Introduction to Pacemaker Modes AAI Pacemaker, VVI Pacemaker and DDD Pacemaker
Single Chamber Pacemakers
This refers to pacemakers that only use 1 lead into the heart. Predominantly this refers to a single lead in the Ventricles (bottom of the heart) but sometimes a single lead is put into the top of the heart (Atria) only.
|VVI Pacing in Atrial Fibrillation|
VVI Pacing – Single Lead in the Ventricles
When a Pacemaker is set to VVI mode it is only interested in the Ventricle (the bottom chambers of the heart). It watches to see if the bottom part of the heart ‘beats’ when it should and on the occasion that it doesn’t ‘beat’ then the pacemaker will send a pulse down the lead and make it contract. This is great in people who have Atrial Fibrillation and occasionally there heart goes too slowly, the reason being is that there is no structured beating in the top part of the heart for us to be interested in – it is fibrillating. See image of VVI Pacing (note that a Pacemaker with 2 leads can be set VVI)
Look at all that nonsense in the top of the heart – We aren’t interested in that so one lead in the bottom will do!
|The activity started by the pacemaker
travels through the top of the heart
before taking a natural pathway down
the ventricles (bottom of the heart)
AAI Pacing Mode – Single Lead in the Atria
When a Pacemaker is set to AAI mode it is only interested in the Atria (the top chambers of the heart). It watches to see if the top part of the heart ‘beats’ when it should and on the occasion that it doesn’t ‘beat’ then the pacemaker will send a pulse down the lead and make it contract. This is great in people who do not have heart block as the signal from the top of the heart (whether it comes naturally or from the pacemaker) will travel freely and down the correct channels into the Ventricle. This gives a completely natural heart beat and therefore is NOT Ventricular Pacing. See image of AAI Pacing (note that a Pacemaker with 2 leads can be set AAI)
An AAI pacemaker is considered for people with Sinus Node Disease this is disease which affects the regularity and rate that the top of the heart beats (thus effecting the overall heart rate).
DDD Pacing Mode – A lead in the Atria and a Lead in the Ventricle
This refers to a pacemaker with a lead in the top of the heart (Atria) and the bottom of the heart (Ventricles)
When a Pacemaker is set DDD (available in dual chamber or BiV pacemakers/ICD’s only) It looks after the top of the heart and the bottom of the heart in the same way as the examples above. In basic terms in a Dual Chamber Pacemaker you have 4 occurrences.
- The Heart Beats Normally – pacemaker just observes.
|This is Called A Sense V Sense|
- The Atria (Top Half) doesn’t Beat – so the pacemaker stimulates the Atria and Ventricles behave normally.
|This is called A Pace V Sense|
- The Atria Beats Normally the Ventricles do not (the signal is BLOCKED at the AV node/junction) – the pacemaker stimulates the Ventricles.
|This is Called A Sense V Pace|
- The Atria doesn’t Beat and the Ventricles do not either – the pacemaker initiates the beat in the top of the heart and the bottom of the heart.
|This is Called A Pace V Pace|
Dual Chamber Pacemakers are great in Heart Blocks where the signal is getting blocked half way at the AV Septum (the red line). The pacemaker can sense a physiological heart rate (in the top of the heart) and make sure that the bottom of the heart beats accordingly. If you run up a hill the pacemaker senses an increase in the top heart rate and increases the bottom heart beat accordingly. This synchrony also makes the heart beat a little more physiological.
This is a very basic introduction to what we mean when we say AAI, VVI and DDD Pacing.
As an end note you can set up a Dual Chamber Pacemaker to many modes which include AAI or VVI 🙂
A complete explanation of these topics and more is available in the book Pacemakers Made Easy by Carl Robinson.
I hope this wasn’t too basic but it was just an introduction!
Best get ready for football!