Care following acute myocardial infarction in the veterans administration medical centers: a comparison with Medicare

Health Services Research, Dec, 2004 by Mary Beth Landrum, Edward Guadagnoli, Rose Zummo, David Chin, Barbara J. McNeil

The Veterans Health Administration (VHA) operates the largest integrated medical system in the United States. In 1996 the system became available to all veterans through an act of Congress. As a result, the number of veterans treated increased from 2.9 million in 1996 to 4.2 million in 2002 (Walsh 2003). This surge in patients and continued interest in monitoring care provided to veterans led the Office of Policy and Planning in the Department of Veterans Affairs to request an external evaluation of care provided to veterans with acute myocardial infarction (AMI). As contractors for this evaluation we compared the care provided to male veterans 65 years of age and older treated for AMI in VHA facilities to that provided to comparable Medicare beneficiaries treated in non-VHA facilities. We compared the two groups of patients according to characteristics of the hospitals to which they were admitted, distances traveled for care, utilization of invasive cardiac procedures, and mortality. We also assessed the robustness of our conclusions to biases arising from unmeasured confounders using sensitivity analyses. Our results complement those of prior studies (Wright et al. 1999; Petersen et al. 2000; Petersen et al. 2003) by comparing utilization and both short- and long-term outcomes in national cohorts of patients treated over the course of three recent years.

METHODS

Study Population

Veterans. We identified all male patients aged 65 and older treated for an AMI (primary diagnoses ICD-9-CM = 410.xx, excluding 410.x2) during the period October 1, 1996, through September 30, 1999 (N = 15,295), using the Patient Treatment File (PTF), a national administrative database that documents all inpatient admissions to VHA hospitals. We excluded (1) those whose AMI was likely a complication of noncardiac surgery (to assure that AMI was the primary reason for the admission (1); n - 172, 1.1 percent) (Wright et al. 1999); (2) those who were likely admitted only to rule out a myocardial infarction (discharged alive in less than three days; n = 246, 1.6 percent); (3) those who were long-term residents in nursing homes (2) (length of stay > 180 days; n = 15, 0.1 percent) (Wright et al. 1999); (4) those who were enrolled in a Medicare health maintenance organization (HMO) at the time of their hospitalization (n - 814, 5.3 percent); and (5) those not initially admitted to a VHA facility (to reduce bias associated with patients initially treated at non-VHA facilities who were transferred to a VHA facility for palliative care; n- 920, 6.0 percent), leaving a cohort of 13,129 patients (some patients met more than one exclusion criteria).

Medicare Beneficiaries. We identified all male patients aged 65 and older treated for AMI (principal diagnoses ICD-9-CM = 410.xx, excluding 410.x2) during the period October 1, 1996, through September 30, 1999 (N = 447,445), using Medicare Part A files. We excluded those who were likely admitted only to rule out an AMI (discharged alive in less than three days) (n = 7,497, 1.7 percent) and those who were enrolled in a Medicare HMO at the time of their hospitalization (n = 34,486, 7.7 percent).

Index Episode. Based on date of admission we created three cohorts of patients according to fiscal year (1997, 1998, and 1999) for each of the two sectors of care. We linked contiguous inpatient records to define an index episode of admission. Because VHA patients may be transferred to non-VHA facilities to receive invasive procedures if they are not available at the VHA hospital (Fleming et al. 1992; Wright et al. 1997; Wright et al. 1999), we included transfers to non-VHA hospitals paid for by either the VHA or Medicare. Patients initially admitted to a VHA facility and then transferred to a non-VHA facility were classified as VHA patients. As they represented less than 10 percent of the VHA cohort, we did not analyze these transferred patients as a separate subgroup and all reported results are for the combined cohort.

Comparison Variables

Characteristics of Admitting Hospitals. We calculated the volume of AMI patients per hospital as the number of admissions for patients aged 65 or older with a primary diagnosis of AMI using data from the PTF and Medicare Part A files for the VHA and non-VHA facilities, respectively. We determined a hospital's capability to perform coronary angiography and coronary artery bypass graft (CABG) based on data contained in PTF and Outpatient Clinic (OPC) files for VHA facilities and from Part A, hospital outpatient, and Part B files for the non-VHA facilities. We counted the number of claims for these procedures for patients age 65 and older with a diagnosis of ischemic heart disease (ICD-9CM = 410-414) and considered a hospital as having coronary angiography capabilities if there were five or more claims for angiography and as having CABG capabilities if ten or more procedures were performed within a given year (McClellan, McNeil, and Newhouse 1994). We then created three binary variables to indicate whether VHA and Medicare patients were admitted to a high-volume facility (more than 2.8 AMI admissions per week, the upper quartile in the distribution across all non-VHA facilities), a facility with angiography capabilities, and a facility with CABG capabilities.

Distances Traveled for Care. We obtained the latitude and longitude representing the geographic center of the zip code of each patient's residence from the United States Census Bureau and the hospital's longitude and latitude from the American Hospital Association's 1999 Survey. We approximated the distance traveled by patients to their admitting hospital as the arc distance along the earth's surface from the geographic center of the zip code of the patient's residence to the hospital. We also estimated the distance between each patient's home and the closest facility. Finally, we determined if VHA and Medicare patients were transferred to a different facility to receive either coronary angiography or a revascularization procedure and estimated the distance from the patient's home to the transfer facility as described above.