By Kristian Webb - 27th Mar 2018 - Course previews

Pacemakers and cardioinhibitory syncope

In this video from our Pacemaker Essentials course, you'll learn how dual-chamber pacemakers treat cardioinhibitory syncope. Discover the different mechanisms that pacemakers use to determine when a patient is about to suffer from a vagal episode and what they do to immediately treat the problem.

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Video Transcript

[00:00:00] Let's have a look at how pacemakers can be used to treat cardioinhibitory syncope. Cardioinhibitory syncope describes fainting in response to a trigger in your external environment. I've listed some of the triggers here. Feel free to pause the video and read through them. I just wanted to demonstrate that there's a full range of triggers. These triggers results 

[00:00:30] in a vagal response. The sympathetic nervous system activity decreases, the parasympathetic nervous system activity increases. And for those of  you in the know, that results in a drop in blood pressure, a drop in heart rate or both. Now, this is a defensive mechanism that the body has in place against high blood pressure. Sometimes, it can be hyperactive, as in these patients and 

[00:01:00] cause the patient to faint. So, how can a pacemaker help? Well, a pacemaker helps in two ways. Firstly, it has to be able to detect when a patient is about to suffer from a vagal episode. Certain pacemakers have specialized algorithms that enable them to do this. Some focus on a rate drop, so a sudden drop in a person's heart rate 

[00:01:30] in this population of patients. Others, look at tiny changes in the impedance of a pacing circuit. We'll come on to pacing circuits later. You don't have to worry about it. All you need to know is that by looking at the impedance of the circuit, the resistance to electricity around the circuit, a pacemaker is able to detect a change in contractility of the heart muscle. So, incredibly, 

[00:02:00] some pacemakers are able to detect when a heart becomes less contractile. Once a vagal episode has been detected, the pacemaker needs to do something about it. Now, we understand the cardiac output is stroke volume times heart rate. But we're fighting against a drop in blood pressure, so in actual effect, now it's not enough for the pacemaker to keep the heart rate at about 60 beats per minute 

[00:02:30] because we are fighting against a drop in blood pressure at the same time. In actual effect, the pacemaker increases the heart rate, typically to around 100 beats per minute, for roughly two minutes. This increases blood flow to the brain during the episodes and will narrowly avoid your vagal syncope. The pacemaker we used to do this is a dual-chamber pacemaker, and I'll explain why. Firstly, 

[00:03:00] an atrial lead is great for getting the information we need to know, that a person is about to have a vagal syncope. Secondly, when we try to increase the heart rate, we pace down the atrial lead. But in vagal syncope, the AV nodes can become sluggish as well and can start to falter. So, in addition to the atrial lead, we need a ventricular lead just in case heart block occurs at the same time. Now, that is why we need 

[00:03:30] a dual-chamber pacemaker. The reason we don't just have a ventricular lead is because during these episodes, we need all the help we can get. With the pacemaker pacing the atria and then the ventricles, we are allowing for that atrial kick, that extra filling of blood from the atria into the ventricles, that increases perfusion around the body and to the brain. Without an atrial 

[00:04:00] lead, the ventricular lead would not be able to do this and actually, the pacemaker will be less effective at combating vagal syncope. So, your takeaway message—dual-chamber pacemakers are used to treat cardioinhibitory syncope. However, you must ensure it has a specialist setting that not all devices have.