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EDITORS

Caran Wilbanks, Editor, Preventing Chronic Disease. Disclosure: Caran Wilbanks has disclosed the following relevant financial relationship: Partner is employed by McKesson Corporation.

CME AUTHOR

Charles P. Vega, MD, Associate Professor and Residency Director, Department of Family Medicine, University of California, Irvine. Disclosure: Charles P. Vega, MD, has disclosed no relevant financial relationships.

AUTHORS AND CREDENTIALS

Disclosures: Julie C. Will, PhD, MPH, owns stock, stock options, or bonds from Johnson & Johnson and Pfizer. Amy L. Valderrama, PhD,and Paula W. Yoon, ScD, MPH have disclosed no relevant financial relationships.

Affiliation: Julie C. Will, Amy L. Valderrama, and Paula W. Yoon, Centers for Disease Control and Prevention, Atlanta, Georgia.

We obtained hospitalization data (1995–2010) from the National Hospital Discharge Survey (NHDS). We obtained ED visit data (1995–2009) from the National Hospital Ambulatory Medical Care Survey (NHAMCS). Both surveys were conducted by the National Center for Health Statistics (NCHS) (9,10). All research activities related to the surveys were reviewed and approved by the NCHS Research Ethics Review Board in accordance with 45 CFR 46. NHDS and NHAMCS are stratified, probability-designed surveys; the NHDS has 3 stages of sampling and the NHAMCS has 4 stages. Although the sampling frames and methods are different for the 2 surveys, at the first and second stages of sampling the surveys select noninstitutional hospitals in geographic areas of the United States, exclusive of federal, military, and Veterans Administration hospitals. Only short-stay hospitals (those with an average length of stay <30 days for all patients) and general hospitals (medical or surgical) are included in the surveys. Hospitals must also have at least 6 beds available for inpatient use. At the final stage, surveys select a systematic random sample of patient visits from either the participating hospital (NHDS) or the ED (NHAMCS). During 2008 through 2010, NCHS used half samples for the NHDS because of limited financial resources.

Response rates for the NHDS hospitals are generally at least 90%; however, in 2008, 2009, and 2010 the rates dropped to about 86%. In NHAMCS, about 90% of hospitals respond to the survey. From the hospitals with EDs, approximately 90% of EDs agree to provide survey information.

We calculated NHDS hospitalization and NHAMCS ED rates according to the technical specifications published by AHRQ for PQI number 13 (8). The numerator consists of all nonmaternal discharges of people aged 18 years or older with an International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9 CM) principal diagnosis code for angina: intermediate coronary syndrome, including unstable angina (411.1), acute coronary occlusion without myocardial infarction (411.81), acute ischemic heart disease (411.89), angina decubitus (413.0), prinzmetal angina (413.1), or angina pectoris (413.9). From both databases, we excluded maternal discharges using a method based on ICD-9 codes alone (11). Other exclusions required by the AHRQ specifications include transfers from another institution (the NHDS database is missing this information before 2001) and discharges with cardiac procedure codes in any field. In the ED analysis, we did not exclude these because transfers into an ED have a different meaning from transfers into a hospital, and cardiac procedures of this type are not generally done in the ED. By excluding cardiac procedures, the number of hospitalizations is reduced by approximately 10% and more serious and complex cases are eliminated. For example, persons who require procedures such as a cardiac pacemaker implant, cardiac valve repair, or coronary bypass are not included in the numerator. The denominators for the rates are from US Census population estimates (12) published by NCHS as part of the documentation package for each year’s survey database (9,10).

For NHDS, after the survey staff selected discharge records for study, demographic and medical data were abstracted by US Bureau of the Census staff (acting as agents for NCHS) or by hospital staff primarily from the records’ face sheets (the first page or cover page containing information such as health and medical requirements listed in an easy-to-use format) and discharge summaries. Editing and quality checks were made by NCHS; then the records were made available for analysis via a computerized database. We used the confidential database at the NCHS’s Research Data Center (which includes variables not available in the NHDS public-use database) for this analysis, which allowed us to use sampling design variables to calculate standard errors. For NHAMCS, hospital staff used medical records to complete the Patient Record Forms (brief, one-page forms that record the required survey information) for the ED visits. We used the public-use database because it included sampling design variables along with demographic and medical information.

In describing the characteristics of patients with preventable visits, we used 3 categories for race: white, black, or other (13). In calculating rates, we did not stratify by race because of sample size concerns. We used 4 US Census regions: Northeast, Midwest, South, and West (12). For insurance, we used only the principal expected source of payment to derive 4 categories; Medicare, Medicaid, private insurance, and other. “Other” included types such as other government insurance, self-pay, hospitalization without a charge, and worker’s compensation. Source of payment was considered missing and excluded from the calculation of percentages if the medical record abstract form or face sheets had “not stated” checked.

We estimated the total weighted number of preventable hospitalizations or ED visits for angina each year for persons aged 18 years or older. Because angina as a primary reason for a visit is rare, we combined 4 years of data to obtain 4 time periods: 1995–1998, 1999–2002, 2003–2006, and 2007 through the most recent year of data available (2010 for NHDS and 2009 for NHAMCS). We summed the census population estimates during these same time periods and used the results to calculate rates per 100,000 population.

We stratified the population by sex and age (18–44, 45–64, and ≥65 years for NHDS; and 18–64 and ≥65 years for NHAMCS). We used only 2 age categories for NHAMCS because using 3 resulted in large standard errors for point estimates. We also produced age- and sex- standardized rates using the 2000 US Census population as the standard population (12).

We used Proc Crosstab in SUDAAN 10.0 (Research Triangle Institute, Research Triangle Park, North Carolina) to calculate 95% confidence intervals (CIs) around the estimates. We did not calculate CIs around the denominators because they were derived from a census of the population. We tested differences between subgroups using z tests with α = .05 as a measure of significance; however, this testing was only done for estimates that were considered reliable according to NCHS standards (ie, estimates based on 30 or more visits and those where the relative standard error is 30% or less). We used the weighted least squares regression test for linear trends for each study subgroup and for the age- and sex-specific rates (14). To examine the assumption of linearity, we examined residuals plotted against the independent variable to verify that the residuals were randomly distributed.

From 1995 through 2010, there were 13,962 records for which angina without procedure was the first-listed diagnosis among persons aged 18 years or older in the NHDS sampled hospitals. This translates to a weighted estimate of 1,926,000 of these hospitalizations for US adults during the 16 years, an average of 120,000 each year.

In 1995–1998, most hospitalizations (57.2%) occurred among persons aged 65 years or older (Table 1); however, this changed by 2007–2010, when there were nonsignificant differences in the percentages between those aged 45 to 64 years (48.1%; 95% CI, 41.9%–54.4%) and those aged 65 years or older (39.7%; 95% CI, 33.7%–46.1%). The distribution of hospitalizations did not vary significantly by sex. From 1995 through 2002, hospitalizations for angina without procedure occurred less frequently in the western US Census region than in other regions. The largest payer for these hospitalizations was Medicare, ranging from 49% to 55% depending on the time period. Private insurance was the second largest payer, ranging from 31% to 35%. In 2003–2006, Medicaid paid for approximately 8% of these hospitalizations.

For both women and men, the rates for preventable angina hospitalizations increased significantly by age within each time period except for the most recent time period (Table 2). Rates dropped significantly from the earlier years (1995–1998) to the later years (2007–2010) for both sexes in every age group (65%–87.7% for women, 70%–85% for men). The highest rates for both sexes occurred from 1995 through 1998 among those aged 65 years or older (women, 287.4/100,000; men, 293.1/100,000).

During 1995–2009, there were 1,796 preventable ED visits for angina among persons aged 18 years or older in the EDs sampled by NHAMCS. This translates to a weighted number of 6,854,508 of these visits for US adults during 15 years, an average of 457,000 each year.

In 1995–1998, most visits (58.9%) were by persons aged 65 years or older (Table 3); however, this changed by 2007–2009, when the differences in the percentages between those aged 18–64 years (54.6%; 95% CI, 47.1%–61.9%) and those aged 65 years or older (45.4%; 95% CI, 38.1%–52.9%) became nonsignificant. The distribution of ED visits did not vary significantly by sex. As would be expected because of the racial composition of the United States, whites had the most visits. The largest payer for these ED visits was Medicare, which paid for about 50% of them during each study period. Private insurance was the second largest payer covering from 31% to 35% of the visits. In 2003–2006 (the most recent period with a reliable estimate for Medicaid), Medicaid paid for approximately 9% of these ED visits.

For women and men, the rates for preventable ED visits for angina were significantly higher for those aged 65 years or older compared with those who were younger (Table 4). Among those aged 65 or older, rates dropped significantly from the earlier years (1995–1998) to the later years (2007–2009) for both sexes in every age group (50% for women, 67% for men). The highest rates for both sexes occurred in 1995–1998 among those aged 65 years or older (women, 933.2/100,000; men, 1,170.5/100,000).

A test of linear trend shows that age- and sex-standardized hospitalization rates for angina (Figure) declined in a significant linear fashion (β = −21/100,000, P = .02). The actual rate declined from 89.1 per 100,000 to 15.8 per 100,000 — an 82% decline. Standardized rates for ED visits also declined in a significant linear fashion (β = −48/100,000, P = .05). The actual rates declined from 291.5 per 100,000 to 158.6 per 100,000 — a 46% decline.