A new blood test could one day give doctors a critical head start on heart attacks, a small new study suggests.

The test looks for cells that normally line the insides of blood vessels. When those cells, called endothelial cells, start to build up in the blood, researchers say they may be an early indicator of trouble.

“When they start to leak and slough off into the blood, that’s a really bad sign. They do that over the course of a few days to a couple of weeks before a heart attack occurs,” says researcher Eric J. Topol, MD, a professor of genomics and director of the Scripps Translational Science Institute in La Jolla, Calif.

“As they continue to slough off, they basically create a crack [in an artery wall]. A blood clot forms to seal the crack. That’s what causes a heart attack,” Topol says.

Slideshow: A Visual Guide to Heart Disease
Identifying Vulnerable Plaques

In recent years, doctors have developed a new understanding of heart attacks. 

They once thought that arteries clog for the same reason that drain pipes do. Gunk like cholesterol that flows through them gradually sticks to the inside walls, hardening over time and narrowing the artery opening. That’s a process called stenosis, and that kind of buildup sometimes does lead to chest pain and heart attacks.

But more often, scientists believe heart attacks happen for a different reason: soft plaques.

Soft plaques are collections of liquid fats and debris that build up hidden away inside artery walls, almost like pimples.

When the layer of cells containing the plaque starts to thin, the plaque can break open. A blood clot forms in response to the plaque rupture. The clot is often what blocks the artery, causing a heart attack.

The problem with soft plaques is that they are hard to detect and may not cause any symptoms.

Indeed, 50% of men and 64% of women who die suddenly of heart attacks have had no previous symptoms of heart disease, according to the American Heart Association.

“Clearly the ability to predict plaque rupture and [heart attack] is one of the most difficult situations that we have in heart disease,” says Barry Kaplan, MD, vice chairman of cardiology at North Shore University Hospital in Manhasset, N.Y. and Long Island Jewish Medical Center in New Hyde Park, N.Y.

Kaplan reviewed the study for WebMD but was not involved in the research.
Test Finds Circulating Cells

The new test uses tiny, protein-coated magnets to pull circulating endothelial cells (CECs), which are normally rare, out of a blood sample.

Similar technology is used in a test for cancer patients. That test identifies circulating tumor cells, which are also rare. In cancer, the test is meant to help doctors and patients determine how aggressive a tumor may be or whether it is responding to treatment.