A new testing protocol identifies patients whose chest pain is heart-related even though their main heart arteries look normal during typical exams, according to results of a new study.

During the usual coronary angiography testing procedure, patients lie on a table while doctors inject dye into the arteries that carry blood to the heart, looking for places in the larger vessels where flow of the dye is impaired or blocked.

“People may have real angina even when the main arteries appear wide open,” study leader Dr. Colin Berry of the University of Glasgow said in a statement.

When angiography is negative, doctors should consider using MRI to observe blood flow while patients are exercising, “especially in women, who are more likely to have small-vessel angina that otherwise goes unrecognized,” Berry said.

“By measuring blood flow with a stress cardiac MRI test, we found that small vessel problems were common,” he added.

In the study, 250 adults with chest pain but no blocked coronary arteries based on angiography all underwent stress cardiac MRI tests, his team reported at the just-concluded American Heart Association scientific meeting in New Orleans.

In half the group, the stress cardiac MRI results were shared with doctors and patients to help guide diagnosis and treatment. In the other group, results of the stress cardiac MRI were not disclosed and treatment decisions were based only on the results of the negative angiograms.

When doctors reviewed the stress cardiac MRI images, about half of participants were diagnosed with microvascular angina, compared with fewer than 1 in 100 when doctors relied only on angiogram tests.

More than half of those diagnosed with microvascular angina were women. The diagnosis was significantly linked with improved quality of life, the researchers also found.

“The results of our study open a new path for people with chest pain,” Berry said.

“Clinical practice should now change to include a stress cardiac MRI test for angina, especially for women with chest pain and no blockages in the main arteries.”