Treating arrhythmias—defibrillation

Defibrillation is a very effective way of treating ventricular arrhythmias, but how does it actually work? By the end of this video, you'll know how defibrillation treats ventricular fibrillation and ventricular tachycardias.

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[00:00:00] So, when we think about our arrhythmia zones, our VT zones, then we can have different levels of therapy in each of them. So, zone one, might simply be a monitoring zone, so while we look at rhythm and record it but we might not want the device to necessarily treat it. If we look at our second zone, then we might try some anti-tachycardia pacing

[00:00:30] and then some defibrillation. And then in our really fast zone, so in our VF zone, we might just have defibrillation. And there's good reason for this, and that is defibrillation is extremely successful at treating ventricular arrhythmias. So, really, the faster and the nastier that rhythms get, is the more we lean towards using defibrillation as our first line of therapy. So, how does defibrillation work?

[00:01:00] Well, a high energy shock is delivered to the heart. The way the device does this is utilizing either one or two coils on the ICD lead and the device itself. What this does is capture a critical mass of tissue, depolarizing it, all at once, and allowing sinus rhythm to regain control of the heart. Now, it's vastly more successful in

[00:01:30] treating these ventricular arrhythmias than ATP, but it does have its downsides. But first, let's look at a real-life example of where ATP was unsuccessful and so the device eventually resorted to a high-energy shock to treat the rhythm. Now, here we can see detection is met. Two episodes of burst ATP are delivered, both unsuccessful. Two episodes of Ramp ATP are delivered, again, unsuccessful. And eventually, the device decides

[00:02:00] to deliver a high-voltage charge, which successfully terminates the arrhythmia. And of course, this protocol, this therapy protocol is a programmable protocol and would have been put in place, by somebody who is programming the device, to work as they want it. Here, they've gone for four episodes of ATP, before resorting to a high-voltage shock. So, how are we able to generate such a high voltage shock from a battery, which is often

[00:02:30] as little as 3.1 volts? Well, it's all down to the capacitor. What the capacitor does is store energy, and the battery is able to pour loads of its energy into the capacitor and fill it up, until it's full with the high voltage charge, ready to go. At that point, the capacitor delivers all the energy in one go, via the ICD lead. Now, the capacitor does take time to charge, and we have to factor

[00:03:00] that into our decision-making process. If you think about the arrhythmia, we have a detection time delay, where the arrhythmia has to be sustained long enough for the device to consider therapy. If detection is met, and the device decides to charge for shock, we have further time before therapy is eventually delivered. Now, it's not something that we get overly concerned about but it's just something to be mindful of, that we detect the arrhythmia and then actually,

[00:03:30] there's going to be a delay until the high-voltage shock is delivered, whilst the capacity charges. Another consideration is battery depletion. Now, obviously, if we think about the battery pouring loads of its energy into the capacitor for every shock, this can really deplete the energy. In actual fact, estimate suggests that for every shock delivered by the device, this can reduce the battery longevity by one month. And if you think that some people can have up to 12 or even more shocks

[00:04:00] during an event, this can have huge implications on how long the device is going to last.