Correlation of Rates of Coronary Artery Bypass Surgery

This is a very famous study, offered here in several versions. One version (#3) was available only in paper form, scanned and inserted here several years ago. The other versions, different dates, etc., were taken more recently from electronic sources and are complete as found.

Correlation of Rates of Coronary Artery Bypass Surgery and Angioplasty Among 305 SMSAs for Medicare Patients
Evelyn Kuhn, Ph. D., Arthur Hanz, M. D. Ph. D., Mario Baras, Ph. D.

Problems and Objectives: The rate of coronary artery bypass surgery (CABG) varies greatly across geographic regions. Reasons for this variation are unknown. This study examined whether the rate of bypass surgery is associated with the rates of related procedures and with physician and hospital resources in the community.

Data and Methods: Three data sources were used for this study. The Health Care Financing Administration (HCFA) provided data on hospitalizations for Medicare patients discharged in 1988. The Area Resource File was used to obtain information for each of 305 SMSAs on the numbers of hospitals with given characteristics and the number of physicians with given training. The number of persons in each age, sex, and race category was obtained from census data. For white patients over the age of 64 we calculated age- and sex-adjusted rates for each SMSA for hospitalizations for CABG, PTCA, and cardiac catheterization (CATH) procedures. We also calculated the age- and sex-adjusted hospitalization rates for two diseases indicating the presence of coronary artery disease in the community: angina and myocardial infarction.

Results and Conclusions: IMe correlation between the rates of CABG and PTCA among the 305 SMSAs was .49 (p < .0001) before and after adjustment for the rates of coronary artery disease. After adjustment for the rate of CATH, however, the correlation between CABG and PTCA rates was nearly eliminated (r=.05, p > .20). Rates of CATH, CABG, and PTCA among SMSAs were significantly correlated with the density of thoracic surgeons and of hospitals with cardiac catheterization and open heart surgery programs. Regional variation accounted for 7% of the variation in CABG rates and 15% for PTCA. These percentages were not reduced after taking into account rates of CATH and physician and hospital resources. Implications: Community rates of CABG and PTCA are highly correlated, and both appear to be driven primarily by the rate of cardiac catheterization. Regional factors not captured in this study also affect the rates of these procedures. [source]

For author affiliations, current addresses, and contributions, see end of text.

Context. Geographic variation in population-based rates of invasive cardiac procedures has been described. However, little is known about variation in rates of noninvasive testing for cardiovascular disease. Echocardiography is the second most common cardiac diagnostic procedure.

Practice Pattern Examined. Population-based rates of echocardiography, adjusted for age, sex, and race, in the United States.

Results. 1 in 10 Medicare beneficiaries underwent echocardiography in 1995. Rates of echocardiography varied by state from 5% in Oregon to 15% in Michigan. Rates tended to be lowest in the Northern Great Plains, the Pacific Northwest, and the Rocky Mountains states. Among the 25 largest metropolitan areas, substantial variation was also apparent. For example, one fourth of Medicare beneficiaries in Miami, Florida, received echocardiography, and this proportion was more than four times greater than that seen in Seattle, Washington.

Conclusion. The likelihood of Medicare beneficiaries having echocardiography is influenced by where they live.

Variation in the provision of health services was first pointed out in the early 1970s. (1) More recently, geographic variation in population-based rates of invasive cardiac procedures, including coronary angiography, (2, 3) coronary artery bypass grafting (CABG), (2-6) and percutaneous coronary interventions, (2,5) has been described. For instance, one study (5) showed that rates of CABG varied more than sixfold across ZIP codes in Los Angeles County, California. Variation persists even when large geographic units are considered. Among Medicare beneficiaries, rates of cardiac catheterization, CABG, and percutaneous transluminal coronary angioplasty vary more than threefold across the United States. (2, 3) Such regional variation in the use of invasive procedures has also been demonstrated among survivors of acute myocardial infarction. (7)

Less is known about geographic variation in the use of noninvasive cardiac diagnostic testing. Wennberg and colleagues (8) previously showed that in northern New England, population-based rates of imaging stress testing varied 3.5-fold by hospital service area and rates of nonimaging stress testing varied by a factor of more than 4.

After electrocardiography (EKGs), the most common cardiac diagnostic procedure is echocardiography (also known as cardiac ultrasonography, or ECHO). Echocardiography provides information about both the structure and the function of the heart, and this information is useful for establishing a diagnosis; assessing prognosis; and determining optimal therapy for several indications, including heart failure, ischemic heart disease, and valve disease. (9) Echocardiography is noninvasive, is relatively inexpensive, and has few risks. Thus, it is frequently used--the number of echocardiographic studies performed in Medicare beneficiaries increased 143% from 1986 to 1989. (10) Not surprisingly, there is concern about overuse. (11) Only a relatively small proportion of echocardiographic studies results in a significant change in clinical management. (12)

We performed this study to answer two questions: What proportion of the Medicare population receives echocardiography each year? How much does the use of echocardiography vary in the United States?

We used the 5% sample from Medicare Part B to identify all Medicare beneficiaries who had echocardiography in 1995 [Current Procedural Terminology (CPT) codes 93307-93325]. Beneficiaries enrolled in risk-contract HMOs and those younger than 65 years of age were excluded. If a beneficiary had more than one echocardiographic procedure in 1995, only the first was counted. The period of eligibility for each beneficiary in the sample was ascertained and used to calculate person-years of observation. The unit of analysis was the hospital referral region (HRR) (4); HRRs are the geographic units of health care for the delivery of tertiary care services and are centered around major metropolitan areas. Each echocardiographic procedure was assigned to the HRR in which the beneficiary resided rather than to the HRR in which the service was delivered. Thus, echocardiography done on a New York City resident in a Miami hospital was attributed to the New York HRR.

Geographic rates were defined by using the number of persons in an HRR who received echocardiography as the numerator and the total number of person-years contributed by beneficiaries in that HRR as the denominator. We used the indirect method to adjust rates for age, race, and sex. (13) Observed and expected counts for HRRs were then cumulated to obtain approximate state rates, although some HRRs cross state borders. For ease of presentation, rates are expressed as percentages.

We used descriptive statistics to assess variation in echocardiography rates. In addition, to minimize any effect of small numbers of events in an HRR on the variability of the rates, we repeated the analysis using only the HRRs corresponding to the 25 largest metropolitan areas.

More than 3 million Medicare beneficiaries (10.5% of all Medicare beneficiaries) underwent echocardiography in 1995. Of these, 85% had one procedure during the year, 12% had two procedures, and 3% had three or more procedures. Given that the average allowable charge for echocardiography is $197, Medicare spent more than half a billion dollars on the procedure in 1995.

Figure 1 illustrates the geographic distribution across the United States. Beneficiaries living in Michigan were three times more likely than beneficiaries living in Oregon to undergo echocardiography. Three populous northeastern states--New York, New Jersey, and Pennsylvania--were among those in which echocardiography was provided most frequently. Areas in which the procedure was used least often tended to be the Northern Great Plains, the Pacific Northwest, and the Rocky Mountain states.

Table 1 shows the summary statistics for variation in the use of echocardiography. Among the states, the average proportion of Medicare beneficiaries receiving echocardiography in 1995 was 9.1% (interquartile range, 6.9% to 10.4%).

Figure 2 shows that more variation was seen among the 25 largest metropolitan areas. In these areas, the average proportion of Medicare beneficiaries who received echocardiography was 12.2% (interquartile range, 10.1% to 13.4%). One quarter of Medicare beneficiaries living in Miami received echocardiography in 1995; this rate was more than four times greater than that for Medicare beneficiaries living in Seattle.

We found that 1 in 10 Medicare beneficiaries had echocardiography at least once in 1995. We also found that a beneficiary's likelihood of receiving echocardiography was related to where he or she lived. The variation by state was about threefold, and the variation among the 25 largest metropolitan areas was even greater.

Because echocardiography is noninvasive and relatively inexpensive from a per-unit perspective, concern has been expressed about the potential for overuse. (11) In addition, the role of echocardiography in patient management and the effect of this procedure on outcome are uncertain. (12) One study (14) found that echocardiography was significantly less useful than the ordering physician expected. In another study, (12) only 10% to 16% of echocardiographic studies resulted in a major change in clinical management. The geographic variation seen in our study is evidence of the lack of consensus about how and in whom echocardiography should be used.

Clinicians might argue that variation in use reflects a variation in need; that is, variation in the underlying disease rate. However, by adjusting rates for age, race, and sex, we accounted for several important cardiac risk factors. In addition, it has generally been found that differences in illness burden explain a small fraction of the variation but not the major portion of it. Wennberg (4) found that rates of CABG and percutaneous transluminal coronary angioplasty were unrelated to rates of acute myocardial infarction in HRRs (R (2), 0.005 and 0.07, respectively).

Why does variation matter? First, variation may indicate uncertainty about the best possible diagnostic and treatment strategy for particular patients. Where consensus about diagnosis and treatment exists, variation tends to be minimized. For example, rates of hospitalization for hip fracture vary little, (4) reflecting the virtual certainty that patients with hip fracture will seek medical attention, receive an accurate diagnosis, and be treated in the hospital. The variation seen in cardiac procedure rates implies less agreement about when and how to diagnose and treat coronary artery disease. Our finding of variation in the use of echocardiography supports this hypothesis.

Second, diagnostic testing may lead to further testing and intervention. We previously showed (8) that rates of stress testing were strongly correlated with rates of subsequent coronary angiography and revascularization. Therefore, the true source of variation may be the decision to test rather than the decision to intervene. Because echocardiography is done for many reasons, it may lead to many intervention options, from valve surgery to medical management of congestive heart failure. However, because we could not identify the reason for echocardiography, we were unable to assess the relation of this test to the use of subsequent interventions. This issue merits further investigation.

Third, diagnostic testing is associated with costs as well as benefits. In this era of cost containment, it behooves clinicians to understand the benefits of a given test and to weigh those benefits against the test's costs. Although the $200 per-unit cost of echocardiography does not seem exorbitant in the current marketplace, the frequency with which the procedure is used results in an annual expenditure of more than half a billion dollars in the Medicare population alone. If the decision to intervene is also dependent on the decision to test, the cost of the probable subsequent intervention should also be considered. If variation is reduced, cost savings could result.

Our study is descriptive in nature and has several limitations. First, because we used Medicare data, our results are not applicable to younger populations, which may include many persons who require echocardiography for such conditions as congenital defects and valve disease. Second, the statistical stability of small area rates has been questioned. However, no HRR had fewer than 46 observed events nor fewer than 73 expected events. Limiting our analysis to the 25 largest HRRs, in which statistical stability was not a problem, actually increased variation.

In summary, we found substantial variation in population-based rates of use of echocardiography. Which rate is the correct rate? Are low-rate areas underserved, are high-rate areas overserved, or is neither of these possibilities true? These are questions for further study.

1. Wennberg J, Gittelsohn A. Small area variations in health care delivery: a population-based health information system can guide planning and regulatory decision-making. Science. 1973;182:1102-8.

2. Kuhn EM, Hartz AJ, Baras M. Correlation of rates of coronary artery bypass surgery, angioplasty, and cardiac catheterization in 305 large communities for persons age 65 and older. Health Serv Res. 1995;30:425-36.

3. Chassin MR, Brook RH, Park RE, et al. Variations in the use of medical and surgical services by the Medicare population.
N Engl J Med. 1986;314:285-90.

4. Wennberg JE. The Dartmouth Atlas of Health Care in the United States. Chicago: American Hospital Publishing; 1998.

5. Carlisle DM, Valdez RB, Shapiro MF, Brook RH. Geographic variation in rates of selected surgical procedures within Los Angeles County. Health Serv Res. 1995;30:27-42.

6. Gittelsohn A, Powe NR. Small area variations in health care delivery in Maryland. Health Serv Res. 1995;30:295-317.

7. Pilote L, Califf RM, Sapp S, et al. Regional variation across the United States in the management of acute myocardial infarction. N Engl J Med. 1995;333:565-72.

8. Wennberg DE, Kellett MA, Dickens JD Jr, Malenka DJ, Kielson LM, Keller RB. The association between local diagnostic testing intensity and invasive cardiac procedures. JAMA. 1996;275:1161-4.

9. ACC/AHA Committee on Clinical Application of Echocardiography. ACC/AHA guidelines for the clinical application of echocardiography. Circulation. 1997;95:1686-744.

10. Frye RL. Does it really make a difference? J Am Coll Cardiol. 1992;19:468-70.

11. Feigenbaum H. Evolution of echocardiography. Circulation. 1996;93:1321-7.

12. Calenda P, Jain P, Smith LG. Utilization of echocardiography by internists and cardiologists: a comparative study. Am J Med. 1996;101:584-91.

13. Kahn HA, Sempos CT. Statistical Methods in Epidemiology. New York: Oxford Univ Pr; 1989.

14. Kim R, Chakko S, Myerburg RJ, Kessler KM. Clinical usefulness and cost of echocardiography in patients admitted to a coronary care unit. Am J Cardiol. 1997;80:1273-6.

This work was part of the Dartmouth Atlas of Health Care and was supported by the Robert Wood Johnson Foundation.

F. Leslie Lucas, PhD, Division of Health Services, Maine Medical Center, Department of Medicine, 22 Bramhall Street, Portland, ME 04102; e-mail: LUCASL@mail.mmc.org.

From "Variation in the Use of Echocardiography" Effective Clinical Practice, March/April 1999. 2:71-75.

Figure 1. Proportion of Medicare beneficiaries receiving echocardiography in the continental United States in 1995. Proportions of Medicare beneficiaries receiving echocardiography in Alaska and Hawaii (data not shown) are each less than 7%.

From "Variation in the Use of Echocardiography" Effective Clinical Practice, March/April 1999. 2:71-75.

From "Variation in the Use of Echocardiography" Effective Clinical Practice, March/April 1999. 2:71-75.

Figure 2. Use of echocardiography among Medicare beneficiaries in the 25 largest metropolitan areas in the United States in 1995.

Correlation of Rates of Coronary Artery Bypass Surgery, Angioplasty, and Cardiac Catheterization in 305 Large Communities for Persons Age 65 and Older

Evelyn M. Kuhn, Arthur J. Hertz, and Mario Baras

Objective. The rate of coronary artery bypass surgery (CABG) has been shown to vary greatly across geographic regions. This study examined whether these rates were associated with the rates of coronary artery angioplasty (PTCA) and with other community characteristics.

Data Sources/Study Setting. The Health Care Financing Administration provided the number of Medicare hospitalizations in 1988 for conditions and procedures related to coronary artery disease. Information on physicians and hospitals was obtained from the Area Resource File, and the number of persons in each age, sex, and race category was obtained from U.S. census data.

Statistical Methods. Age- and sex-adjusted hospitalization rates based on the patient's zip code of residence were calculated at the level of the Metropolitan Statistical Area (MSA) for white patients age 65 or older. Rates were obtained for 305 MSAs for CABG, PTCA, cardiac catheterization, angina, and myocardial infarction.

Principal Findings. The rate of cardiac catheterization had a correlation of .72 with the CABG rate and .64 with the PTCA rate. The correlation of the PTCA and CABG rates with each other was .49. This correlation was not changed by adjusting for the rates of hospitalization for angina or myocardial infarction, but it was reduced to only .05 (ns) after adjusting for the rate of cardiac catheterization. The rates of all three procedures had rank correlations of about .15 with the density of thoracic surgeons and about .30 with the density of hospitals with cardiac catheterization and open heart surgery units.

Conclusions. Community CABG and PTCA rates tend to move in the same direction due to community factors that also affect the rates of cardiac catheterization. These community factors do not appear to include the rate of coronary artery disease, but may include resources or attitudes toward aggressive treatment of coronary artery disease.

Previous studies have found enormous variations in the rate of coronary artery bypass surgery (CABG) across geographic regions (Goldberg, Hartz, Jacobsen, et al. 1992; Chassin, Brook, Park, et al. 1986; Wennberg 1990). Similar variation may occur in the rate of the other major coronary artery revascularization procedure, percutaneous transluminal coronary artery angioplasty (PTCA) (Boutwell and Mitchell 1993). For several reasons it is likely that the rates of these revascularization procedures may be associated: (1) the rate of CABG may be inversely related to the rate of PTCA if PTCA is often an alternative to CABG; (2) the rates may be positively associated if both rates reflect the prevalence of coronary artery disease, access to care, or aggressiveness of treatment. The purpose of the present study was to investigate the relationship in the rates of these procedures.

The data for this study were provided by the Health Care Financing Administration (HCFA) from the 1988 Medicare Provider Analysis and Review (MEDPAR) files (Bureau of Data Management and Strategy 1990). Only data related to the following diagnoses or procedures related to coronary artery disease were analyzed: coronary artery bypass surgery (ICD9 codes 36.1036.19), angioplasty (36.01,36.02,36.05), cardiac catheterization (37.21,37.22, 37.23, 88.5), acute myocardial infarction (410), angina (411.1, 411.8, 413.0, 413.1, 413.9), atherosclerosis (414.0, 414.8, 414.9, 429.2). In addition to the diagnosis and procedure information we had information on the patient's age, sex, race (black, white, and other), and zip code of residence. We did not utilize in the analyses the zip code where the procedure was performed.

These data and data from the 1985 U.S. Census Bureau (1989) were used to calculate hospitalization rates for each of 306 Metropolitan Statistical Areas (MSAs). All of the MSA rates were adjusted for age in five-year intervals, sex, and race by calculating age-, sex-, and race-specific rates and using the U.S. age/sex/race distribution as the standard population. We computed rates for MSAs rather than larger geographical areas because practice patterns are more likely to be uniform for smaller areas. The rates were computed only for persons age 65 or older. Hospitalizations for persons who did not live in one of the 306 MSAs or who were under the age of 65 were eliminated.

Since the number of hospitalizations paid for by Medicare accounts for 95 percent of the hospitalizations for persons over the age of 65 (May et al. 199 1), the rates we calculated should only slightly underestimate the rates for all persons over the age of 65. The rate will be more underestimated for cardiac catheterization than the other procedures because about 8 percent of the cardiac catheterizations for Medicare patients were performed in outpatient clinics rather than hospitals (personal communication, HCFA). To the extent that the rate of cardiac catheterization for hospitalized patients is not a good indication of the rate of cardiac catheterization for all patients, the association of other rates with the rate of cardiac catheterization may be underestimated. No information was available on the regional variation in the percentage of catheterizations performed on outpatients.

There were insufficient numbers of non-white patients to have meaningful results when analyzed separately from white patients. We did not think the African American patients should be grouped with the white patients for analysis, however, since African American patients are managed very differently than white patients (Goldberg, Hartz, Jacobsen, et al. 1992; Harman, Kilbum, O'Donnell, et al. 1991; Ayanian, Udvarhelyi, Gastonis, et al. 1993; Escarce et al. 1993), and conclusions about the rates of procedures for white patients may not apply to African American patients. Therefore, only white patients were included in the analysis.

Information from each MSA on the number of hospitals with cardiac catheterization or open heart surgery facilities and the number of physicians of a given specialty was obtained from the Area Resources File (ARF) made available by the Bureau of Health Professions (Bureau of Health Professions 1989). The number of physicians or hospitals of a given type in each MSA was divided by the number of persons age 65 or older in the MSA to obtain a density of hospital or physician resources. Rates of hospitalization and density of hospital resources for MSAs were also aggregated to the level of nine regions of the country as defined by the U.S. Bureau of the Census (1989).

Pearson correlations were calculated between the rates of all diagnoses and procedures related to coronary artery disease for 305 MSAs. One MSA was excluded from the analysis as an outlier since the adjusted catheterization rate was more than 4.5 standard deviations above the mean. Correlations were performed weighting for the number of persons age 65 or older in each NSA and also without weighting. The weighted and unweighted correlations were very similar, and only unweighted correlations were presented. Correlations were also calculated between the rates of cardiac procedures and the density of hospital and physician resources. Since the density of resources had a very skewed distribution, we used Spearman rank correlations for this analysis.

To adjust a correlation between two rates (e.g., rates of CABG and PTCA) for other rates (e.g., hospitalization rates that may reflect the amount of underlying coronary artery disease in the community), we used standard multiple regression techniques to obtain a partial correlation. A multiple regression analysis was also used to determine the R2 for CABG and for PTCA, that is, the percentage of variation in the rate of a procedure that could be explained by other factors. In this analysis the outcome was the procedure rate, and the explanatory variables included region of the country, the rate of cardiac catheterization, and the density of physician and hospital resources. The percentage of variation explained by region after adjusting for other factors was the R2 when all variables were included in the regression equation minus the R2 when all variables except region were in the equation.

RESULTS

VARIATION IN RATES AMONG MSAs

The variation in the observed rates of CABG and PTCA per 10,000 persons age 65 and over for the communities in the study is shown in Table 1. The rate for communities in the upper decile was more than twice the rate of communities in the lower decile for bypass surgery and more than three times the rate in the lower decile for PTCA.

Variation in factors that may contribute to variations in the rates of the procedures is shown in the bottom part of Table 1. The first three factors are reasons for hospitalization that are affected by the underlying rate of heart disease in a community. The last factor is cardiac catheterization, which is necessary prior to either revascularization procedure.

The correlations of the MSA rates of CABG and PTCA with the other procedures and diagnoses related to coronary artery disease are shown in Table 2. The correlation between the rates of CABG and PTCA is .49, which is significant at the p <.000 1 level. The highest correlations are between the rates

Note: Rates are per 10,000 Medicare patients 65 years old or older, and are adjusted for age and sex.

of cardiac catheterization with CABG (.72) and with PTCA (.64). The other correlations in the table indicate the relationship between the procedure rate and the rate of hospitalization for conditions resulting from coronary artery disease. The rates of these conditions are not ideal indicators of coronary artery disease in the community, however, since they are affected by the community practice patterns as well as by community rates of the condition. A primary reason for hospitalizing a patient with angina-and especially for hospitalizing a patient with atherosclerosis-is that the patient is receiving a procedure related to coronary artery disease. The indication of coronary artery disease that is most independent of practice patterns is the rate of myocardial infarction. This rate has low correlations with the procedure rates.

Our next analysis evaluated whether the rates of CABG and PTCA are correlated because both are high in communities with high rates of coronary artery disease or because of high rates of access to hospital care. In this analysis we adjusted the correlation between CABG and PTCA for the community rates of hospitalization for myocardial infarction and angina. The partial correlation after adjusting for these rates was the same as the unadjusted correlation (.49). After also adding atherosclerosis as an additional adjuster, the partial correlation was reduced to .42, although for reasons given above this is probably an overadjustment. After adjusting for the rate of cardiac catheterization, the correlation between the rates of CABG and PTCA was nearly eliminated, r =.05 (ns).

Note: Rates are per 10,000 Medicare patients 65 years old or older, and are adjusted for age and sex.

The variation among community and regional factors is shown in Table 3, and the relationship between these rates and the rates of cardiac procedures is shown in Table 4. The rates of CABG, PTCA, and cardiac catheterization have significant positive correlations with the density of hospitals with facilities for cardiac catheterization or open heart surgery. Note that both the density of thoracic surgeons and the density of hospitals with open heart surgery units have higher correlations with the rate of PTCA than they do with the rate of CABG. These correlations suggest that bypass surgery facilities are a marker for active heart centers rather than a specific factor that affects bypass surgeries. After adjusting for the density of hospitals with open heart facilities, the density of thoracic surgeons was no longer correlated with the rate of PTCA, -.03 (ns) or with the rate of CABG, .02 (ns).

The rates of hospitalization for cardiac procedures, facilities, and diagnoses among MSAs in the nine census regions of the country are shown in Table 5 and Figure 1. The regions are arranged in order of decreasing CABG rate. The highest rates of myocardial infarction are seen in the New England and NfidAdantic states, yet these states have the lowest and thirdlowest cardiac catheterization rates. The highest rate of cardiac catheterization is found in the South Central states, which do not have unusually high rates of hospitalization for myocardial infarction or angina. The rates of both CABG and PTCA are high in the West South Central states and low in New England and the Mid-Atlantic states. The Mountain and West North Central states have relatively low rates of CABG but high rates of PTCA

The relationship between the rates of CABG and PTCA varied among the regions. For the three regions with at least 40 MSAs in the region the correlations were .36 for the West South Central, .16 for the East North Central, and .65 for the South Atlantic.

The percentage of variation in procedure rates accounted for by region is .07 for CABG and. 15 for PTCA. After adjusting for the MSA rates of cardiac catheterization, cardiac catheterization facilities, and open heart surgery facilities, the percentage variation explained by region was essentially unchanged: .06 for CABG and. 16 for PTCA.

In this study we examined the variation among MSAs in the rates of the two major procedures for coronary artery revascularization: CABG and PTCA. For white persons age 65 or older the rates were highly correlated (r =.49, p <.0001). The rates of both procedures were significantly correlated with the density of thoracic surgeons (r=.13,p <.05 for CABG and r=.15,p <.01 for PTCA), more strongly correlated with the density of hospitals with facilities for cardiac catheterization (r =.32, p <.0001 for CABG and r = .26, p < .0001 for PTCA) and most strongly correlated with the rates of coronary

artery catheterization (r = .72, p < .000 1 for CABG and r = .64, p < .000 1 for PTCA). The current study was performed for Medicare hospitalizations in 1988. It is possible that the factors influencing the procedure rates will change as the health care system evolves.

In a previous study, no correlation was found between the rates of CABG and PTCA among eight Canadian provinces, r =.09 (ns) (Higginson et al. 1992). However, positive correlations between alternative procedures have been found in a much smaller study using 1981 Medicare part B data from 13 communities in eight states (Chassin, Brook, Park, et al. 1986). The alternative procedures with positive correlations were injection of hemorrhoids and hemorrhoidectomy and lower extremity arterial reconstruction and amputation.

Table 5: Hospital Characteristics and Hospitalization Rates by Region
Rate per 10,000*
Hospitals Hospitals
Number Myocardial Cardiac with Cardiac with Open
Region of MSAs Infarction Angina Catherization CABG PTCA Cath Facilities Heart Surgery
East South Central 19 95.1 (3) 133.0 (1) 158.5 (1) 44.7 (1) 22.4 (6) 0.92 (2) 0.54 (4)
West South Central 41 87.8 (5) 119.7 (5) 148.1 (2) 44.6 (2) 26.0 (3) 0.98 (1) 0.78 (1)
East North Central 63 89.8 (4) 125.6 (4) 132.0 (3) 42.3 (3) 25.2 (5) 0.60 (5) 0.38 (6)
Pacific 35 76.9 (8) 109.7 (7) 98.1 (8) 40.3 (4) 27.4 (1) 0.60 (6) 0.41 (5)
South Atlantic 55 85.2 (6) 128.3 (3) 121.7 (4) 38.1 (5) 21.3 (7) 0.48 (7) 0.30 (7)
Mountain 17 78.4 (7) 96.1 (8) 116.9 (6) 35.9 (6) 25.7 (4) 0.80 (4) 0.66 (3)
West North Central 24 75.4 (9) 90.0 (9) 117.7 (5) 34.8 (7) 26.6 (2) 0.91 (3) 0.70 (2)
Mid-Atlantic 34 95.3 (2) 129.4 (2) 103.4 (7) 34.5 (8) 14.4 (9) 0.32 (9) 0.17 (8)
New England 17 104.6 (1) 119.6 (6) 91.7 (9) 33.2 (9) 15.1 (8) 0.37 (8) 0.17 (9)
All MSAs 305 88.1 121.0 116.9 38.7 22.0 0.57 0.38
Non-MSA areas 99.2 141.8 122.0 38.7 21.8 0.12 0.04
*The rank is given in parentheses; the rates are adjusted for age and sex.

[Note the scan of the original paper source did not show these figures and tables -- no effort will be made to re-locate the original. The original would presumably be available in the usual medical libraries.]

artery catheterization (r =.72, p < .0001 for CABG and r =.64, p <.0001 for PTCA). The current study was performed for Medicare hospitalizations in 1988. It is possible that the factors influencing the procedure rates will change as the health care system evolves.

Some possible explanations for a positive correlation between CABG and PTCA are not supported by this study. Since the correlation was not affected by adjusting for hospitalization rates associated with coronary artery disease, it is unlikely that the correlation is due either to variations in the community rates of coronary artery disease or in access to hospital care. Other studies also did not find an association between the rates of coronary artery disease and the rates of bypass surgery (Goldberg, Hartz, Jacobsen, et al. 1992; Gillum 1987).

The correlation between CABG and PTCA may be due in part to variations in the specific resources for performing invasive cardiac procedures. Both the density of surgeons and of hospitals were associated with the rates of the procedures. Surgeon and specialist density have also been found to be related to rates of other procedures (Holahan, Berenson, and Kachavos 1990; Lewis 1969). Our findings are also consistent with the results of previous studies showing that myocardial infarction patients who present to hospitals with facilities for cardiac catheterization, bypass surgery, and angioplasty were much more likely to undergo these procedures than patients presenting to hospitals without these facilities (Blustein 1993; Every, Larson, Litwin, et al. 1993).

A regional effect on the rates of all of the invasive procedures in the current study existed independent of the densities of hospitals and surgeons. Higher rates of CABG and PTCA in the South and the West and low rates in the Northeast were also reported by Boutwell and Mitchell (1993). State rate regulation programs in the Northeastern states have been reported to reduce significantly the availability of CABG and PTCA in that region (Robinson, Barnick, and McPhee 1987).

The best marker we found for communities likely to perform more revascularization procedures is the rate of coronary artery catheterization. This rate may be a marker for community resources and attitudes that affect revascularization rates. The number of catheterizations in a community provides the patient pool for both CABG and PTCA. After taking into account the size of the patient pool, there is no longer any association between the rates of the two procedures.

Chassin has found evidence that communities with higher procedure rates have a higher prevalence of physicians who are enthusiasts of those services, that is, who perform more procedures than other physicians (Chassin 1993). Many historical, cultural, and economic factors might determine whether a high level of enthusiastic physicians are practicing in a given region. Our data suggest that these factors apply to related procedures that are performed by different types of physicians. In other words, the enthusiasm in a community is not just for coronary artery bypass surgery but for invasive treatment of coronary artery disease.

Data for this study were provided by the Health Care Financing Administration.

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Boutwell, R. C., and J. B. Mitchell. 1993. "Diffusion of New Technologies in the Treatment of the Medicare Population." International Journal of Technology Assessment in Heafth Care 9 (1): 62-75.

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Chassin, M. R. 1993. "Explaining Geographic Variations: Ile Enthusiasm Hypothesis." Medical Care 31 (5, Supplement): YS37-YS44.

Chassin, M. R., R. H. Brook, R. E. Park J. Keesey, A. Fink J. Kosecoff, and K. Kahn. 1986. "Variations in the Use of Medical and Surgical Services by the Medicare Population." The New England Journal of Medicine 314 (5): 285-90.

Escarce J.J., K. R. Epstein, D. C. Colby, and J. S. Schwartz. 1993. "Racial Differences in the Elderly's Use of Medical Procedures and Diagnostic Tests." American Journal of Public Health 83 (7): 948-54.

Every, N. R., E. B. Larson, P. E. Litwin, et al. 1993. "The Association Between OnSite Cardiac Catheterization Facilities and the Use of Coronary Angiography after Acute Myocardial Infarction." The New England Journal of Medicine 322 (8): 546-51.

Gillum, R. F. 1987. "Coronary Artery Bypass Surgery and Coronary Angiography in the United States, 1979-1983." American Heart Journal 113 (5): 1255-60.

Goldberg, K. C., A. J. Hartz, S. J. Jacobsen, H. Krakauer, and A. A. Rimm. 1992. "Racial and Community Factors Influencing Coronary Artery Bypass Graft Surgery Rates." Journal of the American Medical Association 267 (11): 1473-77.

Hannan, E. L., H. Kilburn, J. F. O'Donnell, G. Lukacik, and E. P. Shields. 1991. "Interracial Access to Selected Cardiac Procedures for Patients Hospitalized with Coronary Artery Disease in New York State." Mediaal Care 29 (5): 430-4 1.

Higginson, L. A. J., J. A. Cairns, W. J. Keon, and E. R. Smith. 1992. "Rates of Cardiac Catheterization, Coronary Angioplasty and Open-Heart Surgery in Adults in Canada." Canadian Medical Associationjournal 146 (6): 921-25.

Robinson, J. C., D. W. Barnick, and S. J. McPhee. 1987. "Market and Regulating Influences on the Availability of Coronary Angioplasty and Bypass Surgery in U.S. Hospitals." The New England Journal of Midicine 317 (2): 85-90.

U.S. Public Health Service, Bureau of Health Professions, Office of Data Analysis and Management. 1989. The Area Resources File (ARF) System. Rockville, MD: U.S. Department of Health and Human Services. Document No. (HE 20.9302:AF 3/989).

Wennberg, J. E. 1990. "Small Area Analysis and the Medical Care Outcome Problem."

In Agency for Hea lth Care Polity and Research Conference Proceedings. Research Methodology: Strengthening Causal Interpretations of Nonexperimental Data. 177. Bethesda, MD: Agency for Health Care Policy and Research. Publication No. (PHS) 903454, May.

Address correspondence and requests for reprints to Arthur J. Hartz, M.D., Ph.D., Professor, Medical College of Wisconsin, 8701 Watertown Ph-ink Road, Milwaukee, WI 53226. Evelyn Kuhn, Ph.D. is Assistant Professor, Department of Family and Community Medicine, Medical College of Wisconsin. Mario Baras, Ph.D. is Senior Biostatistition in Social Medicine, Hadassah Medical Organization, Jerusalem. This article, submitted to Health Services Research on February 14, 1994, was revised and accepted for publication on November 30, 1994.

Thirty-Day and Six-Month Adjusted Mortality in 1988 for 3812 Hospitals Categorized by Teaching Status and Ownership
Evelyn M. Kuhn, Ph. D., Arthur J. Hartz, M. D. Ph. D., and A. Rimm, Ph. D.

Problem and Objectives: The purpose of this study was to compare thirty-day and six-month adjusted mortality rates for six types of hospitals.

Data and Methods: Data on observed and expected hospital mortality were obtained from the Health Care Financing Administration. We added hospital severity of illness adjusters: 1) the percentage of patients on Medicaid and 2) the number of emergency room visits divided by the average daily census. Hospital type information was from the American Hospital Association 1988 Annual Survey. Six types of acute care hospitals were evaluated: nonteaching hospitals which are (1) private for-profit (537), (2) private nonprofit (2066), (3) public (799), (4) private nonprofit teaching hospitals (237), (5) public teaching hospitals (69), and (6) osteopathic hospitals (104).

Results and Conclusions: The major findings in this study are: 1) The poorer performance of osteopathic hospitals at 30 days is also observed at 180 days; 2) Private nonprofit teaching hospitals had the lowest 30 day and 180 day mortality rates. Implications: The consistently lower mortality for private nonprofit teaching hospitals is contrary to a previous study which suggested that tertiary care teaching hospitals keep patients alive for short periods but have similar longer-term mortality to other hospitals. Differences Between Men and Women with HIV-Related Pnuemocystis carinii pneumonia: Experience from 3,070 Cases in New York City in 1987 Lori A. Bastian, CL Bennett, J. Adams, H. Waskin, G. Divine, B. Edlin, L. Forrest, D. Rodriguez Problem and Objective: Although women make up the fastest-growing group of individuals with acquired immunodeficiency syndrome (AIDS), studies of HIV-infected individuals reported to date have included predominantly or exclusively men.

Data and Methods: We evaluated sex differences in sociodemographic characteristics, hospital characteristics, in-hospital resource use, and short-term mortality rates for 2,526 men and 544 women admitted for their first-episode of HIV-related Pneumocystis carinii pneumonia (PCP) in New York City in 1987.

Results and Conclusions: Compared to men, women were less likely to be white (81 % versus 54%), less likely to have private health insurance (80 % versus 58 %), and more likely to be admitted through an emergency room (79 % versus 71 %) and receive care at hospitals that had less experience with PCP (p < 0. 05). Women were more likely to die in the hospital (33 % versus 24 %) (p <0.05). In a logistic regression model, the risk of death in the hospital was associated with age 60-65 years (adjusted odds ratio [AORI= 2.51, Cl= 1.07-5.86), not having private health insurance (AOR= 1.37, Cl= 1.08-1.75), admission through the emergency room (AOR= 1.54, Cl= 1.21-1.96), and receiving care at hospitals with less experience with PCP (AOR= 1.63, 38 CI=1.15-2.30), but women were not significantly more likely to die in the hospital than men (AOR= 1.18, CI=0.93-1.50). Higher rates of admission through an emergency room and lower rates of private health insurance among women suggest that women with HIV infection may have poorer access to medical care. Additional studies are needed to evaluate the independent effect of being female on mortality for individuals with HIV infection.

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