Recent Advances in Energy Sources and Lesion Assessment Tools
Dr. Vivek Reddy’s talk at AF2017 highlighted advances in mapping and ablation of atrial fibrillation.
In his session Friday afternoon, Vivek Reddy, MD (Mount Sinai Medical Center, New York, NY) discussed various technologies in atrial fibrillation (AF) ablation, including those that are currently being used in patients, as well as others that are still in development or being evaluated in preclinical or animal studies.
“Most AF ablations, as you already know, are currently done with radiofrequency (RF) energy,” he told AF Symposium News before his presentation. “That was the way we started, and even with the advent of all of these other technologies, that is still the number-one way that most AF ablations are performed. So the first group of advances that I’m going to discuss are the ways in which to make RF ablation safer, perhaps more effective, and importantly, faster. The speed of ablation does matter. When you’re using a catheter to make point-by-point lesions, the advantage is that you have the flexibility to create the lesions you want, but the disadvantage is that it takes time to do that.”
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Dr. Reddy continued: “Some of the new ablation catheters have thermocouples on the surface of the catheter tip. By putting the thermocouple right on the tip of the catheter, the operator can know exactly what is happening on the surface of the tissue as they deliver irrigated RF energy into the tissue. It turns out that it actually can predict what is happening deeper in the tissue, and provides a feedback mechanism to guide energy titration. This is not a trivial issue. One of the previous problems with RF ablation was the chance of clots forming on the tip. About a decade ago, saline irrigation was introduced for RF ablation, which prevented clots from forming on the tip; however, with that technology you lost temperature feedback. Therefore, by putting thermocouples on the surface, we actually get back some of the temperature feedback that we lost years ago.”
What does this allow you to do? “The system automatically identifies how much power to deliver, and titrate it up and down as necessary,” said Dr. Reddy. “The first such catheter that we used in patients was made by a company called ACT. We’re doing a study in Europe with their catheter, and will present some of the initial data on safety, performance and effectiveness. There are other catheters with thermocouples on the surface made by other manufacturers, and those catheters are in clinical studies. However, it’s still early, and all of the studies are being done outside of the U.S. at this point.”
He added: “There are two other RF ablation catheters that can potentially help us determine how deep our lesion is as it’s forming. One of them uses fluorescence to provide lesion assessment. The idea is that most living tissue has NADH in it, including myocardial cells. This particular catheter has the ability to emit light using a laser; the laser excites the NADH and emits between 450-470 nm, allowing you to measure the fluorescence that is emitted. So as a catheter touches the myocardium, which has NADH in it, there is a fluorescence peak that is detected — so the operator knows that there is tissue contact. During ablation, the NADH levels fall. This catheter is made by LuxCath. Another company working on lesion assessment is MedLumics, which is using polarization-sensitive optical coherence reflectometry (PS-OCR). It’s a different approach to looking at tissue. It provides very high resolution, but the limitation is that you can only see a maximum of 1.5 to 2 mm deep, which still may be good enough in the atrium. Importantly, it is a way of directly visualizing the tissue as you do the ablation.”
“Finally, the last group of technologies I’m going to present on includes two completely novel ablation technologies with novel energy sources,” said Dr. Reddy. One of them is made by a company called VytronUS and uses ultrasound with a robotically driven catheter. As the catheter manipulates around, it uses ultrasound to first create a three-dimensional anatomy of the chamber. As the catheter is moved, the ultrasound images out the tip of the catheter, and can image and assess distance to create the 3D anatomy. The operator can click on the map where they want the ablation to be done, and the system uses ablative ultrasound energy to ablate that tissue. It’s a completely integrated system. This system has been in clinical trials for the last year outside the United States. The other novel energy technology is called irreversible electroporation (IRE). IRE allows you to apply DC current to tissues, and that transiently opens cell membranes. Depending on how much current you apply, it can cause enough damage that the cells die. Irreversible electroporation is nonthermal, so it’s not like cryo, which cools, or other energy sources that heat. It happens almost instantaneously, so it literally takes milliseconds to do the ablation. It also has some potential advantage of some degree of tissue selectivity. There has been a fair amount of preclinical work that has been published showing that depending on the amount of energy you use, you can selectively ablate cardiac tissue without affecting the esophagus, phrenic nerve, or other tissues. Therefore, it has real potential in terms of the speed and safety of the procedure. I imagine that within the next year or year and a half, there will be patients that will be treated with this, so it’s very exciting.”
What is the potential impact of these findings on clinical practice? “Overall, I think these all have the potential to make procedures more reproducible and faster, as well as safer in some instances. Will they all be successful? I don’t know. But I think some will be.”