Regional Variation across the United States in the Management of Acute Myocardial Infarction
Louise Pilote, M.D., M.P.H., Robert M. Califf, M.D., Shelly Sapp, M.S., Dave P. Miller, M.S., Daniel B. Mark, M.D., M.P.H., W. Douglas Weaver, M.D., Joel M. Gore, M.D., Paul W. Armstrong, M.D., E. Magnus Ohman, M.D., Eric J. Topol, M.D., for The GUSTO-1 Investigators
Background Differences in the management of acute myocardialinfarction have been reported among countries, but few studieshave investigated this issue in regions of the United States.
Methods We compared the management of acute myocardial infarctionamong census regions across the United States, using data fromthe first Global Utilization of Streptokinase and Tissue PlasminogenActivator for Occluded Coronary Arteries trial (GUSTO-1) comprising21,772 patients, and from the American Hospital Association.
Results We found substantial regional variation in the managementof acute myocardial infarction in the United States. Beta-blockers(prescribed for a range of 55 to 81 percent of patients in thevarious regions), nitrates (prescribed for 61 to 77 percent),and angiotensin-converting–enzyme inhibitors (prescribedfor 18 to 23 percent) were used most often in New England, whereascalcium-channel blockers (31 to 42 percent) and lidocaine (14to 43 percent) were used least often there. Similarly, the proportionof patients undergoing various cardiac procedures differed amongregions (range for angiography, 52 to 81 percent of patients;angioplasty, 22 to 35 percent; and coronary-artery bypass surgery,9 to 17 percent) and was lowest in New England. The regionaluse of cardiac procedures was closely related to their availability,except in New England. After the analysis was adjusted for clinicaland hospital variables, patients in New England were found tobe less likely to undergo angiography than patients in the otherregions (odds ratio, 0.37; 95 percent confidence interval, 0.32to 0.42). There was no apparent relation between the use ofcardiac procedures and rates of recurrent infarction or deathat 30 days or 1 year.
Conclusions There is substantial regional variation in the useof cardiac medications and procedures to manage acute myocardialinfarction in the United States. The use and availability ofcardiac procedures are closely related. The management of acutemyocardial infarction in New England is atypical in that therelatively limited availability of cardiac procedures does notaccount for their relatively low use in that region.
Each year, more than a million coronary angiography procedures,approximately 400,000 angioplasties, and 400,000 coronary-arterybypass operations are performed in the United States.1 Coronaryartery disease is highly prevalent, and its management ofteninvolves costly techniques. Thus, understanding the proper roleof invasive diagnostic and therapeutic procedures is criticalfor the provision of high-quality, cost-effective care.
Several studies have reported differences among countries inthe management of acute myocardial infarction and have assessedthe effect of the intensity of care on clinical outcomes.2,3,4,5Important differences have been found, including a much greateruse of cardiac procedures in the United States than in othercountries.5 We studied the extent of variation among regionsof the United States in the management of acute myocardial infarction.
To evaluate differences in patterns of care among U.S. Censusregions and to determine the principal factors responsible,we examined data from the first Global Utilization of Streptokinaseand Tissue Plasminogen Activator for Occluded Coronary Arteriestrial (GUSTO-1). This randomized clinical trial of thrombolyticstrategies included more than 23,000 patients with confirmedacute myocardial infarction from the United States.6 That trialallowed practice patterns to be observed, because decisionsabout all medications except aspirin and thrombolytic agentsand about all cardiac procedures were left to the discretionof the treating physicians.
Methods
Study Population
All 6306 U.S. hospitals with acute care facilities were invitedto participate in the study; 650 (10 percent) agreed to do so.The results of the primary study, conducted between December1990 and February 1993, have been published previously.6 Thestudy included patients with acute myocardial infarction presentingwithin six hours of the onset of chest pain who were eligiblefor thrombolytic therapy. No patients were excluded on the basisof age, the presence of cardiogenic shock, or previous coronary-arterybypass surgery.
The patients were randomly assigned to four different thrombolyticstrategies: streptokinase with subcutaneous heparin, streptokinasewith intravenous heparin, the administration of acceleratedtissue plasminogen activator (t-PA) with intravenous heparin,and the combination of t-PA and streptokinase with intravenousheparin. Since randomization to the four treatment groups wasbalanced across regions of the United States, the analysis reportedhere does not take into account the treatment assignments. Exceptfor treatment with thrombolytic agents, aspirin, and, whereappropriate, beta-blockers, the management of myocardial infarctionwas left to the discretion of the treating physicians. Accordingly,we excluded 1292 patients who were randomly selected to undergoangiography at various intervals after their acute myocardialinfarctions, because their cardiac procedures were dictatedby the research protocol.7 Another 41 patients were excludedbecause they had not had myocardial infarctions.
U.S. Census Regions
We divided the patients into subgroups according to the majorregions defined by the U.S. Census: New England, Mid-Atlantic,South Atlantic, East North Central, East South Central, WestNorth Central, West South Central, Mountain, and Pacific (seethe Appendix). We grouped the East South Central and West SouthCentral regions together as South Central because of the comparativelysmall numbers of patients from those regions.
Characteristics of the Patients
Prospectively collected information obtained from the case-reportforms in the original study included the demographic and clinicalcharacteristics of the patients at the time of enrollment andinformation on their hospital courses up to the time of discharge.6Data on patients who were transferred to a second hospital werealso collected up to the time of their discharge from that hospital.Deaths within 30 days and 1 year after the acute myocardialinfarction were ascertained on the basis of postcards returnedby the patients' families or through telephone contact or registeredmail. Data on the quality of life were collected by interviewinga random one-eighth of the enrolled patients, as previouslydescribed.4
Characteristics of the Hospitals
Data on the hospitals, including whether they had facilitiesfor coronary angiography and revascularization, were obtainedfrom the 1993 data base of the American Hospital Association.8The study sites were matched to this data base so that the datacollected would be specific to the site. The matching was 95percent complete. The 27 sites without matching files were contactedby telephone when data on the hospitals were missing. A totalof 431 patients (2 percent of the overall group) remained forwhom hospital data were missing. These patients were excludedonly from the multiple regression analysis.
Statistical Analysis
To investigate regional variation in the use of cardiac procedures,we performed a stepwise logistic-regression analysis. The followingdemographic and clinical predictors were included in a clinicalmodel: recurrent ischemia, second infarction, shock, congestiveheart failure, acute mitral regurgitation, arrhythmia, timeto thrombolytic treatment, age, sex, family history of heartdisease, hypercholesterolemia, diabetes, smoking, hypertension,infarct location, Killip class, previous angioplasty, and previousmyocardial infarction. All the variables were dichotomous, exceptfor age and time to thrombolytic treatment, which were includedas continuous variables; Killip class, an ordinal variable thatwas included as a continuous variable; and infarct location,a categorical variable that was transformed into the dichotomousvariables anterior and inferior.
A second model, the hospital-facilities model, was created byadding the information on hospital facilities to this clinicalmodel. The availability of angiography, angioplasty, and bypasssurgery was included in the form of patient-specific dichotomousvariables. The effect of the eight regions was introduced intothe second model by creating seven dummy variables, with theMid-Atlantic region used as the reference group.
The logistic-regression models were developed from data on arandom sample of 80 percent of the patients; the model was thenvalidated with reference to the remaining 20 percent.9 Aftervalidation, the model was fitted to the entire data base toprovide more exact estimates of measures. The validated modelsfor the full set of data are reported here. Among the patientseligible for inclusion in the analysis, 12 percent had at leastone missing demographic or hospital variable. We report resultsfor the patients for whom data were complete; when we imputeddata for the patients with missing variables, the results weresimilar.10,11
Results
Study Patients
A total of 21,772 U.S. patients were enrolled in the study afterthe exclusion of patients enrolled in the angiographic substudy.The geographic distribution was as follows: New England, 2318patients (11 percent of the total); Mid-Atlantic, 3758 (17 percent);South Atlantic, 5296 (24 percent); East North Central, 3616(17 percent); South Central, 1333 (6 percent); West North Central,1551 (7 percent); Mountain, 1839 (8 percent); and Pacific, 2061(9 percent). These patients were treated at 596 participatinghospitals (mean, 75 per region). In each region, the participatinghospitals represented an average of 29 percent of the hospitalswith coronary care units, 15 percent of those with intensivecare units, and 13 percent of those with emergency departments.
Demographic and Clinical Characteristics
Overall, the demographic and clinical profile of the patientswas similar across the United States (Table 1). The only notabledifferences were in the prevalence of current smoking (rangeamong regions, 40 to 51 percent of the patients) and hypercholesterolemia(34 to 45 percent) and in the incidence of recurrent ischemia(11 to 29 percent).
Table 1. Demographic and Clinical Characteristics of the Study Patients, According to Region of the United States.
Use of Cardiac Medications
The use of cardiac medications in the hospitals varied greatlyacross the United States (Table 2). New England had the highestpercentages of patients for whom oral beta-blockers, nitrates,and angiotensin-converting–enzyme inhibitors were prescribed,whereas it had the lowest percentages using calcium-channelblockers, digitalis, and other positive inotropic agents. Prescriptionswritten at discharge followed a similar trend, with New Englandhaving the highest percentages of patients receiving beta-blockers,angiotensin-converting–enzyme inhibitors, and nitratesand the lowest percentages receiving calcium-channel blockersand digitalis.
Table 2. Use of Cardiac Medications to Treat the Study Patients, According to region of the United States.
Use of Cardiac Procedures
During hospitalization, 71 percent of all study patients underwentangiography, 30 percent underwent angioplasty, and 13 percentunderwent coronary-artery bypass surgery. As with the use ofmedications, the use of cardiac procedures differed markedlyamong regions, and the pattern in New England was distinct fromthat of the other regions (Table 3). The proportion of patientsundergoing angiography ranged from 52 percent in New Englandto 81 percent in the South Central region. The use of angioplastyranged from 22 percent in New England to 35 percent in the WestNorth Central region, and that of coronary-artery bypass surgeryranged from 9 percent in New England to 17 percent in the SouthCentral region. Among the patients who underwent angiography,however, there was very little regional variation in the proportionswho subsequently underwent revascularization. Despite varyingpercentages of patients who underwent angiography, the extentof coronary vessel disease and the median left ventricular ejectionfraction were similar across regions.
Table 3. Use of Cardiac Procedures in the Treatment of the Study Patients, According to Region of the United States.
The use of other cardiac procedures in the acute care unit alsodiffered regionally. Temporary transvenous pacemakers were usedin 10 percent of all patients (range among regions, 7 to 14percent), pulmonary-artery catheters in 19 percent (range, 15to 22 percent), intraaortic balloon pumps in 6 percent (range,3 to 7 percent), and mechanical ventilators in 17 percent (range,14 to 20 percent).
Other Aspects of Care
The median stays in the hospital and the acute care unit didnot differ substantially across the United States (range, sevento nine days and three to four days, respectively). The proportionsof patients who were transferred to a second hospital rangedfrom 11 percent in the South Central region to 31 percent inthe Mid-Atlantic and South Atlantic regions; in New England,this proportion was 25 percent. Information on the treatmentof patients after an acute myocardial infarction was recordeduntil discharge, at both the initial and the transfer hospital.
Cardiac Care Facilities
Cardiac care facilities differed greatly across the United Statesamong the hospitals participating in the study (Table 4). Theuse of cardiac procedures was directly related to the availabilityof cardiac care facilities, particularly those for angiography(Figure 1). In general, cardiac procedures were least used andleast available in New England, whereas they were most usedand most available in the South Central region.
Figure 1. Positive Association between the Use and the Availability of Coronary Angiography in Regions of the United States.
The outlier status of New England in this analysis is supported by the studentized-residual statistic, which is the distance of the observed value from the regression line, adjusted for the model's variability. The studentized residual for New England was greater than 4, whereas the remaining seven residuals were well within the expected bounds of -2 to 2.
Clinical Outcomes
Regionally, mortality rates ranged from 5.4 to 7.2 percent inthe hospital (P = 0.21), from 5.8 to 7.7 percent at 30 days(P = 0.34), and from 8.6 to 10.3 percent at 1 year (P = 0.24),and rates of second infarctions in the hospital ranged from3.1 to 4.5 percent (P = 0.35) (Table 5). Other clinical outcomes,including functional status and the incidence of chest painand dyspnea, were similar across the United States.4
Table 5. Clinical Outcomes of the Study Patients, According to Region of the United States.
Explaining Regional Variation in Management
Angiography was used as a marker of regional variation becauseafter patients undergo this procedure, there is little furtherregional variation in rates of revascularization (Table 3).The expected rates of angiography generated by our clinicalmodel were quite different from the observed rates but werequite constant across the country, in accordance with the homogeneousclinical profiles (Table 6). The expected rates generated byour hospital-facilities model were generally closer to the observedrates, except in New England, where the expected and observedrates still differed considerably. This trend is also apparentin Figure 1, where the association between the availabilityof angiography and its use is quite strong for most regionsexcept New England, which appears to be atypical.
Table 6. Expected and Observed Rates of Angiography, According to Region of the United States.
Figure 2 shows the odds ratios and 95 percent confidence intervalsfor the factors influencing the use of angiography before dischargefrom the hospital. After adjustment for potentially confoundingclinical and demographic variables, regional variation in thelikelihood of undergoing angiography prevailed. The degree ofvariation was less when hospital characteristics were addedto the model, yielding the following odds ratios (and 95 percentconfidence intervals) for the regions as compared with the Mid-Atlanticregion (the reference category): South Atlantic, 1.6 (1.4 to1.8); South Central, 1.5 (1.3 to 1.8); East North Central, 1.6(1.4 to 1.8); West North Central, 1.0 (0.9 to 1.2); Mountain,1.3 (1.1 to 1.5); and Pacific, 0.9 (0.8 to 1.0). However, patientstreated in New England were much less likely to undergo angiographythan patients treated in other regions (odds ratio, 0.37; 95percent confidence interval, 0.32 to 0.42).
Figure 2. Odds Ratios and 95 percent Confidence Intervals for Various Factors That Influenced the Use of Angiography before Hospital Discharge in 21,772 Study Patients with Acute Myocardial Infarction.
The Mid-Atlantic region was used as the reference category for the regional comparison. Odds ratios to the left of the dashed line indicate that angiography is less likely, and those to the right of the line that it is more likely.
The association between treatment in New England and the decreaseduse of angiography was stronger than the associations foundfor most clinical and hospital characteristics except for theassociation of recurrent ischemia (odds ratio, 2.5; 95 percentconfidence interval, 2.2 to 2.7) and on-site angiography facilities(odds ratio, 1.7; 95 percent confidence interval, 1.5 to 1.9).There was a strong interaction between treatment in New Englandand recurrent ischemia (odds ratio, 2.7; 95 percent confidenceinterval, 2.0 to 3.6). Patients with recurrent ischemia werevery likely to undergo angiography in all census regions exceptNew England, where the procedure was considerably less likelyto be performed.
Discussion
This study demonstrated marked regional variation in the managementof acute myocardial infarction in the United States. The variationwas found in the use of both medications and procedures. Thediscordance between the approach to management in New Englandand that in the other regions was a surprising finding; NewEngland had a lower rate of use of procedures and a more evidence-baseduse of medications.12,13,14
Regional variation in the use of cardiac procedures was notexplained by differences in patient profiles or in the incidenceof complications related to myocardial infarction. However,we found a strong relation between the availability of angiographyin a region and the number of procedures performed there. Thisassociation was less strong in New England than in the otherregions, suggesting that there are other important explanationsfor the different way of managing acute myocardial infarctionin New England.
The use of cardiac medications during hospitalization and atdischarge varied greatly across the United States. New Englandhad the highest percentage of patients for whom medicationsshown to decrease mortality after an acute myocardial infarctionwere prescribed, as compared with other regions, and the lowestpercentage of patients for whom medications shown to have nobenefit or even a detrimental effect were prescribed. In keepingwith the findings of Rogers and coworkers,15 beta-blockers wereunderused in most other regions, whereas calcium-channel blockersand prophylactic lidocaine were overused.
There have been previous reports of regional variation in medicalpractice,16,17,18,19 and an association between the availabilityof cardiac care services and the use of cardiac procedures hasbeen noted,20,21 as it was in our study. Every and coworkersfound that patients with acute myocardial infarction who wereadmitted to hospitals with angiography facilities were aboutthree times more likely to undergo angiography than patientsadmitted to hospitals without such facilities.20 Blustein showeda similar association in New York State.21 In our study, thesame association between the availability and the use of cardiacprocedures was observed, but it did not entirely explain theregional variation and certainly did not explain the more conservativeapproach in New England.
A number of hypotheses could explain the observed variationin the management of acute myocardial infarction. First, medicaluncertainty accounts for some of the variation. Despite thepublication of several clinical trials and practice guidelineson the management of myocardial infarction after thrombolysis,physicians may remain uncertain about the applicability of astudy or guideline to their patients.22,23 The interpretationand applications of such information may be affected by thepresence or absence of leading medical centers in a given regionor by the ratio of specialists to generalists.24 Second, physicians'attitudes and patterns of testing and the preferences of patientsmay differ from region to region and may affect the selectionof treatment.18 Third, inappropriate use of cardiac proceduresmay cause some of the variation.25,26 Finally, nonclinical factors,such as the insurance status of patients and state regulations,may influence the decision-making process.27 Although the prevalenceof managed care could potentially explain the lower rates ofcardiac procedures in New England, this hypothesis would beinconsistent with the higher rates of procedures in the Pacificregion, where managed care is particularly prevalent.
The management of acute myocardial infarction in New Englandappears to be at a halfway point between the less invasive approachpreviously reported in Canada and the more invasive approachin the United States as a whole.2,3,4 The rates of angiography,angioplasty, and surgery among all the Canadian patients inthe GUSTO-1 study were much lower than any of the regional ratesin the United States. Marked differences in the approach tomanagement did not result in marked differences in mortalityand rates of reinfarction, although the study by Mark and coworkerssuggested that adjusted one-year mortality was higher in Canada,and quality of life and functional status lower.4 Too conservativean approach may result in worse outcomes, but an aggressiveapproach will be more expensive and may not yield benefits commensuratewith the extra costs. Identifying the proper balance betweenextra clinical benefits and extra costs is thus of great importance.
The present study was limited by our ability to demonstratea direct relation between variation in procedure rates and clinicaloutcomes. First, this study had limited power to detect short-termdifferences in mortality and functional status among the eightregions. Thirty-day mortality in New England was 6.7 percent,as compared with a mean of 7.0 percent for the other seven regions.The power of our study to detect a difference in mortality ofone percentage point was only 42 percent, and its power to detecta difference of two percentage points was 92 percent. Second,1 year is too short a time in which to observe differences inoutcomes as a function of revascularization; New England's changein rank with regard to mortality — from third lowest after30 days to third highest after 1 year — may, however,be a meaningful trend. Indeed, in randomized trials comparingcoronary-artery surgery with medical therapy, the survival curvesdo not favor surgery until after the first year.28 Finally,we lacked information on the patients' clinical courses andon the frequency of revascularization procedures between dischargeand the 30-day and 1-year follow-up points that might have influencedthe outcomes.
Another limitation of the study was that not all hospitals ineach region participated. The question of selection remainsan issue; 72 percent of hospital sites overall had angiographyavailable on the premises, but only 61 percent of sites in NewEngland had such facilities. Similarly, facilities for angiographywere available in 28 percent of the sites in the data base ofthe American Hospital Association but in only 23 percent ofthose in New England. Sites where angiography was availablewere oversampled, probably because patients with myocardialinfarction are more likely to be treated there first; however,the general regional trend was very similar between the GUSTO-1sites and those in the American Hospital Association data base.
In conclusion, we have demonstrated substantial regional variationin the management of acute myocardial infarction across theUnited States. A more evidence-based approach to the use ofmedications was apparent in New England. The regional variationin the use of cardiac procedures was not due to clinical differencesamong regions but was instead mostly related to the availabilityof these procedures. With respect to the management of acutemyocardial infarction, New England was atypical, in that thesomewhat lower availability of procedures in that region didnot account for their substantially more limited use.
Supported by a grant from the Heart and Stroke Foundation ofCanada (to Dr. Pilote).
We are indebted to Dawn Dykstra for assistance with data management,to Vesna Savor for clerical assistance, and to the GUSTO steeringcommittee for reviewing the manuscript.
Source Information
From the Cleveland Clinic Foundation, Cleveland (L.P., S.S., D.P.M., E.J.T.); Duke University Medical Center, Durham, N.C. (R.M.C., D.B.M., E.M.O.); the University of Washington, Seattle (W.D.W.); University of Massachusetts Medical Center, Worcester (J.M.G.); and the University of Edmonton, Edmonton, Alta., Canada (P.W.A.).
Address reprint requests to Dr. Topol at the Cleveland Clinic Foundation, Department of Cardiology, Desk F25, 9500 Euclid Ave., Cleveland, OH 44195.
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Appendix
The U.S. Census regions described in this article are as follows:New England — Maine, New Hampshire, Vermont, Massachusetts,Rhode Island, and Connecticut; Mid-Atlantic — New York,New Jersey, and Pennsylvania; South Atlantic — Delaware,Maryland, District of Columbia, Virginia, West Virginia, NorthCarolina, South Carolina, Georgia, and Florida; East North Central— Ohio, Indiana, Illinois, Michigan, and Wisconsin; EastSouth Central — Kentucky, Tennessee, Alabama, and Mississippi;West North Central — Minnesota, Iowa, Missouri, NorthDakota, South Dakota, Nebraska, and Kansas; West South Central— Arkansas, Louisiana, Oklahoma, and Texas; Mountain —Montana, Idaho, Wyoming, Colorado, New Mexico, Arizona, Utah,and Nevada; and Pacific — Washington, Oregon, California,Alaska, and Hawaii.
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