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TRENDSUse And In-Hospital Mortality Associated With Two Cardiac Procedures, By Sex And Age: National Trends, 1990–2004
This study used data from the National Hospital Discharge Survey to examine sex- and age-specific trends in use and in-hospital mortality associated with coronary artery bypass graft (CABG) and percutaneous coronary intervention (PCI) among adults age forty-five and older during 1990–2004. Although use rates for PCI increased 58 percent over the study period, CABG use rates declined. In-hospital death rates declined or stayed the same even though comorbidities increased for patients who received the procedures. PCI and CABG use rates for men were at least twice those for women, although women generally had more comorbidities and higher in-hospital death rates.
POLICY MAKERS AND health services researchers have focused much attention in the past two decades on two widely used cardiac surgical procedures: coronary artery bypass graft (CABG) surgery and percutaneous coronary intervention (PCI). Both procedures are performed to relieve the symptoms of angina, improve exercise tolerance, and extend the long-term survival of people with coronary artery disease.1 Technological advances in operative techniques and postoperative care have led to dramatic increases in the use of both procedures. Between 1980 and 1996, the number of hospitalizations for CABG more than tripled, from 136,000 to 367,000, and from 1986 to 2004, the number of PCIs grew fivefold, from 129,000 to 661,000.2 Many studies of CABG and PCI use and outcomes have examined whether procedures were being performed appropriately in the general population.3 Other analyses have focused on the experience of demographic subgroups such as women and minorities.4 Studies based on sex have found that although heart disease is the number-one killer of women, women are less likely than men to receive diagnostic or invasive cardiac procedures and experience worse outcomes following a CABG or PCI procedure.5 In addition, women have been found to undergo cardiac revascularization procedures when they are older and more seriously ill than men receiving these procedures.6 Most of the previous studies of CABG and PCI have relied on state and regional data or have been based on the experience of the Medicare population only. Moreover, the majority of the research conducted was cross-sectional and did not provide information over time. This descriptive study used nationally representative data on use and inpatient mortality following a CABG or PCI procedure to profile trends by sex and age. Also, using the Charlson comorbidity index, we examined coexisting disease for patients undergoing these procedures. For both sexes, we analyzed age-specific rates to elucidate differences in use trajectories, comorbidities, and inpatient mortality that might be obscured by age standardization.
Data. Data for this study are from the National Hospital Discharge Survey (NHDS), which has been conducted annually by the National Center for Health Statistics (NCHS) since 1965. Data are collected from a sample of inpatient records obtained from a national probability sample of nonfederal, short-stay hospitals (defined as those with an average length-of-stay of fewer than thirty days). In 2004 the sample consisted of 439 participating hospitals (92 percent response rate) that provided data on 371,000 discharges. The sample data were weighted to produce national estimates. The weighting process is described and details on the design and operation of the NHDS are provided elsewhere.7 Analyses. Patients with CABG are those with the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code 36.1, and PCI is indicated by ICD-9-CM codes 36.00, 36.01, 36.02, 36.05, 36.06, 36.07 and 36.09.8 Patients did not generally have PCI and CABG during the same hospitalization. In 2004, only 6,000 discharges (weighted) had both procedures, which was less than 1 percent of discharges with PCI and 2 percent of discharges with CABG. Discharges with both procedures reported were counted in both categories. Discharge rates were calculated using U.S. Census Bureau estimates of the civilian population as of 1 July of each year. The Charlson index, as adapted by Richard Deyo and colleagues, classifies patients according to the number and seriousness of their coexisting diseases and is expected to be related to outcomes of care.9 Index components are not designed to refer to the primary disease being treated, which for CABG and PCI includes acute myocardial infarction (AMI). Thus, in constructing the Charlson index for this research, the component indicating AMI (ICD-9-CM code 410) was excluded. All of the other components used by Deyo and colleagues were incorporated in the index.10 We analyzed data for discharges age forty-five and older, who constituted 94 percent of PCI and 96 percent of CABG discharges of all ages in 2004. We compared patterns of use, comorbidity, and in-hospital mortality from 1990 to 2004 for six sex-by-age groups. To increase reliability of the estimates and to maximize the statistical power of these tests, we aggregated data into five three-year groupings. Trends were tested using a weighted-least-squares regression method developed for complex data sets.11 Sex and age differences in measures within a specific time period were tested using the two-sided t-test with a critical value of 1.96. All significance tests employed standard errors generated by SUDAAN, and a significance level of alpha= .05 was used.12
General trends, age forty-five and older, 1990–92 to 2002–04. After years of increasing use of both CABG and PCI, these procedures have taken different trajectories. The CABG discharge rate per 10,000 population age forty-five and older decreased from 34.1 in 1990–92 to 25.2 in 2002–04 (Exhibit 1  ). In contrast, the PCI rate per 10,000 population in this age group rose steadily, from 37.2 in 1990–92 to 59.2 in 2002–04.
Charlson means increased over time for both CABG and PCI discharges, indicating that patients age forty-five and older undergoing these procedures in recent years had more comorbidities (Exhibit 2 ). Although Charlson means were higher for CABG than for PCI discharges throughout the study period, the difference in comorbidities for patients receiving the two procedures narrowed by 2002–04.
In-hospital mortality rates improved overall for CABG (Exhibit 3 ). The rate of hospital deaths per 100 CABG discharges age forty-five and older declined from 4.3 to 3.5 between 1990–92 and 2002–04. The rate of deaths per 100 PCI discharges, however, did not change significantly during this period. In-hospital mortality was greater for CABG, a more invasive procedure, than for PCI, and the ratio of CABG to PCI death rates remained fairly constant across study years at about three to one.
Sex (age forty-five and older). Use trends for CABG and PCI followed similar patterns for males and females age forty-five and older during the fifteen-year period studied. The rate of CABG discharges decreased for male and female discharges, and PCI rates increased for both. Men had consistently higher rates of both of these procedures than women throughout the study period (Exhibit 4 ). For example, in 2002–04 the rate of CABG discharges per 10,000 population for men (38.8) was almost three times the rate for women (13.6). Similarly, men’s PCI discharge rate per 10,000 population (83.0) was more than twice that of women (38.7) in 2002–04.
Charlson index means increased for both men and women age forty-five and older with CABG and PCI during the period studied (Exhibit 5 ). Charlson means were generally higher for women, which indicates that women had more comorbidities than men during hospitalizations for both procedures. In 2002–04, for example, the average Charlson index score associated with CABG was 0.98 for women compared with 0.82 for men. For PCI discharges in 2002–04, the mean Charlson comorbidity score was 0.83 for women, compared with 0.74 for men.
Women generally experienced higher inhospital mortality following these procedures than men (Exhibit 6 ). During the study period, sex differences in in-hospital mortality rates narrowed for CABG. The mortality rate for women age forty-five and older (6.6) was twice that for their male peers (3.3) in 1990–92, but rates were not significantly different by sex in 2002–04 (4.5 and 3.1, respectively) because of a 32 percent decline in CABG mortality for women and no significant change for men over the study period.
In contrast, the in-hospital mortality rate for PCI among discharges age forty-five and older did not change significantly for men or women. The PCI mortality rate for women (2.2) was more than twice the rate for men (1.0) in 1990–92 and remained 67 percent higher in 2002–04 (1.5 compared with 0.9).
Sex by age.
CABG and PCI discharge rates were consistently higher for men than for women across all three age groups during the study period (Exhibit 4
The Charlson comorbidity index increased over time for every sex-age group except for male and female CABG discharges age seventy-five and older (Exhibit 5
Because in-hospital death was an infrequent occurrence, particularly for PCI discharges, many mortality estimates were unreliable, and so sex-by-age tests of time trends were meaningful only for CABG patients. CABG mortality declined between 1990–92 and 2002–04 for women ages 45–64 and 65–74 but not for women age seventy-five and older (Exhibit 6
These findings portray an improving picture for people with heart disease undergoing revascularization procedures. In the fifteen years from 1990 through 2004, in-hospital mortality following a CABG procedure fell significantly, and PCI mortality remained low, while Charlson means generally increased, indicating more comorbidities. Declines in CABG mortality and consistently low mortality rates for PCI despite a higher illness burden suggest that the quality of care for CABG and PCI has improved over time, possibly as a result of technological advances in operative techniques and improvements in postoperative medical care. Also noteworthy are the changing use patterns for CABG and PCI observed over the study period. CABG is the more invasive surgical procedure, traditionally thought to be the better option for certain kinds of cardiovascular disease, such as patients with multivessel disease or proximal left anterior descending artery stenosis.13 However, with the advent of the stent and, more recently, the drug-eluting stent, PCI short- and long-term outcomes have greatly improved, and some believe that these improvements will obviate the need for many CABG procedures.14 Changing use patterns show that a process of substitution is well under way, with PCI rates now more than twice those of CABG rates and coexisting disease increasing for patients undergoing PCI. From a policy perspective, it is not clear whether PCI is more cost-effective than CABG in the long term. Several studies comparing CABG with PCI using stents document higher rates of repeat revascularization among PCI patients, particularly among patients with certain comorbidities and types of lesions.15 For patients at risk for repeat procedures, PCI might not be preferable to CABG with respect to patient outcomes or cost-effectiveness, despite the fact that the initial complications, morbidity, and costs are higher for CABG. These results support the findings of prior studies documenting ongoing sex-related differences in the use of CABG and PCI. Some studies have suggested that sex differences in the use of revascularization procedures could be related to clinical differences between men and women when they seek treatment.16 Other research has investigated whether women are more likely than men to refuse cardiac procedures, opting instead for more conservative medical treatment.17 An alternative explanation is that physician decision making, or bias, might affect access to revascularization.18 The higher comorbidity burden for women age forty-five and older compared with their male counterparts supports the perspective that women undergoing cardiac procedures are in poorer health than men. Some researchers have suggested that women are sicker because they are older at the time they undergo CABG or PCI.19 However, it was the younger women, ages 45–64, with CABG and PCI who had consistently more coexisting diseases than their male counterparts. These findings are not consistent with the view that women are sicker because they are older. Instead, they might suggest that heart disease is less likely to be recognized and treated in younger women so that they are in poorer health and at greater risk of adverse outcomes compared with younger men when they undergo revascularization.20 Future research should more closely examine age-specific variations in cardiac care to elucidate important underlying age and sex distinctions in the recognition and treatment of heart disease. This study has several limitations. Because hospital discharge abstracts are used in the analysis, the data lack clinical detail on the severity and extent of heart disease that could account for observed age and sex differences in use and short-term outcomes following revascularization. Use of the Charlson comorbidity index partially addresses this concern by considering the presence or absence of other coexisting diseases that could affect treatment outcomes. When the Charlson index is used with administrative records, it might underestimate comorbidity burden because not all coexisting conditions might be listed in the records. On the other hand, in cross-sectional discharge databases such as this, it can be difficult to distinguish between diagnoses that were present on admission and complications that developed during the hospital stay.21 Given the absence of clinical information on the indications for revascularization, it is not possible to determine whether men overuse CABG and PCI or, alternatively, whether these procedures are underused among women of similar ages. An additional limitation is that the NHDS was not designed to track readmissions. It is not possible to identify patients who might have had multiple procedures during repeated hospital visits. Thus, the trends reflect hospitalizations rather than individuals. The study does not include information on procedures performed in Veterans Affairs (VA) hospitals. However, both CABG and PCI rates were declining in the latter 1990s in VA hospitals, and in 1999, less than 3 percent of CABG and less than 2 percent of PCI procedures performed in the United States were in VA hospitals.22 DESPITE THE LIMITATIONS, this national study documents important changes in the use and short-term outcomes associated with two cardiac procedures. The good news is that over the past fifteen years, access to CABG and PCI has generally broadened. People with increasing levels of coexisting disease, who previously might not have been considered appropriate candidates for revascularization, have benefited from the technological advances in the treatment of coronary artery disease.
Julia Holmes (JSHolmes{at}cdc.gov) is a senior service fellow at the National Center for Health Statistics (NCHS) in Hyattsville, Maryland. Lola Jean Kozak and Maria Owings are health statisticians there. The views in this paper are those of the authors and do not necessarily reflect those of the government agency or its officials.
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