High Intensity Focused Ultrasound: A New Treatment for Atrial Fibrillation

Describe the High Intensity Focused Ultrasound procedure. How does it differ from radiofrequency (RF) ablation? Also, how is the Epicor Cardiac Ablation System utilized in this procedure? High Intensity Focused Ultrasound is a form of energy that is used to interrupt the electrical conductivity of atrial tissue, thereby not allowing the atrial fibrillation (AF) electrical foci to be propagated through the atrial tissue. As is well known, most atrial fibrillation originates from triggers or foci in or around the pulmonary veins. The Epicor system isolates the left atrium, encircling the ostium of all four pulmonary veins and isolating them electrically. The Epicor device concentrates a focused ultrasonic beam that is directed from the epicardium (meaning outside the heart) or endocardium (inside the heart). Then, by generating different levels of energy, it will ablate or deliver its most intense focal point of energy to different levels of thickness in the atrial tissue. It first delivers this at the innermost layer of the atrium, working outward; so that there is a transmural pattern that is continuous throughout the entire encircling lesion. Thus, two things happen: 1) there is a continuous lesion that goes all the way around the entrance of the pulmonary veins where the atrial fibrillation foci originate, and 2) it is guaranteed to be transmural so that all levels in that encircling lesion are ensured of having a lesion that will interrupt the passage of any electrical foci. For most other energy sources, energy is applied from inside the atrium to the outside of the atrium. It is also usually applied with a handheld device, which means that several factors are operator-dependent: 1) making sure you have a continuous lesion, and 2) making sure that the device when used creates a transmural or full-thickness interruption. However, the Epicor device, once put into place, has a computer-generated algorithm that guarantees the lesion is transmural and continuous that is the advantage of the system! Another difference, in terms of the procedure itself, is that when you are directing an energy source from outside the heart to inside the heart, the energy that passes through the wall of the heart (in this case, the left atrium) may pass all the way through; this energy is then dispersed into the blood pool of the left atrium, so it causes no damage. However, when you are operating from inside the left atrium and are directing your energy source outward to create a fully transmural lesion or ablated tissue, some of the energy may go beyond the epicardium of the left atrium and cause collateral damage to surrounding tissue. Another advantage of the Epicor device is it must be used on the beating heart; therefore, you do not require the use of the heart-lung machine. A lot of other devices that are used must be used from inside the heart, thereby requiring the use of the heart-lung machine and opening up the left atrium to apply the device this has had its own share of problems and mortality issues. However, with the Epicor device, you are able to create an encircling lesion around the pulmonary veins as well as create mitral lines and other lines of electrical disruption that are consistent with the current gold standard for atrial fibrillation operations, the Cox-Maze procedure. Another nice advantage of the Epicor device is it must be used on the beating heart; therefore, you do not require the use of the heart-lung machine. A lot of other devices that are used must be used from inside the heart, thereby requiring the use of the heart-lung machine and opening up the left atrium to apply the device this has had its own share of problems and mortality issues. However, with the Epicor device, you are able to create an encircling lesion around the pulmonary veins as well as create mitral lines and other lines that are consistent with the current gold standard for atrial fibrillation operations, the Cox-Maze procedure.

What are the benefits of High Intensity Focused Ultrasound versus radiofrequency ablation and other treatments available for atrial fibrillation (such as medications, shock, surgery, and pacemakers)? First of all, HIFU is fairly noninvasive, and while it still requires some surgical incision as opposed to catheter-based ablations, which I will discuss later, HIFU can be performed by making a 2- to 3-inch incision on the right side of the chest, between the ribs. Therefore, it doesn't require a full sternotomy, and it certainly doesn't require that the patient be on the heart-lung machine. A lot of the other technologies such as unipolar radiofrequency, bipolar radiofrequency, cryoablation, and laser ablation all require that you use the heart-lung machine and have the left atrium open to acquire the energy source. Another disadvantage is that by opening the left atrium, there is now a rough surface that can be thrombogenic (lead to the formation of blood clots) on the inside of the heart, which has certainly had its share of problems. HIFU, because it uses flowing blood to cool the dispersed energy, is also safe for coronary arteries there is no likelihood you are going to do any damage to any coronary arteries with HIFU. By the way the technology works, there is also no likelihood that you are going to cause any esophageal injuries from this device as well. Another advantage is procedure time HIFU is a relatively quick procedure. Once the whole operation is set up, the actual device time is roughly 10 minutes. Catheter-based ablation techniques also figure into the mix. During these procedures, the catheter is passed through either the arm or the groin, all the way into the heart. Then, using the tip of the catheter, a series of contiguous dots are created that are supposed to be continuous in encircling the focal point of atrial fibrillation the pulmonary veins. However, with catheter-based ablation, there is no good way of guaranteeing that the lesion its continuous and transmural. There certainly have also been a fair number of complications that have cropped up in the literature (such as pulmonary vein stenosis), as well as a success rate that is not as high as that reported by High Intensity Focused Ultrasound. When we first became involved in this, we looked at a number of different technologies, and the success rates reported were not as high as that of HIFU. Therefore, based on success rates, we thought it was worth an investigation to look into this technology. We quickly realized why the success rates are expected to be as they are. Looking at the safety of the device and its ease of use, we decided that out of all the technologies available, this is what we would choose. HIFU is a safe and highly successful operation.

How many patients have been treated at your institution since its inception in last December? Our institution has now treated 22 patients, to date.

What has been the success rate so far in your patients? Here is the interesting thing: not everyone who has atrial fibrillation and is treated with High Intensity Focused Ultrasound leaves the operating room in normal sinus rhythm. After surgery, HIFU patients are put on an anti-arrhythmic for roughly three months, as well as an anticoagulant such as coumadin for six months. The reason is because the tissue that gets ablated does not form scar tissue for several weeks after surgery, so the atrial fibrillation can persist. Therefore, we keep the patient on their medical regimen for about three months, and during that time period we restudy them intermittently with EKGs or a Holter monitor to identify any arrhythmic events that they experience. If in fact at three months they have no further arrhythmia, we stop their antiarrhythmics but leave them on coumadin or blood thinners on the outside chance that they may develop some intermittent occurrence for the next three months. After this time, we stop all medications. To date, five patients have passed the three-month point; all were in sinus rhythm.

When did you first learn about High Intensity Focused Ultrasound? What type of training is needed to perform High Intensity Focused Ultrasound? Dr. Cox had presented his findings and data in October 2003 at a conference at the Cleveland Clinic. Since then, we have been following its progress. As well, we have been in contact with the Epicor representatives to express our interest in their device. We are the first in Pennsylvania to bring this technology to our patients. All surgeons in our group went to a two-day, intensive workshop, conducted by Epicor, at one of their peer-to-peer training sites. Each session included a didactic program and operating room experience. Following this, we visited two other clinicians, Dr. Mark Groh in Ashville, North Carolina and Dr. Mark Mostovytch in Jacksonville, Florida, to observe further their clinical practices and discuss their protocols.

What is the future with this type of treatment? Do you expect this treatment to take over or increase in popularity over standard treatments for atrial fibrillation? I believe the technology of Epicor is based on solid principles guaranteeing a transmural continuous lesion set. I believe the outcome data will prove its superiority. As robotic access develops further and device development follows, the treatment form will be revered as the standard by which others will measure.