Heart attack patients often wind up at hospitals ill-equipped to treat them, and their chances of survival sometimes depend on how quickly they can be transferred to another medical center.

Yet a new study has found that nine out of 10 U.S. heart attack patients needing a transfer wound up waiting longer than the recommended 30 minutes.

As Reuters reports, the key to treating many heart attacks is clearing the blocked coronary artery cutting off blood to the heart and then inserting a small tube called a stent to keep the artery open. The reason so many patients need to be transferred for treatment is that less than a quarter of U.S. hospitals are equipped to perform stenting around the clock.

But in more than half of the cases studied, hospitals took longer than one hour to transfer patients.

“What we are finding is really long delays,” said Dr. Harlan Krumholz of the Yale School of Medicine, who was part of the research team. “Some people are being transferred out even after 90 minutes or two hours. There is no way those people are going to get timely treatment.”

The research, based on 2009 data from nearly 14,000 patients at 1,034 hospitals, was published in the Archives of Internal Medicine.

Another new study in the same medical journal, however, pointed out that stents often fail to provide lasting help for patients with blocked arteries. According to a separate Reuters story, nearly one out of every 10 such patients who get stents wind up back in the hospital within 30 days due to complications.

Experts differed, however, on the extent to which the results point to shortcomings in patient care versus other issues, such as how sick some patients were before undergoing the procedure.