Practice of Coronary Angioplasty in California in 1995
Comparison to 1989 and Impact of Coronary Stenting
Background—This study seeks to analyze changes in the practice of PTCA in California between 1989 and 1995 by use of the Office of Statewide Health Planning and Development (OSHPD) data set.
Methods and Results—All hospital discharges in 1995 with a procedure code for PTCA or stent were identified. The 1995 PTCA data were compared with previously published data from 1989 obtained from the same database. The number of PTCAs performed increased by 49% between 1989 and 1995, from 24 883 to 37 118. The percentage of female patients increased from 29.8% to 32.7% (P=0.0001). The percentage of diabetics increased from 14.4% to 21.6% (P=0.0001) between 1989 and 1995. Procedures on patients with a principal diagnosis of acute myocardial infarction increased from 19.3% of all PTCAs in 1989 to 27.5% of PTCAs in 1995 (P=0.0001). In-hospital mortality increased from 1.4% in 1989 to 1.9% in 1995 (P=0.0001). There were 3087 admissions with stent placement in 1995. In-hospital mortality after stent placement was 0.9% (P=0.0001 versus PTCA). Patients undergoing PTCA in hospitals performing >400 PTCAs in 1995 had a 4% incidence of death or emergency bypass surgery compared with a 6% incidence when PTCAs were performed in hospitals performing ≤400 PTCA in 1995 (P<0.0001). Patients undergoing stent implantation in hospitals performing >75 stent procedures in 1995 had a 1.3% incidence of death or emergency bypass compared with an incidence of 4% when the procedure was performed in a hospital performing ≤75 stent placements in 1995 (P<0.0001).
Conclusions—The 1995 OSHPD data continue to suggest an inverse relationship between hospital PTCA and stent volume and adverse patient outcomes.
PTCA continues to play an expanding role in the revascularization of patients with coronary artery disease. From the inception of coronary angioplasty in 1977 to 1995, worldwide volume of PTCA reached 900 000 cases.1 As with any therapy, it is of great importance to be able to continually assess the outcomes of patients undergoing treatment with PTCA. Yet over time, patient selection, techniques, and equipment for percutaneous coronary revascularization evolve at a faster rate than clinical trials are able to incorporate these changes into controlled studies. Thus, large registries have been used to evaluate changes in patient selection and outcomes between distinct points in time.2 3 However, with few exceptions, registry data are accumulated from high-volume centers with the most experienced operators and earliest access to new technologies3 and therefore might not accurately reflect practice outside those settings.
The California Office of Statewide Health Planning and Development (OSHPD) database collects discharge data from all nonfederal hospitals in California and thus has the potential advantage of reflecting the realities of practice across an entire state. Ritchie et al4 first used the OSHPD database to assess the practice of PTCA in California in 1989. That study documented an increased mortality in older patients, diabetics, and women undergoing PTCA. It further demonstrated an increased mortality in patients undergoing procedures at hospitals where lower annual volumes of PTCA are performed. Since 1989, numerous refinements in the technique of PTCA have been developed.1 In addition, coronary stents have become available. It is the purpose of the present study to assess the changes in PTCA practice in California between 1989 and 1995 as determined from the 1995 OSHPD database. In addition, because 1995 was the first year of a separate procedure code for coronary stent placement, the effect of stenting on in-hospital outcomes is assessed. Finally, the effect of institutional PTCA and stent volume on in-hospital outcomes and resource utilization in 1995 is analyzed.
All nonfederal California hospital discharges from 1995 with International Classification of Diseases (9th Revision) Clinical Modification (ICD-9-CM) procedure codes 36.01 (single-vessel PTCA), 36.02 (PTCA with infusion of thrombolytic agent), 36.05 (multivessel PTCA with or without thrombolytic agent), and 36.06 (PTCA with stent) were obtained from OSHPD. This administrative database includes demographics (age and sex), up to 25 diagnosis codes, up to 25 procedure codes, length of stay, discharge status (including death), and hospital charges for each admission. The timing of procedures is also contained in the database, with the day of admission considered day 0 and the day after admission considered day 1. The first listed diagnosis is defined as the diagnosis responsible for that admission to the hospital. Kaiser Permanente patients were included in the analysis for all variables except hospital charges, which are not available. There was no adjustment for clinical indicators of the severity of illness because the OSHPD database lacks the clinical detail necessary for risk adjustment.
Patients with ICD-9-CM codes 36.10 through 36.19 were classified as having undergone CABG. Emergency CABG was defined as any CABG occurring on the day of or the day after a PTCA or stent procedure. Outcomes after PTCA were compared among hospitals with different PTCA volumes in 1995. Outcomes after stent placement were evaluated as a function of both institutional stent and PTCA volume for 1995.
For statistical analysis, the continuity (Yates’) correction for χ2 analysis, Fisher’s exact tests, and 2-tailed t tests were performed as appropriate. A value of P≤0.05 was considered statistically significant
Table 1⇓ illustrates the clinical and demographic features of patients undergoing PTCA in 1989 and 1995, as well as those having stent implantation in 1995. From 1989 to 1995, the total number of PTCAs performed in California increased by 49%, from 24 883 to 37 118. The mean age of patients increased by ≈2 years between 1989 and 1995, from 62.4 to 64.5 years (P=0.0001). As in 1989, most patients in 1995 were men, but there was a significant increase in women undergoing PTCA in 1995 (29.8% to 32.7%, P=0.0001). The number of diabetics undergoing PTCA increased by 50%, from 14.4% in 1989 to 21.6% in 1995 (P=0.0001). More patients treated with PTCA in 1995 had a diagnosis of prior myocardial infarction (MI) than in 1989 (9.3% versus 11%, P=0.0001). Patients undergoing PTCA in 1995 were significantly more likely to have a principal diagnosis of acute MI than those presenting in 1989 (19.3% versus 27.5%, P=0.0001). The percentage of single-vessel PTCA increased slightly from 1989 to 1995, from 81.6% to 83.6% of PTCA procedures (P=0.0001). The use of multivessel PTCA decreased from 13.4% of coronary interventions in 1989 to 12% of coronary interventions in 1995 (P=0.0001). Similarly, the use of thrombolysis with single-vessel PTCA declined from 5% of procedures in 1989 to 3.3% in 1995 (P=0.0001).
In 1995, stent placement was coded on 3087 discharges or 8% of patients undergoing coronary interventional procedures. Patients undergoing stent placement were of about the same age as patients undergoing PTCA (Table 1⇑). There were relatively more men (70% versus 67.3%, P=0.003) but fewer diabetics (18.5% versus 21.6%, P=0.0001) undergoing stent procedures than PTCA alone in 1995. Fewer patients receiving stents had a principal diagnosis of acute MI than did patients treated with PTCA (18.9% versus 27.5%, P=0.0001). Stents were placed in the context of a single-vessel PTCA in 81% of cases, in the setting of a multivessel PTCA in 13% of cases, and in the setting of single-vessel PTCA with thrombolysis in 3.8% of procedures.
In contrast to the patients undergoing PTCA in 1995, patients receiving stents had a higher rate of prior MI (11% versus 13%, P=0.001), prior PTCA (14% versus 18%, P=0.001), and prior CABG (9.6% versus 10.8%, P=0.001).
Table 2⇓ demonstrates outcomes after PTCA in 1989 and after PTCA and stenting in 1995. The unadjusted, in-hospital mortality in California after PTCA in 1995 was 1.9%. This represented a 36% increase in the 1.4% mortality after PTCA reported in 1989 (P=0.0001). As seen in 1989, in 1995, women, older patients, diabetics, patients undergoing single-vessel PTCA with thrombolysis, patients with a principal diagnosis of acute MI, patients with a principal diagnosis of acute MI who underwent PTCA on day 0 or 1 of their admission, and patients who underwent CABG had significantly higher mortality. A history of prior MI or prior CABG was not associated with increased in-hospital mortality. There were significant increases in mortality between 1989 and 1995 in men, women, patients with a prior MI, and patients undergoing single-vessel PTCA. There was not an increase in mortality between 1989 and 1995 among patients with a principal diagnosis of acute MI and a PTCA at any time during the admission. However, patients with a principal diagnosis of acute MI undergoing PTCA on day 0 or 1 after admission had an increase in mortality from 5.4% in 1989 to 14.5% in 1995 (P=0.0001). The need for CABG during admission fell from 5% in 1989% to 4% in 1995 (P=0.0001). Emergency CABG was performed in 3.3% of patients undergoing PTCA in 1995.
The average length of stay after PTCA was reduced from 4.9±5.4 to 4.2±4.2 days between 1989 and 1995 (P=0.0001). The mean charge per admission increased over the same time from $19 597±18 213 in 1989 to $33 260±29 652 in 1995 (P=0.0001).
The overall mortality in the 3087 patients undergoing a stent procedure in California in 1995 was 0.87%, a significant reduction compared with the 1.9% mortality of patients undergoing PTCA without stenting (P=0.0001). Compared with PTCA, mortality after stent placement was significantly reduced in men, women, patients both ≤62 and >62 years of age, diabetics, patients undergoing stenting in the context of single-vessel PTCA, patients with a principal diagnosis of acute MI, and patients with a principal diagnosis of acute MI and their intervention on hospital day 0 or 1 (Table 2⇑). The difference in mortality between men (0.6%) and women (1.3%) after stent placement did not reach statistical significance. A stent procedure did not significantly reduce mortality compared with PTCA when it was used in the setting of multivessel angioplasty. Stenting reduced the need for emergency bypass surgery by 33%, from 3.3% to 2.2% (P=0.0001). The mortality of patients requiring bypass surgery or emergency bypass surgery was not significantly different between the PTCA and stent patients.
In 1995, the mean length of stay was slightly but significantly greater for patients undergoing stent placement than it was for patients treated with PTCA (4.2±4.2 versus 4.5±3.8 days, P<0.005). Mean hospital charges were also significantly greater in the stented compared with the PTCA patients ($33 260±29 653 versus $40 312±27 529, P<0.0001).
Institutional Volumes and Outcomes
In 1989, the 24 883 PTCAs were performed in 110 hospitals.4 In 1995, the 37 118 PTCAs were performed in 146 hospitals. Thus, the mean number of PTCAs performed per hospital increased from 225 in 1989 to 254 in 1995. Table 3⇓ presents the impact of hospital PTCA volume on clinical outcomes and resource utilization. The annual hospital PTCA volume is dichotomized at 2 levels, 200 and 400 PTCAs per year. In 1989, 64 hospitals (58%) performed ≤200 PTCAs.4 In comparison, in 1995, 67 hospitals (46%) performed ≤200 PTCA (P<0.05). In 1989, 6945 PTCAs (28%) were performed in hospitals with ≤200 PTCAs4 compared with 4642 (12.5%, P<0.0001) in 1995. Finally, in 1989, 9611 PTCAs (39%) were performed in hospitals with a volume of >400 PTCAs4 compared with 21 298 (57.5%) in 1995 (P<0.0001).
When hospitals are divided into those performing ≤200 PTCAs and those performing >200 PTCAs in 1995, the higher-volume hospitals had significant reductions in mortality (2.3% versus 2.0%, P=0.008), emergency CABG (3.2% versus 2.5%, P=0.007), or the combination of death or emergency CABG (5.6% versus 4.5%, P<0.0001). PTCA procedures performed in hospitals with a 1995 volume of >200 cases were associated with a reduction in both length of stay and charges (Table 3⇑).
When hospitals are divided into those performing ≤400 PTCAs and those performing >400 PTCAs in 1995, the reductions in mortality (2.9% versus 1.6%, P<0.0001), emergency CABG (3.0% versus 2.4%, P=0.001), or the combination of death and emergency CABG (5.8% versus 4.0%, P <0.0001) are even more striking. PTCAs performed in hospitals with a 1995 volume of >400 cases also were associated with significantly reduced length of stay and charges (Table 3⇑).
Table 4⇓ presents outcomes and resource utilization for 1995 stent procedures as a function of hospital PTCA volume in 1995. Again, hospital volumes are dichotomized at 2 levels, 200 and 400 PTCAs per year. In 1995, 109 California hospitals placed coronary stents. Of those hospitals, 46% performed ≤200 PTCAs in 1995. Approximately 10% of the stent placements were performed in hospitals performing ≤200 PTCAs in 1995. Twenty-six percent of the stenting hospitals performing >400 PTCAs placed 36% of the stents in California in 1995. There was no difference in mortality, emergency CABG, the combination of death and emergency CABG, length of stay, or mean charges associated with stent placement between hospitals performing ≤200 or >200 PTCAs in 1995. Similarly, there is no difference in mortality, emergency CABG, or the combination of death and emergency CABG associated with stent placement between hospitals performing ≤400 or >400 PTCAs in 1995. There are, however, highly significant reductions in resource utilization when stents were placed in hospitals performing >400 PTCA in 1995. The mean length of stay was reduced from 4.89±3.84 days in hospitals with a 1995 volume of ≤400 PTCAs to 4.3±3.64 days (P=0.0003) in hospitals performing >400 PTCAs. Mean charges were reduced from $42 600±28 674 in hospitals with a 1995 volume of <400 PTCA to $38 920±26 693 (P=0.0004) in hospitals performing >400 PTCAs.
Outcomes after a stent procedure in California in 1995 as a function of institutional stent volume are presented in Table 5⇓. Only 9 hospitals performed >75 stent procedures in 1995, and they accounted for 35% of the total stent procedures. The hospitals with a 1995 stent volume of >75 cases had a mortality of 0.75% compared with 1.0% for hospitals placing <75 stents (P=NS). The incidence of emergency bypass surgery was reduced from 3.0% in hospitals performing <75 stents per year compared with 0.57% in hospitals with the higher stent volume (P <0.0001). Stent placement performed in the 9 hospitals with a 1995 stent volume of >75 resulted in a combined end point of mortality plus emergency CABG in 1.3% of cases compared with a 4% incidence of mortality or emergency CABG in the 109 hospitals where ≤75 stents per year were placed (P<0.0001). Mean length of stay and mean charges, indicators of resource utilization, were significantly reduced in hospitals performing >75 stent procedures in 1995.
In this analysis of the statewide PTCA experience in California in 1995, we have documented a 49% increase in the number of PTCAs performed in California between 1989 and 1995. Part of this expansion is due to the increased representation of patients who originally had limited access to this treatment modality. These include women, diabetics, the elderly, and patients with admission for acute MI. Interestingly, there was an actual decrease in the use of PTCA for multivessel revascularization between 1989 and 1995, perhaps in recognition of the problem of restenosis. Thus, rather than attracting new patients by offering a less invasive alternative to multivessel bypass surgery, this study suggests that new patients over this 6-year interval were likely to have come from the ranks of those previously treated medically. This is of significant socioeconomic import, given the cost of percutaneous revascularization and the fact that randomized trials of medical management versus angioplasty have not shown a survival advantage for treatment of stable angina, unstable angina, or non–Q-wave MI with PTCA.5 6 7
The broader application of PTCA between 1989 and 1995 was accompanied by increased in-hospital mortality. One explanation for this increase is that the expansion in treatment of women, diabetics, the elderly, and patients with a recent MI—all subgroups known to have a higher mortality—leads to higher overall mortality. Of particular concern and worthy of further study is the 14.5% mortality in patients treated with PTCA on day 0 or 1 of an admission for an acute MI. Unfortunately, it is not possible to determine the hemodynamic status of these patients or whether they were treated with primary angioplasty or rescue angioplasty after failed thrombolysis.
An alternative explanation for the increase in 1995 PTCA mortality is the fact that significant numbers of PTCAs in California continue to be performed in low-volume hospitals with higher mortality. In contrast, in New York state, where the mean number of PTCA per hospital was 594 in 1994, the overall mortality associated with PTCA from 1991 to 1994 was only 0.9%.8 In a study of 6 hospitals with >1000 PTCAs per year, the overall mortality in 1993 to 1994 was 1.3%, and the incidence of emergency CABG was 2.1%.9
The use of stents in California in 1995 was limited and may represent undercoding, given that 1995 was the first year for a unique ICD-9-CM code for stent placement. Nevertheless, the data reflect a relatively conservative approach to patient selection compared with PTCA. Relatively more men and fewer diabetics were treated than with PTCA, perhaps reflecting the use of stents in larger coronary vessels. Also, fewer stents were placed in patients with a principal diagnosis of acute MI, possibly in an attempt to minimize thrombotic complications.10
In-hospital outcomes after stent placement were strikingly superior compared with those after PTCA in 1995. Overall mortality was reduced from 1.9% to 0.87% (P<0.0001). In addition, the mortality rates of men, women, younger patients, older patients, diabetic patients, patients undergoing single-vessel PTCA, and patients with principal diagnosis of acute MI were all reduced. Because only in-hospital mortality is presented, the effect of stent placement would appear to be due to the prevention or expedient treatment of coronary dissections, reducing the incidence of abrupt vessel closure, prolonged ischemia, and myocardial infarction.11 12 The reduction in the rate of emergency CABG, from 3.3% with PTCA to 2.2% with stent placement, also supports such a mechanism of benefit. Although the patients treated with stents may have been at slightly lower risk, it is unlikely that their baseline characteristics accounted for all the reduction in mortality. Interestingly, patients undergoing multivessel PTCA in addition to stent placement did not realize a mortality benefit, possibly because in-hospital mortality is determined by complications arising predominantly from the unstented coronary lesions treated with PTCA alone.
In 1995, 46% of hospitals in California performed less than the volume of 200 PTCAs per year recommended by the American College of Cardiology and American Heart Association (ACC/AHA),13 a decrease from the 58% of California hospitals that performed <200 PTCAs in 1989.4 These low-volume hospitals accounted for 12.5% of the state’s PTCAs. Patients treated in these low-volume hospitals had significant increases in the incidence of death or emergency CABG. In addition, the length of stay and hospital charges were greater in the low-volume hospitals. Only 26% of hospitals performed >400 PTCAs in 1995, accounting for 58% of the PTCAs performed in California. Patients treated in these high-volume hospitals had significantly less risk of dying or needing to undergo emergency CABG. Resource utilization was also significantly reduced in these high-volume hospitals.
Luft et al14 proposed 3 hypotheses to explain the inverse relationship between hospital volume and mortality. First, greater experience by high-volume centers results in better outcomes. However, it is unclear why experience does not accumulate over time. The 1989 OSHPD data document the same volume-mortality relationship as the present study,4 yet the low-volume hospitals have had 6 more years of experience from which to draw. Thus, either experience does not account for the entire explanation or perhaps there is some characteristic of providers in low-volume centers that prevents the accumulation or integration of experience. The second hypothesis is selective referral to high-volume centers. However, because data regarding hospital volumes or outcomes are not generally available in California, that is an unlikely explanation for these findings. The third possibility is that the patients treated at low-volume hospitals are sicker. However, studies in which patients are stratified according to their severity of disease continue to find the inverse relationship between hospital volume and mortality or CABG for all subgroups.15 Regardless of the explanation, performing PTCAs only in California hospitals with an annual volume >400 PTCAs would have resulted in 202 fewer deaths and 93 fewer emergency bypass operations in 1995.
Of note, stenting appeared to neutralize the effect of institutional PTCA volume on the in-hospital outcomes of death and emergency CABG. However, a benefit in terms of reduced length of stay and hospital charges was maintained when stent placement was performed in hospitals performing >400 PTCAs in 1995. Finally, institutional stent volume appeared to have an effect on outcomes from stenting, with those hospitals placing >75 stents in 1995 have a 50% reduction in the end point of death or emergency CABG compared with hospitals placing ≤75 stents in 1995.
These results should be interpreted in light of several important study limitations. First, administrative data have certain deficiencies in terms of clinical detail. Important prognostic features, such as ejection fraction or number of diseased vessels, are not available. Also, there is no separate code for such procedures as rotational atherectomy, directional atherectomy, or laser angioplasty, which are coded as PTCA and might falsely influence both the outcomes and charges attributed to PTCA. There are no OSHPD data on physician PTCA volume that might have provided additional insight into patient outcomes. Finally charges, rather than costs, are contained in the OSHPD data set. Charges are not a precise measure of resource utilization because each hospital converts cost to charges with different formulas.
In summary, this study documents a significant expansion in the use of PTCA in California with some worsening of outcomes. It further documents the significant effect of stent placement on reduction in in-hospital mortality. Finally, it confirms previous studies suggesting that institutional volume is a major determinant of outcome after PTCA and that nearly half of California hospitals fall below the ACC/AHA recommendations for institutional volume. Although morbidity and mortality after stent placement do not appear to be affected by hospital PTCA volume, resource utilization is inversely related to PTCA volume. Finally, there is an inverse relationship between hospital stent volume and patient outcome, particularly the need for emergency CABG. In total, these findings suggest that regionalization of angioplasty services should be given serious consideration.
- Copyright © 1999 by American Heart Association
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