Acute coronary syndrome national statistics: Challenges in definitions

Background Increasing convergence in the management of acute myocardial infarction (AMI) and unstable angina (UA) has led some to consider whether these 2 diagnoses should be consolidated into acute coronary syndrome (ACS) for the purpose of coronary heart disease surveillance. Methods We used the 1988-2001 Nationwide Inpatient Sample, which has demographic and diagnosis data on 6 to 7 million discharges per year from a sample of US nonfederal hospitals. We identified discharges with a first- or all-listed diagnosis of AMI (international Classification of Diseases, Ninth Revision, Clinical Modification 4 7 0) or UA (International Classification of Diseases, Ninth Revision, Clinical Modification 411) and defined ACS-first as a primary diagnosis of either condition and all-listed ACS as codes 410 or 411 among any diagnoses. Sampling weights were applied to produce yearly national discharge estimates; annual population estimates were used to calculate yearly hospital discharge rates; rates were then adjusted to the 2000 standard population. Results Rates of first- and all-listed AMIs changed little. Rates of first-listed UA fell 87% from 29.7/10000 in 1988 to 3.9/10000 in 2001. This sharp decline was seen among all age and sex groups. Consequently, rates of ACS as a primary diagnosis declined 44%. In contrast, discharge rates for all-listed UA and ACS declined only modestly. Conclusions As a primary diagnosis, UA is disappearing. Rates of first-listed ACS are quite sensitive to the decline in UA. Although discharge data based on first-listed diagnoses have been used to estimate the national incidence of AMI, they may not provide accurate data regarding current trends for ACS.