Long-Term MI Outcomes at Hospitals with Or Without On-Site Revascularization

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; PϽ.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; PϽ.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; PϽ.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]).

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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 ␤-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, in-hospital invasive cardiac procedure facilities, with AMI from Manitoba and 112234 procedure use, and mortality. Hospital herein also respectively termed inva- patients with AMI from California readmissions were identified using lon- sive- vs noninvasive-procedure hospitals) AUROC of 0.77 in both samples).20,22 gitudinal linkages. Physician claims data regardless of potential downstream hos- for the entire province was obtained pital transfers. During the study period, Procedure Use from the Ontario Health Insurance Plan there were 197 acute care hospitals in Coronary angiography and revascular- and were used to determine emergency Ontario. Three rural isolated hospitals ization procedure rates were deter- and postdischarge physician visits. Both were excluded from the analysis because mined using procedure codes in the hos- physician claims and hospital dis- census data information needed to obtain pitalization and physician claims charge abstracts were used to deter- socioeconomic status in isolated rural databases. The exact date of referrals for

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procedures could not be determined and emergency department visits. Car- hierarchy, thereby producing confi- from the administrative data. How- diac readmissions were identified when dence intervals (CIs) that are artifi- ever, as reasonable surrogates for wait- patients were readmitted to hospital with cially narrow. Multilevel analysis al- ing times, we calculated the number of a most responsible diagnosis of recur- lows one to incorporate correctly days from the index AMI admission to rent MI (ICD-9 code 410), congestive variables measured at different levels of the date of coronary angiography and the heart failure (ICD-9 code 428), or an- the hierarchy and produces more accu- number of days from angiography to re- gina (ICD-9 code 411 or 413). In total, rate estimates of significance. Multi- vascularization. Generally, these surro- 96.9% of patients readmitted to hospi- level analyses adjusted for age, sex, so- gate measures will slightly overesti- tal also had concomitant emergency as- cioeconomic status (average household mate true procedural waiting time. We sessments, suggesting that the vast ma- income), illness severity (ie, individual divided these process factors into 2 pe- jority of readmissions reflected urgent risk factors comprising the estimated 30- riods: those occurring during the in- clinical need rather than an elective in- day mortality at the time of index ad- dex admission and those occurring dication (eg, elective angiography). mission), index revascularization pro- within the first 6 months of follow-up. Emergency department visits were iden- cedures, as well as the 4 proxy measures tified using claims data. of processes listed above. The order with Other Hospital Characteristics which variables were entered into the Administrative data lack detailed infor- Statistical Analysis models did not significantly alter the re- mation about processes of care during Clinical characteristics of patients were sults. Multilevel analyses were imple- the index admission. Nonetheless, compared between the 2 groups. Dif- mented using HLM version 5.26 post-MI outcomes may be influenced by ferences in procedural rates, outpa- Statistical significance was defined as other physician and hospital character- tient visits, mortality, and cardiac re- PϽ.05 for all analyses. We used SAS sta- istics, which include attending physi- admission were examined using ␹2 tistical software version 6.12 (SAS In- cian specialty, hospital volumes (based analyses. Intergroup hospital differ- stitute Inc, Cary, NC) for the remain- on the annual number of patients ad- ences in procedural waiting times, out- ing statistical analyses. mitted to the MI facility20), hospital patient visits, and hospital bed-days teaching status, and geographical prox- were tested using the t test. RESULTS imity to the nearest tertiary facility (from Crude mortality rates were exam- Baseline Clinical and latitudinal and longitudinal coordi- ined at 5 years to ensure equivalent fol- Process Characteristics nates or “as the crow flies”23). Such eco- low-up duration for all patients. Long- The cohort included 25697 patients. logical indicators may serve as proxy term survival and time-to-first-cardiac TABLE 1 illustrates the distribution of measures of intersite differences in pro- readmission were analyzed by hospital baseline demographic, socioeconomic, cesses of care. Attending physician spe- group and compared using Kaplan- clinical, and in-hospital process charac- cialty and physician specialty visits were Meier plots and the log-rank test. Mor- teristics between patients at the 2 types identified using hospital discharge ab- tality comparisons censored patients at of hospitals. Although patients at inva- stracts and Ontario Health Insurance 5 years although time-to-first-cardiac re- sive-procedure hospitals had signifi- Plan claims data, respectively. admission censored patients at 5 years cantly higher rates of coronary angiog- Although the majority of invasive- or death. Nonfatal outcomes were ex- raphy and myocardial revascularization procedure centers are also large- amined both individually and com- procedures during the index hospital- volume institutions and teaching hos- bined (ie, the first cardiac readmission ization, there were many other factors pitals, the majority of large-volume and or emergency department visit). that also differed between the 2 types of teaching hospitals are not invasive- To determine which factors best institutions. For example, although pa- procedure centers. Moreover, formal di- accounted for the overall invasive- tients who were admitted to invasive- agnostic testing for collinearity across procedure effect on fatal and nonfatal procedure centers were more affluent, hospital and physician-level variables did outcomes, we constructed multivari- they were also at higher risk of early mor- not reveal any variance inflation factor able models that sequentially added pa- tality, with a predicted 30-day mortal- greater than 5.0. Therefore collinearity tient-level, physician-level, and hospital- ity rate of 16.2% vs 14.7% for noninva- was not a significant issue for this analy- level characteristics. Such analysis sive-procedure centers (PϽ.001). sis (ie, the maximum variance inflation models the hierarchical nature of the Patients admitted to invasive-proce- factor across explanatory variables for data, which consist of patients nested in dure hospitals were also more likely to the 190 hospitals was 2.6).24 physicians, who in turn are nested in be admitted to a teaching facility and a hospitals, with characteristics mea- large-volume hospital and assigned to an Outcomes sured at different levels of this hierar- attending cardiologist. All patients were tracked for a mini- chy.25 A traditional regression model will TABLE 2 illustrates that follow-up and mum of 5 years. Long-term outcomes in- tend to underestimate SEs for charac- treatment factors also differed between cluded mortality, cardiac readmissions, teristics measured at higher levels of the the 2 types of institutions. For example,

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patients at invasive-procedure hospitals Outcomes vasive-procedure hospitals were driven were more likely to be followed up by a Unadjusted 5-year survival was similar by lower angina readmissions (log- cardiologist than a general practitioner between groups. However, patients ini- rank ␹2, 17.86; PϽ.001) and emer- while elderly patients admitted to non- tially admitted to invasive-procedure gency department visits (log-rank ␹2, invasive-procedure hospitals were less hospitals had lower nonfatal adverse out- 311.09; PϽ.001), with a weak trend to likely to receive a prescription for aspi- comes at 5 years following AMI com- lower reinfarction rates (log-rank ␹2, rin, ␤-blockers, angiotensin-converting pared with patients admitted to nonin- 1.14; P=.29). Among patients experi- enzyme inhibitors, or statins within 90 vasive-procedure hospitals (FIGURE 1). encing nonfatal outcomes, the time to days following discharge. The nonfatal outcome advantages at in- first event was significantly longer for those patients initially admitted to invasive-procedure hospitals (470 vs 375 Table 1. Baseline Patient, Physician, Hospital, and Process Characteristics for Patients With Acute Myocardial Infarction (AMI) Initially Admitted to Invasive- vs Noninvasive-Procedure days, PϽ.001). Patients admitted to in- Hospitals in Ontario* vasive-procedure centers had fewer to- Invasive-Procedure Noninvasive- tal cardiac readmissions (11 fewer car- Hospitals Procedure Hospitals diac readmissions per 100 AMI patients, Variables (n = 2832) (n = 22 865) P Value PϽ.001), fewer angina readmissions (12 Patient Factors fewer angina readmissions per 100 AMI Demographics Age, mean, y 66.3 66.6 .19 patients, PϽ.001), and fewer emer- Men 66.5 65.1 .13 gency department visits (57 fewer emer- Average household income, $† 53 150 49 255 Ͻ.001 gency visits per 100 AMI patients, Clinical status at admission PϽ.001). There were no significant dif- Cardiogenic shock 3.3 2.3 Ͻ.001 ferences in the number AMI readmis- Congestive heart failure 22.7 18.1 Ͻ.001 sions (P=.43), congestive heart failure re- Pulmonary edema 1.0 1.5 .05 admissions (P=.93), or cumulative Cardiac dysrhythmia 18.0 12.6 Ͻ.001 length of hospital stay after discharge Malignancy 3.3 3.4 .61 (P=.92). Diabetes with complications 2.1 1.5 .01 Stroke 7.2 3.3 Ͻ.001 Accounting for the Acute renal insufficiency 2.4 1.3 Ͻ.001 Invasive-Procedure Effect Chronic renal insufficiency 4.0 1.6 Ͻ.001 on Outcomes Predicted 30-day mortality 16.2 14.7 Ͻ.001 FIGURE 2 examines residual invasive- Invasive cardiac procedures Coronary angiography during 25.3 7.6 Ͻ.001 procedure effects on 5-year outcomes the index hospitalization when sequentially adjusted for patient- Myocardial revascularization 11.4 3.2 Ͻ.001 level, physician-level, and hospital- during the index hospitalization level characteristics. All nonfatal out- Time from AMI to angiography, d 6.3 11.3 Ͻ.001 comes were aggregated, given that the Time from AMI to revascularization, d 9.5 14.9 Ͻ.001 determinants for each nonfatal out- Length of hospital stay, d 10.7 9.2 .001 Ͻ come were similar to one another. Physician Factors Figure 2A examines the invasive- Attending physician specialty Cardiology 70.2 18.1 Ͻ.001 procedure hospital effects on mortal- Internal medicine 21.6 52.5 Ͻ.001 ity, and Figure 2B examines the inva- General practice 5.9 29.2 Ͻ.001 sive-procedure hospital effects on nonfatal outcomes. Hospital Factors Figure 2A illustrates that adjust- Hospital volume High (Ն100 cases/y) 96.3 71.4 Ͻ.001 ments for age, sex, and socioeconomic Medium (34-99 cases/y) 3.7 21.5 Ͻ.001 status do not significantly alter the odds Low (Յ33 cases/y) 7.1 0 Ͻ.001 ratio (OR) of death for patients admit- Teaching status 89.1 9.1 Ͻ.001 ted to invasive-procedure vs noninvasive- Distance to a tertiary facility, km procedure hospitals (adjusted OR, 1.07; Ͻ10 100 22.8 Ͻ.001 P=.15). After adding clinical factors into 10-50 0 34.5 Ͻ.001 the model (ie, those clinical variables Ͼ50 0 42.7 Ͻ.001 comprising the predicted 30-day risk of *Data are presented as percentages unless otherwise indicated. Invasive-procedure hospitals include those with on- site angiography and revascularization facilities. Noninvasive-procedure hospitals are those without those services. mortality), admission to invasive- †Average household income (Canadian dollars) was obtained from 1991 Canadian census data and corresponds to procedure hospitals (adjusted OR, 0.86; the Enumeration Area of Residents. P =.003) becomes protective against

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mortality. Some of the protective effects teaching status and not because of higher subdividing hospitals into 4 groups: of invasive-procedure hospitals are revascularization rates themselves. teaching and invasive-procedure, teach- explained by index revascularization pro- ing and noninvasive-procedure, non- cedures themselves, as illustrated by the Subgroup Analyses teaching and invasive-procedure, non- attenuated effect when index revascu- To explore the relationship between teaching and noninvasive-procedure. larization procedures are added to the teaching status, invasive-procedure cen- The postdischarge rates of aspirin (67% model (adjusted OR, 0.92 for invasive- ters, and nonfatal outcomes further, we vs 61.5%, PϽ.001), ␤-blockers (48.4% procedure hospitals; P=.07). However, first compared baseline and follow-up vs 39.6%, PϽ.001), cardiology fol- there are no incremental protective effects differences between hospital catego- low-up rates at 90 days (33.4% vs 19.8%, of invasive-procedure hospitals on mor- ries. Differences in follow-up specialty PϽ.001), and the total number of fol- tality after adjusting for the remaining care most distinguished teaching from in- low-up cardiology visits (2.8 vs 1.9, physician-level and hospital-level char- vasive-procedure hospitals (TABLE 3). PϽ.001) were all higher in teaching and acteristics (adjusted OR, 1.01 for invasive- We then performed subgroup analyses noninvasive-procedure hospitals than in procedure hospitals; P=.82). Figure 2B illustrates that the unad- Table 2. Downstream Follow-up Care After Discharge From the Index Acute Myocardial justed invasive-procedure effects on non- Infarction Hospitalization in Patients Initially Admitted to Invasive- vs Noninvasive-Procedure fatal outcomes (unadjusted OR, 0.65; Hospitals in Ontario* 95% CI, 0.52-0.82; PϽ.001) is not sig- Invasive-Procedure Noninvasive-Procedure P Variables Hospitals Hospitals Value nificantly altered when sequentially ad- Medication use within 90 days justing for patient-level (adjusted OR, of discharge† 0.68; 95% CI, 0.53-0.89; PϽ.001), and Aspirin 66.4 62.1 .002 physician-level (adjusted OR, 0.72; 95% ␤-Blockers 50.2 40.5 Ͻ.001 CI, 0.56-0.92; PϽ.001) characteristics. ACE inhibitors 40.7 37.9 .05 Index revascularization procedure use HMG-CoA reductase inhibitors 5.9 4.0 .002 (statins) does not explain any of the morbidity Calcium channel blockers 29.7 38.4 Ͻ.001 advantages at invasive-procedure hos- Physician specialty follow-up pitals. However, the protective effects of by 90 days after discharge invasive-procedure hospitals on nonfa- Cardiology 25.8 21.0 Ͻ.001 tal outcomes are partially negated when Internal medicine 42.0 49.3 Ͻ.001 adding geographical proximity (ad- General practice 69.5 72.6 Ͻ.001 justed OR for invasive-procedure hos- Procedures from discharge to 6 months Coronary angiography 10.4 14.6 Ͻ.001 pitals, 0.84; 95% CI, 0.63-1.12; P=.24), Myocardial revascularization 7.1 7.4 .56 and entirely negated when adding teach- *Data are presented as percentages unless otherwise indicated. Invasive-procedure hospitals include those with on- ing status into the multilevel model (ad- site angiography and revascularization services. Noninvasive-procedure hospitals are those without those services. ACE indicates angiotensin-converting enzyme; HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A. justed OR for invasive-procedure hos- †Medication use pertaining to patients aged 65 years and older. pitals, 0.98; 95% CI, 0.73-1.30; P=.87). In contrast, the protective effects of Figure 1. Death and Nonfatal Outcomes After Acute Myocardial Infarction (AMI) at teaching status on nonfatal outcomes Invasive- and Noninvasive-Procedure Hospitals were not negated when adding either invasive-procedure hospitals or geo- A Death B Nonfatal Outcomes graphical proximity into the models 1.0 (FIGURE 3). Moreover, nonfatal out- 0.8

come benefits of teaching status per- 0.6 sisted when excluding patients re- 0.4 ferred for index revascularization Invasive-Procedure Hospitals 0.2

procedures (adjusted OR for teaching Survival Event-Free Noninvasive-Procedure Hospitals status, 0.71; 95% CI, 0.56-0.90; P=.005), and when excluding those patients trans- 012 345 13245 Years Years ferred from noninvasive- to invasive- No. at Risk procedure hospital facilities (adjusted Invasive2832 2137 2003 1875 1763 16792457 1355 1055 834 656 537 OR for teaching status, 0.68; 95% CI, Noninvasive22 865 17 330 16 140 15 189 14 282 13 55519 832 8613 6147 4692 3700 2986

0.53-0.88; P=.004). Most of the nonfa- Nonfatal outcomes include the first of recurrent cardiac hospitalization (MI, angina, congestive heart failure) tal outcome advantage initially ob- or emergency department visits. Five-year survival rate was equal between the 2 hospital groups (log-rank ␹2, served for invasive-procedure hospi- 0.006; P=.94), A. Five-year nonfatal event-free survival was higher at invasive- vs noninvasive-procedure hospitals (log-rank ␹2,158.6; PϽ.001), B. tals was explained by the hospital’s

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Figure 2. Invasive-Procedure Hospital Effect for Predicting Death and Nonfatal Outcomes

A DeathB Nonfatal Outcomes Favors Favors Favors Favors Invasive- Noninvasive- Invasive- Noninvasive- Procedure Procedure Procedure Procedure Hospitals Hospitals Hospitals Hospitals

Model 1: Crude

Model 2: Model 1 and Age

Model 3: Model 2 and Sex

Model 4: Model 3 and Socioeconomic Status

Model 5: Model 4 and Clinical

Model 6: Model 5 and Index Revascularization

Model 7: Model 6 and Attending Physician Specialty

Model 8: Model 7 and Hospital Volume

Model 9: Model 8 and Proximity to Tertiary Care Hospitals

Model 10: Model 9 and Teaching Status

0.75 0.8751.0 1.125 1.25 0.5 0.751.0 1.25 1.5 Adjusted Odds Ratio Adjusted Odds Ratio (95% Confidence Interval) (95% Confidence Interval)

Model 1 illustrates the unadjusted odds ratio (OR) for the invasive-procedure hospital effect for predicting death at 5 years after acute myocardial infarction, A; and for predicting nonfatal outcomes (the first of a recurrent AMI admission, angina admission, congestive heart failure admission, or an emergency department visit) at 5 years after AMI, B. Sequential models illustrate how the effect size (ORs) for invasive-procedure hospitals change when adjusting for patient, physician, and hospital- level characteristics using hierarchical multilevel modeling.

tals were associated with lower nonfa- vascularization procedures modeled as Figure 3. Teaching-Hospital Effect for tal event rates, whereas the 1 nonteach- time-varying covariates. Independent Predicting Nonfatal Outcomes ing and invasive-procedure hospital had predictors of lower risk of nonfatal out- Favors Teaching higher nonfatal event rates (P=.003) af- comes included postdischarge use of as- Hospitals ter AMI. After eliminating the 1 non- pirin (adjusted hazard ratio [HR], 0.94; Model 1: Patients and Physician-Level Factor teaching and invasive-procedure hospi- 95% CI, 0.90-0.98; P=.002), ␤-block- tal from the analysis, the results did not ers (adjusted HR, 0.89; 95% CI, 0.85- change. That is, teaching status still ac- 0.93; PϽ.001), and statins (adjusted HR, Model 2: Model 1 and Invasive-Procedure counted for the invasive-procedure ef- 0.84; 95% CI, 0.78-0.92; PϽ.001). All Hospitals fect in nonfatal outcomes. variables were associated with a lower To further explore the relationship risk for nonfatal outcomes. In contrast,

Model 3: Model 2 and among teaching hospitals, postdis- postdischarge use of calcium channel Geographical Proximity charge cardiac care, and nonfatal out- blockers (adjusted HR, 1.19; 95% CI, comes after AMI, a supplementary time- 1.14-1.24; PϽ.001), and follow-up gen- dependent covariate analysis was eral practitioner visits (adjusted HR, 1.24; 0.25 0.50.75 1.0 1.25 Adjusted Odds Ratio performed since outpatient physician vis- 95% CI, 1.17-1.31; PϽ.001) were asso- (95% Confidence Interval) its and therapies occur at different time ciated with a higher risk of nonfatal out- intervals after discharge. This analysis comes among elderly patients. Under- Model 1 illustrates the unadjusted odds ratio (OR) for the teaching-hospital effect for predicting nonfatal out- was confined to the subgroup of pa- going a revascularization procedure after comes (the first of a recurrent acute myocardial infarc- tients aged 65 years and older given that discharge was not a significant prediction [AMI] admission, angina admission, congestive heart failure admission, or an emergency department visit) outpatient medication data were only tor of nonfatal outcomes after AMI (ad- at 5 years after AMI. Sequential models illustrate how available for these patients. Due to the justed HR, 0.98; 95% CI, 0.85-1.14; the effect size (ORs) for teaching hospitals change when limitations of the HLM software pack- P=.83). In total, downstream processes adjusting for patient, physician, and hospital charac- 26 teristics using hierarchical multilevel modeling. age, a hierarchical analysis could not of care had a marginal impact on ex- be used for this analysis. Accordingly, plaining the protective effects of teach- nonteaching and noninvasive-proce- conventional statistical techniques using hospitals among elderly patients (ad- dure hospitals. Both teaching and inva- ing Cox regression models were incor- justed HRs for teaching hospitals, 0.75; sive-procedure (P=.01) and teaching and porated with postdischarge medication 95% CI, 0.69-0.81 before and 0.78; 95% noninvasive-procedure (P=.04) hospi- use, physician visits, and downstream re- CI, 0.72-0.85 after adjustments for down-

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stream processes of care, respectively; al Use of Strategies to Open Occluded We demonstrated that the benefits of PϽ.001 in both models). Arteries in Acute Coronary Syndromes invasive-procedure hospitals on nonfa- (GUSTO-II)clinicaltrialexaminingnon– tal outcomes were largely explained by COMMENT Q-wave MI and unstable angina demon- teaching status. In our statistical mod- Our study demonstrated that Ontario pa- strated that at 6 months, US patients had els, teaching status likely served as a tients admitted to hospitals with on- an absolute rate reduction of 3% for re- proxy for an uncertain number of un- site revascularization facilities had lower currentMIcomparedwiththeirCanadian measured process characteristics. One recurrent cardiac hospitalization rates, counterparts.10 The authors concluded distinguishing process difference be- but similar rates of survival compared that the different outcomes may have tween teaching hospitals and invasive- with patients admitted to hospitals been attributed to differences in proce- procedure institutions was in their re- without on-site revascularization facili- dure rates between the 2 countries. spective downstream processes of care ties. The determinants of fatal out- Our study serves to illustrate the com- after discharge from the index AMI ad- comes were different from those for non- plex interrelationships between proce- mission. Patients admitted to teaching fatal outcomes. In contrast to fatal events, dure use, secondary process character- hospitals were more likely to be fol- the effect of invasive-procedure hospi- istics, case-mix factors, and outcomes. lowed up by cardiac specialists after dis- tals on nonfatal outcomes was ex- Many other factors apart from differ- charge from hospital, independent of plained by other ecological variables— ences in the use of procedures on the whether hospitals had on-site revascu- hospital teaching status and to a lesser index admission distinguish hospitals larization facilities. Indeed, our sub- extent geographical proximity (to ter- with from those without on-site revas- group analysis determined that the use tiary centers). Despite the variation in cularization facilities. For example, AMI of evidence-based therapies predicted cardiac intervention rates that existed be- patients admitted to invasive-proce- lower rates of recurrent cardiac admis- tween invasive-procedure and nonin- dure hospitals in this study had a more sions and emergency department visits vasive-procedure hospitals, differences adverse risk profile, were wealthier, had and accounted, albeit marginally, for in the utilization rates of invasive car- longer initial lengths of hospital stay, and some of the protective effects of teach- diac procedures themselves did not ac- were more likely admitted to an attending status on nonfatal outcomes. It is count for outcomes at the hospital level. ing cardiologist than were patients admit- plausible that follow-up care is an im- Our results are consistent with the vast ted to noninvasive-procedure hospitals. portant determinant of nonfatal out- majority of studies demonstrating no Moreover, different process measures comes after AMI. Although a relation- significant relationship between inter- may have also existed during follow- ship between outpatient care and hospital (or regional) variations in pro- up. Although outpatient prescription morbidity outcomes after AMI is specu- cedure rates and survival following rates of evidence-based therapies were lative, such a relationship has been dem- AMI.2-9,12,13 Our findings are also consis- higher for those patients initially admit- onstrated to exist in other disease- tent with studies that have demon- ted to invasive-procedure hospitals, spe- specific cohorts (eg, congestive heart strated lower rates of recurrent cardiac cialty follow-up care varied less mark- failure).27,28 Moreover, at least one other admissions for groups incorporating edly than during the index admission. study has noted an interaction among higher rates of cardiac procedures after Postdischarge myocardial revasculariza- coronary intervention rates, on-site pro- MI.4-6,10,13 tion rates were similar between the 2 cedural capacity, and teaching status af- Manyinvestigatorshaveusedsucheco- groups. Accordingly, 2 groups of hospi- ter AMI.29 Most studies comparing hos- logical designs to draw conclusions about tals (or regions) cannot be distin- pitals with on-site revascularization the relative merits of higher vs lower guished solely based on a single process facilities with those without have not ad- cardiac intervention rates after MI. For characteristic (eg, rates of revasculariza- justed for differences in teaching status example, a recent substudy of the Glob- tion procedures). or downstream processes of care.2-4,14

Table 3. The Factors That Most Distinguish Teaching From Invasive-Procedure Hospitals for Patients Admitted With Acute Myocardial Infarction in Ontario* Invasive-Procedure Noninvasive-Procedure Teaching Hospitals Nonteaching Hospitals P Hospitals Hospitals P Variables (n = 21 089) (n = 4608) Value (n = 2832) (n = 22 865) Value Index angiography 20.2 7.2 Ͻ.001 25.3 7.6 Ͻ.001 Index revascularization 9.1 3.0 Ͻ.001 11.4 3.2 Ͻ.001 Attending cardiology physician 70.5 13.7 Ͻ.001 70.2 18.1 Ͻ.001 Attending general practice physician 0.5 32.3 Ͻ.001 5.9 29.2 Ͻ.001 Cardiology follow-up by 90 days 30.9 19.5 Ͻ.001 25.8 21.0 Ͻ.001 after discharge *Data are presented as percentages unless otherwise indicated. Invasive-procedure hospitals include those with on-site angiography and revascularization services. Noninvasive- procedure hospitals are those without those services.

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One noteworthy study limitation the 2 settings without fully accounting 10. Fu Y, Chang WC, Mark D, et al, for the GUSTO II Investigators. Canadian-American differences in the involves the lack of clinical detail spe- for myriad patient and process-of-care management of acute coronary syndromes in the cifically related to the initial infarct char- variables that may actually explain any GUSTO IIb trial. Circulation. 2000;102:1375-1381. 11. Scull GS, Martin JS, Weaver WD, Every NR, for acteristics, postinfarct left ventricle func- observed outcome differences. the MITI Investigators. Early angiography versus con- tion, and in-hospital pharmacological servative treatment in patients with non-ST eleva- Author Affiliations: Institute for Clinical Evaluative Sci- tion acute myocardial infarction. J Am Coll Cardiol. therapies. Although we adjusted for a ences (Drs Alter, Naylor, Austin, and Tu); Divisions of 2000;35:895-902. number of clinical, institutional, and Cardiology, Schulich Heart Center (Dr Alter), and Gen- 12. Pilote L, Califf RM, Sapp S, et al, for the GUSTO eral Internal Medicine (Dr Tu), Sunnybrook and Wom- Investigators. Regional variation across the United physician-related characteristics, we ac- en’s College Health Science Center; and University of States in the management of acute myocardial infarc- knowledge that additional clinical and Toronto Clinical Epidemiology and Health Care Re- tion. N Engl J Med. 1995;333:565-572. search Program (Drs Naylor and Tu), Department of 13. Yusuf S, Flather M, Pogue J, et al, for the OASIS process measures, both during the in- Public Health Sciences (Drs Austin, Tu, and Naylor), Registry Investigators. Variations between countries in dex admission and following discharge, and Dean’s Office (Dr Naylor), Universtiy of Toronto, invasive cardiac procedures and outcomes in patients Toronto, Ontario. with suspected unstable angina or myocardial infarc- may have altered our results or may have Author Contributions: Study concept and design: Al- tion without initial ST elevation. Lancet. 1998;352: helped explain why teaching status ac- ter, Naylor, Austin, and Tu. 507-514. counted for the morbidity advantages of Acquisition of data: Alter and Tu. 14. McClellan M, McNeil BJ, Newhouse JP. Does more Analysis and interpretation of data: Alter, Naylor, intensive treatment of acute myocardial infarction in the invasive-procedure hospitals. The time- and Tu. elderly reduce mortality? JAMA. 1994;272:859-866. dependent covariate analysis incorpo- Drafting of the manuscript: Alter and Naylor . 15. Batchelor WB, Peterson ED, Mark DB, et al. A com- Critical revision of the manuscript for important in- parison of US and Canadian cardiac catheterization prac- rated conventional rather than hierar- tellectual content: Alter, Austin, and Tu. tices in detecting severe coronary artery disease after myo- chical techniques. Accordingly, we cau- Statistical expertise: Alter and Austin. cardial infarction. J Am Coll Cardiol. 1999;34:12-19. Obtained funding: Naylor and Tu. 16. Psaty BM, Koepsell TD, Lin D, et al. Assessment and tion against overinterpreting the results Study supervision: Naylor and Tu. control for confounding by indication in observational of our subgroup analysis. Nonetheless, Draft, design, and analysis: Alter. studies. J Am Geriatr Soc. 1999;47:749-754. 17. Go AS, Rao RK, Dauterman KW, Massie BM. the inability of procedures themselves Funding/Support: This project was supported by an operating grant from the Canadian Institutes of Health Re- A systematic review of the effects of physician specialty to have accounted for hospital-related search (CIHR). The Institute for Clinical Evaluative Sci- on the treatment of coronary disease and heart failure outcome differences was a finding inde- ences is supported in part by a grant from the Ontario in the United States. Am J Med. 2000;108:216-226. Ministry of Health. Dr Alter is a recipient of the New 18. Di Salvo TT, Paul SD, Lloyd-Jones D, et al. Care of acute myocardial infarction by noninvasive and inva- pendent of the type and number of Investigator Award from CIHR. Dr Naylor was sup- sive cardiologists. J Am Coll Cardiol. 1996;27:262-269. ported as a Senior Scientist of the Medical Research variables entered into our statistical 19. Tu JV, Naylor CD, Austin P: Temporal changes Council of Canada. Dr Tu is supported by a Canada Re- in the outcomes of acute myocardial infarction in On- models. Furthermore, since hospital- search Chair in Health Services Research. tario, 1992-1996. CMAJ. 1999;161:1257-1261. Disclaimer: associated outcomes varied according The results, conclusions, and opinions are 20. Tu JV Austin P, Naylor CD, Iron K, Zhang H. Acute to a limited set of covariates, it seems un- those of the authors, and no endorsement by the Min- Acute myocardial infarction outcomes in Ontario. In: Nay- istry, the Institute, or the CIHR is intended or should lor CD, Slaughter PM, eds. Cardiovascular Health and likely that additional covariates would be inferred. Services in Ontario: An ICES Atlas. Toronto, Ontario: have changed our overall conclusions. Institute for Clinical Evaluative Sciences; 1999:83-110. Finally, our data were comprehensive, REFERENCES 21. Alter DA, Naylor CD, Austin P, Tu JV. Effects of 1. 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