Factors Associated With Rehospitalization in PatientsWith Acute Myocardial Infarction

Charles Maynard, PhD, Nathan R. Every, MD, and W. Douglas Weaver, MD

Rehospitalization of patients surviving acute myo-cardial infarction (AMI) is common; in a consec-

utive, unselected series of patients, over half wererehospitalized within 12 months of developing AMI.1

In this same group, only a small percentage of patientswere free of significant cardiac events or symptoms ofangina pectoris in the year following AMI. In theMyocardial Infarction Triage and Intervention (MITI)prehospital treatment trial, which included only thosepatients eligible for thrombolytic therapy, 28% ofpatients were readmitted to the hospital in the yearafter AMI.2 There are many reasons for rehospitaliza-tion; these include progression of coronary artery dis-ease requiring coronary revascularization, the occur-rence of significant cardiac events such as unstableangina pectoris, reinfarction, congestive heart failure,or cardiac arrhythmias, as well as poor general healthand emotional well being.3,4 The purpose of this studyis twofold: first, to determine the occurrence of rehos-pitalization in patients who survived an initial hospi-talization for AMI, and second, to identify sociode-mographic, medical history, and clinical factorsassociated with rehospitalization.

• • •This study consisted of 5,629 consecutive individ-

uals who developed AMI before discharge or death in19 Seattle area hospitals from 1988 to 1990. The focusis on the 5,051 or 90% of patients who were dis-charged alive. These patients are part of the MITIregistry that contains 12,331 consecutive patients hos-pitalized in King County, Washington, from January1988 to June 1994. A description of the registry, itspatients, and key variables has been provided.5

Information for the initial hospitalization was ab-stracted from medical records and entered into theMITI registry. Data concerning rehospitalization andvital status were obtained from the state of Washing-ton episode of illness file, which contains hospitaldischarge abstract data, as well as death certificateinformation for residents of the state of Washington.Using key identifiers such as social security number,the first 2 letters of last and first names, date of birth,and gender, the MITI Registry was linked to theepisode of illness file from 1988 to 1993. All surviv-ing patients had a minimum of 3 years of follow-up

information pertaining to vital status and rehospital-ization.

Outcomes of interest included rehospitalization forcardiac reasons at 1, 2, and 3 years after hospitaldischarge. Rehospitalization for cardiac reasons wasdefined by the appropriate International Classificationof Diseases, 9th Revision Clinical Modification diag-nosis codes (390 to 429), including, but not limited tothose for AMI, unstable angina pectoris, and conges-tive heart failure. A second outcome included theutilization of cardiac catheterization and/or revascu-larization defined as coronary angioplasty and/or cor-onary artery bypass graft surgery at 1, 2, and 3 yearsafter hospital discharge. Procedures were identified bythe appropriate International Classification of Dis-eases, 9th Revision Clinical Modification procedurecodes.

Key independent baseline variables obtained fromthe MITI registry were age, gender, and race, as wellas medical history variables such as angina pectoris,previous myocardial infarction, congestive heart fail-ure, hypertension, and coronary artery surgery. Ther-apy and procedures employed during the indexhospitalization were also obtained and includedthrombolytic therapy, coronary angiography, coronaryangioplasty, and coronary artery bypass surgery. Fi-nally, cardiac events occurring during the index hos-pitalization were assessed and included congestiveheart failure, reinfarction, and prolonged angina oc-curring $24 hours from hospital admission.

The chi-square statistic andt test were used tocompare baseline characteristics of those rehospital-ized versus those who were not. Stepwise logisticregression was used to identify predictors of cardiacrehospitalization at 1 year as well as revascularizationat 1 year. All variables that achieved a statisticalsignificance of p,0.05 were allowed to enter themodel.

The average age of the 5,051 survivors was 65613 years; 33% were women, and 8% were nonwhite.Patients who were rehospitalized within 3 years ofinitial hospital discharge were older, more oftenwomen, and more often had histories of angina pec-toris, previous myocardial infarction, congestive heartfailure, hypertension, or coronary artery surgery (Ta-ble I). Patients who received thrombolytic therapy,coronary angiography, or coronary artery bypass sur-gery during the index hospitalization were less oftenrehospitalized, whereas those who had congestiveheart failure or recurrent angina during the initialhospitalization were more likely to be rehospitalized.

Cumulative survival for patients surviving the in-dex hospitalization was 90% at year 1, 84% at year 2,and 80% at the third year after discharge (Table II).Rehospitalization for cardiac reasons occurred in 40%

From the Department of Medicine, University of Washington, Seattle,Washington and Heart and Vascular Institute, Henry Ford HealthSystem, Detroit, Michigan. This study was supported in part by grantR01HL3854 from the National Heart Lung and Blood Institute, Be-thesda, Maryland, an unrestricted grant from Genentech Inc., SanFrancisco, California, and by grant R01HS08632 from the Agencyfor Health Care Policy and Research, Rockville, Maryland. Dr. May-nard’s address is: MITI Coordinating Center, 1910 Fairview AVE E#204, Seattle, Washington 98102. Manuscript received April 23,1997; revised manuscript received and accepted May 21, 1997.

©1997 by Excerpta Medica, Inc. 0002-9149/97/$17.00 777All rights reserved. PII S0002-9149(97)00515-8

of patients during the first year after discharge, and bythe third year, over half of the patients had beenrehospitalized. Rehospitalization during which AMIoccurred was apparent in 16% of all patients duringthe first year, and by the third year, one-fifth of pa-tients were rehospitalized for AMI. The utilization ofcardiac procedures was most apparent in the first yearafter hospital discharge; the use of revascularizationwas minimal in years 2 and 3 (Table II).

To determine why these rehospitalizations oc-curred, stepwise logistic regression was used to iden-tify predictors of rehospitalization in the year follow-ing hospital discharge (Table III). The followingfactors were associated with an increased likelihood ofrehospitalization: (1) history of congestive heart fail-ure, (2) history of angina pectoris, (3) female gender,

(4) history of hypertension, (5) his-tory of coronary artery bypass sur-gery performed before the index hos-pitalization, and (6) prolongedangina during the index hospitaliza-tion. The following variables wereassociated with a lower likelihood ofrehospitalization: (1) coronary arterybypass surgery performed during theindex hospitalization, and (2) coro-nary angiography performed duringthe index hospitalization.

In a similar fashion, stepwise lo-gistic regression was used to identifyfactors associated with the use of re-vascularization in the year followinghospital discharge (Table IV). Thefollowing factors were associatedwith increased use of revasculariza-tion in the year following discharge:(1) coronary angiography performedduring the index hospitalization, (2)history of angina pectoris, (3) the useof thrombolytic therapy during theindex hospitalization, and (4) historyof hypertension. The following wereassociated with lower likelihood ofrevascularization: (1) coronary arterybypass surgery performed during theindex hospitalization, (2) advancedage, (3) history of congestive heartfailure, and (4) nonwhite race.

• • •The major result of this study was that within 3

years of hospital discharge over half of the patientswere rehospitalized for cardiac reasons; in 20% ofthese events, patients developed subsequent AMI. Theproportion of patients rehospitalized in Seattle areahospitals was less than that for a single institution inGoteborg, Sweden, where 54% of patients were re-hospitalized in the first year following AMI.1 Rehos-pitalization of survivors of AMI is common and notmarkedly different from the proportion of survivors ofout-of-hospital cardiac arrest who were hospitalized inthe year following that event (56%).6 It is remarkablethat the scientific literature contains such little infor-mation about rehospitalization of patients with AMI.

Whereas the current study has shown that rehospi-talization was more frequent for patients with exten-sive cardiac histories and women, other investigationshave demonstrated that psychosocial factors also areimportant.3,4 A study from Norway reported that in-creased hospitalization in patients with AMI was as-sociated with a higher number of previous hospital-izations for heart disease, more pre-AMI cardiaclimitations, less cardiac lifestyle knowledge, and ahigher initial level of emotional distress.3 In anotherstudy, poor psychosocial functioning and cardiacsymptoms were associated with increased rehospital-ization of patients with AMI.4 A study of rehospital-ization of elderly patients with congestive heart failurefound that up to 50% of readmissions were prevent-

TABLE I Baseline Characteristics

All(n 5 5,051)

Rehospitalized(n 5 2,731)

Not Rehospitalized(n 5 2,320) Value

Age (yrs) 65 6 13 66 6 13 64 6 13 ,0.0001Women 33% 36% 30% ,0.0001Non-white race 8% 8% 8% 0.99Medical history

Angina pectoris 36% 40% 32% ,0.0001Previous AMI 22% 26% 19% ,0.0001Congestive heart failure 10% 13% 7% ,0.0001Systemic hypertension 46% 49% 43% ,0.0001Coronary surgery 10% 12% 7% ,0.0001

In-hospital treatmentsThrombolytic therapy 20% 19% 22% 0.017Coronary angiography 58% 54% 63% ,0.0001Coronary angioplasty 24% 23% 26% 0.056Coronary surgery 11% 9% 15% ,0.0001

In-hospital eventsCongestive heart failure 30% 33% 27% ,0.0001Reinfarction 3% 3% 3% 0.93Prolonged angina 25% 27% 24% 0.015

TABLE II Survival and Rehospitalization for Survivors of Acute MyocardialInfarction

Variable Year 1 Year 2 Year 3

Survival 90% 84% 80%Rehospitalization—any cardiac event 40% 49% 54%Rehospitalization—myocardial infarction 16% 18% 20%Coronary angiography 13% 16% 20%Coronary angioplasty 9% 10% 12%Coronary surgery 7% 9% 10%

TABLE III Predictors of Rehospitalization in the Year FollowingHospital Discharge

Variable Odds Ratio95% Confidence

Interval

Coronary surgery 0.48 0.38–0.59Congestive heart failure (history) 1.44 1.19–1.75Angina pectoris 1.22 1.05–1.41Women 1.19 1.04–1.37Systemic hypertension (history) 1.18 1.05–1.33Coronary surgery (history) 1.31 1.05–1.63Coronary angiography 0.82 0.71–0.94Prolonged angina during index

hospitalization1.22 1.05–1.41

778 THE AMERICAN JOURNAL OF CARDIOLOGYT VOL. 80 SEPTEMBER 15, 1997

able, and were in part related to failed social supportsystems, as well as noncompliance with respect tomedications or diet and inadequate follow-up.7 An-other study of older patients with congestive heartfailure indicated that a nurse-directed multidisci-plinary intervention reduced hospital readmission forheart failure by half.8 These findings indicate thatincreased professional support is needed in patientswith extensive cardiac histories and poor quality oflife. Finally, cardiac rehabilitation programs may alsoreduce the need for further hospitalization.9

In this study, coronary angiography or coronaryartery bypass surgery performed during the index hos-pitalization were associated with lower likelihood ofrehospitalization. The situation with respect to revas-cularization in the year following the index hospital-ization was different in that bypass surgery was asso-

ciated with a lower likelihood of revascularization, butthe use of coronary angiography and/or thrombolytictherapy increased the likelihood of revascularizationprocedures. Thus, coronary bypass surgery was asso-ciated with lower likelihood of rehospitalization andrevascularization.

In conclusion, in Seattle area hospitals, rehospi-talization of patients surviving AMI was frequent,particularly for women and those with extensivecardiac histories.

1. Herlitz J, Karlson BW, Sjolin M, Ekvall HE, Hjalmarson A. Prognosis duringone year of follow-up after acute myocardial infarction with emphasis on mor-bidity. Clin Cardiol 1994;17:15–20.2. Brouwer MA, Martin JS, Maynard C, Wirkus M, Litwin PE, Verheugt FWA,Weaver WD. Influence of early prehospital thrombolysis on mortality and event-free survival.Am J Cardiol1996;78:497–502.3. Maeland JG, Havik OE. Use of health services after a myocardial infarction.Scand J Soc Med1989;17:93–102.4. Nelson EC, Ferreira PL, Cleary PD, Gustafson D, Wasson JH. Do patients’health status reports predict future stays for patients with acute myocardialinfarction.Family Pract Res J1994;14:119–126.5. Maynard C, Litwin PE, Martin JS, Weaver WD. Gender differences in thetreatment of and outcome of acute myocardial infarction.Arch Intern Med1992;152:972–976.6. Maynard C for the CASCADE Investigators. Rehospitalization in survivingpatients of out-of-hospital ventricular fibrillation (the CASCADE Study).Am JCardiol 1993;72:1295–1300.7. Vinson JM, Rich MW, Sperry JC, Shah AS, McNamara T. Early readmissionof elderly patients with congestive heart failure.J Am Geriatr Soc1990;38:1290–1295.8. Rich MW, Beckham V, Wittenberg C, Leven CL, Freedland KE, Carney RM.A multidisciplinary intervention to prevent the readmission of elderly patientswith congestive heart failure.N Engl J Med1995;333:1190–1195.9. Ades PA, Huang D, Weaver SO. Cardiac rehabilitation predicts lower rehos-pitalization costs.Am Heart J1992;123:916–921.

Dynamic Analysis of Heart Rate May PredictSubsequent Ventricular Tachycardia

After Myocardial InfarctionTimo H. Makikallio, MD, MSc, Tapio Seppanen, PhD, K.E. Juhani Airaksinen, MD,

Juhani Koistinen, MD, Mikko P. Tulppo, MSc, Chung-Kang Peng, PhD,Ary L. Goldberger, MD, and Heikki V. Huikuri, MD

Twenty-four-hour electrocardiographic record-ings provide information on the vulnerability of

patients with heart disease to life-threatening ar-rhythmias.1– 4 Assessment of ventricular ectopicbeats and episodes of nonsustained ventriculartachycardia (VT) have been used to predict the riskof future life-threatening arrhythmias. More recent

investigations have shown that analysis of heart rate(HR) variability can also predict the risk of arrhyth-mic events after an acute myocardial infarction(MI).5,6 However, traditional indexes of HR vari-ability based on mean and variance1,2 may lack theability to detect subtle but important changes ininterbeat HR behavior.7 The purpose of this studywas to test the hypothesis that dynamic analysis ofRR intervals can reveal abnormalities in HR behav-ior in patients with vulnerability to VT that are notdetected by traditional measures of HR variability.We compared fractal correlation properties and ap-proximate entropy with conventional measures ofHR variability in 3 age-matched groups: patientswith a prior Q-wave MI with vulnerability to VT,patients with a prior Q-wave MI without vulnera-bility to VT, and a control group of healthy sub-jects.

From the Division of Cardiology, Department of Medicine, Universityof Oulu, Oulu, the Merikoski Rehabilitation and Research Center,Oulu, Finland; and the Cardiovascular Division, Beth Israel DeaconessMedical Center, Harvard Medical School, Boston, Massachusetts.This study was supported by grants from the Finnish Foundation forCardiovascular Research, Helsinki, Finland, National Aeronautics andSpace Administration, Washington D.C., and The G. Harold andLeila Y. Mathers Charitable Foundation, Mt. Kisco, New York. Dr.Huikuri’s address is: Division of Cardiology, Department of Medicine,University of Oulu, Kajaanintie 50, 90220 Oulu, Finland. Manuscriptreceived February 14, 1997; revised manuscript received and ac-cepted May 14, 1997.

TABLE IV Predictors of Revascularization in the YearFollowing Hospital Discharge

Variable Odds Ratio95% Confidence

Interval

Coronary surgery 0.08 0.04–0.15Age (per decade) 0.84 0.77–0.90Coronary angiography 1.50 1.22–1.84Angina pectoris 1.36 1.18–1.57Congestive heart failure (history) 0.60 0.42–0.86Nonwhite race 0.60 0.42–0.86Thrombolytic therapy 1.30 1.06–1.60Systemic hypertension (history) 1.19 1.01–1.40

©1997 by Excerpta Medica, Inc. 0002-9149/97/$17.00 779All rights reserved. PII S0002-9149(97)00516-X