There are measurably higher death rates for patients having a heart attack when ambulances have to be diverted from the closest emergency department for at least 12 hours, according to a report in the Journal of the American Medical Association.

Researchers from the University of California San Francisco and the Naval Graduate School of Business and Public Policy, Monterey, Calif., analyzed records from 149 emergency departments for 13,860 Medicare patients for four densely populated California counties between 2000 and 2005 and compared mortality rates for times ambulances went to the nearest hospital and for when the nearest hospital's emergency room was too busy and ambulances were diverted elsewhere.

“While demand on emergency care is increasing, supply of emergency care is decreasing,'' the authors said in a UCSF news release. “If these issues are not addressed on a larger scale, ED conditions will deteriorate, leaving significant implications for all.''

The seven-day mortality rate for patients going to the nearest ER was 9% compared with 10% when ambulances were being diverted for 12 or more hours. Other mortality rates for undiverted vs. diverted were: 15% and 19% after 30 days; 22% and 26% for 90 days; 28% and 33% nine months; and 29% and 35% after a year. The researchers noted that their findings were limited to elderly patients and that patients who died before an admission could be generated were excluded, so these “mortality rate differences should be considered a conservative estimate.”

The authors suggest that a more integrated “restructuring of hospital and largest system-level resources” may be required to lessen diversions and improve outcomes, as well as initiating patient-flow improvement strategies at the hospital level to reduce the need for diversions.

The counties studied were Los Angeles, San Francisco, San Mateo and Santa Clara, and they constituted 63% of California's population at the time of the 2000 census. The study was funded by the Robert Wood Johnson Foundation, National Institutes of Health and UCSF.