ORIGINAL CONTRIBUTION Long-term MI Outcomes at Hospitals With or Without On-site Revascularization David A. Alter, MD, PhD Context Many studies have found that patients with acute myocardial infarction (AMI) C. David Naylor, MD, DPhil who are admitted to hospitals with on-site revascularization facilities have higher rates Peter C. Austin, PhD of invasive cardiac procedures and better outcomes than patients in hospitals without such facilities. Whether such differences are due to invasive procedure rates alone or Jack V. Tu, MD, PhD to other patient, physician, and hospital characteristics is unknown. Objective To determine whether invasive procedural rate variations alone account ARK TWAIN REPUTEDLY for outcome differences in patients with AMI admitted to hospitals with or without said: “To a man with a on-site revascularization facilities. hammer, every nail looks Design Retrospective, observational cohort study using linked population-based ad- like it needs driving.” ministrative data from a universal health insurance system. MThis aphorism is reflected in the oft- Setting One hundred ninety acute care hospitals in Ontario, 9 of which offered in- replicated finding that, when patients vasive procedures. with acute myocardial infarction (AMI) Patients A total of 25697 patients hospitalized with AMI between April 1, 1992, are admitted to hospitals with on-site re- and December 31, 1993, of whom 2832 (11%) were in invasive hospitals. vascularization facilities, they undergo Main Outcome Measures Mortality, recurrent cardiac hospitalizations, and emer- percutaneous coronary intervention gency department visits in the 5 years following the index admission, adjusted for (PCI) and coronary artery bypass graft patient age, sex, socioeconomic status, illness severity, and index revascularization (CABG) surgery much more often than procedures; attending physician specialty; and hospital volume, teaching status, those admitted to hospitals without such and geographical proximity to invasive-procedure centers and compared by hos- facilities.1 Many studies have now com- pital type. pared patient outcomes in these 2 prac- Results Patients admitted to invasive-procedure hospitals were much more likely to tice settings, and most have demon- undergo revascularization (11.4% vs 3.2% at other hospitals; P,.001). However, many strated similar survival but better quality other clinical and process-related factors differed between the 2 groups. Although mor- of life or lower rates of recurrent car- tality rates were similar between the 2 institution types, the nonfatal composite 5-year diac admissions for patients experienc- event rate (ie, recurrent cardiac hospitalization and emergency department visits) was ing higher rates of revascularization.2-13 lower for patients initially admitted to invasive-procedure hospitals (71.3% vs 80.4%; These comparisons and conclu- unadjusted odds ratio [OR], 0.65; 95% confidence interval [CI], 0.52-0.82; P,.001). This advantage persisted after adjustment for sociodemographic and clinical factors sions rest on the assumption that a and procedure utilization (adjusted OR, 0.68; 95% CI, 0.53-0.89; P,.001). How- single ecological variable (being admit- ever, the nonfatal outcome advantages of invasive-procedure hospitals were ex- ted to a hospital with or without PCI plained by their teaching status (adjusted OR, 0.98; 95% CI, 0.73-1.30; P=.87). and CABG surgical capacity) and the Conclusions In this sample of patients admitted with AMI, the differing outcomes associated variation in one aspect of of apparently similar patients treated in 2 different practice settings were explained by process of care (higher or lower rates multiple competing factors. Researchers conducting observational studies should be of revascularization) account for the cautious about attributing patient outcome differences to any single factor. 14,15 outcome differences. By design, JAMA. 2001;285:2101-2108 www.jama.com other differences in characteristics of the patients, the admitting hospital, or the Author Affiliations are listed at the end of this MD, PhD, Institute for Clinical Evaluative Sciences, attending physicians, along with myriad article. G106-2075 Bayview Ave, Toronto, Ontario, Canada other potential differences in fol- Corresponding Author and Reprints: David A. Alter, M4N 3M5 (e-mail: [email protected]). ©2001 American Medical Association. All rights reserved. (Reprinted) JAMA, April 25, 2001—Vol 285, No. 15 2101 Downloaded From: https://jamanetwork.com/ on 10/01/2021 MI OUTCOMES AND ON-SITE REVASCULARIZATION low-up care, are given much less atten- mine cardiac procedure use. Patients communities is suppressed. Four insti- tion as determinants of outcome. Our aged 65 years or older were linked to the tutions had on-site angiography-only study examines the validity of such as- Ontario Drug Benefit Program to iden- facilities comprising 3.5% of the sample sumptions using a cohort of AMI pa- tify discharge rates of evidence-based population and were also excluded from tients from Ontario. We hypothesized secondary-prevention therapies (eg, as- the analysis because of small sample size. that ecological variables may be highly pirin and b-blockers). The Ontario Reg- Accordingly, comparisons were made correlated with other factors and that istered Persons Database allowed us to between 2 hospital groups: the 9 hospi- procedural differences alone are un- determine out-of-hospital deaths. To tals with on-site angiography and revas- likely to explain the outcome differ- maintain patient confidentiality, all link- cularization capabilities and the 181 hos- ences between hospitals (and, by ex- ages were conducted using scrambled pitals with no invasive-procedure tension, regions) with high vs low rates health card numbers. facilities. of cardiac procedures after AMI.16-18 We constructed a cohort of all patients admitted with a most responsible diag- Socioeconomic and Clinical Factors METHODS nosis of AMI (International Classifica- Since neighborhood income level has Overall Framework tion of Diseases, 9th Revision, Clinical been shown to be an important predic- To date, no study has compared the out- Modification [ICD-9-CM] code 410) in tor of outcomes following AMI in On- comes of hospitals with high and low Ontario between April 1, 1992, and tario,21 we used the 1991 official Cana- rates of invasive cardiac procedures December 31, 1993. The accuracy of AMI dian census data to calculate the average within Canada, where the interven- coding in the OMID database has been household income for each patient’s tion rates are markedly lower than in previously validated through large prov- postal code. To control for variations in the United States. Therefore, we first set ince-wide chart audits.19,20 We excluded patient severity of illness on admission, out to confirm whether patients with non-Ontario residents, those with invalid we used the Ontario AMI mortality pre- AMI at hospitals with on-site revascu- Ontario Health Card numbers, those diction rule for 30-day and 1-year mor- larization facilities have outcome ad- younger than 20 or older than 105 years, tality rates.20 The variables in this model vantages vs hospitals without on-site re- those discharged alive whose total length include age, sex, cardiac severity (eg, con- vascularization facilities in Ontario. If of hospital stay was fewer than 4 days, gestive heart failure, cardiogenic shock, such findings could be confirmed, we those for whom AMI was coded as a hos- arrhythmias), and comorbid status (eg, would then test our primary hypoth- pital complication, those transferred from diabetes mellitus, stroke, acute and esis that the reasons the differences another acute care facility, and those with chronic renal disease, and malig- might be attributed wrongly to a single no link postal code information for nancy), as derived from the ICD-9 codes distinguishing characteristic of the ad- income data. To reduce the chances that present in the 15 secondary diagnostic mitting hospital—a high rate of per- subgroups within the cohort varied in fields of the hospitalization database. This formance of revascularization proce- severity of cardiovascular disease, we also prediction rule was derived in a differ- dures—when many other patient, excluded any patient who had been hos- ent subset of the OMID database (ie, all physician, and process-related differ- pitalized with AMI in the year preced- AMI patients admitted between April 1, ences might play as much a role. ing the index admission. Details about 1994, and March 31, 1997) with areas the OMID database and the rationale for under the receiver operating character- Patient Selection these criteria have been published else- istic curve (AUROC) of 0.775 for 30- The Ontario Myocardial Infarction Da- where.19-21 day mortality and 0.793 for 1-year mor- tabase (OMID) links a variety of popu- tality rates. The predictive accuracy of the lation-based administrative data sources. Hospital Groups model was confirmed in the cohort of pa- Hospital discharge abstracts compiled by Patients were categorized by on-site pro- tients with AMI used in this study (ie, the Canadian Institutes of Health Infor- cedural characteristics at their admit- AUROC were 0.76 for 30-day mortality mation yielded data pertaining to the in- ting hospitals (eg, on-site invasive car- and 0.78 for 1-year mortality) and inde- dex admission: patient demographics, ill- diac procedure facilities vs no on-site pendently validated on 4836 patients ness severity, comorbidity,