![]() In this instance, we can see the right ventricular lead has pulled away from the myocardium and is now set in the middle of the ventricle. These most commonly occur within four to six weeks of pacemaker implant. A lead displacement is where the lead has come away from where it is meant to be. We have lead displacement, a lead insulation break or a lead fracture. So let's have a look at a few of these bigger problems, which will lead to your failure to capture. No matter how much voltage we are delivering, it is not going to make the tissue depolarize. ![]() to 8 volts at 1 millisecond, yet this is still insufficient, which could suggest we have an infinite pacing threshold. So, if you are seeing loss of capture, which can be seen on this ECG, here, you can be quite confident that something catastrophic has happened to the lead and that is because the chances are the pacemaker has increased the output pulse ![]() The important fact is that this person will still have a healthy heart rate. at their next follow-up or in pacemaker clinic, and we can do something about it. In actual fact, the pacemaker is still performing. And you can see that the pacemakers recognize the problem adapted and we're still managing to cause the atrial tissue to depolarize. In most pacemakers, this will be around 8 volts at 1 millisecond. And what pacemakers usually do is just ramp up their output posts to the max. Now, these are hypothetical numbers but if the threshold did suddenly increase, the pacemaker is smart Again, here, it requires 5.5 volts at 0.4 milliseconds and 6.5 volts at 0.4 milliseconds. made up figures again and all of a sudden the atrial tissue, for whatever reason, requires an output pulse of 6 volts at 0.4 milliseconds to capture the tissue. Although you may have set the output pulse to 2 volts at 0.4 milliseconds, the pacemaker has a safety mechanism to deal with the occurrence of a suddenly large threshold. The output pulse is always large enough to trigger the depolarization. These slight fluctuations in the tissue's threshold And even as high as 1.25 volts at 0.4 milliseconds. Then it might go up to 1 volt at 0.4milliseconds, down again to 0.75 volts at 0.4 milliseconds. It's 0.7 volts at 0.4 milliseconds, here. And we can see actually that in the real world, the threshold does fluctuate. They're hypothetical values for the minimum amount of energy required to trigger a depolarization in the atria When we program an output pulse, we find the threshold of the tissue and we make sure the output pulse is twice as large as the minimum amount of energy required to trigger a depolarization. So what is happening? When a pacemaker is delivering an output pulse, but it is failing to have an effect this is usually a very bad sign and I'd like And here, I've just marked on for clarity, all those events where the pacemaker has failed to capture. actually, all of these output pulses, they're represented by these pacing spikes, fail to trigger a ventricular depolarization. And on the ECG example below, we can see that, You can also have permanent or absolute or chronic failure to capture. When some of the output pulses are successful but some aren't successful, this is intermittent. However, if we look at a few heartbeats along the ECG, we can see that this output pulse has failed to trigger a ventricular depolarization. Here, we can clearly see that the output pulse, which is represented by this pacing spike has triggered a ventricular depolarization and that is what we would usually expect to see. Failure to capture is when the output pulse from the pacemaker fails to make the target chamber depolarize. This chapter will ensure that you do not fall Why is this so important? Well, I've known unnecessary surgeries to resolve problems that actually could have been solved with a small programming change. In many cases, a tweak to the programming is sufficient. ![]() In this chapter, you will learn how to recognize the most common problems that occur and how they can be resolved. Now, I wish the pacemakers were infallible and once implanted, they never went wrong.
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