Location may play a role in how long patients survive following an MI, according to a new analysis.
Researchers found that patients admitted to high-performing hospitals after their MIs lived between 0.74 and 1.14 years longer compared with patients treated at low-performing hospitals. They defined performance based on 30-day risk-standardized mortality rates. The survival advantage persisted over a 17-year follow-up period.
Lead researcher Emily M. Bucholz, MD, of Boston Children’s Hospital, and colleagues published their results online in the New England Journal of Medicine on Oct. 6.
They analyzed data on 119,735 patients who enrolled in the Cooperative Cardiovascular Project (CCP), a nationally representative cohort study of fee-for-service Medicare beneficiaries who were hospitalized with acute MI between 1994 and 1996. The patients were admitted to 1,824 hospitals and were followed for 17 years.
Patients were excluded if they were admitted directly from the ambulatory surgery department, transferred from other acute care hospitals and left the hospital against medical advice.
The researchers placed hospitals into five groups based on case-mix severity. They found that patients admitted to hospitals with the highest expected mortality rates were typically older, had a higher prevalence of diabetes and were less likely to have undergone previous coronary revascularization. Those patients also had higher rates of shock and heart failure when admitted to the hospital and were less likely to have received reperfusion therapy or aspirin.
Within each of the case-mix stratum, patients admitted to the highest performing hospitals had the highest probability of survival and patients admitted to the lowest performing hospitals had the lowest probability.
In the lowest case-mix stratum, patients treated at high-performing hospitals lived an average of 1.07 years longer compared with those treated at low-performing hospitals. In the highest case-mix stratum, patients at high-performing hospitals lived an average of 0.83 years longer.
After adjusting for patient sociodemographic, clinical characteristics and other factors, the researchers found that patients treated at high-performing hospitals lived an average of 1.14 years longer than patients treated at low-performing hospitals in the lowest case-mix stratum and 0.84 years longer in the highest case-mix stratum.
All of the differences in survival were statistically significant.
“These findings were consistent across case-mix strata, which indicates that the relationship between hospital performance and long-term patient outcomes is independent of hospital case mix,” the researchers wrote. “The survival advantage for patients treated at high-performing hospitals arose from differences in survival during the first 30 days after hospitalization and then persisted during the remainder of follow-up.”
The researchers acknowledged the study had a few limitations, including that they applied several patient and hospital exclusion criteria when calculating risk-standardized mortality rates, which could have limited the generalizability of the findings to other patient populations. They also mentioned that approximately 7 percent of the patients were still alive after 17 years, so they had to calculate the life expectancy for these patients.
In addition, they did not have information on patients who lost Medicare eligibility. Further, the observational design of the study meant that unmeasured factors could have confounded the results. They also mentioned that the quality of care following MIs has improved since the study began in the mid-1990s.
Despite those limitations, the researchers found that high-performing hospitals had a survival advantage shortly after patients were admitted and that the advantage remained during the follow-up period.
“If high-performing hospitals admitted patients with lower risk than what was captured by the risk model, we would expect the survival curves to continue to diverge,” they wrote. “The fact that the survival curves remain parallel after the first 30 days suggests that the association of early hospital performance with outcomes is the result of quality differences and not residual confounding. Our results suggest that investing in initiatives to improve short-term hospital performance may also improve patient outcomes over the long term.”