Care following Acute Myocardial Infarction in the Veterans Administration Medical Centers: A Comparison with Medicare

OBJECTIVE: To compare patients treated for acute myocardial infarction (AMI) in a Veterans Health Administration (VHA) facility to similar patients treated under Medicare. DATA SOURCES: Administrative data on 13,129 elderly male veterans hospitalized for AMI in a VHA facility between October 1, 1996, and September 30, 1999, and a matched set of male Medicare beneficiaries with AMI treated in a non-VHA facility during the same time period. STUDY DESIGN: We conducted a retrospective cohort study using propensity score methods to identify a matched set of male elderly AMI patients treated either in a VHA facility or in a non-VHA facility under Medicare. We compared the two groups of patients according to characteristics of the admitting hospital, distances traveled for care, the use of invasive procedures, and mortality. We assessed the robustness of our conclusions to biases arising from unmeasured confounders using sensitivity analyses. PRINCIPAL FINDINGS: VHA patients were significantly less likely than Medicare beneficiaries to be admitted to high-volume facilities (for example, 25 percent versus 46 percent in 1999, p<0.001) or facilities with the capability to perform invasive cardiac procedures. Compared to Medicare patients, VHA patients traveled almost twice as far to their admitting hospital. The VHA patients were significantly less likely to undergo coronary angiography or revascularization in the 30 days following their AMI (p<0.001 for all comparisons). Veterans treated in the VHA had significantly higher mortality at one-year in all years studied (for example, 35.2 percent versus 30.6 percent in 1999). The proportion of elderly VHA patients admitted to high-volume facilities increased and 30-day mortality rates decreased between 1997 and 1999. Using sensitivity analyses to assess possible effects of unmeasured confounders, we could explain some but not all of the observed mortality differences. CONCLUSIONS: We observed differences in the way care for AMI patients was structured, in the use of invasive therapies, and in long term mortality between patients treated in VHA hospitals and those treated in non-VHA facilities under Medicare. Future research should focus on explanations for the differences between the two systems and for the reduction in short-term mortality among VHA patients. Further study of these differences both between and within the systems of care may help identify cost-effective strategies to improve care in both sectors

Influence of the Solvent Quality on Ring Polymer Dimensions

We present a systematic investigation of well-characterized, experimentally pure polystyrene (PS) rings with molar mass of 161 000 g/mol in dilute solutions. We measure the ring form factor at θ- and good-solvent conditions as well as in a polymeric solvent (linear PS of roughly comparable molar mass) by means of small-angle neutron scattering (SANS). Additional dynamic light scattering (DLS) measurements support the SANS data and help elucidate the role of solvent quality and solution preparation. The results indicate the increase of ring dimensions as the solvent quality improves. Furthermore, the experimental form factors in both θ-solvent and linear matrix behave as ideal rings and are fully superimposable. The nearly Gaussian conformations of rings in a melt of linear chains provide evidence of threading of linear chains through rings. The latter result has implications for the dynamics of ring–linear polymer mixtures