MONDAY, Aug. 8 (HealthDay News) -- At some U.S. hospitals, nearly everyone who has cardiac catheterization to diagnose heart disease is found to have major blockages requiring some kind of action.

But in other hospitals, relatively few are found to have a major blockage when undergoing this procedure, indicating that many patients may be getting unnecessary procedures, according to a study in the Aug. 16 issue of the Journal of the American College of Cardiology.

"We're not doing as well as we thought. We need to improve," said study author Dr. Pamela S. Douglas, the Ursula Geller professor of cardiovascular research at Duke Clinical Research Institute in Durham, N.C. "You don't want to do this in people who don't need it."

Cardiac catheterization is when a doctor threads a small tube called a catheter into the heart from the groin or the arm. Through images obtained from angiography, the doctor can see blockages that might signal problems ahead.

This study is a follow-up to a 2010 paper by the same group of researchers that found that "the rate at which obstructive coronary artery disease was found nationally was much lower than everybody expected," Douglas said.

The new study may be the first to look at how hospitals differ.

This time, Douglas and her colleagues reviewed data on almost 600,000 patients with no known heart disease who had elected to undergo coronary angiography from 2005 to 2008 at one of almost 700 hospitals nationwide.

Obstructive coronary artery disease (CAD) was defined as a 50 percent or higher blockage of a major vessel.

While some hospitals found major blockages in all patients undergoing the procedure, others only found blockages in 23 percent of patients. The rates stayed consistent at institutions over the three years.

It also seemed clear, though, why hospitals varied so much.

Those that found lower rates of obstructive CAD tended to perform the procedure on lower-risk patients, including those who were younger and had no or atypical symptoms.

Hospitals at the other end of the scale seemed to select their patients more carefully, only performing the procedure on higher-risk patients, such as those with hypertension or diabetes. They also were less likely to prescribe aspirin, beta blockers, blood thinners and statins, and more likely to be low-volume centers, meaning they perform fewer of these procedures.

"When we looked at the average rate of finding obstructive coronary artery disease, we found that all hospitals are not the same," Douglas said. "There is substantial variation."

"That would represent a pattern of care in that particular institution compared to another institution," she added. "It's not just a patient-by-patient decision but decisions determined by the practice or culture in a particular hospital, whether hospitals are more or less aggressive."

Douglas suggests that the guidelines for making decisions on who undergoes this procedure should be tightened.

"There's a need for consensus agreement amongst cardiologists, and some standards as to which kinds of patients should undergo catheterization and which shouldn't," she said.

The American College of Cardiology will issue such criteria later this year, she added.

Dr. John Gassler, a professor of medicine at the University of Rochester Medical Center in New York, finds the study "intriguing" but doesn't feel it answers the question of overuse of diagnostic catheterization.

"There are many factors involved in making this decision," he said.

More information

The U.S. National Library of Medicine has more on cardiac catheterization.