Predicting aortic aneurysm with 98% accuracy

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Northwestern University researchers have developed the first physics-based metric to predict whether or not a person might someday suffer an aortic aneurysm, a deadly condition that often causes no symptoms until it ruptures.

In the new study, the researchers forecasted abnormal aortic growth by measuring subtle "fluttering" in a patient's blood vessel. As blood flows through the aorta, it can cause the vessel wall to flutter, similar to how a banner ripples in the breeze. While stable flow predicts normal, natural growth, unstable flutter is highly predictive of future abnormal growth and potential rupture, the researchers found.

Called the "flutter instability parameter" (FIP), the new metric predicted future aneurysm with 98% accuracy on average three years after the FIP was first measured. To calculate a personalized FIP, patients only need a single 4D flow magnetic resonance imaging (MRI) scan.

Using the clinically measurable, predictive metric, physicians could prescribe medications to high-risk patients to intervene and potentially prevent the aorta from swelling to a dangerous size.

The research was published this week (Dec. 11) in the journal Nature Biomedical Engineering.

"Aortic aneurysms are colloquially referred to as 'silent killers' because they often go undetected until catastrophic dissection or rupture occurs," said Northwestern's Neelesh A. Patankar, senior author of the study. "The fundamental physics driving aneurysms has been unknown. As a result, there is no clinically approved protocol to predict them. Now, we have demonstrated the efficacy of a physics-based metric that helps predict future growth. This could be transformational in predicting cardiac pathologies."

An expert on fluid dynamics, Patankar is a professor of mechanical engineering at Northwestern's McCormick School of Engineering. He co-led the study with Dr. Tom Zhao, who specializes in first principles biomechanics.

Growing danger

An aortic aneurysm occurs when the aorta (the largest artery in the human body) swells to greater than 1.5 times its original size. As it grows, the aorta's wall weakens. Eventually, the wall becomes so weak that it can no longer withstand the pressure of blood flowing through it, causing the aorta to rupture. Although rare, an aortic rupture is usually unpredictable and almost always fatal.

Several prominent people have died from aortic aneurysm, including Grant Wahl, a sports journalist who died suddenly one year ago at the 2022 FIFA World Cup. Other celebrity deaths include John Ritter, Lucille Ball and Albert Einstein.

"Most people don't realize they have an aneurysm unless it is accidentally detected when they receive a scan for an unrelated issue," Patankar said. "If physicians detect it, they can suggest lifestyle changes or prescribe medication to lower blood pressure, heart rate and cholesterol. If it goes undetected, it can rupture, which is an immediate catastrophic event."

"If it ruptures when the person is outside of a hospital, the death rate is close to 100%," Zhao added. "The blood supply to the body stops, so critical organs like the brain can no longer function."
Removing the guesswork

For current standard of care, physicians estimate chance of rupture based on risk factors (such as age or smoking history) and the size of the aorta. To monitor a growing aorta, physicians track it with regular imaging scans. If the aorta starts to grow too quickly or become too large, then a patient often will undergo a surgical graft to reinforce the vessel wall, an invasive procedure that carries its own risks.

"Our collective lack of understanding makes it hard to monitor aneurysm progression," Zhao said. "Doctors need to regularly track the size of an aneurysm by imaging its location every one to five years depending on how fasts it grew previously and whether the patient has any associated diseases. Over this 'wait and see' period, an aneurysm can fatally burst."

To remove the guesswork from predicting future aneurysms, Patankar, Zhao and their collaborators sought to capture the fundamental physics underlying the problem. In extensive mathematical work and analyses, they discovered that problems arise when the fluttering vessel wall transitions from stable to unstable. This instability either causes or signals an aneurysm.

"Fluttering is a mechanical signature of future growth," Patankar said.