Nassir F. Marrouche
As more people live longer, the incidence of atrial fibrillation (AF), an often asymptomatic heart-rhythm disturbance that can lead to stroke, is growing day by day. A worldwide patient evaluation program, and new technologies based on the use of magnetic resonance imaging, are setting the stage for early detection and safer, more personalized treatment.
How many people suffer from atrial fibrillation?
Marrouche: AF is the most common cardiac arrhythmia or heart-rhythm disturbance. It accounts for over 60 % of all arrhythmias. Officially, more than three million people in the U.S. have it. Unofficially, the number is probably closer to five million. And since we have a rapidly aging society, the number of people with AF is expected to double by around 2020. The longer we live, the more scarring we have in our hearts. This scarring, or fibrotic tissue, can cause rhythm disturbances. In the U.S. alone, we expect to see ten million cases of AF by 2020, and perhaps 20 million by 2030. What's more, the numbers are growing at about the same rate worldwide. Overall, about 1.9 % of the 6.8 billion people alive today have atrial fibrillation. Additionally, about 28 % of AF episodes are completely asymptomatic, meaning you don't feel them at all and you don't know you have a serious heart disease. If you do have symptoms, they could be shortness of breath, chest pain, and most commonly, palpitation.
Can AF cause stroke?
Marrouche: Yes. Today in the U.S., at least one out of five people who arrive in emergency rooms with a stroke are there because of AF. Here's what happens: With AF, the left atrium of the heart beats about 500 to 600 times per minute. But the lower chamber, the left ventricle, moves more slowly. As a result, some of the blood pools in the left atrial appendage, and that blood can form clots. At some point, part of a clot may be pumped out, go to the brain, and cause a stroke. Additionally, 30 % of AF patients go on to develop heart failure, a condition in which the heart is unable to supply sufficient blood flow to meet the body's needs. AF is also associated with a much higher chance of sudden cardiac death compared with patients who do not have it. So this disease is a major concern. In the U.S. we spend around $15.4 billion per year to treat fibrillation-caused strokes and associated hospitalizations.
How has AF been treated until now?
Marrouche: Most patients are managed with anti-arrhythmic drugs and medications to avoid clotting. But statistics show that these regimens do not improve the incidence of stroke and mortality rates. In the U.S., a small minority of patients, about 60,000 per year, are treated with ablation therapy — the use of a catheter to ablate, or burn, parts of the surface area of the left atrium to make it electrically inactive and incapable of causing a rhythm disturbance. The procedure can cure AF. However, there are a number of concerns. Since it is performed using X-ray fluoroscopy, the images are somewhat indistinct and have a 2-second delay that can result in either excessive or insufficient ablation. Consequently, arrhythmia recurrence and procedural complication rates can be very high.
You are introducing a new methodology and treatment for AF...
Marrouche: Correct. There are two parts to this. The first is an evidence-based patient classification system, with four stages. The fourth stage, Utah 4, represents a very advanced disease state. Classification begins with an MR scan designed to determine the actual extent of damage, or fibrosis, in the heart. In fact, starting in May 2010, the University of Utah officially established a network of 28 medical centers around the world that have begun using this classification system to stage AF patients. This is the first step toward personalized management of this condition. The second part is the ablation procedure. If a patient turns out to be Utah 1, meaning that less than 5 % of their left atrium is fibrotic, we ablate the damaged tissue and the cure rate is nearly 100 %. The classification system is designed to catch patients early — before fibrosis becomes widespread — and treat them right away. Additionally, thanks to the system we have developed, we can definitively tell patients what their risk of stroke is and take corrective actions immediately.
You are also developing a new treatment for AF, right?
Marrouche: Yes. We have teamed with Siemens and SurgiVision, a Memphis, Tennessee-based medical device company, to develop a new procedure. Instead of using X-rays and their relatively indistinct images, the new procedure will use a 3-Tesla Siemens MR scanner. For the first time ever, the physician will see continuous, real-time 3D images of the patient's heart and the exact location of a SurgiVision MR-compatible catheter. When the catheter is in exactly the right place, ablation can begin.
Where are we on the road to clinical introduction?
Marrouche: We are getting close. We know how to make the procedure safe. My hope is that next year we will begin performing it on humans under an investigational device exemption. In fact, as we speak, we are building a dedicated electrophysiology MRI ablation suite in Utah for this purpose.
What role has Siemens Healthcare played in all of this?
MacLeod: Siemens is a natural partner because the University of Utah's Medical School has transitioned to Siemens products across the imaging spectrum. Our relationship with Siemens has focused on the development of real-time image acquisition and MRI-guided ablation techniques. The resulting software they have developed has become the centerpiece of all of our MRI experiments. It allows us to continuously acquire and display images from the scanner. This in turn makes it possible to visualize the ablation lesions as they are formed by the therapy and it allows the physician to determine exactly where and how much energy should be deposited in a specific area of the heart.
Where would you like the technology to be in five years?
MacLeod: We would like to have a system that would give us the same kind of temporal resolution as ultrasound, about 30 frames per second. Our best temporal resolution today is around 5 frames per second with acceptable image quality. At the same time, we need a slightly higher level of spatial resolution than what is currently possible in order to distinguish regions within the posterior wall of the left atrium, which is only two to four mm thick and is where the disease tends to be located. Further ahead, our vision is to develop a marker that can identify those regions with tissue characteristics that make them vulnerable to electrical disturbance but which are not present in a healthy heart.
In what ways do you expect the new procedure to change outcome and costs?
Marrouche: The new procedure will improve patient outcomes because it will reduce the incidence of strokes and increase the cure rate for ablation procedures. As for costs, I can't predict exact numbers, but it will be a major change.