What do AF maps mean? 🤯

We've been quiet for the last few weeks as we have been crunching the numbers and presenting the initial findings of our AF research projects at the big Cardiology conferences. As they are now public, we will share our findings on BartsAF over the next few weeks! Thank you to all the participants in the different studies- hopefully, this early work will lead to continued steps forward in understanding this common and complex heart rhythm disorder. Be sure to subscribe to stay up to date!

We were invited to present this work at Heart Rhythm Society 2023 in New Orleans- the biggest gathering for cardiac electrophysiologists in the World!

Mapping AF

For those of you who have had an AF ablation, you may have looked to your left (if you were awake!) and seen the giant TV screens that the doctors and physiologists are staring at so intently. You may have seen a red and purple blob like the one below. It's a reconstruction of your heart and we covered this briefly here.

In the heart, we can visualize the electrical activity of the heartbeat through a process called electroanatomical mapping. This 'map' helps us identify regions where electrical signals are most abnormal, known as Low Voltage Areas (LVAs).

A left atrial 'electro-anatomical map' based on data acquired during the mapping stage from catheters placed inside the heart prior to ablation. The chamber shown is the left atrium and the prongs sticking out are the pulmonary veins and the left atrial appendage. The purple sections suggest normal voltages whereas the other colours are low-voltage areas.

Interestingly, when your heart is in AF, the map often shows more of these abnormal areas compared to a map of the same heart made a few minutes later. So it may not represent a true, fixed abnormality. These areas of 'false scars,' are mysterious- they appear abnormal during AF but look healthy when the heart is in a normal rhythm.

We don't fully understand why this happens and what the relevance of these temporary abnormal areas that disappear during AF is.

Are these additional abnormal areas real, or just 'noise' seen during AF?

These are two maps made from the same patient on the same day. During AF you can see more low-voltage (non-purple) areas...why does this happen?

Why It Matters: Aiming For A Healthy Heartbeat

Perhaps these 'false scars' may appear because of the erratic nature of electrical activity during AF, causing some areas of the heart to slow down, not unlike a traffic jam during rush hour which disappears when rush hour is over.

If these 'false scars' are more than just noise, they may be important in maintaining AF. If so, they could be potential targets for treatment by catheter ablation.

But this is just a theory, and thus what we went on to study and report.

During the AF catheter ablation procedure, we used a special mapping catheter and technology (Omnipolar Technology) to make 'High Definition' maps during AF and sinus rhythm. We did this in 26 patients in the AFHF study and found that actually the majority of the abnormal areas seen during AF were in fact this 'false scar' and were not seen during normal rhythm. But the amount of true and false scars per patient correlated- this means if a patient had a lot of false scars, they also had relatively a lot of true scars when in normal rhythm and vice versa, if only a little bit of false scars, then usually only a little bit of true scar was seen.

We went on to explore the distributions further- looking at how false and true scar was distributed across different segments of the heart chamber. The differences here were more subtle but the true scar was more likely to be found on the back wall (the blue area on the left image below).

We also considered whether the heart's 'terrain' might be a cause of the traffic jams and so whether the abnormalities seen during AF were more likely to be seen in these less smooth areas. (the red strips on the right-sided image)

these two models of the left atrial chamber of the heart have been coloured to show the segmental analysis we performed- on the left is the five-segment division to look at the distribution across the back, front, left, right, and bottom. the model on the right has been crudely shaded red on the ridges where the walls are more distorted and blue in the flat, central regions.

This image shows a lot of information but the main take-away is that false scar was seen on all segments of the heart and was more common than the true scar areas.

Here is the amount of false (or functional) scar as a percentage of the total wall in our study patients. A greater proportion of the heart in these complex regions was this false scar

Understanding the patterns: The Journey Continues

This study was an exploratory report of this phenomenon and we were glad to be able to share it with the Cardiology community at HRS. It raises many questions that we hope we will be able to go on to answer over the next year.

Remember, this was a small study involving 26 patients, and more research is needed. But every discovery brings us one step closer to understanding conditions like AF, leading to better treatments, and ultimately, healthier hearts.

Next week we'll cover some novel findings from our AFFU-Apple Watch trial that was awarded an Arrhythmia Alliance AF Pioneer award this year- stay tuned