Population Health Research Net

DATA LINKAGE CASE STUDY

Age-and-Sex-Specific Trends in the Incidence of Hospitalised Acute Coronary Syndromes in Western Australia⁽¹⁾

Overview:

Monitoring population trends in the incidence of acute coronary heart disease (CHD) is essential for investigating the impact of primary prevention of this disease and its associated health care burden.

The research team were aware that whilst the incidence of myocardial infarction (MI) - or heart attack - has declined during the past four decades in many populations, they found there was limited population data measuring trends in acute coronary syndromes (ACS).

The research was therefore aimed at examining temporal trends in the incidence of hospitalised Acute Coronary Syndromes from 1996 to 2007 in a population-based setting using data from the Western Australian Data Linkage System. The research also identified trends in Myocardial Infarction and Unstable Angina incidence and investigated whether these trends differed by age and sex.

What data were used to perform the study?

The Western Australian Data Linkage System based at the Western Australian Department of Health was used to identify all incident ACS hospitalisations between 1996 and 2007.

The dataset for this study contained all hospital and death records for patients hospitalised with a discharge diagnosis of Coronary Heart Disease between January 1, 1986 and December 31, 2007 in Western Australia. Incident events were identified between 1996 and 2007, using a 10-year lookback period from each admission to determine incident status. Data for the study was obtained from two core datasets of the WA Data Linkage System which routinely capture all public and private hospitalisations (Hospital Morbidity Data Collection) and all registered deaths.

The study population was restricted to those 35-84 years of age because the diagnosis of ACS in the Hospital Morbidity Data Collection was considered unreliable in the very elderly.

What were the main results of the study?

There were 29,421 hospitalisations for Acute Coronary Syndrome in people 35-84 years of age in WA from 1996 - 2007.  66.6% of these were men. The significant majority (95.5%) of all incident ACS admissions were non-fatal and in Unstable Angina cases, 99% were non-fatal.

The average age of MI (heart attack) for women was 68.2 years, compared with 65.2 years for women with UA (unstable angina).

For men the average age for incident ACS hospitalisation was 61.3 years. The average age for women with incident ACS fell by 2.6 years over the study period but was unchanged in men.

The researchers results demonstrated declining age-standardised incidence of Acute Coronary Syndrome in men (1.7%/per year) and women (1.6%/per year), changes that were primarily driven by annual declines in unstable angina incidence of 3.0% in men and 2.5% in women and less so by declines in heart attack incidence.

Age-specific incidence rates of ACS showed differing trends by sex. While the research showed that there were similar decreasing trends in the incidence of ACS for women aged 55 to 64, 65 to 74 and 75 to 84 years of age, there was a significant increasing trend of 2.3% per year in women aged 35 to 54 years of age.

The incidence of heart attack in women also decreased between 55 and 84 years of age, but in contrast there was a marked increase in women aged 35 to 54 years of age.

Incidence rates for unstable angina showed substantial annual declines in all age groups for both sexes except for the 35 to 54 year old women in whom rates were unchanged.

The study also importantly discovered a disturbing significant increase in the incidence of Acute Coronary Syndrome, primarily MI or heart attack, in younger women.

What did the authors conclude from their results?

This whole-population study demonstrated a declining incidence of hospitalised Acute Coronary Syndrome (ACS) from 1996 to 2007. These encouraging trends are considered reflective of primary prevention efforts over several decades.  Additionally, these overall trends have occurred despite the introduction of troponin, a highly sensitive biomarker for the diagnosis of MI, which has been shown to weaken declining trends in MI incidence in other populations.

However, the study also showed that the age-standardised results mask age and sex differences, notably in women 35 to 54 years of age in whom ACS incidence has significantly increased. The research group determined this warrants further investigation to determine if the impact of troponin testing is selectively greater in this group or whether the recent reversal in the prevalence of cardiovascular risk factors such as diabetes and obesity has contributed to this trend.

In conclusion the age-standardised incidence of Acute Coronary Syndrome (ACS) decreased significantly in Western Australia from 1996 to 2007.

However, an increase in ACS incidence in women aged 35 to 54 years is troubling and warrants further investigation.

What has happened since this study was published?

Further research is planned into the factors contributing to these findings, including the impact of cardiovascular risk factors and cardiac biomarkers on the apparent adverse trends in younger women.

¹ Nedkoff LJ, Briffa TG, Preen DB, Sanfilippo FM, Hung J, Ridout SC, Knuiman M, Hobbs M. Age- and Sex-Specific Trends in the Incidence of Hospitalized Acute Coronary Syndrome in Western Australia. Circ Cardiovasc Qual Outcomes. 2011;4:557-564.

This study was supported by the University of Western Australia and the National Health and Medical Research Council of Australia. The authors wish to acknowledge the Data Linkage Branch, Department of Health (WA), for the extraction and provision of the linked data used in this study.