After examining a national registry of emergency medical service (EMS) calls, a team of doctors from the University of California San Francisco have found that ambulances take almost four minutes longer to respond to cardiac arrest cases in lower income neighborhoods than they do in high-income neighborhoods.

"When it comes to a cardiac arrest, every minute counts," study leader Dr Renee Hsia, a professor of emergency medicine at UCSF and an emergency physician at Zuckerberg San Francisco General Hospital and Trauma Center, said in a statement. Past research has shown that for every minute that passes without CPR or defibrillation, people experiencing cardiac arrest – when the heart stops pumping – have a 7 to 10 percent lower chance of survival. Overall, less than 10 percent of individuals who suffer such an event outside a hospital survive.   

"Our findings show that health care disparities exist at the system-level, including ambulance transport times," she said. "As hospital closures and the cost of health care continue to rise, we must examine how to ensure access to care for our most vulnerable."

Dr Hsia and her colleagues chose to focus on ambulance response times after past studies showed that barriers to prehospital care have a large impact on medical access as a whole. And the investigation is particularly timely given that many privately owned EMS companies have gone out of business in recent years, leaving the public with fewer operating ambulances. The authors speculated that this might disproportionately affect residents of low-income communities, who are known to rely more heavily on prehospital care and have a higher incidence of life-threatening illnesses.

For their analysis, now published in JAMA Network Open, the team examined the association between the median income of zip codes in 46 out of 50 states (a total of 2,497 counties) and four metrics of EMS timeliness – time to the scene, on-scene time, transport time, and total time – when responding to 9-1-1 calls for cardiac arrest. They used the most recent data, from 2014, available in the National Emergency Medical Services Information System (NEMSIS), a voluntary national registry of EMS activations funded by the National Highway Traffic Safety Administration.

The study ultimately included 37,550 patients in high-income areas and 8,192 in low-income areas. For the richest zip codes, average total EMS time was 37.5 minutes, compared with 43.0 minutes for the poorest. Even after adjusting their calculations for delays associated with more urban regions, time of day, and day of the week, Dr Hsia’s group found that EMS time remained 10 percent longer in the most low-income communities, which they say translates to a 3.8-minute slower overall response time.

"That stacks the odds against survival for low-income patients," Hsia said. "As a society, we might hope that public services, such as ambulances, would be equally accessible, but our results show that this is not the case, even for deadly conditions like cardiac arrest."

This medical care inequality is likely to persist or even worsen, the team asserts, as public agency-operated EMS transportation continues to dwindle due to the rise of private ambulance services. These companies may prioritize profit over need, and therefore choose to place many of their dispatch centers in proximity to wealthy neighborhoods, leaving the poor areas in the lurch.