Noninvasive Imaging Gets to the Heart of Cardiac Disease Risk

A new method of analyzing images from routine heart scans can identify patients most at risk for cardiovascular diseases such as heart attack and stroke, and the method may help doctors deploy therapeutic interventions earlier and more effectively.

The approach, described in the 12 July issue of Science Translational Medicine, noninvasively measures blood vessel inflammation as an early warning signal for artery plaques that might go on to rupture and cause major cardiac events.

"This is a routine, outpatient, convenient test that can be done quickly and easily," said Keith Channon, a study author and senior researcher at the University of Oxford.

Non-invasive imaging of fat surrounding the coronary artery can predict heart attack risk. | A.S. Antonopoulos et al., Science Translational Medicine (2017)

Computerized tomography (CT) scans are already common components of clinical evaluations for chest pain. Alexios Antonopoulos and colleagues at University of Oxford devised a method to use CT scan images to home in on inflamed arteries before blood vessel plaques progress to becoming dangerously unstable.

"The key advantage of this method is to be able to detect early changes in blood vessels that precede cardiovascular disease," said Caitlin Czajka, an associate editor at Science Translational Medicine.

Every year, roughly 750,000 Americans have a heart attack and cardiovascular disease accounts for one in every four deaths in the United States, making it the leading cause of death for both men and women. Roughly half of those heart attacks happen in individuals without detectable narrowing in the coronary arteries because small deposits of cholesterol and other plaque-forming substances can break free and clog narrow blood vessels elsewhere.

"The likelihood of a coronary artery blockage to cause a heart attack is not necessarily related to degree of narrowing alone. This leaves many people unaware that they are at high risk," said Channon.

To create a better diagnostic, the researchers developed a metric called CT fat attenuation index (FAI) that is based on measurements of inflammation-induced changes in the layer of fat that surrounds blood vessels. Higher FAI means more inflammation, which predisposes artery plaques to rupture, potentially causing cardiac events.

"Our heart arteries are surrounded by fat. The fat detects inflammation, becoming more watery and less fatty as it sits next to an inflamed artery," said Charalambos Antoniades, a senior author on the paper at the University of Oxford.

The researchers confirmed that FAI correlated with blood vessel inflammation by directly comparing CT scans from 453 patients undergoing cardiac surgery with laboratory samples of artery tissue taken during the procedures. The researchers went on to quantify FAI in 273 additional patients (156 with and 117 without significant coronary plaques), where they observed that FAI decreased around the culprit arterial lesions after rupture in five patients who experienced heart attacks. No changes occurred around stable blood vessel plaques.

According to the authors, clinicians could use changes in FAI to monitor whether patients respond to therapies, or to proactively treat people at risk for arterial plaque rupture.

"By detecting those individuals who don't have narrowings, but are in the process of developing them, we may deploy interventions early enough to prevent heart disease. For example, we could deploy [cholesterol-lowering] statins in patients who don't meet the current criteria," Antoniades said.

Although the measure does not require any specialized scanning technology or image-acquisition routines, calculating FAI is computationally demanding — requiring roughly 45 minutes of time by a skilled technician. The researchers are working to make their software more widely available and accessible.

Clinical follow up studies to confirm the predictive value of FAI for cardiac events are ongoing and the authors expect to publish the results by the end of 2017.

"We are very excited and proud of our findings," said Channon. "This has really been the holy grail of the management of coronary artery disease, which has, up until this point, not been possible."

[Credit for associated image: A.S. Antonopoulos et al., Science Translational Medicine (2017)]