Apolitically Incorrect » AF Research

Heart Arrhythmias and MRI

Rob Oakes — Tue, 24 Mar 2009 17:41:28 +0000

After nearly 18 months of work, my research group finally published our big study! It should appear in the journal of the American Heart Association, “Circulation” on April 7, 2009. This also means that I can finally talk about what I’ve been doing for the last long while.

Atrial fibrillation (AF) is the most common – and perhaps most insidious – form of heart arrhythmia (a change in the normal electrical patterns of the heart) in existence. It affects millions of people and while it isn’t life-threatening in its early stages, it eventually leads to stroke or heart attack in many of those people who are afflicted with it.

Unfortunately, the current ways of treating AF are completely inadequate. The class of medication used for treatment (anti-arrhythmics) often cause more problems than they prevent, and interventional treatment is still highly experimental. It is, therefore, all but a guarantee that the AF will become more serious over time. Patients cannot be as physically active as they used to be and eventually must adjust to the symptoms of the disease.

A great part of the reason why AF is so difficult to treat is that we lack a good understanding of what causes it. About fifteen years ago, some researchers in France recognized that the random spots of electrical activity within the pulmonary veins (which return blood to the heart from the lungs) were a likely source of the arrhythmia. As a result, there is an entire arm of interventional treatment designed to destroy these spots and isolate the pulmonary veins so that bad electrical signals are unable to influence the heart as a whole. While this is effective in some people, it doesn’t work for everyone.

More recently, other researchers found that AF actually changes the underlying tissue of the heart (a process known as remodeling), which results in other electrical and mechanical adaptations. These changes make the arrhythmia more serious as well as difficult to treat. Even though the changes are a sign that the person has a more advanced form the arrhythmia, the only way to ascertain the degree of change is to invasively measure electrical changes from the inside surface of the heart.

That is, until about a year ago. In the Circulation paper, we describe a method to determine how much the heart has remodeled by using MRI. We also showed that the degree of change is the single best indicator of how the patient will respond to treatment. While this may seem obvious, it isn’t something that could be measured easily or safely before. Now, we have a tool which allows us to see how the heart changes over time in response to AF. This will lead to a better understanding of the disease, and provide insight in how to treat it.

The image below shows an example of just how good this detection can be. The first column of images (A) shows a three dimensional model of the human left atrium. In the top row, we are looking at the back (or posterior) view of the left atrium. The pointy bits projecting to the left and right are the pulmonary veins. In the bottom row, we are looking at the atrial septum – part of the wall that divides the heart into left and right sides. The really interesting information is in the second column (B) which shows a 3D model where two different types of tissue have been identified. Healthy tissue (shown in blue) and diseased tissue (shown in green).

This particular patient has some diseased tissue, though overall the heart looks fairly healthy. What is striking, however, is how well this diseased tissue compares to the measurements made by invasive mapping (taken during a catheter intervention). On the back side (top) we can see a donut of unhealthy tissue, and on the right side (in the septum), we can see a hook of unhealthy tissue. The location and shapes of these tissue are mirrored on the invasive maps (C). And all of this can be determined without exposing a patient to radiation or needing to cut them open!

These types of MRI techniques open a whole new branch of research that can be done on the heart that has important implications for more than AF research. The remodeling and changes observed in AF can be seen in atrial tachycardia and even some types of ventricular arrhythmias. Moreover, it appears to be related to other conditions, like coronary artery disease or ischemia (from smoking, for example). More on that later, though. If interested, you can find the complete text of the Circulation article here.

Atrial Fibrillation Study Published

Rob Oakes — Mon, 20 Oct 2008 16:32:54 +0000

I am happy to note that the first of my papers with the Atrial Fibrillation Group at the University of Utah was published! The full text can be found here. While I know that I have an obvious bias, the paper is still very important. It describes the University of Utah's methodology for visualizing tissue damage following the ablation. Further, it lays the groundwork for the next studies: the detection of low voltage tissue prior to ablation, and the determination of what ablation parameters will result in the induction of scar. All in all, a nice little paper.

As an add on interest, we found that the degree of enhancement (or damage) seemed to relate to how well people did following the procedure. There are a lot of theories flying around as to why this might be the case. My own personal theory is that targeted ablation induces a change in diseased tissue. I was also happy to notice that we aren't the only people who see it as such. Our study was of sufficient interest that it was accompanied by editorial comment, as a highlighted article. Not bad, if I might be allowed a smug moment.

For those that care about such things, here is the citation:

McGann CJ, Kholmovski EG, Oakes, RS, Blauer JJ, Daccarett M, Segerson N, Airey KJ, Akoum N, Fish E, Badger TJ, DiBella EV, Parker D, MacLeod RS, Marrouche NF. New magnetic resonance imaging-based method for defining the extent of left atrial wall injury after ablation of atrial fibrillation. J Am Coll Cardiol. 2008 Oct 7; 52(15): 1263-71. PMID: 18926331.

If you'd like to take a look at the full article, you can get the accepted draft from the Science and Technology page.

AF and Smoking

Rob Oakes — Sun, 17 Aug 2008 15:14:39 +0000

Several weeks ago, while working on the revisions for a larger study, I noticed an important trend. Patients who suffer a recurrence of atrial fibrillation following catheter ablation quite often have a history of smoking. "That's interesting," I thought at the time. I then successfully stopped thinking about it, so that I could think about other important things. The ability of men to focus only on the task at hand being what it is. While spending time at Dr. Marrouche's party last night, I ran into Brent Hill. Brent is the research coordinator for the Division of Cardiology. While talking, I mentioned the finding. He got quite excited about it. So excited, in fact, that he thought about co-opting the idea for his thesis. Some additional ideas that he shared:

By what mechanism does smoking cause a recurrence of AF following the procedure? Might it be due to smoking induced ischemia?
Is the effect mitigated by the number of cigarettes which the person smokes per day?
Would offering smoking cessation materials help to increase the effectiveness of the ablation procedure?

Interesting things to think about! I think the next step is to formulate a number of specific hypotheses and draw up a formal proposal. At that point, it would be interesting to approach Marrouche and get his take on it.

Update

Though it may have been interesting to further think about and develop a map of how AF and smoking relate, I do not think that will ever be a possibility; unfortunately. Due to a number of personal reasons, I have decided that it is time for me to leave the AF group. I have greatly enjoyed the time that I have been able to work with the people in the group, but it is possible that my future lies somewhere outside of medicine. I will be posting a "Swan Song" shortly which describes my thoughts of how the various projects interconnect, but that will be my last thoughts on atrial fibrillation and its treatment.

Apolitically Incorrect » AF Research

Heart Arrhythmias and MRI

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