The Paced Heart Beat and Septal Lead Positioning
A contraction that is initiated by a pacemaker is different to a one that occurs naturally here I explain why.
|Picture A. Natural Ventricular Conduction
|A natural heart beat
allows the Ventricles to contract at the same time thanks to the clever electrical circuitry that involves the His Bundles and the Pirkinje Fibres. If you are unsure of what I am talking about you need to read How the Heart Beats
first and this will make much more sense 🙂
In essence a natural ventricular heart beat looks like picture A: The electrical signal received from the top chambers of the heart passes quickly through the tissue and both ventricles contract at pretty much the same time. This enables the most efficient pumping of blood to the lungs and the rest of the body. This is the best way as it has been developed over millions of years of evolution and or God whatever your thinking. Either way its genius.
Now the majority of pacemakers have the Ventricular wire position in the Right Ventricular Apex (RV apex). This can be see in Picture B.
|Picture B. RV Apex Paced
In Picture B, I have also shown the conduction (order of cell contraction) that is happening during a ‘paced beat’. You can see that it is very different. What happens is the Right Ventricle starts to contract first before the Left Ventricle. This means that the contraction itself is a little slower with one occurring after the other instead of both simultaneously.
This leads to a slight twisting of the heart as it contracts and a less efficient heart beat.
Studies have shown that this order of conduction occurring over and over can change the structure of the heart and can lead to Heart Failure and Atrial Fibrillation. This is because the forces on the heart have been altered.
If you were to think about how the Sea shapes the coastline, if the direction and force of the waves onto the land would suddenly change, over time the coastline too would be changed.
The difference in contraction is quite evident on an ECG, you don’t have to be an expert to see how different these are 🙂
Normal Heart Beat ECG –
Paced Heart Beat ECG –
|Picture C: Septal Lead Position
and Ventricular Conduction
Since it has been shown that the paced beat can have a negative affect on the heart over time, solutions have been sort after. The main solution that is currently used is placing the Ventricular lead in the Septum (wall between the left and right Ventricle). This kind of pacing utilises the natural conduction pathways and leads to a more physiological contraction. This is shown in picture C.
This also produces a much more similar ECG to the RV Apex lead position and studies are starting to show that it has less long term implications to a persons health.
Thanks for reading, I decided on this post as my next will be focusing on how we reduce Right Ventricular Pacing in pacemakers.
A complete explanation of these topics and more is available in the book Pacemakers Made Easy by Carl Robinson.
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