Study: New genetic test effective in detecting coronary artery disease

Scripps doctor hopes new technique can reduce number of unnecessary angiograms

A local cardiologist hopes that a new study he helped write will eventually reduce the number of unnecessary angiograms performed nationwide.

Dr. Eric Topol, chief academic officer of Scripps Health, said the study, published Monday in the Annals of Internal Medicine, shows that 23 genetic markers detectable in a patient's blood can help spot coronary artery disease.

The disease occurs when arteries become blocked, often leading to a heart attack. According to the National Institutes of Health, coronary artery disease is the leading cause of death in the United States.

Patients usually end up at their doctors' offices with chest pain and undergo one or more tests to determine whether their arteries are blocked.

Electrocardiograms or echocardiograms can help spot blockages by measuring the amount of electrical activity in the heart or by using sound waves to get a peek at heart muscle function.

Magnetic imaging can also be used and is often combined with a "stress test" that has a patient walk on a treadmill to get his or her blood pumping while various instruments measure blood flow.

But these tests ---- all noninvasive, which means they do not require the insertion of instruments into the body ---- can be inconclusive. The only conclusive way to tell if a patient's arteries are truly blocked is to do an angiogram, which requires inserting a catheter ---- a long thin tube ---- into a patient's artery, usually through an incision in the groin or leg.

While the NIH lists catheterization as "low risk," it can have complications, including bleeding and infection at the insertion point, damage to blood vessels, and an allergic reaction to a special dye used to make blockages visible.

Topol, the study's chief investigator and lead author, noted that many patients also cringe at the notion of a catheter snaking through their arteries to their heart.

And many, he said, ultimately find that they really did not need to go through the process in the first place.

"More than 2 million angiograms are done every year, and 30 percent of them are totally normal," Topol said.

The study, which Scripps participated in with many other organizations, looked at genetic markers in 526 nondiabetic patients who showed symptoms of coronary artery disease.

The study tested blood samples of these patients, looking for the presence of 23 genetic markers thought to signal the presence of artery blockage.

Patients also underwent a traditional coronary angiography to determine conclusively whether they did nor did not have at least one blood vessel that was at least half blocked.

The results showed that the genetic markers were "marginally" more effective than other noninvasive techniques, from stress tests to electrocardiograms, in determining who had coronary artery disease.

Even if it is only marginally better than other noninvasive tests, Topol said the genetic testing is still a breakthrough, because it can be used with other methods.

In cases where other tests are inconclusive, he said, the genetic test could be the final determinant that helps a patient avoid an unnecessary angiogram.

"If you come out with a really low score from this gene test, then the likelihood that you have coronary artery disease is very low," he said.

Topol said that while a large and more in-depth study is needed to prove the initial conclusions valid, cardiologists can already order a genetic test made by CardioDX of Palo Alto to detect the markers.

Call staff writer Paul Sisson at 760-901-4087.


