Length of Hospital Stay After Acute Myocardial Infarction in the Myocardial Infarction Triage and Intervention (MITI) Project Registry

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1 JACC Vol. 28, No CLINICAL STUDIES MYOCARDIAL INFARCTION Length of Hosptal Stay After Acute Myocardal Infarcton n the Myocardal Infarcton Trage and Interventon (MITI) Project Regstry NATHAN R. EVERY, MD, MPH, JOHN SPERTUS, MD, MPH, STEPHAN D. FIHN, MD, MPH, MARK HLATKY, MD, FACC,* JENNY S. MARTIN, RN, W. DOUGLAS WEAVER, MD, FACC, FOR THE MITI INVESTIGATORS Seattle, Washngton and Stanford, Calforna Objectves. Ths study sought to dentfy current trends n length of stay n patents wth an acute myocardal nfarcton and to evaluate whch demographc, clncal, procedural and hosptalrelated factors explan the varaton and reducton n length of stay observed durng the study perod. Background. Hosptal length of stay s an mportant contrbuton to cost of care. Prevous studes of length of stay after acute myocardal nfarcton have been performed largely on admnstratve data bases and do not reflect current practce patterns. Methods. We used unvarate and multvarate models to evaluate whch demographc, clncal and admnstratve factors nfluenced length of stay n 11,932 patents wth acute myocardal nfarcton admtted to 19 Seattle-area hosptals between 1988 and Results. Length of hosptal stay decreased from (mean -+ SD) to days durng the study perod. Demographc and clncal characterstcs known at the tme of admsson explaned only 6% of varaton n length of stay, whereas hosptal complcatons, procedure use and type of admttng hosptal explaned an addtonal 27% of varaton. The use of prmary angoplasty and early dagnostc coronary angography predcted a shorter length of stay; however, none of the measured varables explaned the 29% reducton n length of stay that occurred between 1988 and Conclusons. Although hosptal complcatons, procedure use and hosptal characterstcs are mportant predctors of length of hosptal stay, none of these factors explans the 29% reducton n length of stay observed n postmyocardal nfarcton patents between 1988 and It s lkely that unmeasured economc and admnstratve factors play mportant roles n nfluencng hosptal length of stay. (J Am Col Carclol 1996;28:287-93) Durng the past three decades, hosptal length of stay has been the most mportant determnant of the total cost of care (1). In acute myocardal nfarcton, as n many medcal and surgcal condtons, the mean length of stay has been dramatcally reduced. The earlest clncal gudelnes recommended a 3-week length of stay to reduce the rsk of myocardal rupture (2). In the late 1970s, based partally on a seres of observatonal studes and controlled trals, mean length of stay was reduced to 7 to 10 days n low rsk patents (3-5). Most recently, length of hosptal stay has been further reduced to -<6 days n patents wth no complcatons (6). Ths most recent reducton n length of stay may be a result of changng From the Northwest Health Servces Research and Development Feld Program, Seattle Veterans Affars Medcal Center, Seattle, Washngton; *Departments of Health Research and Polcy and Medcne, Stanford Unversty, Stanford, Calforna; and the MITI Project, Dvson of Cardology, Unversty of Washngton, Seattle, Washngton. Ths study was supported by Grant R01 HL38454 from the Natonal Heart, Lung, and Blood Insttute, Natonal Insttutes of Health, Bethesda, Maryland and by Grant HS08362 from the Agency for Health Care Polcy and Research, Rockvlle, Maryland. Manuscrpt receved October 13, 1995; revsed manuscrpt receved March 26, 1996, accepted Aprl 2, Address for correspondence: Dr. Nathan R. Every, MITI Coordnatng Center, 1910 Farvew Avenue East, Seattle Washngton demographc or clncal characterstcs of patents or advances n the treatment of acute myocardal nfarcton, such as thrombolytc therapy (7) or prmary angoplasty (8). However, underlyng economc pressures may also nfluence practce styles ndependent of patent and treatment characterstcs. Prevous studes (9-14) have used large admnstratve data bases to show that age, gender and race as well as nsttutonal and nsurance-related factors nfluence length of stay. However, nearly all the studes on ths topc, have been lmted by lack of clncal detal or have examned older practce patterns predatng recent clncal and health care system changes. The Myocardal Infarcton Trage and Interventon (MITI) Project regstry, a communty-wde chart-based data base, was establshed n 1988 to study communty patterns of care for all Seattle-area patents wth an acute myocardal nfarcton. Ths regstry provdes mportant data about trends n patterns of care durng a perod of sgnfcant advances n the treatment of acute nfarcton. The purpose of the present study was to dentfy clncal and nonclncal factors that nfluence hosptal length of stay and to analyze whch factors were assocated wth any observed reducton n length of stay durng the 7-year observaton perod by the Amercan College of Cardology /96/$15.00

2 288 EVERY ET AL. JACC Vol. 28, No. 2 HOSPITAL STAY AFTER MYOCARDIAL INFARCTION Methods Patents. The subjects of the present study were 11,932 patents admtted wth an acute myocardal nfarcton to 1 of the 19 hosptals partcpatng n the MITI Project. Characterstcs of the regstry, data-gatherng procedures and relablty have been prevously descrbed (15). Brefly, the MITI project s a collaboratve effort to evaluate new treatment strateges for patents wth an acute myocardal nfarcton and ncludes a regstry of all patents admtted for suspected myocardal nfarcton n the Seattle metropoltan area. The regstry contans detaled data about all patents who had an acute myocardal nfarcton at dscharge or death, as confrmed by medcal records. For patents transferred to a dfferent nsttuton durng the ndex hosptal stay, charts were abstracted at the recevng faclty such that each patent had a contnuous care record. The study was approved by the Unversty of Washngton Human Subjects Revew Commttee. The present analyss ncluded consecutve patents admtted wth an acute myocardal nfarcton between January 1988 and Aprl Patents wth an acute nfarcton admtted after resusctaton from cardac arrest as well as those dagnosed wth an acute nfarcton after admsson for another condton (e.g., orthopedc surgery) were excluded from the analyss. Hosptals partcpatng n the MITI regstry nclude 2 unversty hosptals, 2 staff-model health mantenance organzaton (HMO) hosptals, 1 Veterans Affars (VA) hosptal and 14 communty hosptals that served predomnantly fee-for-servce patents (managed-care market share n these hosptals was -5% durng the majorty of the study perod). Durng most of the study perod, 11 (57%) of the partcpatng hosptals had on-ste catheterzaton laboratores, and 2 (10%) routnely performed prmary angoplasty n elgble patents. Data collected. Traned abstractors collected detaled data from patent records wthn 3 months after dscharge or death. Demographc varables ncluded age, gender and race (coded as whte or nonwhte). Prehosptal and emergency department varables ncluded type of transport to the hosptal (911 call or other), duraton of cardac symptoms before emergency department evaluaton, electrocardographc (ECG) locaton of the nfarcton, vtal sgns on admsson and new evdence of congestve heart falure. Informaton from the cardac hstory ncluded pror myocardal nfarcton, heart falure, angna, hypertenson, percutaneous coronary angoplasty or bypass surgery. Data on hosptal course ncluded the presence of cardogenc shock, nfarct extenson, recurrent chest pan, left ventrcular ejecton fracton for those who underwent ether contrast or nuclear ventrculography (44% of the populaton), use of thrombolytc therapy, cardac catheterzaton, coronary angoplasty or bypass surgery. Coronary angoplasty was defned as ether prmary, performed <6 h after admsson wthout the concomtant use of thrombolytc therapy, or salvage, all other angoplasty n the settng of acute nfarcton. Coronary angography was defned as early when the procedure was performed <24 h after admsson and was not n the settng of prmary angoplasty. Postdscharge readmsson data were obtaned by lnkng the MITI regstry to the Washngton State Comprehensve Hosptal Abstract Reportng system (CHARS). The CHARS data base ncludes hosptal perod data, vtal status and hosptal charge data for every hosptal admsson n the state of Washngton. Socoeconomc status data were obtaned by lnkng MITI regstry patent address to populaton-based geocodes. In ths methodology, patents n the MITI regstry are assgned mean and medan ncome and educatonal status on the bass of census data from the lnked geocode. Statstcal methods. Length of stay was calculated from the date of hosptal admsson to the date of dscharge, ncludng any hosptal transfers that occurred. Because length of stay was not normally dstrbuted, we used the natural logarthmc transformaton of length of stay as the dependent varable n ths model. Frst unvarate comparsons were made usng one-way analyss of varance to explore the nfluence of demographc, nsttutonal and clncal varables on length of stay (e.g., comparng length of stay n all female vs. male patents). To study trends and factors that ndependently nfluenced hosptal length of stay, we used a seres of lnear regresson models wth the natural logarthmc transformaton of length of stay as the dependent varable. Patents who ded n the hosptal were excluded from the prmary lnear regresson models. To evaluate possble bas from the excluson of these cases, a separate model was evaluated that ncluded patents who ded n the hosptal. Factors sgnfcantly assocated wth length of stay n unvarate comparsons (p < 0.05) entered stepwse as ndependent varables nto the model. Adjusted length of stay was calculated by multplyng the mean length of stay by the beta coeffcent. An ntal model ncluded only demographc, hstorcal and comorbdty varables avalable on admsson. The second model ncluded all varables n the frst model as well as hosptal complcatons, such as heart falure or stroke. The thrd model ncluded all prevous varables as well as process of care varables, such as the use of cardac procedures or admsson to an HMO hosptal. We adjusted for case severty usng clncal varables collected n the MITI data base, such as pror heart falure or myocardal nfarcton, and then, for comorbd condtons, usng a separate severty adjustment that summed a count of the number of secondary dscharge dagnoses (fve addtonal dscharge dagnoses were collected by abstractors). In ths method, patents wth multple comorbd condtons (e.g., dabetes or obstructve pulmonary dsease) would have a hgher comorbdty score. Ths method of severty adjustment has recently been evaluated and compared favorably wth other more complcated severty adjustment methods (16). To explore factors that may have nfluenced the observed reducton n length of stay between 1988 and 1994, a regresson model was used that ncluded all sgnfcant varables from the full model wth the addton of multple nteracton terms. Interacton terms ncluded cohort year wth the varable of nterest. For example, an nteracton term was added that ncluded cohort year and patent age to evaluate whether

3 JACC Vol. 28, No. 2 EVERY ET AL. 289 HOSPITAL STAY AFTER MYOCARDIAL INFARCTION t Hosptal Number Fgure 1. Medan (thck hash marks), mean (thn hash marks) and 25th and 75th percentles (vertcal bars) for length of stay n the 19 partcpatng hosptals n the Myocardal Infarcton Trage and Interventon Project regstry. ncreasng patent age had a more mportant assocaton wth length of stay n 1988 than n Addtonal nteracton terms ncluded year wth gender, prevous cardac hstory, the use of coronary angography, angoplasty and bypass surgery as well as hosptal type. Results Baselne characterstcs. There were 11,932 patents admtted to the 19 hosptals partcpatng n the MITI regstry. They were predomnantly male (65.5%) and whte (88%), wth a mean age of 66.1 years. Overall, 57% of patents underwent coronary angography, 23% underwent coronary angoplasty (ths ncludes 7.3% who underwent prmary angoplasty), and 11.4% had bypass surgery durng the ntal hosptal perod. The mean (_+SD) length of stay was 7.45 _ 5.1 days (medan 7). Hosptal length of stay vared consderably between Seattle area hosptals (Fg. 1). Unvarate analyss. In the unvarate analyses, patent factors that were assocated wth a longer length of stay ncluded female gender, prevous myocardal nfarcton or heart falure; recurrent nfarcton after admsson, and heart falure or stroke durng the hosptal perod (Table 1). Wth each decade of lfe, there was an approxmate half-day ncrease n length of stay untl the seventh decade, where length of stay. remaned nearly constant. Length of stay was reduced 29%, from nearly 8.5 days n 1988 to 6.0 days n 1994 (Fg. 2). Comorbd condtons appeared to nfluence length of stay. Patents wth no secondary dscharge dagnoses had a mean length of stay of 5.2 days versus 5.6, 6.2 and 8.5 days for patents wth two, three and four secondary dscharge dagnoses, respectvely (p = ). Because bypass surgery had a strong assocaton wth length of stay, the remanng unvarate analyses were stratfed by the use of bypass surgery. Hosptal and treatment factors resultng n a longer length of stay ncluded the absence of on-ste angography at the admttng hosptal, the use of coronary angography and the use of bypass surgery (Table 2). Although the use of salvage angoplasty was assocated wth a longer length of stay, the use of prmary angoplasty was assocated Table 1. Unvarate Results: Mean and Medan Length of Stay, Patent Factors Length of Stay Wthout Wth Varable Varable Varable [mean (medan)] [mean (medan)] p Value Whte race 7.7 (6.0) 7.8 (7.0) 0.89 Female gender 8.1 (7.0) 7.5 (6.0) Pror nfarcton 7.8 (7.0) 7.4 (7.0) Pror heart falure 8.3 (7.0) 7.3 (7.0) Recurrent nfarcton at 10.2 (8.0) 7.7 (7.0) hosptal admsson CHF at hosptal admsson 9.6 (8.0) 6.9 (6.0) 0.04 Stroke at hosptal admsson 16.2 (13.0) 7.9 (7.0) CHF = congestve heart falure. wth a shorter length of stay. The type of admttng hosptal also had an effect on length of stay. Patents admtted to VA hosptals had a much longer stay (9.8 days); HMO and unversty hosptals ntermedate (8.4 days) and fee-for-servce hosptals the shortest (7.5 days) (Table 3). For each type of hosptal, there was a nearly equvalent relatve reducton n length of stay between 1988 and 1994: fee-for-servce (7.8 to 5.5 days), HMO (8.8 to 6 days), VA (9.4 to 7.9 days) and unversty hosptals (8.3 to 6.6 days). To test the hypothess that dagnostc and therapeutc procedure use (e.g., advances n technology) was assocated wth the 29% reducton n length of stay observed durng the study perod, the percent reducton n length of stay between 1988 and 1994 was calculated and compared n patents wth and wthout specfc procedures (Table 4). Overall, the reducton n length of stay n patents undergong cardac procedures was nearly dentcal to that n patents managed wthout cardac procedures. Multvarate analyss. To evaluate whch demographc, clncal and hosptal-related factors ndependently nfluenced length of stay, we constructed a seres of lnear regresson models. In the frst model, factors known at admsson (e.g., Fgure 2. Medan, mean and 25th and 75th percentles for length of stay by year of admsson. Between 1988 and 1994, there was a 2.5-day decrease n mean length of stay. Format as n Fgure lo 8 Length-of-Stay (Days) e 4 2 o Cohort Year 1988

4 JACC Vol. 28, No EVERY ET AL. HOSPITAL STAY AFTER MYOCARDIAL INFARCTION Table 2. Unvarate Results: Mean Length of Stay, Hosptal and Treatment Factors Length of Stay: All Patents Length of Stay: Patents Wthout CABG Wth Wthout p Wth Wthout p Varable Varable Varable Value Varable Varable Value On-ste angography Use of angography Use of PTCA Use of CABG Use of thrombolyss Prmary PTCA CABG = coronary artery bypass graft surgery; PTCA = percutaneous translumnal coronary angoplasty. demographcs, patent hstory, presentng sgns and symptoms and comorbdty) were entered. Demographc factors that predcted a longer adjusted length of stay ncluded ncreasng age (0.6 day ncrease for each decade) (Fg. 3). Nether nonwhte race nor female gender was sgnfcantly assocated wth length of stay n ths lmted model. Clncal characterstcs that predcted a longer length of stay ncluded a hstory of heart falure (mean 7.5 days, 95% confdence nterval [CI] 7.3 to 7.9, vs. mean 7.0 days), angna (7.3 days, 95% CI 7.2 to 7.5) or hypertenson (7.3 days, 95% CI 7.2 to 7.5). Each addtonal comorbd dagnoss resulted n a 0.7-day (95% CI 0.6 to 1.0) ncrease n length of stay (p ). Nether hstores of myocardal nfarcton nor bypass surgery were predctve of a longer length of stay. Patents wth admsson systolc blood pressure <90 mm Hg (7.7 days, 95% CI 7.1 to 8.6), as well as patents wth ether anteror or multple nfarct locatons, had a longer length of stay (7.7 days, 95% CI 7.5 to 8.2, and 7.6 days 95% CI 7.5 to 7.8, respectvely), whereas admsson heart rate >90 beats/ran was not assocated wth length of stay. The only factor that predcted a shorter length of stay was a hstory of angoplasty (6.4 days, 95% CI = 6.1 to 6.8). In ths model, whch ncluded factors known at the tme of admsson, very lttle varaton n length of stay was predcted (R 2 = 5.8%). In the next model, clncal events and complcatons that occurred durng the hosptal perod were added. In-hosptal complcatons, ncludng nfarct extenson (8.2 days, 95% CI 7.8 to 8.7) (Fg. 4), heart falure (9.0 days, 95% CI 8.8 to 9.2), recurrent chest pan (8.4 days, 95% CI 8.2 to 8.6), cardogenc shock (8.8 days, 95% CI 7.9 to 9.7) and stroke (13.5 days, 95% Table 3. Unvarate Results: Mean Length of Stay, Health Care Organzaton Length of Stay Patents All p Wthout p Hosptal Type Patents Value* CABG Value* Fee-for-servce Unversty HMO VA medcal center *p versus fee-for-servce cohort. CABG = coronary artery bypass graft surgery; HMO = health mantenance organzaton; VA = Veterans Affars. CI 12.1 to 14.7) were predctve of a longer length of stay. Ths entre model, ncludng all the demographc and hstorcal varables entered n the frst model, accounted for 14% of the varaton n length of stay. In the full model that ncluded hosptal and process of care varables (Fg. 5), the use of early dagnostc coronary angography (6.2 days, 95% CI 6.0 to 6.5), the use of prmary angoplasty (length of stay 6.8 days, 95% CI 6.5 to 7.1), the avalablty of on-ste angography (6.7 days, 95% CI 6.6 to 6.95) and later years of hosptal admsson (0.3-day decrease n length of stay/year, 95% CI 0.2 to 0.4) each ndependently predcted a shorter length of stay. The use of thrombolytc therapy (8.2 days, 95% CI 8.0 to 8.3), any coronary angography (8.2 days, 95% CI 8.1 to 8.4), salvage angoplasty (7.6 days, 95% CI 7.3 to 7.9), as well as bypass surgery (12.7 days, 95% CI 12.2 to 13.2) predcted a longer length of stay. Compared wth fee-for-servce hosptals, patents admtted to VA hosptals had a much longer adjusted length of stay (9.5 days, 95% CI 8.9 to 10.1), whereas length of stay at HMO and unversty facltes was ntermedate but stll sgnfcantly longer than the fee-for-servce system (7.8 days, 95% CI 7.5 to 8.1, and 7.5 days, 95% CI 7.2 to 7.8, respectvely) (Fg. 4). Ths fnal model, whch ncluded demographc, clncal and process of care varables, explaned 33% of the varaton n hosptal length of stay (R 2 = 0.33). There were no mportant dfferences n ths model when we ncluded patents who ded n the hosptal. To evaluate whch factors were assocated wth the 29% Table 4. Reducton n Length of Stay n Patents Wth and Wthout Procedures Between 1988 and 1994 Length of Stay (days) Percent Reducton Coronary angography No angography Early angography No early angography Prmary PTCA No prmary PTCA Thrombolyss No thrombolyss PTCA = percutaneous translumnal coronary angoplasty.

5 JACC Vol. 28, No. 2 EVERY ET AL. 291 HOSPITAL STAY AFTER MYOCARDIAL INFARCTION Pror PTCA Pror Angna Pror Hypertenson Increased Age (10 yrs) Pror Heart Falure Multple nfarct locaton Anteror Infarct SBP<90 Co-morbdty ] I q~ tl I I Adjusted length-of-stay Fgure 3. Multvarate adjusted length of stay wth 95% confdence ntervals (horzontal bars) for factors known at hosptal admsson. Factors assocated wth a longer length of stay are shown to the rght of the dashed lne, whch represents mean length of stay for all patents n the model. PTCA = percutaneous translumnal coronary angoplasty; SBP = systolc blood pressure (mm Hg). reducton n length of stay between 1988 and 1994, a seres of nteracton terms were entered nto the fnal regresson model. Each nteracton term ncluded the year of the cohort wth one of the varables of nterest. In ths model, none of the nteracton terms (year by age, gender, race, cardac hstory, clncal complcatons, comorbdty, procedure use or hosptal type) was sgnfcantly assocated wth length of stay. Thus, t s unlkely that any of the measured factors n the present study can explan the decrease n length of stay observed durng the study perod. Dscusson Length of hosptal stay s an mportant determnant of the cost of medcal care (1). For condtons that nearly always requre hosptal admsson, such as acute myocardal nfarcton, lmtng hosptal length of stay s an obvous component of cost contanment. Hosptal length of stay has been decreasng for nearly all medcal and surgcal condtons, and the treatment for acute myocardal nfarcton has been no excepton. Fgure 4. Multvarate adjusted length of stay wth 95% confdence ntervals (horzontal bars) for hosptal complcatons. Ths model also ncludes all factors known at hosptal admsson (not shown). Factors assocated wth a longer length of stay are shown to the rght of the dashed lne, whch represents mean length of stay for all patents n the model. Infarct extenson Recurrent Chest Pan Heart Falure@hosptal Cardogenc Shock Stroke@hosptal Adjusted length-of-stay (days) Early angograrn Prmary PTCA On-ste angography Salvage PTCA "hrombolytc Therapy Bypass Surgery HMO Hosptal Unversty Hosptal VA Hosptal 6 ~h 1t I Adjusted length-of-stay (days) Fgure 5. Multvarate adjusted length of stay wth 95% confdence ntervals (horzontal bars) for procedural and hosptal-related factors. Ths model also ncludes all factors from the prevous models (not shown). Factors assocated wth a longer length of stay are shown to the rght of the dashed lne, whch represents mean length of stay for all patents n the model. HMO = health mantenance organzaton; PTCA = percutaneous translumnal coronary angoplasty; VA = Veterans Affars. The reasons for ths reducton n length of stay are multfactoral. In acute myocardal nfarcton, clncal nnovatons such as reperfuson therapy (5,7) may have contrbuted to a reducton n length of stay; however, economc pressures to ncrease effcency and elmnate unnecessary care may also be mportant factors. Varaton n length of stay. In the present study, we used a large clncal data base that ncluded extensve demographc, clncal and nsttutonal data from nearly 12,000 patents wth an acute nfarcton to document trends n length of stay and to dentfy many of the factors that nfluence length of stay. Factors known at admsson explaned only 6% of the varaton n length of stay. Older age, a hstory of heart falure, angna or hypertenson as well as an ncreased number of comorbd condtons predcted a longer length of stay, whereas a hstory of myocardal nfarcton or bypass surgery were not assocated wth dfferences n length of stay. Infarct-related complcatons accounted for an addtonal 10% of varaton n length of stay, and factors that were assocated wth a longer length of stay ncluded recurrent myocardal nfarcton, heart falure or stroke durng the hosptal perod. Factors reflectng the process of care, such as the use of cardac procedures, were even more mportant n understandng length of stay n ths populaton and explaned an addtonal 17% of varaton. Patents who underwent salvage angoplasty or bypass surgery had a longer length of stay than those wthout these procedures. In contrast, the length of stay was -1 day shorter n patents who underwent early dagnostc coronary angography and -0.5 day shorter n those who underwent prmary angoplasty. Although prevous studes of ths populaton suggested that those patents admtted to hosptals wth on-ste angography facltes were more lkely to undergo angography (17), the present analyss showed that patents admtted to these hosptals had a length of stay that was one-thrd of a day shorter than patents admtted to hosptals wthout these facltes. We I

6 292 EVERY ET AL. JACC Vol. 28, No. 2 HOSPITAL STAY AFTER MYOCARDIAL INFARCTION suspect that ths fndng resulted from the requrement for hosptal transfer when procedures were requred n patents admtted to hosptals wthout catheterzaton facltes. Based solely on ths fndng, t s mpossble to determne whether ths shorter length of stay offsets hgher costs assocated wth the greater use of cardac procedures. The type of admttng hosptal also had a sgnfcant nfluence on length of stay. Patents admtted to the sngle VA medcal center ncluded n ths study had a length of stay that was nearly 3 days longer than patents admtted to fee-forservce hosptals despte the excluson of patents transferred to the VA medcal center from other out-of-regon VA hosptals. Patents admtted to staff model HMO or unversty hosptals had a >0.5-day longer length of stay than patents at the fee-for-servce hosptals. Although some have argued that unversty hosptals attract "scker" patents, the ncreased length of stay perssted after adjustment for both nfarctrelated complcatons and eomorbd condtons. Decrease n length of stay. Overall, the 29% reducton n length of stay observed durng the study perod was mpressve. Unfortunately, none of the measured varables could explan ths decrease. For example, nether changng demographcs nor patent clncal characterstcs were assocated wth the decrease. More surprsng, however, s that procedure utlzaton was not assocated wth the reducton n length of stay. That s, although patents undergong prmary angoplasty or early dagnostc catheterzaton had a shorter length of stay than those who dd not, the proportonate reducton n length of stay durng the study perod was not dfferent between these patents and those treated more conservatvely. Because none of the numerous measured varables could explan the observed reducton n length of stay, we tested several other nonclncal factors that mght help to explan the reducton: 1) To evaluate whether hgher readmsson rates explaned the results, we compared readmsson rates at 1 year between patents admtted n 1989 and 1993 and found hgher readmssons for the 1989 cohort. Thus, t s unlkely that earler patent dscharge wth a hgher rate of subsequent readmssons was assocated wth the decreased length of stay. 2) We found no substantal dfferences n educaton or adjusted ncome between the 1989 and 1993 cohorts. Thus, t s unlkely that changes n socoeconomc status were responsble for the decrease n length of stay. We also compared dscharge medcatons n the 1989 and 1993 cohorts and found that a sgnfcantly hgher proporton of patents n 1993 were dscharged wth ether asprn or beta-adrenergc blockng agents, or both. Ths may be a marker for mprovements n general medcal care durng the study perod that mght have nfluenced length of stay. In the fnal analyss, however, we must speculate that unmeasured varables, such as nsurance-related factors, hosptal admnstratve pressures or changes n physcan practce styles, were an mportant nfluence n the observed reducton n length of stay. Prevous studes. Prevous studes evaluatng a varety of condtons have dentfed several factors that help to explan varaton n length of stay. These nclude chronologc age, admsson dagnoss, surgery status (electve versus emergent), hosptal characterstcs (9), type of nsurance payment (10), physcan ratngs of severty of llness (11) as well as varous severty ndexes (13,14,18,19). The effect of teachng hosptals on length of stay has been controversal, wth one study showng a longer length of stay n teachng hosptals (12) and one a shorter length of stay (10,20). Several studes have been performed examnng length of stay n patents wth an acute myocardal nfarcton. Usng a 1987 admnstratve data set of 4,033 patents dagnosed wth an acute nfarcton, Young and Cohen (21) found that an ncreased length of stay was assocated wth advancng age, female gender, a larger number of chronc dseases and admsson to a teachng hosptal. In contrast to the present study, hosptals wth on-ste catheterzaton facltes were assocated wth an ncreased length of stay. However, ths analyss dd not adjust for the use of procedures resultng from the angogram, thereby underestmatng the potental mpact of a dagnostc angogram on length of stay. Other older analyses have assocated creatne knase soenzyme peak, presence of an anteror nfarcton and the use of ether predscharge stress testng or 24-h ambulatory montorng wth ncreased length of stay (22,23). In a study that s most comparable to the present analyss, Chert and Naylor (24) evaluated factors that predcted length of stay n 11,411 patents usng admnstratve data collected between 1990 and The mean length of stay was 9.9 days versus 7.4 days n the present Amercan study. Older age, female gender, nfarct-related complcatons and comorbdty were assocated wth a longer length of stay. Smlar to the present study, patents who underwent angography had a longer length of stay, and there was a trend toward a shorter length of stay n patents admtted to hosptals wth on-ste angography. However, only 12% of varaton n length of stay was explaned by the Canadan study compared wth 33% n the present analyss. Ths dfference llustrates the better predctve power of a clncal than an admnstratve data base. The present study has several other advantages over prevous work: 1) The MITI regstry s a more contemporary data base, reflectng the most recent changes n health care delvery; 2) we were able to examne the effects of the most recent advances n the management of myocardal nfarcton, such as the use of prmary angoplasty or thrombolytc therapy; and 3) none of the reported studes, to our knowledge, evaluated whether technologc advances n the treatment of acute nfarcton were assocated wth the profound decrease n length of stay that has been observed n patents wth acute nfarcton. Study lmtatons. There are mportant lmtatons to the present study: 1) Data were collected n only one cty; thus, these data must be nterpreted cautously n a settng wth dfferent practce styles or a rural settng. 2) We were also lmted by the presence of a sngle, large, staff-model HMO and a sngle VA medcal center. 3) Despte a major mprovement n understandng length of stay varaton n the management of myocardal nfarcton, nearly 67% of varaton remans unexplaned. 4) We were unable to explan the observed

7 JACC Vol. 28, No. 2 EVERY ET AL. 293 HOSPITAL STAY AFTER MYOCARDIAL INFARCTION decrease n length of stay. Clearly, there were unmeasured varables that may have contrbuted to our understandng of length of stay n ths settng. The addton of more detaled nsurance-related data, such as the use of economc or admnstratve ncentves or physcan proflng, as well as more detals about the ndvdual physcans such as age and educaton, mght have been an mportant addton to the measured varables. Conclusons. There has been a substantal decrease n the length of stay n postnfarcton patents n the Seattle area over the past 6 years. Although demographc characterstcs, past clncal hstory, procedure utlzaton, hosptal complcatons and hosptal characterstcs are mportant factors n explanng varaton n length of stay, none of the measured factors explans the reducton n length of stay observed durng the study perod. Future research should evaluate other nonclncal factors, such as admnstratve ncentves or the use of practce gudelnes, to better understand unque nfluences on hosptal length of stay. References 1. Lave JR, Lenhardt S. The cost and length of a hosptal stay. Inqury 1976;13: Groden BM, Allson A, Shaw GB. Management of myocardal nfarcton: the effect of early moblzaton. Scot Med J 1967;12: Hutter AM, Sdel VW, Shne KI, DeSancts RW. Early hosptal dscharge after myocardal nfarcton. N Engl J Med 1973;288: Abraham AS, Sever Y, Wensten M, Dollberg M, Menczel J. Value of early ambulaton n patents wth and wthout complcatons after acute myocardal nfarcton. N Engl J Med 1975;292: McNeer JF, Wagner GS, Gnsberg PE, et al. Hosptal dscharge one week after acute myocardal nfarcton. N Engl J Med 1978;298: Natonal Regstry of Myocardal Infarcton-2. Quarterly report: Washngton data. Aprl, 1995: Topol EJ, Burek K, O'Nell WW, et al. A randomzed controlled tral of hosptal dscharge three days after myocardal nfarcton n the era of repeffuson. N Engl J Med 1988;318: Grnes CL, Browne KF, Marco J, et al. A comparson of mmedate angoplasty wth thrombolytc therapy for acute myocardal nfarcton. N Engl J Med 1993;328: Knaus WA, Wagner DP, Zmmerman JE, Draper EA. Varaton n mortalty and length of stay n ntensve care unts. Ann Intern Med 1993;118: Lave JR, Frank RG. Effect of the structure of hosptal payment on length of stay. Health Ser Res 1990;25: Kelleher C. Relatonshp of physcan ratngs of severty of llness and dffculty of clncal management to length of stay. Health Serv Res 1993;27: Smmer TL, Nerenz DR, Rutt WM, et al. A randomzed controlled tral of an attendng staff servce n general nternal medcne. Med Care 1991;29 Suppl:ss Horn SD, Sharkey PD. Measurng severty of llness to predct patent resource use wthn DRGs. Inqury 1983;20: Iezzon LI, Ash AS, Cobb JL, Moskowtz MA. Admsson MedsGroups score and the cost of hosptalzatons. Med Care 1988;26: Weaver WD, Esenberg MS, Martn JS, et al. Myocardal Infarcton Trage and Interventon Project, phase I: patent characterstcs and feasblty of prehosptal ntaton of thrombolytc therapy. J Am Coll Cardol 1990;15: Melf C, Holleman E, Arthur D, Katz B. Selectng a patent characterstcs ndex for the predcton of medcal outcomes usng admnstratve clams data. J Cln Epdemol 1995;48: Every NR, Larson EB, Ehn SD, et al. The assocaton between on-ste cardac catheterzaton facltes and the use of coronary angography after acute myocardal nfarcton. N Engl J Med 1993;329: Sutclffe SA, Vncent P. Factors related to length of stay n lamnectomy patents. J Neurosurg Nuts 1985;17: Tartter PI. Determnants of post-operatve stay n patents wth colorectal cancer: mplcatons for dagnostc related groups. Ds Colon Rectum 1988;31: Udvarhely SI, Rosborough T, Lofgre RP, Lure N, Epsten AM. Teachng status and resource use for patents wth acute myocardal nfarcton: a new look at the ndrect costs of graduate medcal educaton. Am J Publc Health 1990;80: Young GJ, Cohen BB. The process and outcome of hosptal care for Medcad versus prvately nsured hosptal patents. Inqury 1992;29: Heller RF, Dobson AJ, Steele PL, et al. Length of hosptal stay after acute myocardal nfarcton. Aust NZ J Med 1990;20: Lee TH, Gottleb LK, Wetman kl, et al. Length of stay of patents wth uncomplcated acute myocardal nfarcton at three Boston hosptals. J Gen Intern Med 1988; Chen E, Naylor DC. Varaton n hosptal length of stay for acute myocardal nfarcton n Ontaro, Canada. Med Care 1994;32: