Cardiac Pacemaker and Atrial Fibrillation – Simplified

Pacemakers and Atrial Fibrillation

This post is a follow up to the ‘What is Atrial Fibrillation’ article I recently uploaded .
So Atrial Fibrillation causes an irregular heart beat. This irregular heart beat can fall in to a few rough categories, of which some require a pacemaker.
Fast – The Ventricular rate (Bottom Chambers and main pumping chambers of the Heart) beat irregularly but at intervals predominantly over 100 bpm.(This may be treated with a drug e.g. a Beta Blocker). There are no pauses between beats of longer than 3s.
Pacemaker Atrial Fibrillation
Atrial Egram – AF
Well Controlled – though irregular, this Ventricular rate tends to be nicely sat between 60-100 bpm. (This may be down to medication such as Beta Blockers) and there is no pauses of above 3s.
Tachy-Brady AF – Some peoples AF can go fast and then slow at any time and are therefore a little trickier to manage.

Slow – The irregular Ventricular rate is slow and anywhere from 15-50 bpm. This is normally accompanied by pauses longer than 3s.
Now if Atrial Fibrillation is ‘well controlled‘ then a pacemaker does not feature, the patient is unlikely to have too many symptoms as a result though breathlessness is still a common complaint in these patients.
If the patient has ‘fast’ Atrial Fibrillation then they will often be treated with medications that lower the heart rate. Once on these medications the patient will usually have an ECG or Heart Monitor to see how much impact the drug is having on them. If the heart slows too much then the doctor would consider reducing the dosage. 
Occasionally patients have ‘Tachy-Brady’ AF some moments the heart is racing and at other times it slows down. When the patient is in fast AF, medication works well to keep the heart rate down.  However when the AF rate drops naturally, the drugs will still be having an impact and the heart may slow down too much. If  it is vital for these patients to remain medicated then a pacemaker can be used in addition to medications to make sure the heart doesn’t periodically slow down too much.
In ‘Slow’ AF a pacemaker is often used to alleviate symptoms such as dizziness, syncope (fainting) and fatigue caused by the heart simply going so slowly.
There is also two types of pacemaker that we use with Atrial Fibrillation. A Single Chamber Pacemaker and A Dual Chamber Pacemaker. The decision process of which pacemaker to use is simple….
If the patient is in PERMANENT AF we would use a single chamber pacemaker called a VVI device. This means is that it has one lead that is attached in the lower chamber of the heart (Ventricle). There is no point putting a further lead in the top of the heart because it is fibrillating, so we cannot make it beat and the information it is giving us is garbage – we just aren’t interested. 
So you have one Ventricular lead,  this watches the bottom chambers of the heart and if there is a long gap between heart beats then the pacemaker will fire and initiate a beat! (This stops you passing out in the supermarket and crushing the Eggs you were carrying).
If the Pacemaker is in PAROXYSMAL AF (posh word for AF that comes and goes like an annoying neighbour) then we would implant a Dual Chamber Pacemaker. This pacemaker works by watching the top of the heart and ‘knowing’ if it is in Sinus Rhythm or Atrial Fibrillation. When the patients heart is in Sinus Rhythm the pacemaker uses a mode that allows it to interact as little as possible when the patient goes into Atrial Fibrillation. The Atrial Lead (Top lead) can recognise when the Atria is fibrillating (twitching) and flip into a mode where it works just like the single chamber pacemaker in the example above. If we didn’t have this functionality then the patient could end up being ‘paced’ more than is necessary and we always try to avoid this. 
Now I hope this has cleared up how Atrial Fibrillation and Pacemakers interact. There are lots of pacemaker algorithms (clever bits of software) that look to minimise or treat AF with varying success. I will cover these at a later date. But for all intents and purposes these are the basics. I hope they have helped.

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

Time to pick up the other half 🙂
Thanks for Reading
Cardiac Technician
Image courtesy of Danilo Rizutti / FreeDigitalPhotos.net

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