Does more intensive treatment of acute myocardial infarction in the elderly reduce mortality? Analysis using instrumental variables.
OBJECTIVE
To determine the effect of more intensive treatments on mortality in elderly patients with acute myocardial infarction (AMI).


METHODS
Analysis of incremental treatment effects using differential distances as instrumental variables to account for unobserved case-mix variation (selection bias) in observational Medicare claims data (1987 through 1991).


METHODS
Survival to 4 years after AMI.


RESULTS
Patients who receive different treatments differ in observable and unobservable health characteristics, biasing estimates of treatment effects based on standard methods of adjusting for observable differences. Patients' differential distances to alternative types of hospitals are strong independent predictors of how intensively an AMI patient will be treated and appear uncorrelated with health status. Thus, differential distances approximately randomize patients to different likelihoods of receiving intensive treatments. Comparisons of patient groups that differ only in differential distances show that the impact on mortality at 1 to 4 years after AMI of the incremental ("marginal") use of invasive procedures in Medicare patients was at most 5 percentage points; this gain was achieved during the first day of hospitalization and therefore appears attributable to treatments other than the procedures. Admission to a hospital treating a high volume of AMI patients was associated with an effect on mortality at 4 years of less than 1 percentage point, again arising on day 1. Patients living in rural areas experienced acute mortality that was an additional 0.6 percentage-point higher, after controlling for less access to intensive treatments.


CONCLUSIONS
For elderly patients with AMI, the aspects of treatment most affecting long-term survival relate to care within the first 24 hours of admission. The survival benefits from greater use of catheterization and revascularization procedures appear minimal in marginal patients.
McClellan
M
M
Department of Health Care Policy, Harvard Medical School, Boston, MA.
McNeil
B J
BJ
Newhouse
J P
JP
D000368:Aged; D000704:Analysis of Variance; D006328:Cardiac Catheterization / Q000706:statistics & numerical data*; D015897:Comorbidity; D005260:Female; D006297:Health Services Accessibility / Q000706:statistics & numerical data; D006302:Health Services Research / Q000379:methods; D006761:Hospitals / Q000145:classification / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D015233:Models, Statistical; D009203:Myocardial Infarction / Q000401:mortality* / Q000628:therapy*; D009204:Myocardial Revascularization / Q000706:statistics & numerical data*; D010043:Outcome and Process Assessment, Health Care / Q000706:statistics & numerical data; D015983:Selection Bias; D016019:Survival Analysis; D013673:Technology Assessment, Biomedical; D014481:United States / Q000453:epidemiology