Pacemakers and ICD’s – Minimising Percentage Pacing – Part 1

Part 1 Minimising % Ventricular Pacing

Why we want to minimise Ventricular pacing and a very simple example of this.

If you remember that when a standard pacemaker is implanted the lead that makes the bottom of the heart contract goes into the right ventricle. As a general rule of thumb technicians set up pacemakers and ICD’s to minimise how frequently the Ventricle (bottom of the heart) is paced.
Firstly you are probably interested in exactly WHY we want to reduce Ventricular pacing. Well this falls down to two main studies. One study found that pacemaker patients who’s pacemaker paced the right ventricle had a higher incidence of hospital admissions due to heart failure. You can see this study here: Heart Failure During Cardiac Pacing.
Pacemaker Lead Position Heart
Leads shown in the right Atrium and Right Ventricle
Another study has shown that incidence of Atrial Fibrillation were greater in those with Ventricular pacing than those with just Atrial Pacing (AAI). Again if you are interested in this study it can be found here: A Comparison of Atrial and Dual Chamber Pacing.
So there we have two pretty good reasons to try and minimise ventricular pacing you can add saving battery in there as a third if you so wish.

The reason these problems can occur is because of the Paced Heart Beat not being as Physiological as a natural heart beat.

Before I go any further however I want to explain that there are heart conditions where we do not want to minimise ventricular pacing and also heart conditions where we simply can’t.
In Biventricular pacemakers we would like to take control of how the ventricles contract, we do this by pacing the right and left ventricle at the best time to restore ‘Synchrony’. Thus we want to pace as close to 100% of the time as we can.
In some heart conditions where the structure of the heart has been affected e.g. HOCM which stands for Hypertrophic Obstructive Cardiomyopathy. It can be beneficial to pace in the right ventricle as the variance in the way the heart contracts actually helps with blood flow from the left ventricle around the body, again we then want to pace 100% of the time.
Permanent Complete Heart Block (CHB). Permanent CHB means that not one signal is making its way through the AV Node (no signals are travelling from the top of the heart to the bottom of the heart) therefor the pacemaker becomes responsible for all correctly timed contractions in the bottom of the heart.
The reason I quickly detailed these three examples was to show that sometimes pacing the Ventricle is unavoidable and if you read the studies you will see that it does not always lead to the problems we discussed. Therefor it is a balancing act for healthcare professionals to treat the condition primarily and secondary to that – could we reduce right ventricular pacing?
The next question is how do we reduce Ventricular Pacing?
It stands to reason that if you have a pacemaker you are assuming that when your heart needs it, the pacemaker kicks in and when your heart doesn’t need help, the pacemaker watches quietly in the background. In some of the simpler heart conditions this is pretty much the reality. In chronic Atrial Fibrillation where there is one lead in the bottom of the heart it will sit and watch and pace when required. In the majority of heart conditions this is not so straight forward.
The truth of the situation is that a pacemaker will occasionally kick in when it is not always necessary, we call this inappropriate pacing. Pacemaker manufacturers are always striving to develop software solutions that minimise inappropriate pacing.
The example below is the simplest way to explain what I mean.
A patient has a natural heart resting heart rate of 70 beats per minute but every now and again they can get a little bradycardic (a slow heart rate) and they can feel very lightheaded. To treat this a pacemaker was implanted and set up to kick in when the heart rate drops below 60bpm. The patient feels great. The problem is that when this patient sleeps their heart rate can naturally drop below 60bpm without it being a sign of trouble but instead as a result of the patients sleep state (where our bodies slow down). This patient as a result receives inappropriate pacing at night – the pacemaker is kicking in when it doesn’t need to.
The pacemaker manufacturers solved this problem with software. The software quite simply allowed the technician set a ‘sleep rate’ a different base rate that can be set for certain hours when the patient is sleeping. The patients sleep rate was put down to 50bpm and this minimised his inappropriate pacing.
So that is how software can be used to minimise inappropriate pacing and help reduce the increased risk of Atrial Fibrillation and Heart Failure.

A complete explanation of these topics and more is available in the book Pacemakers Made Easy by Carl Robinson.

In the next post I will explain the problems with reducing inappropriate pacing in Dual Chamber Devices and how the manufacturers have come up with solutions to solve this 🙂

Remember to leave any comments or questions you have at the bottom!!

Thanks for Reading
Time for a Cuppa and some Rich Tea Biscuits
Cardiac Technician
If you have any concerns relating to this article then please contact your Doctor/Cardiologist to discuss them. Local hospitals often have pacemaker/cardiology support groups so if you find out which is your nearest one, they are also great resources for patients and their families.

Image courtesy of [ xedos4] / FreeDigitalPhotos.net

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