How a Biventricular Pacemaker is Implanted – What is a Biventricular Pacemaker

Simplified – Biventricular Implant Cardiac Pacemaker

This post is in direct response to a question I received after my previous post on a basic pacemaker implant.  

I will be doing more detailed explanations of Biventricular Pacemakers as although they share much of the same technology they really are very different. For instance with a standard pacemaker we try and minimise the amount of time the pacemaker has to kick in. With Biventricular pacemakers we aim to get the pacemaker to be working 100 percent of the time! This post is about the implanting of them….

Please read my explanation of how a basic pacemaker is implanted first or this won’t be as simple!

I do need to explain a little bit more about Biventricular pacemakers before I can answer the question effectively!

So a basic pacemaker is there as a back up to make sure your heart doesn’t go too slow and also to make sure the signals from the top of your heart get to the bottom of the heart. It can do all of this successfully with a lead in the right ventricle and an additional lead in the right atrium where required. In these patients the pumping action of their heart is still working well but occasionally the heart needs a kick up the arse!

The Hearts four ChambersThere is also a population of patients where the heart isn’t pumping efficiently because the bottom chambers of the heart aren’t contracting at the same time (they aren’t working as a team). The heart doesn’t necessarily go too slow or have pauses in rhythm, but each individual beat doesn’t pump enough blood. We can assess the amount of blood being pumped with each beat and call it the ‘Ejection Fraction’. Patients with low ejection fractions are often candidates for a Biventricular pacemaker! 

A Biventricular pacemaker works by synchronising the bottom chambers of the heart (RV and LV). In its simplest form this is making sure that the left ventricle and the right ventricle contract at the same time. 

Analogy time! Picture a plastic bag (the heart) full of water (blood) held out in front of you by a friend (who will be getting wet). In scenario A) you slap the plastic bag from the left and then immediately after you slap it from the right, water comes out the bag but not masses. Now scenario B) you slap both sides of the bag at the same time! Watch the water fly out! In both scenarios the same amount if energy has been applied (a slap from the right and a slap from the left) but the timing is KEY!….

This is the job of a BiV to take scenario A and make it scenario B. By controlling the timing of forces acting in the heart you can influence how much blood is expelled.

The implantation of a Biventricular pacemaker involves a Right Ventricular lead (minimum) and an extra lead on the left ventricle of the heart so we can get left and right sides beating in synchrony!
Lead of the pacemaker entering the heart.
No direct pathway from these veins
to the left side of the heart.
This poses a bit of an issue, with a regular pacemaker we use the cephalic or subclavian veins as a pathway to the required destination (see pacemaker implant). These blood vessels don’t go anywhere near the left side of the heart (See The Heart Simplified). So how are we going to get a lead to the left hand side of the heart?

Luckily the heart has some of its own plumbing that we can use. There is a network of veins that carries the de-oxygenated blood that the heart has used and deliver it to the Right Atrium! Some of these blood vessels are quite large and allow us to feed a lead (albeit against the flow of blood) down them to different areas of the heart!!!

The biventricular lead positioned in the heart
The Coronary Sinus in the Atrium gives access
to the hearts veinous network. Which we

The entry to this network of veins is called the coronary sinus, it’s a small hole at the bottom of the right atrium.  See Picture to the right       ——————————–>

To position the biventricular lead we feed a soft wire down the usual pathway of veins into the right atrium and then we try and manoeuvre this lead into the coronary sinus! this can take a while!  
Picture trying to get your house key into your door at home in total darkness… You know it’s there and there are things like the door handle letting you know you are in the right area but it may still take a little while! This is made more difficult by the Thebesian valve but I will talk about that more in another post, please google it if you wish to know more! 

Wahoooo (internal dialogue from the doctor) we have found the coronary sinus and we slowly advance the wire forward a little into the hearts network of veins. 

Road map of the Venous Network Coronary Sinus
Dye is injected revealing the ‘Map’ of Veins

We slide a Catheter over the wire (essentially a long tube) and into the network of veins.

Once in position we would like a map of the patients veins (every patients veins are different) so we inject some dye down the tube which lights up on the x-ray. This helps us select our vein of choice we want one that goes over the left ventricle! The lead is then put down the catheter (tube) and into the desired blood vessel!

Those of you on the ball may have noticed something very different about this lead, it’s not in the heart tissue! It’s pressed up against the side. This is true and works adequately but does mean we normally require a but more energy to be delivered by the pacemaker to make that half of the heart contract!

Now remember how the leads attached for the basic pacemaker with a passive and active fix?!? The Biventricular leads (LV leads) secure themselves in a very different way! The vein is smooth so we can’t use prongs to grip it, and the walls very thin so we can’t go screwing it in! So we wedge it in! They come with a range of kinks and bends on the end of the lead that are pushed into the vessel and wedge themselves there! 
I always think of this as the child who put his arm up a vending machine too far steeling chocolate and gets it stuck! The shape, size and features of his arm mean that though it might go in there alright… It doesn’t mean it will come out alright! Though in this case we want to lead to get stuck!
Once the lead is in place we test it in the same way as any other lead, checking impedance and threshold! When we are happy we attach the Biventricular pacemaker and stitch you back up! 

Now we understand how it is implanted you can see it clearly in this fantastic animation below,

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

THE PAD would like to thank The Sorin Group (Pacemaker Specialists) for this helpful animation on how a biventricular pacemaker is implanted.

Once this is in, it will hopefully improve your ejection fraction!

Right time for a Cornetto

Thanks for Reading

Cardiac Technician

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