In this video from our Pacemaker Essentials course, you'll learn how to use and adjust a pacemaker’s vectors if the output pulse is too high (which might drain the battery) or the amplitude of sensed events is too low (which might cause the pacemaker to miss something).
Here are the other videos in our series on pacemaker problems:
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This hands-on course takes the mystery out of pacemakers and gives clinicians a solid grounding in pacemaker therapy. You'll learn how pacemakers work, how to optimize a patient’s pacemaker therapy, and how to recognize and troubleshoot common problems. By the end of the course, you’ll feel comfortable addressing the most common pacemaker issues without having a pacemaker expert on hand!
[00:00:00] In pacing clinic, when we are reviewing a patient's pacemaker, we quite often see things that are cause for slight concern. These may be slightly high thresholds or small signal amplitudes. Now, what do I mean by this? Well, if we have higher thresholds, something like three volts at one millisecond, to be safe, we would
[00:00:30] set the pacemaker output pulse to six volts at one millisecond and we can see that the pacemaker will still perform appropriately. However, using this much energy every time you need to trigger a depolarization will be a huge drain on battery. Ultimately, their device will not last as long and in their lifetime, they will end up having more surgeries to replace their pacemaker. The other issue of small
[00:01:00] signal aptitudes can be seen, here. We have some ventricular complexes but they're very small. They're only just over 2 mV, which is where our ventricular channel sensitivity is set to. So, although there’s two problems, the important thing to do is not to panic. It does not immediately mean that we have to do something drastic about the device. There are actually programming changes we can make to try and help this.
[00:01:30] The main one is to try a different pacing circuit. These are sometimes called vectors. And vector just describes the direction of the electrical current. In this example, we are set up bipolar. So, we're using two electrodes on the lead to pace and sense. Now, in this configuration we've just seen, we're having high thresholds and our signal amplitude is not very good.
[00:02:00] So, what we can do is try a unipolar setup. So here, we're using one of the electrodes on the pacemaker lead, and we're using the pacemaker itself as the other electrodes. Now, you can see we've changed the direction of the electrical current. And this is why we sometimes refer to them as a change in pacing vector. Now, quite often, by making that small change, we can go back and look at our values again. Now, in this patient,
[00:02:30] their threshold is returned to a nice 1 volt at 0.4 milliseconds. This enables us to put the output pulse at 2 volts at 0.4 milliseconds and still maintain safe function of the pacemaker without the additional drain on the battery. 2 volts at 0.4 milliseconds is a very normal output pulse for a pacemaker and so this person will have good longevity from their device.
[00:03:00] Again here, we can see that the amplitude size has also improved. Before we were just marginally over 2 mV and now we can see these ventricular sensed events are much greater than the 2 mV, that the ventricular sensitivity is set to. This will put your mind at rest that the pacemaker will continue to function normally. Now, if we consider a quadripolar lead, think about all the possible options we have and all the vectors on offer.
[00:03:30] It's really incredible. So, a quadripolar lead gives us a huge amount of options. So, your takeaway message—if the intrinsic signal amplitude is small or the threshold is high, then try an alternative pacing circuit and see if that helps.