Association Between Ambulance Diversion and Survival Among Patients With Acute Myocardial Infarction

Study Questions:

What is the association between ambulance diversion hours and mortality rates among patients with acute myocardial infarction (AMI)?


This was a case-crossover design of 13,860 Medicare patients with AMI from 508 zip codes within four California counties (Los Angeles, San Francisco, San Mateo, and Santa Clara) whose admission date was between 2000 and 2005. Data included 100% Medicare claims data that covered admissions between 2000 and 2005, linked with date of death until 2006, and daily ambulance diversion logs from the same four counties. Among the hospital universe, 149 emergency departments (EDs) were identified as the nearest ED to these patients. The main outcome measure was the percentage of patients with AMI who died within 7 days, 30 days, 90 days, 9 months, and 1 year from admission (when their nearest ED was not on diversion and when that same ED was exposed to <6, 6 to <12, and ≥12 hours of diversion out of 24 hours on the day of admission).


Between 2000 and 2006, the mean (standard deviation) daily diversion duration was 7.9 (6.1) hours. Based on analysis of 11,625 patients admitted to the ED between 2000 and 2005, and whose nearest ED had at least three diversion exposure levels (3,541, 3,357, 2,667, and 2,060 patients for no exposure, exposure to <6, 6 to <12, and ≥12 hours of diversion, respectively), there were no statistically significant differences in mortality rates between no diversion and exposure to less than 12 hours of diversion. Exposure to 12 or more hours of diversion was associated with higher 30-day mortality versus no diversion status (unadjusted mortality rate, 392 patients [19%] vs. 545 patients [15%]; regression adjusted difference, 3.24 percentage points; 95% confidence interval [CI], 0.60-5.88); higher 90-day mortality (537 patients [26%] vs. 762 patients [22%]; 2.89 percentage points; 95% CI, 0.13-5.64); higher 9-month mortality (680 patients [33%] vs. 980 patients [28%]; 2.93 percentage points; 95% CI, 0.15-5.71); and higher 1-year mortality (731 patients [35%] vs. 1,034 patients [29%]; 3.04 percentage points; 95% CI, 0.33-5.75).


The authors concluded that the exposure to at least 12 hours of diversion by the nearest ED was associated with increased 30-day, 90-day, 9-month, and 1-year mortality.


This multisite, multicounty analysis using daily ambulance diversion and patient-level data suggests that when the nearest ED is on diversion, a lower proportion of patients is admitted to hospitals with catheterization capacity, and a higher proportion is admitted to for-profit and government hospitals. Furthermore, lengthy periods of ED diversion are associated with higher mortality rates among patients with a time-sensitive condition such as AMI. These findings point to the societal need for more targeted interventions to appropriately distribute system-level resources in such a way to decrease crowding and diversion, so that patients with time-sensitive conditions such as AMI are not adversely affected. Future studies will need to assess the various mechanisms through which diversion might adversely affect patient care, so that policies targeting the right mechanisms may be adapted for better care that translates into better clinical outcomes for patients in need.

Keywords: Outcome Assessment (Health Care), Ambulance Diversion, Myocardial Infarction, Patient Care, San Francisco, California, Emergency Service, Hospital, Los Angeles, United States

< Back to Listings