TORONTO, ON—Patients undergoing coronary artery bypass graft surgery could have reduced their risk of dying by having it performed in any one of 27 U.S. states rather than Ontario, according to a new peer-reviewed study from independent research organization the Fraser Institute.

The average risk of dying in hospital for patients undergoing coronary artery bypass graft surgery (CABG) in Ontario in 2004 was almost twice as high as Minnesota and Massachusetts and considerably higher than Colorado, Michigan, Maryland and Arizona, says the study, A Comparative Analysis of Mortality Rates Associated with Coronary Artery Bypass Graft (CABG) Surgery in Ontario and Select U.S. States.

“For a patient choosing where to have surgery, the main objective is to minimize risk. Minimizing risk means avoiding hospitals and jurisdictions that have high rates of risk-adjusted mortality. Since the estimates that are calculated have a range, avoiding risk means choosing the hospital or jurisdiction that has the lowest maximum probable mortality rate,” said Nadeem Esmail, Fraser Institute director of health system performance studies and study co-author.

An Ontario patient who had the surgery performed at an average Minnesota or Massachusetts hospital would have reduced their probable upper limit risk of mortality by about 41 percent. Among the 32 U.S. states whose mortality rates were compared to Ontario’s, only Vermont, Arkansas, New Hampshire, Utah, and Oregon had higher upper limit risk-adjusted mortality rates than Ontario in 2004.

“By simply crossing the border to either Michigan or New York, an Ontario patient could have reduced their probable upper limit mortality rate by 39 or 36 percent,” Esmail said.

The coronary artery bypass graft (CABG) surgery mortality rate is a widely used health outcome measure since the surgery is performed in high numbers, requires complex surgical and perioperative care, and has easily measurable rates of adverse events. The methodology used for calculating bypass surgery mortality rates in a standard way was developed by the U.S. Agency for Healthcare Research and Quality (AHRQ) with Stanford University. This measure has been shown to reflect the quality of care in hospitals where better processes of care may lead to lower mortality rates.

The study also examined average risk-adjusted mortality rates, and found that 20 of the 32 U.S. states for which data were available had statistically significant lower average risk-adjusted mortality rates than Ontario. This was also true for the United States as a whole. Only Arkansas had a statistically significant higher average mortality rate following CABG surgery than Ontario in 2004.

“Just as troubling as Ontario’s relative performance to that of the majority of U.S. states in 2004 is the fact that the gap between the performance of hospitals in Ontario and of those in many U.S. jurisdictions widened markedly between 2003 and 2004. For example, Minnesota’s average mortality rate as a proportion of Ontario’s went from 69 percent to 52 percent between 2003 and 2004. The average for the United States fell from 89 percent of Ontario’s risk-adjusted average mortality rate to 71 percent between 2003 and 2004,” Esmail added.

“Though it may be possible for a patient to have a less risky procedure at a higher-risk institution due to the variance in mortality rates among surgeons, it is nevertheless true that an average patient of average risk would be better off in some Ontario hospitals than others, and would be better off in the majority of U.S. states than they would be in Ontario,” Esmail said.