Outcomes of Percutaneous Coronary Interventions Performed at Centers Without and With Onsite Coronary Artery Bypass Graft Surgery FREE

The number of percutaneous coronary interventions (PCIs) has grown tremendously since its introduction by Gruentzig in 1976; more than 561 000 PCIs are performed in the United States each year.¹ Spurring this growth has been the successful development of new techniques and adjunctive pharmacologic therapies^{2 - 7} with substantial improvements in outcomes for broad patient populations, particularly a dramatic decline in the need for emergency post-PCI coronary artery bypass graft (CABG) surgery.^{8 - 9}

The decreased risk of post-PCI complications has rekindled a decade-long debate on whether it is safe to perform PCI in hospitals without onsite cardiac surgery programs. The debate has focused on the treatment of ST-segment elevation myocardial infarctions (MIs) for which primary PCI has well-documented benefits over thrombolysis in selected settings.¹⁰ The Atlantic Cardiovascular Patient Outcomes Research Team (C-PORT) trial reported better outcomes for primary PCI vs thrombolysis in 11 community hospitals without CABG surgery programs¹¹ and researchers at the Mayo Clinic described their successful collaboration in assisting a referring hospital without onsite cardiac surgery to develop a PCI program for both emergent and elective angioplasty.¹² Wharton et al¹³ reported that outcomes for primary PCI performed in select hospitals without onsite cardiac surgery were comparable with those outcomes reported for the cohort of patients transferred for primary PCI in the Air Primary Angioplasty Myocardial Infarction (PAMI) trial.

In the United States, hospitals with catheterization laboratories but without onsite cardiac surgery are rapidly developing PCI programs in hopes of improving patient care and remaining competitive.¹⁴ Whether such unselected centers can achieve outcomes equal to those with onsite surgical programs is unclear. We performed a national study to compare outcomes for patients undergoing PCI who were treated at US hospitals without and with onsite cardiac surgery in the fee-for-service Medicare program between January 1, 1999, and December 1, 2001.

We obtained the Medicare Provider Analysis and Review (MEDPAR) and denominator files between January 1, 1999, and December 31, 2001, from the Center for Medicare & Medicaid Services. The MEDPAR files contain data on each hospitalization for fee-for-service Medicare enrollees and includes personal identifiers, hospital identifiers, dates of admission and discharge, diagnoses and procedures as identified by the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes,¹⁵ and admission acuity. The denominator files contain Medicare demographic data and date of death. The 2001 Medicare Provider of Service file and the 2000 American Hospital Association Annual Survey of Hospitals were used to characterize the hospitals included in our study. Our study was considered exempt from institutional review board approval because no primary data collection was involved and mechanisms were instituted to protect patient confidentiality.

The analytic cohort was drawn from all fee-for-service Medicare enrollees who were aged at least 65 years and who underwent PCIs (ICD-9-CM codes 36.01, 36.02, 36.05, 36.06, and 36.09) at acute care facilities between January 1, 1999, and December 31, 2001 (N = 786 555). We excluded patients with unknown procedure dates (n=4833), selected the first procedure per person during the study period (n=125 771 PCIs), and excluded patients who had a CABG surgery during the hospitalization but before PCI (n=624). We also excluded patients with PCIs occurring after December 1, 2001, to allow 30 days of follow-up (n=16 077), and excluded patients who had their PCIs in hospitals that opened or closed CABG surgery programs during the study period (n=13 396), resulting in a final analytic cohort of 625 854 patients.

For each patient undergoing PCI, MEDPAR files were used to construct an episode of care around the index PCI admission. The episode of care included all transfers between acute care facilities, allowing identification of patients transferred for either PCI or CABG and their outcomes, regardless of where subsequent care was delivered.

Patients were classified as undergoing a primary or rescue PCI (primary/rescue PCI) or a non-primary/rescue PCI. We defined a primary/rescue PCI as a procedure that met all of the following criteria: emergent admission; primary diagnosis of acute MI (ICD-9-CM codes 410.X0, 410.X1, excluding subendocardial infarctions 410.70 and 410.71) or a primary diagnosis of a complication of an acute MI (ICD-9-CM codes 785.51, 785.59, 429.5, 429.6, and 429.71) with a secondary diagnosis of acute MI; PCI on the day of admission; and not transferred into the PCI-performing hospital.

Main outcome measures included CABG surgery following a PCI at any time during the episode of care, including those occurring after transfer from a hospital without cardiac surgery to one with cardiac surgery; and post-PCI mortality, defined as death occurring during the episode of care or within 30 days of the PCI procedure.

All MEDPAR claims for PCI and CABG were used to identify which hospitals performed PCI and CABG surgery. Hospitals with onsite cardiac surgery programs were initially identified based on whether they billed for at least 2 CABG operations per year (ICD-9-CM codes 36.10-36.17 and 36.19) during the study period. We used the 2001 Medicare Provider of Service file, as well as internet and telephone searches, to identify any errors or changes in hospital identifiers that could have misclassified institutions. Hospitals (n = 101) in which the first CABG surgery occurred after the first quarter of 1999, the last CABG surgery occurred before the last quarter in 2001, or hospitals that experienced an extended hiatus in CABG surgery bills were considered new, closed, or in flux, respectively, and removed from the analysis.

We categorized hospitals by annual average Medicare PCI volume. Because not all hospitals billed for PCI in all 3 study years, annual average volume was calculated as the total number of PCI procedures divided by the number of years in which the hospital billed for at least 2 PCIs. We categorized hospitals without onsite cardiac surgery by their proximity to a facility with cardiac surgery by mapping hospital ZIP codes to previously defined Hospital Service Areas (HSAs),¹⁶ local health care markets for community-based inpatient care. We determined whether hospitals without onsite cardiac surgery were in an HSA where another hospital offered that service. Additional hospital characteristics were obtained by merging to the 2000 American Hospital Association file (no match was available for 58 hospitals).

Univariate comparisons using SAS version 8.0 (SAS Institute, Cary, NC) of hospital and patient characteristics and outcomes by the absence or presence of onsite cardiac surgery were made using χ² tests. P < .05 was considered statistically significant. Multiple logistic regression models were used to assess the relationship between onsite cardiac surgery and outcomes, adjusting for differences in patient characteristics.¹⁷ We used overdispersed binary logistic models (Stata version 8.0, StataCorp, College Station, Tex) to adjust for clustering of outcomes within hospitals.¹⁸ Predictor variables were entered in the model as indicator variables. Patient characteristics included age group (65-69, 70-74, 75-79, 80-84, or ≥85 years), sex, race (black or nonblack), discharge year, urgency of index admission (elective, urgent, emergent), acute MI (when assessing outcomes for non-primary PCI), comorbidity, use of stent, and the number of vessels revascularized (single-vessel or multivessel PCI). Race was obtained from the Medicare denominator file, which uses Social Security Administration demographic data. Comorbidity was determined using the Dartmouth-Manitoba modification of the Charlson comorbidity index (range of scores: 0, 1, 2, or ≥3).¹⁹ Using ICD-9-CM codes from the PCI admission, the presence of prior MI, peripheral vascular disease, diabetes mellitus, chronic pulmonary disease, rheumatologic disease, malignancy, metastatic solid tumor, dementia, and AIDS were weighted according to their relative effects on mortality and summed. Renal and liver disease, traditional components of the Charlson comorbidity score, were omitted because they may represent procedural complications rather than preexisting conditions. For the post-PCI mortality, we did not formally test for an interaction because the stratified analysis gave descriptive information about the consistency of effect across strata and was supplementary to our main findings.

A total of 178 hospitals without onsite cardiac surgery performed a total of 8168 PCIs and 943 hospitals with onsite cardiac surgery performed 617 686 PCIs, meeting study criteria from January 1, 1999, to December 1, 2001 (Table 1). Seventy (39.3%) of the hospitals without onsite CABG surgery were located in HSAs with an institution that supported cardiac surgery. Compared with hospitals with onsite cardiac surgery, those without onsite cardiac surgery were somewhat less likely to be located in metropolitan areas, less likely to be teaching hospitals, and had fewer beds. The majority of hospitals without onsite cardiac surgery performed 25 or less Medicare PCIs per year, while only a small minority of hospitals with onsite cardiac surgery were low-volume hospitals.

Demographics and clinical characteristics according to type of facility are summarized in Table 2. Patients’ age, sex, race, and measurable comorbidites were similar in the 2 types of facilities; however, patients who had their PCIs in hospitals without onsite cardiac surgery were more likely to be emergently admitted, have acute MI as their principal diagnosis, and have undergone a primary/rescue PCI, but less likely to have been transferred in from an outside institution. Regardless of the type of facility, multivessel interventions were uncommon and stent use was frequent. The proportion of patients treated at very low-volume hospitals (≤25 Medicare PCIs per year) differed by onsite status, accounting for 25.3% of patients at hospitals without onsite cardiac surgery but only 0.1% of patients at hospitals with onsite cardiac surgery.

Overall, combined in-hospital and 30-day postprocedure mortality (Table 3) was nearly twice as high in hospitals without CABG surgery as in those with CABG surgery (unadjusted P <. 001). Postprocedure CABG rates were more comparable though statistically different. For the primary/rescue PCI population, there was no significant difference in mortality rate between hospitals without vs with onsite cardiac surgery (unadjusted P = .24). For patients with non-primary/rescue PCI, mortality was significantly higher in the hospitals without a cardiac surgery program (unadjusted P <. 001). The CABG rates did not differ significantly between hospitals without vs with onsite CABG surgery in either stratum.

The increased risk of post-PCI mortality in institutions without a cardiac surgery program persisted after adjustment for differences in case mix (Figure). Overall, the odds of death for patients having their PCIs in hospitals without onsite cardiac surgery was 29% higher than for patients having PCIs in hospitals with cardiac surgery (OR, 1.29; 95% confidence interval [CI], 1.14-1.47). As in the unadjusted analysis, this difference was confined to the non-primary/rescue PCI cohort, in which the odds of mortality were 38% higher in hospitals without onsite cardiac surgery (OR, 1.38; 95% CI, 1.14-1.67). There was no difference in the mortality OR between types of facilities for the primary/rescue PCI population. There were no significant differences in the adjusted ORs for post-PCI CABG overall or by indication.

Given these findings, we noted patient and hospital characteristics for patients treated at hospitals without vs with onsite cardiac surgery, stratified by the indication for the procedure (Table 4). Compared with the non-primary/rescue PCI group who were treated at sites with cardiac surgery, those patients cared for at sites without cardiac surgery were more often emergently admitted, more often had a diagnosis of acute MI, and were less likely to be cared for at high-volume sites. The characteristics of patients in the primary/rescue PCI group did not differ substantially by type of institution except for procedure volumes of their operating institutions; among these patients, 92.4% of patients with onsite cardiac surgery were cared for at high-volume institutions compared with only 8.5% of patients without onsite cardiac surgery.

To further examine the finding of increased risk for post-PCI mortality in hospitals without onsite cardiac surgery, we did a series of stratified analyses on the non-primary/rescue PCI population (Table 5). Although not all comparisons reached statistical significance, the direction of the findings was consistent across most subgroups. Patients admitted with elective, urgent, and emergent types in the non-primary/rescue PCI group were all more likely to die when they had their procedure performed in a hospital without onsite cardiac surgery. Excluding patients transferred in from another hospital did not change the finding nor did limiting the analysis to patients without a diagnosis of acute MI. Limiting the analysis to hospitals in metropolitan areas, in service areas with at least 1 cardiac surgery program, to nonteaching hospitals, or to hospitals performing 50 or less Medicare PCIs per year did not change the observation of increased mortality in institutions without onsite programs in cardiac surgery. Of note, the increase in mortality was primarily confined to hospitals performing 50 or less Medicare PCIs per year.

There is considerable disagreement about whether hospitals without onsite cardiac surgery programs should be developing PCI programs.^{11 ,20 - 21} The current study was specifically designed to address the safety of PCI without onsite cardiac surgery. Although centers without and with onsite cardiac surgery had similar outcomes for primary/rescue PCI, the majority of PCIs performed in these institutions were for other indications. These patients with non-primary/rescue PCI experienced a substantially higher risk of mortality when they had their PCIs at institutions without cardiac surgery programs.

Much of the literature on PCI at centers without onsite cardiac surgery in the United States consists of single institution reports or of a few that shared interventional staff.^{12 ,22 - 29} Issues of patient selection and operator and hospital experience raise concerns about their generalizability. Registry reports from Germany, France, and England^{30 - 32} suggest that both primary and non-primary PCI can be performed effectively and safely without onsite cardiac surgery. However, because of centralization of services in these countries, average hospital (and likely operator) volumes are higher overseas than in our study.

In the United States, a study of primary PCI at 10 Seattle-area hospitals³³ found that outcomes were similar for patients receiving their procedures at institutions without and with onsite cardiac surgery. The C-PORT study¹¹ evaluated the use of PCI vs thrombolysis in patients admitted with an ST-elevation MI to any of 11 institutions with new PCI facilities dedicated to primary PCI and without cardiac surgical programs. This study found no differences in hospital mortality between the 2 treatment groups but significantly lower rates of recurrent MI and stroke in the primary PCI cohort. A registry of Air PAMI–eligible patients who presented to 1 of 19 hospitals with no surgery onsite and underwent primary PCI (The PAMI-No SOS Study¹³ ) reported shorter times to reperfusion and comparable clinical outcomes compared with patients randomized to the intervention group of Air PAMI. By design, however, both the C-PORT and PAMI-No SOS studies^{11 ,13} included only hospitals with experienced interventional cardiologists and support staff who were actively engaged in improving quality of care.

Does the absence of readily available cardiac surgery explain the excess mortality for the non-primary/rescue PCI population in hospitals without such programs? We cannot unambiguously answer this important question. In hospitals without cardiac surgery, only 21.8% of post-PCI CABG surgeries occurred on the day of PCI compared with 45.0% in hospitals with cardiac surgery. On the other hand, limiting the analysis to HSAs with at least 1 cardiac surgery program did not substantially change the adjusted OR.

Are the patients receiving non-primary/rescue PCI treated in hospitals without onsite cardiac surgery systematically different than those cared for in hospitals with cardiac surgery? There was a higher incidence of emergency admissions and acute MI diagnoses in hospitals without onsite cardiac surgery. However, mortality was increased in hospitals without onsite cardiac surgery for patients admitted both emergently and nonemergently, as well as for patients admitted with and without an acute MI, although the increases were not always statistically significant. In addition, by placing patients transferred for their PCI with the non-primary/rescue group, we may have biased the analysis against programs with cardiac surgery, because centers with cardiac surgery and a large referral base might be more likely to receive transfer patients who had failed thrombolysis than smaller centers without cardiac surgery.

More of the hospitals with cardiac surgery were teaching institutions. Limiting the analysis of the non-primary/rescue PCI population to the nonteaching hospitals did reduce the magnitude of the risk but did not change the direction of our findings. Hospital PCI volume is inversely related to outcomes^{34 - 37} and hospitals without onsite cardiac surgery were much more likely to have lower annual PCI volumes than hospitals with onsite surgery. Stratifying by hospital PCI volume, low-volume hospitals (2-25 PCIs per year) without onsite cardiac surgery had a nonsignificant higher mortality for patients receiving non-primary/rescue PCI than institutions with cardiac surgery, borderline significant higher mortality for hospitals with a Medicare volume of 26 to 50 PCIs per year, and a comparable mortality rate across higher volume institutions.

Why was mortality for the primary/rescue PCI population comparable for institutions without vs with onsite cardiac surgery? One possibility is that a successful program in primary/rescue PCI requires the development of a hospital-wide system of care for early recognition and prompt treatment of patients with an ST-segment elevation MI. It may be that hospitals without onsite cardiac surgery are especially careful to select only the most appropriate of patients for this procedure and to get them treated in a timely fashion. In our study, however, removing the small number of patients treated at hospitals without cardiac surgery that did not perform primary/rescue PCI did not change our findings. It may be that the risk-benefit ratio for primary PCI is more oriented toward the benefit side than that for a PCI for other indications.

Several limitations of this study should be considered. First, our analysis includes only Medicare patients. However, 45% to 50% of all PCIs are performed on patients aged 65 years or older.⁸ Although younger patients face a lower overall mortality risk, there is no reason to believe that the differences in mortality by hospital type would differ for this patient population. Risk adjustment using administrative data has known limitations and our patient populations may be somewhat heterogeneous. We attempted to adjust for such differences in our multivariate modeling and by examining stratified analyses, such as admission acuity. Because PCI hospitals without onsite cardiac surgery are a relatively new phenomenon and because they tend to be low-volume institutions, it is difficult to separate the effects of low volume, age of the program, and lack of cardiac surgery facilities. Our stratified analyses do suggest that, even limiting the comparison to low-volume institutions, the effect remains.

Although much of the recent debate in the United States has focused on whether hospitals without cardiac surgical programs should offer primary PCI for the treatment of MI, these data suggest that the discussion should be broadened to include the safety of PCI in these hospitals for patients with other procedural indications. Once primary PCI programs are established, there are incentives to expand services and offer non-primary PCI as well, including regulatory and purchaser pressure to meet minimum volume criteria; financial incentives allowing institutions to allocate the substantial fixed cost of supporting primary/rescue PCIs to a much larger potential pool of patients; and marketing incentives that may help garner or maintain market share for other cardiology services.¹⁴ There is a growing body of evidence suggesting that the use of health care is related to the supply of resources.^{38 - 40}

If PCI programs are allowed to develop in centers without onsite cardiac surgery, patients being treated by primary/rescue PCI will likely benefit. However, 78% of PCIs at institutions without cardiac surgery programs were not primary/rescue PCIs and these patients’ outcomes were poorer than those in hospitals that had onsite cardiac surgery. Given that the absolute risk reduction in short-term mortality for primary PCI over thrombolysis (about 2%⁴¹ ) is comparable with the increase in mortality for the non-primary/rescue PCI populations in hospitals without cardiac surgery, PCI performed at hospitals without cardiac surgery may be doing more harm than good.