat like the Greek letter delta. So, this is a delta wave and this is pathognomonic for Wolff-Parkinson-White syndrome, which is often a cause of SVT in children.
- Another type of tachyarrhythmias is ventricular tachycardia. This is an example of where a patient has a re-entrant loop within the confines of the ventricles.
- This creates a wild pattern of electrical constriction that’s just going back and forth and we have a very, very rapid heartbeat. So rapid that the body really has a hard time generating enough blood pressure, the ventricle is already contracting again before it’s really capable of filling. This can be very life-threatening.
- Here you can see that wild, jagged, sawtooth figure that you typically see in an EKG in a patient with ventricular tachycardia.
- You can also get V-fib which is similar and also life-threatening.
- We have atrial tachycardias such as an interatrial beat.
- You can have a supraventricular tachycardia that’s a re-entrant like Wolff-Parkinson-White.
- You can sometimes see junctional tachycardias. These are typically only seen in children who previously had cardiac surgery and have a damaged piece of muscle that’s not operating.
- And then you can see ventricular tachycardias and fibrillation. Those are typically from primary problems of the muscle like cardiomyopathy. You might see it in patients with congenital heart disease in an abnormally growing muscle. And you might see it in electrolyte abnormalities, especially hyperkalemia.
Treatment of TachyarrHythmias
How do we manage these various types of tachycardia?
Well, atrial tachycardia is typically less dangerous because the ventricles are still firing. Probably, it’s just the atria that aren’t doing right.
- What we’d like to do is slow the rate at which the electrical signals can get from the atria into the ventricles. A good drug for that is beta-blockers. We’ll put these children on beta-blockers so that while there may be some atrial tachycardia, there will not be ventricular tachycardia, which is going to significantly interfere with maintaining our blood pressure.
- We often might use digoxin or flecainide or any of these drugs to control, again, that risk of ventricular tachycardia.
For reentrant tachycardias, we’re going to treat the patient differently depending on whether they are stable or unstable. Let me give you an example.
- A child comes in who is two years old and has a heart rate of 220 and it’s been like that for a week. This is an example of a child with a stable reentrant tachycardia. Let’s say this child has Wolff-Parkinson-White syndrome.
- The way we’re gonna reverse this is through a dose of adenosine. Adenosine is a short-acting drug. It’s gone in about six seconds. The way we’re gonna give this drug is we’re gonna place a decubital IV with a stopcock three ways: we’re gonna push the adenosine, quickly flip it, and push a saline flush.
- Now we’re gonna watch the heart rate. What you’ll see is the child’s very fast heart rate is going to flat-line. This child will have no heartbeat at all for probably six seconds. And then we hope it will restart appropriately.
- Cardiologists are very, very grateful if you can capture this on the EKG while you do it, because it will help them understand exactly which way the reentrant tachycardia was going which may help them with a cure later on down the line.
- But if a patient is unstable, if they are sick, if they have hypotension, it’s going to be very hard to take the time to set up all this stuff and get the stopcock and get the decubital IV.
- In this case we’re going to do synchronized cardioversion. Remember, this is different than un-synchronized. Un-synchronized is how you shock out V-tach or V-fib; this is synchronized to the heartbeat, so you have to apply the paddles and then wait for the machine to find the rhythm and it’s gonna synchronize it at the right time during the cycle so it can stop that reentrants.
For V-tach and V-fib, which are life-threatening tachyarrhythmias, we’re gonna treat them again differently depending on whether the patient is stable or unstable.
- If the patient is stable with V-tach which is unusual, they’ll be treated with lidocaine or amiodarone. Some of these patients have a few rapid beats and then pop out of it.
- If they have V-tach with pulsus, we’re going to do synchronized cardioversion.
- If they have V-fib or pulseless V-tach, that’s when we do regular old defibrillation — shock, shock, shock, epi, shock, etc down the line like you learn in adults.
Prevention of TachyarrHythmias
You can prevent tachyarrhythmias in children but only in a certain population.
There are some children who have a unique problem of a prolonged QT. You can see on this drawing of an EKG an example of a child with prolonged QT. The distance between the Q wave and the end of the T wave is too long. So, when you look at this, you find a QTC and that should generally be less than 450.
In patients with a prolonged QT at baseline, they may have a syndrome that’s causing that. There are two relatively well-known prolonged QT syndromes that are genetic.
- One is called Romano-Ward and that’s the most common one, and
- Another one that’s less common which is called Jervell Lange-Nielsen. This one is interesting because it also comes with deafness in the family.
If you have a patient with a prolonged QT syndrome, we generally will put them on a controlling medication so that they won’t then get a tachyarrhythmias, something like propranolol.
In summary of tachyarrhythmias
- WPW is a common cause of reentrant tachycardia and that’s where you see that delta wave.
- There are some genetic causes I mentioned too of prolonged QT syndrome. Patients with prolonged QT need to be on lifelong medication to prevent them from going into V-tach or V-fib.
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