(Reuters Health) - When ambulances go on diversion, bypassing the nearest hospital because emergency rooms are overcrowded, black patients may be more likely to die following a heart attack than their white counterparts, a U.S. study suggests.

Researchers examined data on more than 91,000 patients admitted to California hospitals for a heart attack from 2001 to 2011. They didn’t find a meaningful difference in one-year survival odds between black and white people when hospitals went on ambulance diversion for less than six hours on the day of patients’ heart attacks.

But when hospitals diverted ambulances for longer, black patients were more likely to die within a year of their heart attack, the study team reports in Health Affairs.

“Black patients still fared worse compared to white patients even though both experienced the same level of diversion, had the same access to technology, received the same measurable treatment, and were treated in similar hospitals,” said lead study author Dr. Renee Hsia, an emergency physician at Zuckerberg San Francisco General Hospital and Trauma Center.

Ambulance diversion happens when emergency departments are too crowded to take care of any more patients, and the goal is to send people instead to other hospitals that may be able to treat them sooner.

“You can imagine it’s like being at a grocery checkout stand, where one line is way too long, so you self-adjust to go to a shorter line. In healthcare, though, since you can’t see how crowded each ER is, the system tries to put you in a shorter line,” Hsia said by email.

“The problem, however, is that the next checkout line is at least several miles away, if not more, and the items in your grocery cart - basically your organs - have an expiration date of a few minutes to a few hours,” Hsia added. “So you can see, it’s a precarious situation.”

Overall, 52 percent of white patients and 48 percent of black patients went to the nearest hospital because ambulance diversion was not necessary.

In the entire group, 23 percent of patients died within one year of their heart attacks.

When black patients had a heart attack on a day that the nearest hospital was on diversion for about six to 12 hours, however, their odds of dying within one year were 4.1 percentage points higher than for white people.

When the closest hospital was on diversion for 12 hours or more on the day patients had a heart attack, black people had one-year mortality odds 3.1 percentage points higher than white people.

But based on the one-year risk of dying in the entire group, a 4 percentage point increase for blacks represents nearly a 19 percent increase in risk relative to whites, the authors point out.

Limitations of the study include the reliance on hospitals to accurately report ambulance diversion data to local health officials, the authors note. It’s also possible that some patients didn’t have heart attacks at home, the address used to determine their nearest hospital, and might have instead been closer to the hospital where they were treated.

Results from California also might not apply to other places in the U.S., particularly states with more rural populations, the researchers add.

Still, previous studies have found ambulance diversion isn’t uncommon for heart attack patients and when it happens, they have higher odds of dying, said Dr. Joaquin Cigarroa, clinical chief of the Knight Cardiovascular Institute at Oregon Health and Science University in Portland.

Individual patients can’t control whether ambulance diversion happens, but they can take steps to increase their survival odds when they suspect they’re having a heart attack, Cigarroa, who wasn’t involved in the study, said by email.

“Recognize signs and symptoms of a heart attack, dial 911, and ask to be taken to the nearest hospital with a heart catheterization laboratory,” Cigarroa said.

Signs can include chest pain, shortness of breath, breaking out in a cold sweat, dizziness or nausea, according to the American Heart Association.

Patients should also make sure they leave the hospital with the right medications, which might include blood thinners, or drugs to lower cholesterol or blood pressure.

“In addition, prior to discharge, make sure you are referred to a cardiac rehab program and have a follow-up with a heart doctor,” Cigarroa said.

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