Tachyarrhythmias (Tachycardia): Definition

00:01 Let's switch gears and talk about tachyarrhythmias -- when your heart is beating too fast.

00:07 So, getting back again to locations within the heart let's start with the sinus node, and this is by far the most common cause of tachyarrhythmia in children.

00:16 So, in children and infants who present with a high heart rate, it's usually a normal response to an abnormal condition.

00:25 Classically one might think of fever.

00:28 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.

00:39 Both the fever and the heart rate go up at the same time, but the heart rate isn't caused by the fever.

00:46 Likewise, medications can certainly cause a sinus tachycardia.

00:50 Any medications such as albuterol which we commonly use is a beta-agonist which will speed up the heart at the SA node.

00:59 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.

01:10 And likewise, pain often causes a high heart rate in children.

01:15 Alternatively, there can be some pathologic causes of high heart rate in children that we have to be aware of.

01:22 SVT or supraventricular tachycardia is generated above the AV node and usually below the SA node it's in the atria.

01:33 So, let's take a look at this.

01:35 We can have atrial tachycardia.

01:38 So, there are several different types of atrial tachycardia, one could be an intra-atrial re-entrant tachycardia.

01:47 This is an area where a group of atrial cells are signaling to each other.

01:53 Their signal is just going around and around and around very quickly because of aberrancy in that atrial muscle and that's causing a continuous fibrillation of the atria.

02:05 If you were to open up the patient and look inside, their atria would look like a bag of worms undulating in there.

02:12 And in this EKG you can see right here is a case of atrial fibrillation.

02:16 If you look very carefully at that line, it's sort of wiggling along like a little bag of worms.

02:22 Now, if this is happening, that signal can get transduced through the AV node and the patient may result in having a tachycardic rhythm.

02:32 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.

02:45 Another possibility is a re-entrant tachycardia.

02:49 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.

03:04 Let's dive into that.

03:06 This is Wolff-Parkinson-White syndrome.

03:09 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.

03:24 If that starts going very, very fast, these patients can have sustained heart rates between 220 and 240, even higher.

03:32 What's key is there isn't any variability to their heart rate.

03:35 When you watch them on the monitor they're at 226 and they're staying there.

03:39 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.

03:50 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.

03:59 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.

04:12 In other words, it's pre-excitation.

04:14 This creates an earlier sweep to that QRS complex which makes a figure somewhat like the Greek letter delta.

04:22 So, this is a delta wave and this is pathognomonic for Wolff-Parkinson-White syndrome, which is often a cause of SVT in children.

04:30 Another type of tachyarrhythmia is ventricular tachycardia.

04:33 This is an example of where a patient has a re-entrant loop within the confines of the ventricles.

04:40 This creates a wild pattern of electrical constriction that's just going back and forth and we have very, very rapid heartbeat.

04:48 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.

05:00 This can be very life-threatening.

05:02 And here you can see that wild, jagged, sawtooth figure that you typically see in an EKG in a patient with ventricular tachycardia.

05:13 You can also get V-fib which is similar and also life-threatening.

05:19 So, let's go over the tachycardia causes in children.

05:23 We have atrial tachycardias such as an intraatrial beat.

05:28 You can have a supraventricular tachycardia that's a re-entrant like Wolff-Parkinson-White.

05:34 You can sometimes see junctional tachycardias.

05:37 These are typically only seen in children who previously had a cardiac surgery and have a damaged piece of muscle that's not operating right.

05:45 And then you can see ventricular tachycardias and fibrillations.

05:49 Those are typically from primary problems of the muscle like a cardiomyopathy.

05:55 You might see it in patients with congenital heart disease in an abnormally growing muscle.

06:01 And you might see it in electrolyte abnormalities, especially hyperkalemia.