The results of this study demonstrate considerable variability in the use of coronary artery revascularization procedures in VA and non-VA hospitals. In the VA, not only were overall rates lower, but also both the number of CABS performed and age adjusted rates declined from 1991 to 1999, whereas in the National Hospital Discharge Survey and the Nationwide Inpatient Sample, both the estimated number of procedures and age adjusted rates increased during the time for which data were available. The findings for men undergoing PCI were somewhat different in that in all 3 settings there were increases in both the number of procedures as well as the age-adjusted rates. However, in the VA starting in 1996 there was a noticeable decline in the age-adjusted rates of both PCI and CABS; this decline was also evident in the National Hospital Discharge Survey for CABS.
Age adjusted rates of CABS and PCI were lower in the VA than in the other 2 settings, but it is important to put these rates in perspective. In 1993 in New York State, the age adjusted rate of isolated CABS for all patients was 120.6 per 100,000, somewhat lower than the VA rate of 166.0 per 100,000 for men.[5
] By contrast, the age adjusted rate for CABS in Ontario, Canada, was only 67.4 per 100,000.[6
] Presumably, the rates for New York State and Canada would be higher if only men were included. A similar pattern was apparent for PCI; in New York State, the age adjusted PCI rate for women and men was 127.8 per 100,000, very similar to the VA rate of 139.8 per 100,000 and higher than the Canadian rate of 57.2 per 100,000.[6
The comparison of VA rates to those in New York State and the province of Ontario in Canada is relevant because of the similarity to the VA health care system in the key dimensions of global budgeting and regionalization of services. Hospitals in New York State are heavily regulated compared to most of the rest of the United States. They are capped in the amount of budget growth annually, and provision of costly, highly complex services such as CABS and PCI is limited. Similar constraints are in place in the province of Ontario, to an even greater degree than in New York State.
There are several explanations as to why age adjusted rates in the VA were lower than those reported in the 2 national surveys. First, not all veterans who are users of VA healthcare services undergo coronary revascularization procedures in VA hospitals.[7
] This may be particularly true for veterans who are eligible for Medicare and receive treatment for acute coronary syndromes in non-VA hospitals that are closer to their residences and have cardiac catheterization and open heart surgery facilities. For veterans undergoing elective procedures, it may be that they lived far away from one of the 51 hospitals that performed CABS and/or PCI and elected to undergo procedures closer to their homes. In short, veterans undergoing revascularization procedures in non-VA centers were not included in the age-adjusted rates reported in this paper, and this in part could account for the lower rates. The extent to which veterans of all ages undergo revascularization procedures outside the VA is not known. It is also possible that older veterans were not candidates for the CABS or PCI due to excessive comorbidity; there is evidence that older veterans may have poorer health than non-veterans or veterans who are hospitalized in non-VA facilities. [9
] Finally, although there is no evidence to support this, decision making for revascularization procedures may be more conservative in the VA.
An explanation for the decline in use rates may have to do with the rapidly aging veteran population. The number of veteran users age 75 and older increased 177% from 210,000 in 1991 to 582, 000 in 1999, whereas the US male population 75 years and older increased only 27% from 4.8 to 6.1 million. Veteran users 75 years and older comprised almost 20% of the veteran population in 1999, yet in the US, men 75 and over accounted for only 7% of the male population 20 years and older. This higher proportion of older veteran users, coupled with the fact that comparatively fewer older men underwent revascularization procedures in the VA, may in part explain the decline in use rates in veterans.
The results of this study must be considered in the light of two limitations. First, it is important to recognize that the age adjusted rates from the 2 national surveys were estimates based on case weights.[11
] The 2 surveys produced somewhat different estimates of both the number of procedures performed and age adjusted rates, because in part, the surveys probably selected different hospitals. While these surveys include hospitals representative of those in the United States, they do not necessarily contain hospitals that are indicative of those performing cardiac revascularization procedures. These differences may also be due to the fact that the Nationwide Inpatient Sample reported up to 15 procedure codes as opposed to only 4 in the National Hospital Discharge Survey. The number of codes reported in the VA was much larger, but this did not result in higher use rates for the VA.
Due to both sampling and coding issues, the national surveys may incorrectly estimate the number of revascularization procedures. Using the Nationwide Inpatient Sample, which identifies the hospital, we estimated age-adjusted rates for CABS and PCI in New York State for 1993. The age adjusted rate of CABS for both women and men in New York State was 198 per 100,000, which is higher than the 121 per 100,000 reported by Tu et al. [6
], who had counts of all surgeries performed in New York State. On the other hand, our counts of CABS were estimated by applying case weights to the hospitals in the survey. The situation with respect to PCI was different; the estimated age adjusted rate for New York in 1993 in the Nationwide Inpatient Sample was 142 per 100,000, similar to 128 per 100,000 reported by Tu et al.[6
A second limitation of this study has to do with the choice of denominators. For the 2 surveys, the United States male population 20 years and older was used, whereas in the VA, the number of eligible veteran users was employed. As has been seen, the proportion of older individuals in the US census was relatively constant, whereas in the VA the proportion of users 75 years and older doubled during the study period. The VA denominators include users of health care, whereas the denominators for the national survey include both users and non-users. Given potential over-estimation of the number of procedures in the 2 national surveys, possible under-estimation of the number of procedures in the VA, and differences in the types of denominators, it is possible that age adjusted rates of procedure use were too high for the national surveys and too low for the VA.