In-hospital mortality in acute myocardial infarction according to population density and primary angioplasty procedures volume

Background: Low population density may be associated with high mortality in acute myocardial infarction (AMI) patients. The purpose of this study was to investigate the effect of population density and hospital primary percutaneous coronary intervention (PCI) volume on AMI in-hospital mortality in Japan. Methods and Results: This is a retrospective study of 64,414 AMI patients transported to hospital by ambulances. The main outcome measure was in-hospital mortality. The median population density was 1,147 (interquartile range, 342-5,210) persons/km². There was a significant negative relationship between population density and in-hospital mortality (OR for a quartile down in population density 1.086, 95% CI 1.042-1.132, P<0.001). Patients in less densely populated areas were more often transported to hospitals with a lower primary PCI volume, and they had a longer distance to travel. By using multivariable analysis, primary PCI volume was found to be significantly associated with in-hospital mortality, but distance to hospital was not. When divided into the low- and high-volume hospitals, using the cut-off value of 115 annual primary PCI procedures, the increase in in-hospital mortality associated with low population density was observed only in patients hospitalized in the low-volume hospitals. Conclusions: Increased in-hospital mortality related to low population density was observed only in AMI patients who were transported to the low primary PCI volume hospitals, but not in those who were transported to high-volume hospitals.