Diaphragmatic Pacing/ Phrenic Nerve Pacing - Twitching After a Pacemaker/ICD Implant

Diaphragmatic Pacing Phrenic Nerve Pacing
Diaphragmatic Pacing - Twitching After a Pacemaker/ICD Implant

What is Diaphragmatic Pacing?


A complication most commonly seen in Biventricular Pacemakers is something called Diaphragmatic Pacing... without being dangerous it is often uncomfortable and is often like fast constant hiccups for the patient - it is not something that people can learn to live with, so the pacemaker will need to be adjusted and in the worst case scenario the lead will need to be re-sited (move into a slightly different position). Diaphragmatic Pacing, sometimes called Phrenic Nerve Pacing occurs when the newly introduced Pacemaker lead, irritates or stimulates the Phrenic Nerve.

This complication occurs most commonly in BIVENTRICULAR Pacing!

What is the Phrenic Nerve?


The Phrenic Nerve is actually a pair of nerves, one on the left hand side and one on the right, they run between the lungs and the wall of the heart. The nerves are responsible for signals that move between the Brain and your Diaphragm. See Below :)

Diaphragmatic Pacing Phrenic Nerve Pacing

The Diaphragm is a large dome like muscle beneath the lungs. It is actually the muscle that controls your breathing, by contracting and relaxing it draws air in through your nose and mouth and into the lungs. Control over this process is 'semi automatic' - breathing will be instigated automatically without an individual consciously thinking about it. However a person can also consciously influence the process - think about when you hold your breath, take a deep breath or hyperventilate.

IF the Phrenic Nerve is 'tickled' this can cause sudden contractions of the diaphragm - resulting in a sudden short gasp of breath or a hiccup sensation. This is what is happening during Diaphragmatic Pacing. 

Why is it more common in Biventricular Pacemakers?


In my post on Biventricular Pacing - I explain that an additional lead is used and that this lead is positioned in a blood vessel that runs on the outside of the heart muscle. The position if the tip of this lead is very close to the Left Phrenic Nerve and as a result the two can often interact even though we do not want them too!

Look at how close the phrenic nerve runs to the outside of your left ventricle. This is where a Left Ventricular Lead sits in a Biventricular Pacemaker - which is why it is most common in these devices.

Diaphragmatic Pacing Phrenic Nerve Pacing

When the electrical pulse is sent down the Left Ventricular Lead it also stimulates the Phrenic Nerve and causes the patients Diaphragm to twitch!!

We can often resolve this issue by reprogramming the pacemaker (adjusting the settings)

How can this be stopped with Reprogramming the Pacemaker?


Reducing Power

Pacemakers all work on the principle that the more energy (electricity) you send down the lead, the more cells are excited. Send too little energy down the lead and not enough cells are excited enough to start the chain reaction that is a heart beat. So we have to make sure we are sending enough energy down the pacemaker lead to make the heart beat! 

As technicians we have a general rule of thumb that we find the minimum energy required (specific for each person) to make the heart 'beat'. The reason we do this is to reach the happy middle ground between safety and saving battery power! So if somebody required 1 Volt delivered over 0.4ms we set the pacemaker up to deliver 2 Volts at 0.4ms. It is often this amount of energy that is causing the problem - the higher the Voltage the greater amount of tissue excited and in turn the greater the chance of the Phrenic Nerve being affected! 

So one programming adjustment that we can make to 'cure' the diaphragmatic pacing, is to reduce the amount of energy being sent down the Left Ventricular Lead (the one that normally stimulates the Phrenic Nerve). 

Now those of you that are on your toes, will have realised that this probably contravenes the 'Times 2' safety rule we have just discussed. 

We are however able to do this in the LV Lead for one main reason...
If you have an RV Lead in this will make the heart beat - the LV Lead is there to help the heart beat more efficiently (read my posts on Biventricular Pacemakers).

Therefore, if worst comes to the worst and the LV Lead does not stimulate the heart at you will have a return of Heart Failure symptoms and not Asystole (NO HEART BEAT). On return of these symptoms you can seek help and the pacemaker team and your Cardiologist will re-evaluate your case.

A Change of Direction

As technicians we also have the option to change the 'direction' of the electrical charge. We call this the POLARITY.  Now please bear with me as this may take a bit of explaining!

Until now we have just discussed pacemakers delivering a charge down a lead, in actual fact part of the heart makes the circuit through which the electrical current passes.

The fact electricity requires a circuit is a concept you are probably familiar with..

  • Birds do not get electrocuted when they land on power lines  
  • Taser guns have two electrical prongs that the electricity passes between. 

Diaphragmatic Pacing Phrenic Nerve Pacing
This is the same with a pacemaker, some of your tissue (mostly Cardiac) is involved in the circuit. It is the electricity passing around this circuit that captures the tissue and makes your heart beat.

In its simplest form we can change most modern pacemakers from 'Bipolar' to 'Unipolar' and vice versa. We are changing the circuit used by the pacemaker and therefore the Cardiac tissue involved.

Cast your eyes left and in the top picture you can see the pacemaker and lead. This is what we call a BIPOLAR lead because it has two exposed 'electrodes'. I realise you may have to squint to see these I have drawn them in pink!

When set 'Unipolar' the pacemaker uses itself, ONE of these electrodes and some of your flesh and blood to make the circuit (Middle Picture).

When set BIPOLAR, the pacemaker uses the TWO available electrodes and some of your tissue to complete the circuit (bottom picture of the three).
You can quite clearly see that the circuit involves different areas of soft tissue.

In a Biventricular Device we have a few different configurations that we can set the circuit to - but the priniciple is the same. By altering the circuit you are selecting and discriminating the soft tissue involved in the circuit. If a person Phrenic Nerve is being included in the electrical circuit then you may have Diaphragmatic pacing - you could then change the configuration (polarity) to descriminate/eliminate the Phrenic nerve from the circuit.

In the image below I have shown a few polarity options we have in a Biventricular Pacemaker - each involves different areas of soft tissue.

Diaphragmatic Pacing Phrenic Nerve Pacing

If altering the energy delivered and/or altering the 'polarity' of the device are unable to 'cure' the Diaphragmatic Pacing then surgery may be required to re position the lead somewhere further form the Phrenic Nerve.

NB 

Sometimes Diaphragmatic Pacing can be intermittent and this is because the Phrenic Nerve is only occasionally being 'irritated' by the pacemaker lead. One common trigger is the patient laying on their left hand side - where the lead is pushed together with the Phrenic nerve. Another is when a person sneezes or coughs - this changes the pressures within the chest and again brings the lead and the nerve closer together. If you were to draw two dots on either side of a balloon, when inflated these dots will be quite far apart, when you deflate the balloon however the dots will come very close together - this is the same principle - a sudden exhalation can bring everything in the chest cavity closer together, bringing the Phrenic Nerve closer to the pacemaker lead tip.

I hope this has shed some light as I know a lot of my readers have experienced some Diaphragmatic Pacing in the past!

Time to e-mail my mate Neville in Australia ..

Thank you for reading

Cardiac Technician

In my next post I interview somebody who experienced quite bizarre Diaphragmatic Pacing!


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