Advanced Imaging Research Shows a More Accurate Link to Atrial Fibrillation

Thirty-five years ago, people were stunned when Jim Fixx, the 52-year-old author of The Complete Book of Running, dropped dead of a heart attack while on his daily run. The picture of cardiovascular health, Fixx ate right, exercised regularly, had given up smoking years ago, and yet….

Fast-forward 30 years. Attendees of the 2014 American Heart Association’s Scientific Sessions in Chicago were stunned by the presentation of Loyola University Chicago Stritch School of Medicine cardiologist Mark Rabbat, whose research had uncovered a more accurate predictor of atrial fibrillation (AFib), the number one risk factor for stroke, than body mass index (BMI).

Specifically, Dr. Rabbat’s study showed a statistically significant correlation between the fat layer and scarring in the left atrium that causes AFib. By contrast, the correlation between BMI and scarring in the left atrium was not significant.

“We opened Pandora’s Box with this study,” smiles Dr. Rabbat, an associate professor of Medicine and Radiology within the Division of Cardiology at Loyola University Medical Center and first author of the study. “What we found was many people who would not be considered obese by their BMI still have high volumes of fat around their hearts, which could put them at risk for atrial fibrillation and ultimately stroke. BMI may fail to completely inform us of a patient's true cardiovascular risk."

He adds, “This breakthrough naturally sparked a tremendous amount of debate."

What is not debatable is the impact of AFib on public health. According to the Centers for Disease Control, as many as 6.1 million people in the United States have AFib, the most common type of heart arrhythmia and a risk factor for stroke. Each year, AFib leads to more than 750,000 hospitalizations and contributes to an estimated 130,000 deaths. The condition costs the United States about $6 billion each year.

Since the release of the initial study, Epicardial adipose tissue volume predicts extent of left atrial fibrosis in patients with atrial fibrillation, Dr. Rabbat has initiated a number of new studies to gain a deeper understanding of the association between the fat layer around the heart—called epicardial adipose tissue or EAT— and AFib, and the interplay with other risk factors.

“For many years, it was believed that the localized fat around the heart was harmless, inert tissue. It now appears that EAT is metabolically active and releases mediators that trigger inflammation, causing fibrosis (scarring) in the left atrium. Fibrosis is part of the mechanism that causes the irregular heartbeat of AFib,” explains Dr. Rabbat.

A Chicago native who completed a residency in Internal Medicine and fellowships in Cardiovascular Medicine and Advanced Cardiovascular Imaging at the Cleveland Clinic and Loyola, uses a number of advanced, non-invasive cardiac imaging technologies in his quest to unlock the secrets of EAT. These technologies include magnetic resonance imaging (MRI) to precisely measure EAT volume and the amount of fibrosis present in the left atrium and 3D imaging to view the interaction of physiology and hemodynamics. These advanced imaging technologies play an integral role in research and in diagnosing and guiding treatment of patients at Loyola University Medical Center’s nationally ranked cardiology and heart surgery program.

As exciting as Dr. Rabbat’s findings are, they do present a conundrum. For years, people have been warned about obesity and encouraged to change their diets and add regular exercise to reduce the risk of heart disease. Should people continue these traditional “heart healthy” behaviors if BMI is less of an issue than the fat around the heart itself? At the same time, should thin individuals be more concerned about their cardiovascular health?

While there are no medical treatments to specifically target EAT, Dr. Rabbat says the accepted practices of weight loss through diet, exercise, or bariatric surgery will help manage the risk of heart disease. Slender adults should practice moderation as well. He predicts new screening tests using advanced imaging technologies will be developed to diagnose and guide treatment of EAT as research shows more about fat around the heart and how it affects AFib. 

“Research creates opportunities to challenge and question knowledge, and ultimately to improve the quality and effectiveness of care for our patients,” says Dr. Rabbat.