The American Journal of Managed Care August 2010
Clinical and Economic Outcomes After Introduction of Drug-Eluting Stents
Introduction of drug-eluting stents resulted in improved clinical outcomes for patients and reduced overall procedural costs.
Background: In clinical trials, drug-eluting stents (DES) improve clinical outcomes but are more expensive than bare-metal stents (BMS).
Objective: To assess clinical and economic outcomes of all percutaneous coronary intervention (PCI) procedures in a general interventional cardiology practice before and after DES introduction in 2003.
Methods: We identified all patients undergoing PCI in 2000-2002 early cohort, pre-DES era) and from 2004 through April 31, 2006 (late cohort, DES era) in a large PCI registry. Logistic and Cox proportional hazard models estimated the risk of adverse events; generalized linear modeling predicted economic outcomes.
Results: We compared 4303 early-cohort patients with 3422 late-cohort patients. Most early-cohort patients (90%) had BMS implanted; the rest had atherectomy or balloon angioplasty only. Among late-cohort patients, 83% had DES, 14% BMS, and 6% balloon angioplasty or atherectomy only. In-hospital adverse-event rates and incidence of death or myocardial infarction (during a median follow-up of 22 months) were similar. Follow-up procedures were significantly fewer in the later era (hazard ratio for target lesion revascularization: 0.58; 95% confidence interval [CI], 0.50-0.68). Although catheterization lab supply costs were higher in the DES era, length of stay following index PCI and overall practice costs were reduced, on average, 0.40 days and $2053 in the late cohort (95% bootstrapped CI of adjusted mean difference, −$2937 to −$1197). Follow-up cardiac hospitalization costs were similar at 1 year.
Conclusions: Patients undergoing PCI following DES introduction experienced improved clinical outcomes during follow-up and reduced overall procedural costs, despite higher stent acquisition costs.
(Am J Manag Care. 2010;16(8):580-587)
We assessed clinical and economic outcomes of all percutaneous coronary intervention procedures before and after introduction of drug-eluting stents (DES) in 2003.
- The DES era was associated with improved clinical outcomes during follow-up and with reduced in-hospital costs.
These data suggest that costly new technologies can be introduced into a general practice setting while maintaining and improving patient outcomes and overall cost structures.
Trial-based economic analyses have assessed the cost-effectiveness of DES, but these analyses have significant limitations.14-17 For example, trials focus on DES versus BMS comparisons, whereas in clinical practice patients and devices are selected by operators based on clinical circumstances. Trial-based analyses restricted to DES versus BMS fail to take into account the proportion of patients with lesions who do not receive stents, and do not include patients that receive DES for so-called “offlabel” indications in day-to-day clinical practice.1 Although analyses of use among patients at higher risk in practice settings are emerging,18-24 economic analyses of the impact of the introduction of new technologies such as DES on overall clinical practice are limited. Whether DES can be introduced into a busy interventional practice in a cost-effective manner remains uncertain. Therefore, we assessed clinical and economic outcomes of all PCI procedures in a general interventional practice encompassing time periods before and after introduction of DES. We hypothesized that expensive new technologies such as DES can be introduced while managing and maintaining overall costs and expenses.
Study Design and Sample
All patients undergoing PCI at the Mayo Clinic are prospectively followed according to a well-established protocol, the Mayo Clinic PCI registry.25 This database contains demographic, clinical, angiographic, and outcome data, as well as follow-up hospitalization information. Patients are interviewed in person or by telephone at 6 and 12 months after the procedure and yearly thereafter to assess follow-up events. For cardiac-related hospitalizations that occur outside our local setting, discharge summaries are obtained and abstracted.
Drug-eluting stents became commercially available in the United States in March 2003. Because 2003 was a transitional year from BMS to DES, we compared outcomes among all patients undergoing PCI from January 1, 2004, through April 31, 2006 (late cohort, DES era) with all patients treated from January 1, 2000, through December 31, 2002 (early cohort, pre-DES era). To gain the best perspective on the impact of DES introduction on the overall practice, no specific patient subsets were excluded, such as those treated with balloon angioplasty alone or those with high-risk disease such as myocardial infarction (MI) and cardiogenic shock. Procedures were performed as previously described, all with overnight stays.26 Patients who underwent multiple procedures had the initial procedure within each time period analyzed, and follow-up procedures were classified as adverse events. As required by State of Minnesota statute, we excluded patients who refused consent for medical records research.
The Mayo Clinic is an integrated healthcare delivery system, in which physicians are salaried and physician and administrative leaders are accountable for both professional and technical costs. We have previously described our management responses to economic pressures caused by falling reimbursements. These led to a number of active ongoing cost-containment strategies.27 Briefly, these included development of preferred supplier relationships, critical analyses of utilization (particularly high-cost supply items), analyses of processes of care, and elimination of non–value-added utilization. For example, use of smaller vascular access sheaths, increased use of transradial access, fewer prolonged glycoprotein inhibitor infusions, and virtual elimination of routine postprocedure heparin infusions led to earlier ambulation. Case mix also changed, with gradual elimination of vascular brachytherapy and expansion of primary PCI for MI. Acquisition costs for ancillary supplies such as balloons, wires, and guiding catheters are continuously and vigorously negotiated using competitive bidding processes.
Clinical outcomes of interest included procedural success (defined as <50% residual stenosis and without in-hospital death, Q-wave MI, or coronary artery bypass surgery), in-hospital death, any MI, stroke, or target lesion revascularization; and target lesion failure rates during follow-up (defined as death, MI, or target lesion revascularization). We defined MI as the presence of any 2 of the following: an episode of angina lasting >20 minutes, a rise in the serum creatine kinase or creatine kinase MB isoenzyme concentration greater than 2-fold, or ST-segment changes or new Q-waves on serial electrocardiograms indicative of myocardial damage. The Mayo Clinic Risk Score was used to assess the risk profile of treated patients.28
Economic analyses were conducted from the provider perspective and focused on direct costs associated with the index PCI (procedural costs) as well as postprocedural length of stay (LOS) (days from procedure to hospital discharge date). The rate of cardiac-related hospitalizations and associated costs also was assessed during 1 year following initial PCI (follow-up costs).
Procedural Costs. We used administrative data to track hospital and physician service use and related expenditures for index PCI episodes. Utilization was valued using standard methods by grouping services into the Medicare Part A and Part B classification. Part A billed charges were adjusted using department level hospital cost-to-charge ratios and wage indexes. Part B physician service costs were proxied based on Medicare reimbursement rates.
Follow-up Costs. To value cardiac hospitalizations during follow-up, we matched observed procedure and diagnosis combinations to episodes of similar case mix occurring in the 2004 Nationwide Inpatient Sample. Sponsored by the US Agency for Healthcare Research and Quality, the Nationwide Inpatient Sample contains data from approximately 8 million hospital stays each year, including estimated hospital (nonphysician) costs.29 All costs presented have been adjusted to reflect 2007 constant dollars.
Continuous data are summarized as mean ± standard deviation. Discrete data are presented as frequency (percentage). Patient characteristics and observed in-hospital clinical outcomes were compared using the t test for continuous data, the Mann-Whitney rank sum test for ordinal data, and Pearson’s χ2 test for categorical data, as appropriate. Kaplan-Meier estimated adverse-event rates during follow-up were compared using the log rank test. Follow-up began at the time of PCI and included in-hospital events.
We used propensity score methods to account for observed potential confounding factors.30,31 Logistic regression estimated the probability (propensity score) that a patient was from the DES-era group given clinical and angiographic characteristics. We included variables whose unadjusted associations with time era were significant at the .15 level. Patients with propensity scores outside the range common to both eras were excluded from propensity-score–adjusted analyses. Five propensity score strata of nearly equal size were defined.
We used logistic regression to estimate adjusted odds ratios (ORs) for in-hospital events and Cox proportional hazard models to estimate the hazard for adverse events during follow-up within stratum. These 5 estimates were then combined using an inverse-variance weighted average. The resulting estimate and its confidence interval (CI) were exponentiated back to the OR or hazard ratio (HR) scale.
Observed costs and LOS were compared using t tests and nonparametric bootstrapped CIs.32,33 Generalized linear modeling assessed the impact of treatment era on in-hospital costs34 and assumed a logarithmic link function and a gamma, inverse Gaussian, or Poisson distribution based on the modified Park test recommended by Manning and Mullahy.35 We assumed a negative binomial distribution function with log link in the model assessing LOS.
The effect of time era on hospitalization rates and costs during the year of follow-up were assessed using 2-part models to account for the overabundance of zero values.36 For the 2-part model specifications, logistic regression was used in part 1 to estimate the probability of experiencing hospitalization (or costs) conditional on patient characteristics; part 2 used either a Poisson specification to assess hospitalization rates (among those with events) or an inverse Gaussian distribution function with log link in cost models. Models adjusted for person weights to account for right censoring of data. All statistical tests were 2-sided, and P values less than .05 were considered significant. SAS version 9.1 (SAS Institute Inc, Cary, NC) was used in the analyses.
We identified 4303 early-cohort patients and 3422 latecohort patients undergoing PCI. Baseline characteristics are outlined in Table 1. The mean age of patients undergoing PCI was about 67 years, and 70% were male. More than half (57%) had previously experienced an MI, including a substantial proportion in the week prior to the index procedure 4% had preprocedural shock; and roughly 16% had a history of congestive heart failure. About a quarter of patients were diabetic, and 18% were current smokers. The Mayo Clinic Risk Scores were similar between cohorts.
The vast majority of PCIs (70%) were performed for urgent or emergent indications on inpatients. Bare-metal stents were used in 90% of cases of early-cohort patients; the remainder had balloon angioplasty alone. In the late cohort, however, DES were used in 83% of cases, BMS in 14%, and balloon angioplasty alone in 5%. Utilization of glycoprotein 2b/3a inhibitors fell from 65% in the early cohort to 56% in the late cohort (P <.001) as the rate of dual oral antiplatelet therapy increased.
Observed in-hospital clinical outcomes by treatment era are shown in Table 2. Procedural success was obtained in 95% of cases in both time periods, and postprocedural thrombolysis in myocardial infarction 3 flow (normal antegrade flow) in all treated lesions was obtained in 94% and 95% of the early and late cohorts, respectively (P = .019). In-hospital deaths rates were similar between groups, with death occurring in fewer than 2% of cases. In-hospital MI occurred in 5% and 4% of the early and late cohorts, respectively (P = .005), and in-hospital bypass surgery was required in 1% of cases in both time periods. The incidence of in-hospital death, MI, and target lesion revascularization was 7% of cases in both cohorts.