Cardiac Pacemaker – Pacing Percentages – Pacemaker Dependent
What does the term “100% paced” actually mean? Does that mean that my pacemaker is working 100% of the time or does it mean something else?
I received this question last night and it does bring up a subject I had been meaning to explain – Pacing Percentages.
In dual chamber devices you actually have two pacing percentages, one for the top of the heart (Atria) and one for the bottom of the heart (Ventricles). These tell us what percentage of the time that part of the heart needed to be told to beat by the pacemaker. So the short answer is Yes, 100% Paced means that the pacemaker always has to make that part of the heart beat. If the patient was 50% paced, this describes a person for whom the pacemaker is having to initiate 50% of the beats.
From starting this website and dealing with my patients I know that patients focus on this number as a benchmark for their cardiac/pacemaker health. PLEASE DON’T 🙂
This number is how dependent you are on the pacemaker to relieve your symptoms and not necessarily how dependent you are on the pacemaker to keep you alive. I will give an example which will hopefully help explain this concept…
A patient goes to the doctor complaining of being dizzy and lightheaded. Tests show that this patient has a heart rate of 40-50 BPM (Beats per minute) and requires a simple top chamber pacemaker (AAI Device) to increase his heart rate. The pacemaker is implanted and the base rate (the slowest the pacemaker will let the heart get) is set to 60BPM. On his first follow up, it is found that he is 100% paced. This is because his heart never gets the chance to initiate a beat because it does it too slowly and the pacemaker gets bored of waiting! (Ever asked somebody to do something and they have taken so long you have decided to go ahead and do it yourself?)
So even though he is 100% paced if his pacemaker stopped working the chances are his heart would return to 40-50BPM and he will just have a return of symptoms.
Am I Pacing Dependent?
So if you are 100% paced it does NOT necessarily mean you are dependent on the pacemaker to stay alive – just that it works a lot of the time to relieve you symptoms.
Why do technicians focus on this number then?
Well studies have shown that the more you pace the heart, over time this could cause a decrease in the hearts pumping functionality (Ejection Fraction). In essence, the more you pace the heart the less efficient the heart will work over time. So us technicians do try and decrease the percentage of time that the pacemaker is initiating a beat to minimize any side effects the pacemaker could have.
Like any medication there is a side effect and that’s why the minimum dose that works to relieve your symptoms is the right dose. That is what we are doing with this number, we are trying to minimise your dose to reduce potential side effects 🙂
This is becoming less of an issue as moving forward Cardiologists have started using septal lead placement (putting the lead in a different area of the heart) to try and minimise this side effect – especially in the younger population.
A complete explanation of these topics and more is available in the book Pacemakers Made Easy by Carl Robinson.
I hope this has relaxed some of you and dispelled a few myths about pacing 🙂
Time for a Cup of Tea (how very British)
Thanks for Reading
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