Calculating the 30-day Survival Rate in Acute Myocardial Infarction: Should we Use the Treatment Chain or the Hospital Catchment Model?

Introduction: Acute myocardial infarction (AMI) is a potentially deadly disease and significant efforts have been concentrated on improving hospital performance. A 30-day survival rate has become a key quality of care indicator. In Northern Norway, some patients undergoing AMI are directly transferred to the Regional Cardiac Intervention Center at the University Hospital of North Norway in Tromsø. Here, coronary angiography and percutaneous coronary intervention is performed. Consequently, local hospitals may be bypassed in the treatment chain, generating differences in case mix, and making the treatment chain model difficult to interpret. We aimed to compare the treatment chain model with an alternative based on patients' place of living.

Methods: Between 2013 and 2015, a total of 3,155 patients were registered in the Norwegian Patient Registry database. All patients were categorized according to their local hospital's catchment area. The method of Guo-Romano, with an indifference interval of 0.02, was used to test whether a hospital was an outlier or not. We adjusted for age, sex, comorbidity, and number of prior hospitalizations.

Conclusions: We revealed the 30-day AMI survival figure ranging between 88.0% and 93.5% (absolute difference 5.5%) using the hospital catchment method. The treatment chain rate ranged between 86.0% and 94.0% (absolute difference 8.0%). The latter figure is the one published as the National Quality of Care Measure in Norway. Local hospitals may get negative attention even though their catchment area is well served. We recommend the hospital catchment method as the first choice when measuring equality of care.