[Influence of number of citizens greater than 50 years of age on prevalence of acute myocardial infarction: epidemiological study of Sapporo residents].

BACKGROUND: Epidemiological studies have investigated the prevalence of acute myocardial infarction (AMI) in towns, medium cities and counties in Japan. The prevalence of AMI in a large city such as Sapporo has never been reported because of the difficulty of monitoring all patients with AMI. The population of middle-aged and senior residents has increased dramatically in Japan, and the impact of aging population on the prevalence of AMI is unknown.

OBJECTIVES: This study determined the prevalence of AMI in Sapporo in 2003, and investigated the relationship between the population of older citizens and the prevalence of AMI within individual regions of Sapporo.

METHODS: A questionnaire designed to focus on AMI was sent to every hospital in Sapporo offering services in internal medicine, cardiology, cardiovascular surgery, or surgery. Clinical and epidemiological data was requested on all patients presenting with AMI in 2003, including: municipal ward of patient's address, age, sex, whether hospitalization occurred via ambulance or through the out-patient clinic, whether the patient was transferred to another hospital for further treatment, whether the patient died, or was discharged alive.

RESULTS: Responses were received from 114 of 140 hospitals (81.4%), including all 32 hospitals performing cineangiography. As 799 patients were reported with AMI in 2003, the prevalence of AMI of Sapporo in 2003 was 42.9/100,000 residents. Forty-six patients was excluded because the absence of data on the questionnaire. Data was available for analysis in 753 AMI patients (537 males and 216 females, range 30-101 years, mean age 67.9 years). The prevalence of AMI was 60.8/100,000 in males and 22.1/100,000 in females (p < 0.05). Ninety-four deaths (57 males and 37 females) were attributed to AMI (range 48-99 years, mean age 75.2 years), for an overall mortality rate of 12.5%. AMI was a less frequent cause of death in the female population than the male population (male 6.5/100,000 and female 3.8/100,000, p < 0.05), but AMI was more frequently fatal in women (10.6% in males vs 17.1% in females, p < 0.05). Both AMI and fatality were more common with increasing age. Sapporo has 10 municipal wards. The prevalence of AMI in 3 wards was significantly higher than in the other municipal wards, these differences were more prominent when the prevalence of AMI was corrected for the population distribution of patients > or = 50 years old (p < 0.05). Significant correlations between the number of citizens and number of patients with AMI were observed in every age cohort divided into 10 years old > or = 50 years old, and the slopes of those regression lines increased with age cohort. Admission was via the outpatient clinic for 364 patients and 341 patients arrived by ambulance. The fatality rate did not differ between the two routes for admission.

CONCLUSIONS: AMI was more frequent in men than women in Sapporo, but AMI was more frequently fatal in females. Prevalence and fatality rate of AMI increased with age, and prevalence of AMI was determined by the number of senior citizens in certain wards.