Hospital costs for various time periods after AMI were calculated by multiplying reported departmental charges for each admission by the relevant departmental cost-to-charge ratio, and adding in per diem costs based on each hospital’s annual Medicare cost reports (7). Reported costs reflect accounting conventions and potentially idiosyncratic cost allocation practices, and so may differ from true economic costs. However, as the results that follow illustrate, reported costs are highly correlated with real resource use, and the methods that follow focus on differences in cost trends rather than absolute cost levels.

Application of exclusion criteria developed in previous work led to an analytic sample of ≈646,000 patients. These AMI cohort creation methods have been described and validated in detail previously (8, 9); for example, validation studies using linked medical record data indicate that >99.5% of cases identified using these criteria represent true AMIs.

Two principal dimensions of hospital technological capabilities were measured: hospital volume and capacity to perform intensive cardiac procedures. A hospital’s capability to perform catheterization and revascularization over time was determined from hospital claims for performing these procedures, using techniques applied previously (7). For example, a hospital was categorized as a “catheterization hospital” in a given year if at least three catheterizations were performed on elderly AMI patients. Hospitals performing catheterization after 1984 but not in 1984 were categorized as acquiring catheterization capability. Procedure capability was emphasized because previous research has documented that technology adoption has a substantial impact on technology use and costs. Hospitals were classified as high-volume or not by summing their total number of initial elderly AMI admissions and dividing them into two groups based on whether or not their volume was above the median volume over the entire time period (≈75 AMIs per year).

Patient zip code of residence at the time of AMI was used to calculate each patient’s distance to the nearest hospital with each level of procedure capability (no procedure capacity, procedure capacity, acquired procedure capacity) and to the nearest high-volume hospital. The patient’s differential distance to a specialized type of hospital was the difference between the estimated distance to the nearest hospital of that type minus estimated distance to the nearest hospital. These distance measures are highly correlated with travel times to hospitals (10), and in any case random errors in distance measurement do not lead to inconsistent estimation of treatment effects using the grouped-data methods developed here.

Trends in AMI Treatments, Costs, and Outcomes

Table 1 describes the elderly AMI population in 1984, 1987, and 1990. The number of new AMIs declined slightly over time and average age increased, consistent with national trends in AMI incidence. Though the demographic composition of the cohorts was otherwise similar over time, comorbidities recorded at the time of initial admission suggest that the acuity of AMI patients may have increased slightly. In particular, the incidence of virtually all serious comorbidities increased steadily between 1984 and 1990. These trends may also reflect increasing attention to coding practices over time, though evidence from chart abstractions suggests that “upcoding” has declined (11). A growing share of patients were admitted initially to hospitals that performed catheterization and revascularization. This trend reflected both substantial adoption of these technologies by hospitals—around 19% of patients were admitted initially to hospitals that adopted technology between 1984 and 1990 —and a more modest trend toward more initial selection of these intensive hospitals for AMI treatment. As a result, the share of patients admitted to hospitals that did not perform catheterization declined from 44% to 39%, and the share of patients admitted to high-volume hospitals increased from 45% to 48%.

The AMI cohorts differed substantially in treatment and costs. Catheterization rates in the 90-day episode of care after AMI increased from 9% in 1984 to 34% in 1990. Use of coronary artery bypass surgery (bypass) also increased

Table 1. U.S. elderly AMI patients, 1984–1990: Trends in characteristics, treatments, outcomes, and expenditures

 

Year of AMI

Variable

1984 (n=220,345)

1987 (n=215,301)

1990 (n=211,259)

Age (SD)

75.6 (7.0)

75.9 (7.2)

76.2 (7.3)

Female

48.7

49.9

49.8

Black

5.3

5.6

5.7

Rural

29.5

30.4

30.1

Cancer

1.1

1.5

1.6

Pulmonary disease

8.3

11.3

12.8

Dementia

0.7

1.0

1.2

Diabetes

13.9

17.9

18.8

Renal disease

3.3

5.1

6.1

Cerebrovascular disease

2.1

2.6

2.8

Initial admit to hospital with catheterization by 1984

37.5

38.4

40.7

Initial admit to hospital adopting catheterization 1985–1990

18.1

19.0

20.0

Initial admit to high-volume hospital

44.9

46.0

48.7

90-day catheterization rate

9.3

24.0

33.9

90-Day PTCA rate

1.1

5.6

10.5

90-Day CABG rate

4.8

8.3

11.7

1-year admissions

1.96

1.99

2.10

1-year total hospital days

20.5

19.4

20.4

1-year total special care unit days

6.0

6.8

7.3

1-day mortality rate

8.9

8.3

7.2

1-year mortality rate

40.0

39.0

35.6

2-year mortality rate

47.3

46.0

42.5

1-year total hospital costs (1991 dollars)

$12,864

$14,228

$16,788

2-year total hospital costs (1991 dollars)

$14,142

$15,571

$18,301

PTCA, percutaneous transluminal coronary angioplasty; CABG, coronary artery bypass graft surgery.



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