4D flow MRI research offers cardiac patients new insights into disease

Bicuspid aortic valve (BAV) is a condition where people are born with only two flaps in their aortic valve instead of the normal three flaps. It affects up to two per cent of the population and BAV patients are also known to have weakness of the aorta — the main blood vessel of the heart that can suddenly rupture and lead to death.

While the medical community has long believed that patients with BAV were genetically predisposed to having aortic weakness, new research out of the Cumming School of Medicine, in partnership with the Martha and Richard Melman Family Bicuspid Aortic Valve Program at Northwestern Medicine in Chicago, has discovered there may be more at play in managing BAV-related diseases. The study was published online in the Journal of the American College of Cardiology on Aug. 17. 

New research using 4D flow MRI technology (an imaging technique that allows for visualization of blood flow in real-time) in a cohort of 20 BAV patients in the Chicago area, with tissue samples analyzed in Calgary, has revealed that abnormal blood flow from the two-flap valve can create the weakness in the aorta. Currently, open-heart surgery is the single best option for treatment, and is recommended to most patients to prevent life-threatening complications. This research provides encouraging data for improving risk assessment and the surgical treatment of BAV patients going forward.

Pictured above are, from left, David Guzzardi, PhD student and Dr. Paul Fedak, the authors of the study.

4D MRI technology allows a look inside the patient’s aorta

“As surgeons we have always treated these patients with invasive surgery to ensure the weak aorta was removed, preventing rupture,” says Dr. Paul W.M. Fedak, lead author of the study and cardiac surgeon and scientist at the Libin Cardiovascular Institute of Alberta and adjunct associate professor at Northwestern University Feinberg School of Medicine in Chicago.

“Patients with BAV are not all the same but we treat them, with respect to the timing and extent of surgery, as if they are all the same," says Fedak. "Based on these new findings, we found we can use 4D flow MRI technology to look inside a patient’s aorta and assess the unique blood flow pattern of that individual patient to plan the optimal surgical approach.”

The researchers compared the shear stress levels in the patients’ aortas (as measured through 4D flow MRI), with biopsy samples taken from those same patients, and looked for specific tissue biomarkers of the disease.

“We found that the blood vessel wall is very abnormal in the region where we tracked abnormal blood flow, compared to the region where normal blood flow was tracked,” says David Guzzardi, PhD student at the university's Libin Cardiovascular Institute and first author of the study. “This provides the most conclusive evidence to date that abnormal blood flow through the bicuspid valve may play a role in causing the disease.”

Most patients are unaware they have the condition and may only find out incidentally through tests for other medical conditions, or when there are aortic complications such as aneurysms or rupture.

Phil Mittertrainer is a BAV patient who had aortic surgery done by Fedak to prevent it from rupturing.

“I was very fit and active in sports, yet the doctors told me I needed open-heart surgery to remove my bicuspid aortic valve and enlarged aorta," he says. "I was lucky they discovered it. The public needs to know more about this common problem. If the aorta ruptures it is game over.”

Personalizing surgical treatment for BAV patients 

The 4D MRI technology in Calgary is only currently used for research but researchers hope this study will eventually lead to its use for clinical purposes.

“This study is important for patients as it may change how we treat people with BAV who require open-heart surgery to remove an enlarged aorta,” says study collaborator Dr. Patrick McCarthy, executive director at the Bluhm Cardiovascular Institute and chief of cardiac surgery at Northwestern University.

“Our work suggests that using 4D flow MRI may help us identify the diseased areas from the healthy ones, and by using this map we can plan a more personalized surgical approach for each patient we treat," says McCarthy. "We can be less aggressive in some patients and perhaps avoid invasive surgery, and more aggressive in others who are at higher risk.”

Funding for the study was provided by the National Institute of Health.