Early Prediction of Acute Myocardial Infarction from Clinical History, Examination and Electrocardiogram in the Emergency Room BjOrn W. Karlson, MD, Johan Herlitz, MD, PhD, Olof Wiklund, MD, PhD, Arina Richter, MD, PhD, and Ake Hjalmarson, MD, PhD
The possibility of early prediction of acute myocardial infarction (AMI) was assessed in 7,157 consecutive patients coming to our emergency room during a Pi-month period with chest pain or other symptoms suggestive of AMI. Df these patients 921 developed an AMI during the first 3 days in the hospital. Df the 4,690 patients admitted to hospital, 1,576 (34%) had a normal admission electrocardiogram, and SO of these (6%) developed AMI. Df 1,964 patients with an abnormal electrocardiogram without signs of acute ischemia (42% of those admitted), 266 (14%) developed AMI, and 663 (51%) of 1,109 patients with acute ischemia on the eiectrocardiogram (24%) developed AMI. All patients were prospectiiely classified in the emergency room on the basis of history, clinical examination and electrocardiogram into 1 of 4 categories, according to the initial degree of suspicion of AMI. Df 279 admitted patients judged to have an obvious AMI (6% of the 4,6SO), 245 (88%) actually developed AMI; of 1,426 with a strong suspicion of AMI (30%), 478 (34%) developed one; of 2,519 with a vague suspicion of AMI (64%), 192 (8%) developed one; and of 466 with no suspicion of AMI (lo%), 6 (1%) developed one. Thus, only a low percentage of the patients with a normal initial electrocardiogram or a vague initial suspicion of AMI developed a confirmed AMI. (AmJCardiol1991;68:171-175)
any patients come to the emergencyroom of every hospital with chest pain or other symptoms suggestiveof acute myocardial infarction (AMC). Only a minority of thesepatients developa confirmed AMI. Most of the patients judged sufficiently likely in the emergency room to have an AMI are admitted to a coronary care unit, but only 16 to 50% of them actually develop a confirmed AMIle Although many of the patients do not develop an AMI, they are not necessarily admitted needlessly, since they may have unstable angina pectoris, severeheart failure, arrhythmias, or other symptoms requiring treatment in a coronary care unit. However, there is great interest in the early prediction of infarction in order to be able to select high-risk patients for immediate intensive care. The possibility of early intervention aimed at myocardial salvage,especially with thrombolytic agents, further underlines the importance of early diagnosis.This study describesour experiencewith predicting developmentof AM1 in consecutive,unselected patients presenting to the emergencyroom of a single hospital with chest pain or other symptoms suggestiveof AMI.
M
METHODS Patients: Sahlgrenska Hospital, Goteborg, Sweden,
servesa population of about 230,000. All patients presenting to the emergency room between February 15, 1986, and November 9, 1987, with chest pain or other symptoms suggestiveof AM1 were consecutively registered. A full history was taken, including details of previous AMIs and angina pectoris. A standard 1Zlead electrocardiogram was regisFrom the Division of Cardiology, Department of Medicine I, Sahl- tered soon after admissionto the emergency room and grenska Hospital, Goteborg, Sweden. This study was supported by classified the following day into 1 of the following grants from The SwedishHeart Foundation,The Gothenburg Society of Medicine, Arbetsmarknadens Fiirs&ringsaktiebolag, The Medical groups by an experiencedmember of our study group: Faculty of the University of Gothenburg,The SwedishSocietyof Medi- ( 1) normal (no pathologic signs); (2) pathologic but no cine, RousselNordiska AB, Trygg Hansa Insurance Co., Skandia In- signs of acute &hernia (e.g., old infarction, bundle suranceCo., ICI-Pharma AB, SjutirsaXrings AB Eir’s 50-year Foundation, Leo and Hans Osterman’sFund, and Ollie and Elof Ericsson’s branch block, nonspecific ST-T changes); (3) signs of Foundation. Manuscript received November 26, 1990;revised manu- acute ischemia (ST elevation >l mm in leads aVL, script receivedMarch 21, 1991, and acceptedMarch 23. aVF, I, II, III, V5-V6 or >2 mm in leads VI-V4; ST Addressfor reprints: Bjijrn W. Karlson, MD, Division of Cardiolodepression Ll mm; T-wave inversion; Q wave L2 mm gy, Department of Medicine I, SahlgrenskaHospital, S-413 45 Giiteborg, Sweden. deep) in 22 leads. Thus, the attending doctor did not PREDICTION OF ACUTE MYOCARDIAL INFARCTION
171
TABLE I Final Diagnosis During First Three Days in the Hospital in Relation to Initial Suspicion of AMI in 4,690 Patients Categories 1 (n = 279)
2 (n = 1,426)
3 (n = 2,519)
245 203 14 9 5 1
478 175 163 172 478 80
192 34 171 225 752 261
6 1 8 13 56 48
Diagnosis missing
0
0
5
0
Discharged within 1 day with no suspicion of AMI
5
55
Confirmed AMI Q-wave AMI Possible AMI Myocardial ischemia Possible myocardial ischemia Diagnosis other than myocardial ischemia
classify the electrocardiogram for the study, and his treatment of the patient was independent of the official study classification. Basedon history, clinical examination, and standard 12-lead electrocardiogram recorded soon after admission to the emergency room, all patients were prospectively classitkd by the doctor on duty into 4 categories depending on the degree of initial suspicion of AMI: (1) obvious AM1 - typical symptoms, and ST elevation with or without Q waves on the initial 12-lead electrocardiogram; (2) strong suspicion of AMI, which included subcategories- a, typical symptoms, but an electrocardiogram without ST elevation or Q waves,b, atypical symptoms, but ST-T changes or Q waves on the electrocardiogram, c, suddenonset of severecongestive heart failure without ST elevation on the electrocardiogram, and d, unstable angina pectoris regardless of electrocardiogram; (3) vague suspicion of AM1 - difficulties in the interpretation of the symptomsand no signs of acute ischemia on the electrocardiogram; and (4) no suspicionof AM1 - a, no suspicionof coronary artery disease,and b, stable angina pectoris. For the subsequentdiagnosisof a confirmed AMI, 2 of the following criteria had to be full&d: (1) chest pain with a duration of 2 15 minutes, (2) serum aspartate aminotransferaseabove the normal range in samples from 12 different days, and (3) appearance of new Q waves in >_2 leads on a IZlead standard electrocardiogram. For the diagnosis of a possible AMI, chest pain and at least 1 of the following criteria had to be present: (1) 1 serum aspartate aminotransferase above the normal range, or 1 creature kinase above the normal range; and (2) appearanceof a new Q wave in only 1 lead of a 12-lead standard electrocardiogram. For the diagnosis of myocardial ischemia, at least 1 of the following signs of ischemia had to be present in L2 leads of a 1Zlead standard electrocardiogram (without elevations of serum aspartate aminotransferaseor creatine kinase): (1) ST depression of L 1 mm, (2) ST elevation of L 1 mm, or (3) T-wave inversion. For the diagnosisof possiblemyocardial ischemia, there had to 172
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be a clinical suspicion of myocardial ischemia, but no electrocardiographic signs of ischemia. RESULTS Of the 7,157 patients who came to the emergency room with chest pain or other symptoms suggestiveof AM1 during the study, 4,690 (66%) were admitted to hospital, with 2,223 (3 1%) being primarily admitted to the coronary care unit. Diagnosis in relation to initial suspicion of acute myocardial infarction. Of the 4,690 patients admitted
to the hospital, 279 (6%) were consideredto belong to category 1, 1,426 (30%) to category 2, 2,519 (54%) to category 3, and 466 (10%) to category 4. Of the total study population of 7,157 patients seenin the emergency room, 284 (4%) were consideredto belong to category 1, 1,431 (20%) to category 2, 2,532 (35%) to category 3, and 2,910 (41%) to category 4. Table I lists the diagnosesmade during the first 3 days in the hospital in relation to initial degreeof suspicion of AMI. Among patients considered to have an obviousAM1 in the emergencyroom, 88% actually developeda confirmed AM1 during the first 3 days in the hospital. This figure was higher in patients without (93%) than with (81%) a previous history of coronary artery disease.(The percentagesin relation to previous history of coronary artery diseaseare not listed in the tables.) Among patients classified into category 2 (i.e., strong suspicion of AMI), 34% developeda conlkrned AMI. Also, this figure was somewhathigher in patients without (37%) than with (32%) a previous history of coronary artery disease.In patients judged to have a vague suspicion of AM1 (category 3), 8% developeda confirmed AMI. There was no difference between patients with (8%) or without (7%) a history of previous AM1 or angina. In category 4 (the patients considered to have no suspicion of AMI), 1% developed a confirmed AMI. Most of the patients who developed a confirmed AM1 (52%) were classified into category 2. Although the percentage of patients developing infarction was
JULY 15, 1991
TABLE II Number of Patients with Different Admission Electrocardiographic Number Developing AMI in 4,690 Patients Admitted to the Hospital
Patterns in Relation to Initial Suspicion of AMI and
Categories
Normal ECG* Pathologic ECG* but no acute ischemia Acute ischemia* on ECG ST elevationt ST depressiont T-wave inversiont P wavet
lObvious AMI (n = 279)
2Strong Suspicion of AMI (n = 1,426)
3Vague Suspicion of AMI (n = 2,519)
4No Suspicion of AMI (n = 466)
Total (n = 4,690)
4 (2) 16 (6) 259 (237) 232 (216) 90 (81) 45 (40) 94 (90)
300 649 474 165 235 155 56
1,047 (37) 1,118 (91) 328 (64) 52 (15) 135 (32) 165 (27) 13 (5)
225 (1) 181 (4) 48 (1) 15 (1) 14 (0) 23 (0) 2 (0)
1,576 1,964 1,109 464 474 338 165
*Information is missing in 50 patients. tlnformation is missing in 72 patients. Numbers in parentheses are the patients who developed acute myocardial AMI = acute myocardial infarction; ECG = electrocardiogram.
infarction
(50) (167) (261) (136) (116) (73) (47)
(90) (268) (563) (368) (229) (140) (142)
during first 3 days in the hospital.
much higher in category 1, only 27% of all infarctions often in men (56%) than in women (42%) for all types were in this category. Becauseof the large number of of acute &hernia on the initial electrocardiogram (not patients in category 3, almost as many infarctions de- listed in the Table). Somepatients had > 1 type of elecveloped in this category (21% of total) as in category 1. trocardiographic abnormality. Eighty-nine of 258 patients with only ST depression (34%) and 53 of 186 Infarct development in relation to initial suspicion of with only T-wave inversion (28%) developedAMI. acute myocardial infarction and admission electrocarTen percent of all AMIs were diagnosedin patients diiram (Table II): A normal initial electrocardiogram in the emergency room was registered for 1,576 of the with a normal electrocardiogram on admission, 29% in patients (34%) admitted to the hospital. One percent of patients with a pathologic electrocardiogram but withthe patients in category 1, 21% in category 2, 42% in out acute ischemia, and 61% in patients whose electrocategory 3 and 49% in category 4 had normal electro- cardiogram showed acute ischemia. In patients with a normal admission electrocardiocardiograms. Abnormal electrocardiograms but withgram, 50% of the patients in category 1, 17% of those out signs of acute ischemia were found in 1,964 of admitted patients (42%), with almost similar percentages in category 2, 4% of those in category 3 and 0.4% of being found in categories 2, 3 and 4. Signs of acute the patients in category 4 developedAMI. Among pamyocardial &hernia on the electrocardiogram were tients with an abnormal electrocardiogram but with no present in 1,109 of all patients admitted (24%), with signs of acute ischemia, the percentageof patients who ST elevation in lo%, ST depression in lo%, T-wave developedAM1 ranged from 38% in category 1 to only inversion in 8% and Q waves in 4% (these figures add 2% in category 4. In patients with signs of acute ischup to >24, because some of the electrocardiograms emia on the initial electrocardiogram, the highest pershowed >l sign of acute ischemia). Ninety-three per- centagesof patients who developedAM1 were found in cent of patients in category 1, 33% in category 2, 13% category 1: 95% of those with new Q wavesand 93% of in category 3 and 11% in category 4 had acute isch- those with ST elevation. Also, in category 2, the percentagesof patients who developedinfarction were high emia on the electrocardiogram. For example, of 1,576 patients with a normal elec- 111patients wrth Q waves (82%) and ST elevation trocardiogram, 90 (6%) developed an AMI, a figure (82%), and were 49 and 47%, respectively, in patients that was higher in patients with (8%) than without with ST depressionand T-wave inversion. Twenty per(4%) a history of coronary artery disease.Among 1,964 cent of the patients in category 3 and 2% of those in patients with an abnormal electrocardiogram but with category 4 with electrocardiograms showing ischemia no signs of acute ischemia, 268 (14%) developeda con- developedan infarction. firmed AMI. In these patients, infarct developmentdid not differ between those with and without a history of DISCUSSION ischemic heart disease (14%). Among 1,109 patients Chest pain or other symptoms suggestiveof AM1 with signs of acute ischemia on the electrocardiogram, occur frequently. At our hospital, patients with these 563 (51%) developed a confkmed AMI. The propor- symptoms mad& up 19% of all those presenting to the tion was highest in patients with Q waves (86%), fol- medical emergencyroom.* The evaluation of these palowed by ST elevation (79%), ST depression (48%) tients is often difficult. The fact that only lessthan half and T-wave inversion (36%). An AM1 developedmore of the patients admitted to the coronary care units actuPREDICTION OF ACUTE MYOCARDIAL INFARCTION
173
ally develop AMP7 reflects the present strategy of most hospitals, i.e., to admit any patient with a suspicion of AM1 to the coronary care unit. Recently, the possibility of effective early intervention, especiallywith thrombolytic agents,has further emphasizedthe importance of the early diagnosis of AMI. In the emergencyroom the physician on duty traditionally uses history, clinical status and electrocardiogram to diagnose or exclude AMI. In this study, we looked at the accuracy of this early diagnosis, first when a combination of these variables was used, with the patients being prospectively categorized according to the initial degree of suspicion of AMI, and then when the electrocardiogram was used alone. In our study, 20% of the patients admitted actually developed AMI, and thus many patients without an infarct were hospitalized. This incidenceof infarction may seemlow; however, we did not study a coronary care unit population, but included in the analysis all patients admitted to a hospital bed. A similar infarction rate has previously been reported.g When we look at the results of our categorization of the patients, we find that categories 1 and 2 together make up 1,705 of the 4,690 patients (36%) admitted from the emergency room, and that 723 of the 921 AMIs (78%) developedin thesepatients. However, 192 of the AMIs (21%) developedin the 2,519 of all hospitalized patients (53%) belonging to category 3. Thus, 1 of 5 AMIs developedin patients with a vague suspicion of AM1 in the emergency room. These data strongly indicate that patients in category 3 should be admitted. However, only 8% of the patients in category 3 developed AMI, and it appearsjustifiable to observe these patients initially in a regular or intermediate ward for transfer to the coronary care unit when necessary. In previous studies on the possibility of diagnosing myocardial infarction in the emergency room, it has been shown that the physician’s estimate of the probability of infarction is a good predictor of infarction,5 and different meansto help the emergencyroom physicians have been developed.A predictive model basedon 4 clinical variables improved the accuracy of infarct diagnosis when compared with clinical judgment.‘O A computer-derived protocol combined with the physician’s clinical judgment improved the accuracy and positive predictive value of the admitting doctor’s decision that the patients should be admitted to an intensive care area.2A mathematic instrument basedon 9 variables increased diagnostic accuracy and reduced the admission rate to the coronary care unit.” However, thesedifferent diagnostic aids have not come into widespread clinical use. In our study, 1,109 of the admitted patients (24%) had an ischemic electrocardiogram. Of these patients, 174
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 68
563 (51%) developedAMI, totaling 61% of all AMIs. Most of the admitted patients - 1,964 (42%) - had an abnormal electrocardiogram without acute ischemic signs; 268 (14%) of these patients developedAMI, totaling 29% of all AMIs. Thus, 66% of the admitted patients had abnormal electrocardiograms.Of thesepatients, 27% developed AMI, totaling 90% of all 921 AMIs. In 2 studies on patients in coronary care units, 64 and 77%12J3had abnormal electrocardiograms,and AM1 developedin 57 and 41% of these patients, respectively. In 2 studies on patients admitted to the hospital (i.e., not just to the coronary care unit but to general wards as well) becauseof suspectedAMI, 63 and 83% had abnormal electrocardiograms, with rates of AM1 of 34 and 63%, respectively.3J4 We found ST elevation and new Q waves on the admission electr~ardiogram to. be the most predictive patterns for AMI, and ST depressionand T-wave inversion to be less predictive. These findings are in accordance with previous results.l 5 Of our admitted patients, 1,576 (34%) had a normal initial electrocardiogram. Only 90 (6%) of these patients developed AMI, but that still indicates that 10% of all AMIs developedin patients with a normal electrocardiogram in the emergency room. In other studies, between 12 and 37% of patients admitted for suspectedinfarction had normal initial electrocardioand AM1 occurred in 10 to 40% of grams,3~12~14~16~17 these patients3J2J4J7Thus, our study showed a lower rate of infarct development, and suggeststhat it is not necessaryto observepatients with normal electrocardiograms in the coronary care unit, unlessthey have typical symptomsof AMI, severeheart failure or any other reason for coronary care unit treatment. Table II showsthat the percentageof patients developing AM1 in relation to the initial electrocardiogram also varies with the clinical suspicionof AMI, expressed as categories 1 to 4. Thus, for patients with normal electrocardiograms, the percentages developing AM1 are high in categories 1 and 2, but, as expected,low in categories 3 and 4. Likewise, for patients with abnormal electrocardiogramswithout acute &hernia and for patients with acute ischemic electrocardiographic patterns, the rate of infarct developmentis lower the lower the clinical suspicion of AMI. Few patients were judged to belong to category 1, which probably reflects the difficulty of diagnosing AM1 without hospital observation. According to the defmition, all 279 patients in category 1 should have ST elevation. However, only 232 (83%) actually had ST elevation, and 4 patients (2%) even had a normal electrocardiogram, which is an example of the discrepancies between the reading of the doctor on duty and the official study reading of the electrocardiogram.
JULY 15, 1991
Other methods of early diagnosisof AM1 are cardiac enzyme determinations and thallium scintigraphy. Analysis of creatine kinase and creatine kinase-MB in the emergency room has not been shown to be a useful method,4J8J9but myoglobin analysis has been demonstrated to give early information on the diagnosis.20 Myocardial scintigraphy has been proposedas an additional method for evaluation of patients with suspected AMI in the emergency room.21*22 However, this method cannot be performed in every hospital and, like the enzyme analyses,takes considerabletime.
admitted to the emergencyroom with symptomssuggestiveof acute myocardial infarction. J Intern Med; in press. 9. FesmireFM, Percy RF, Wears RL, MacMath TL. Risk stratification according to the initial electrocardiogramin patients with suspectedacute myocardial infarction. Arch Intern Med 1989;149:1294-1297, 10. Tierney WM, Roth BJ, Psaty B, McHenry R, Fitzgerald J, Stump DL, Anderson K, Ryder KW, McDonald CJ, Smith DM. Predictors of myocardial infarction in emergencyroom patients. Crit Care Med 1985:13:526-531. il. PozenMW, D’Agostino RB, Mitchell JB, RosenfeldDM, Guglielmino JT, Schwartz ML, TeebagyN, Valentine JM, Hood WB. The usefulnessof a predictive instrumentto reduceinappropriate admissionsto the coronary care unit. Ann Intern Med 1980;92:238-242. 12. Slater DK, Hlatky MA, Mark DB, Harrell FE, Pryor DB, Califf RM. Outcome in suspectedacute myocardial infarction with normal or minimally abnormal admission electrocardiographic findings. Am J Cardiol 1987;60: 766-770. Acknowledgment: We thank Peter Nicol, MD, 13. Brush JE, Brand DA, Acampora D, Chalmer B, Wackers FJ. Use of the Kiiping, Sweden, for help in the preparation of the initial electrocardiogramto predict in-hospital complicationsof acute myocardial infarction. N Engl J Med 1985;312:1137-1141. manuscript. 14. Behar S, Schor S, Kariv I, Bare11V, Modan B. Evaluation of electrocardiogram in emergencyroom as a decision-makingtool. Chest 1977;71:486-491. IS. Rude RE, PooleWK, Muller JE, Turi 2, Rutherford J, Parker C, Roberts R, Raabe DS, Gold HK, Stone PH, Willerson JT, Braunwald E, and the MILLS Study Group. Electrocardiographicand clinical criteria for recognition of acute REFERENCES 1. Selker HP, Griffith JL, Dorey FJ, D’Agostino RB. How do physiciansadapt myocardial infarction based on analysis of 3,697 patients. Am J Cmdiol 1983;52:936-942. when the coronary care unit is full. A prospective multicenter study. JAMA 16. Mulley AG, Thibault GE, Hughes RA, Bamett GO, Reder VA, Sherman 1987;257:1181-1185. EL. The courseof patients with suspectedmyocardial infarction. The identifica2. Goldman L, Weinberg M, Weisberg M, Olshen R, Cook EF, Sargent RK, LamasGA, DennisC, Wilson C, DeckelbaumL, FinebergH, Stiratelli R, andthe tion of low-risk patients for early transfer from intensive care. N Engl J Med Medical House Staffs at Yale-New Haven Hospital and Brigham and Women’s 1980;302:943-948. 17. Yusuf S, PearsonM, Sterry H, ParishS, RamsdaleD, RossiP, Sleight P. The Hospital. A computer-derivedprotocol to aid in the diagnosisof emergencyroom entry ECG in the early diagnosisand prognostic stratification of patients with patients with acute chest pain. N Engl J Med 1982;307:588-596. 3. Morris AL, Reimer J. Suspectmyocardial infarction: hospital management suspectedacute myocardial infarction. Eur Hearf J 1984;5:690-696. 16. Lee TH, WeisbergMC, Cook EF, Daley K, Brand DA, Goldman L. Evaluaand prognosis.C&r Cardiol 1983;6:285-291. tion of creatine kinaseand creatine kinase-MB for diagnosingmyocardial infarc4. EisenbergJM, Horowitz LN, Busch R, Arvan D, Rawnsley H. Diagnosisof tion. Clinical impact in the emergencyroom.Arch Intern Med 1987;147:115-121. acute myocardial infarction in the emergencyroom: a prospectiveassessmentof clinical decisionmaking and the usefulnessof immediatecardiac enzymedetermi- 19. Lee TH, Cook EF, WeisbergM, Sargent RK, Wilson C, Goldman L. Acute chest pain in the emergencyroom. Identification and examination of low-risk nation. J Commun Health 1979;4:190-198. patients. Arch Intern Med 1985;145:65-69. 5. Tierney WM. Fitzgerald J, McHenry R, Roth BJ, Psaty B, Stump DL, Anderson K. Physicians’estimatesof the probability of myocardial infarction in 20. Ohman EM, CaseyC, BengtsonJR, Pryor D, Tormey W, Horgan JH. Early detectionof acute myocardial infarction: additional diagnosticinformation from emergencyroom patients with cheat pain. Med Decis Making 1986;6:12-17. serumconcentrationsof myoglobin in patients without ST-elevation. Br Heart J 6. Lee TH, Rouan GW, Weisberg MC, Brand DA, Cook EF, Acampora D, 1990;63:335-338. Goldman L, and The Chest Pain Study Group. Sensitivity of routine clinical criteria for diagnosingmyocardial infarction within 24 hours of hospitalization, 21. Mace SE.Thallium myocardial scanningin the emergencydepartmentevaluAnn Intern Med 1987;106:181-186, ation of chest pain. Am J Emerg Med 1989;7:321-328. 7. Bloom BS, PetersonOL. End results, cost and productivity of coronary-care 22. Wackers FJT, Lie KI, Liem KL, Sokole EB, SamsonG, van der Schwt J, Durrer D. Potential value of thallium-201 scintigraphy as a meansof selecting units. N Engl J Med 1973;288:72-78. 6. Karlson BW, Herlitz J, PetterssonP, Ekvall H-E, Hjalmarson A. Patients patients for the coronary care unit. Br Hear? J 1979;41:111-117.
PREDICTION OF ACUTE MYOCARDIAL INFARCTION
175
The possibility of early prediction of acute myocardial infarction (AMI) was assessed in 7,157 consecutive patients coming to our emergency room during a Pi-month period with chest pain or other symptoms suggestive of AMI. Df these patients 921 developed an AMI during the first 3 days in the hospital. Df the 4,690 patients admitted to hospital, 1,576 (34%) had a normal admission electrocardiogram, and SO of these (6%) developed AMI. Df 1,964 patients with an abnormal electrocardiogram without signs of acute ischemia (42% of those admitted), 266 (14%) developed AMI, and 663 (51%) of 1,109 patients with acute ischemia on the eiectrocardiogram (24%) developed AMI. All patients were prospectiiely classified in the emergency room on the basis of history, clinical examination and electrocardiogram into 1 of 4 categories, according to the initial degree of suspicion of AMI. Df 279 admitted patients judged to have an obvious AMI (6% of the 4,6SO), 245 (88%) actually developed AMI; of 1,426 with a strong suspicion of AMI (30%), 478 (34%) developed one; of 2,519 with a vague suspicion of AMI (64%), 192 (8%) developed one; and of 466 with no suspicion of AMI (lo%), 6 (1%) developed one. Thus, only a low percentage of the patients with a normal initial electrocardiogram or a vague initial suspicion of AMI developed a confirmed AMI. (AmJCardiol1991;68:171-175)
any patients come to the emergencyroom of every hospital with chest pain or other symptoms suggestiveof acute myocardial infarction (AMC). Only a minority of thesepatients developa confirmed AMI. Most of the patients judged sufficiently likely in the emergency room to have an AMI are admitted to a coronary care unit, but only 16 to 50% of them actually develop a confirmed AMIle Although many of the patients do not develop an AMI, they are not necessarily admitted needlessly, since they may have unstable angina pectoris, severeheart failure, arrhythmias, or other symptoms requiring treatment in a coronary care unit. However, there is great interest in the early prediction of infarction in order to be able to select high-risk patients for immediate intensive care. The possibility of early intervention aimed at myocardial salvage,especially with thrombolytic agents, further underlines the importance of early diagnosis.This study describesour experiencewith predicting developmentof AM1 in consecutive,unselected patients presenting to the emergencyroom of a single hospital with chest pain or other symptoms suggestiveof AMI.
M
METHODS Patients: Sahlgrenska Hospital, Goteborg, Sweden,
servesa population of about 230,000. All patients presenting to the emergency room between February 15, 1986, and November 9, 1987, with chest pain or other symptoms suggestiveof AM1 were consecutively registered. A full history was taken, including details of previous AMIs and angina pectoris. A standard 1Zlead electrocardiogram was regisFrom the Division of Cardiology, Department of Medicine I, Sahl- tered soon after admissionto the emergency room and grenska Hospital, Goteborg, Sweden. This study was supported by classified the following day into 1 of the following grants from The SwedishHeart Foundation,The Gothenburg Society of Medicine, Arbetsmarknadens Fiirs&ringsaktiebolag, The Medical groups by an experiencedmember of our study group: Faculty of the University of Gothenburg,The SwedishSocietyof Medi- ( 1) normal (no pathologic signs); (2) pathologic but no cine, RousselNordiska AB, Trygg Hansa Insurance Co., Skandia In- signs of acute &hernia (e.g., old infarction, bundle suranceCo., ICI-Pharma AB, SjutirsaXrings AB Eir’s 50-year Foundation, Leo and Hans Osterman’sFund, and Ollie and Elof Ericsson’s branch block, nonspecific ST-T changes); (3) signs of Foundation. Manuscript received November 26, 1990;revised manu- acute ischemia (ST elevation >l mm in leads aVL, script receivedMarch 21, 1991, and acceptedMarch 23. aVF, I, II, III, V5-V6 or >2 mm in leads VI-V4; ST Addressfor reprints: Bjijrn W. Karlson, MD, Division of Cardiolodepression Ll mm; T-wave inversion; Q wave L2 mm gy, Department of Medicine I, SahlgrenskaHospital, S-413 45 Giiteborg, Sweden. deep) in 22 leads. Thus, the attending doctor did not PREDICTION OF ACUTE MYOCARDIAL INFARCTION
171
TABLE I Final Diagnosis During First Three Days in the Hospital in Relation to Initial Suspicion of AMI in 4,690 Patients Categories 1 (n = 279)
2 (n = 1,426)
3 (n = 2,519)
245 203 14 9 5 1
478 175 163 172 478 80
192 34 171 225 752 261
6 1 8 13 56 48
Diagnosis missing
0
0
5
0
Discharged within 1 day with no suspicion of AMI
5
55
Confirmed AMI Q-wave AMI Possible AMI Myocardial ischemia Possible myocardial ischemia Diagnosis other than myocardial ischemia
classify the electrocardiogram for the study, and his treatment of the patient was independent of the official study classification. Basedon history, clinical examination, and standard 12-lead electrocardiogram recorded soon after admission to the emergency room, all patients were prospectively classitkd by the doctor on duty into 4 categories depending on the degree of initial suspicion of AMI: (1) obvious AM1 - typical symptoms, and ST elevation with or without Q waves on the initial 12-lead electrocardiogram; (2) strong suspicion of AMI, which included subcategories- a, typical symptoms, but an electrocardiogram without ST elevation or Q waves,b, atypical symptoms, but ST-T changes or Q waves on the electrocardiogram, c, suddenonset of severecongestive heart failure without ST elevation on the electrocardiogram, and d, unstable angina pectoris regardless of electrocardiogram; (3) vague suspicion of AM1 - difficulties in the interpretation of the symptomsand no signs of acute ischemia on the electrocardiogram; and (4) no suspicionof AM1 - a, no suspicionof coronary artery disease,and b, stable angina pectoris. For the subsequentdiagnosisof a confirmed AMI, 2 of the following criteria had to be full&d: (1) chest pain with a duration of 2 15 minutes, (2) serum aspartate aminotransferaseabove the normal range in samples from 12 different days, and (3) appearance of new Q waves in >_2 leads on a IZlead standard electrocardiogram. For the diagnosis of a possible AMI, chest pain and at least 1 of the following criteria had to be present: (1) 1 serum aspartate aminotransferase above the normal range, or 1 creature kinase above the normal range; and (2) appearanceof a new Q wave in only 1 lead of a 12-lead standard electrocardiogram. For the diagnosis of myocardial ischemia, at least 1 of the following signs of ischemia had to be present in L2 leads of a 1Zlead standard electrocardiogram (without elevations of serum aspartate aminotransferaseor creatine kinase): (1) ST depression of L 1 mm, (2) ST elevation of L 1 mm, or (3) T-wave inversion. For the diagnosisof possiblemyocardial ischemia, there had to 172
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be a clinical suspicion of myocardial ischemia, but no electrocardiographic signs of ischemia. RESULTS Of the 7,157 patients who came to the emergency room with chest pain or other symptoms suggestiveof AM1 during the study, 4,690 (66%) were admitted to hospital, with 2,223 (3 1%) being primarily admitted to the coronary care unit. Diagnosis in relation to initial suspicion of acute myocardial infarction. Of the 4,690 patients admitted
to the hospital, 279 (6%) were consideredto belong to category 1, 1,426 (30%) to category 2, 2,519 (54%) to category 3, and 466 (10%) to category 4. Of the total study population of 7,157 patients seenin the emergency room, 284 (4%) were consideredto belong to category 1, 1,431 (20%) to category 2, 2,532 (35%) to category 3, and 2,910 (41%) to category 4. Table I lists the diagnosesmade during the first 3 days in the hospital in relation to initial degreeof suspicion of AMI. Among patients considered to have an obviousAM1 in the emergencyroom, 88% actually developeda confirmed AM1 during the first 3 days in the hospital. This figure was higher in patients without (93%) than with (81%) a previous history of coronary artery disease.(The percentagesin relation to previous history of coronary artery diseaseare not listed in the tables.) Among patients classified into category 2 (i.e., strong suspicion of AMI), 34% developeda conlkrned AMI. Also, this figure was somewhathigher in patients without (37%) than with (32%) a previous history of coronary artery disease.In patients judged to have a vague suspicion of AM1 (category 3), 8% developeda confirmed AMI. There was no difference between patients with (8%) or without (7%) a history of previous AM1 or angina. In category 4 (the patients considered to have no suspicion of AMI), 1% developed a confirmed AMI. Most of the patients who developed a confirmed AM1 (52%) were classified into category 2. Although the percentage of patients developing infarction was
JULY 15, 1991
TABLE II Number of Patients with Different Admission Electrocardiographic Number Developing AMI in 4,690 Patients Admitted to the Hospital
Patterns in Relation to Initial Suspicion of AMI and
Categories
Normal ECG* Pathologic ECG* but no acute ischemia Acute ischemia* on ECG ST elevationt ST depressiont T-wave inversiont P wavet
lObvious AMI (n = 279)
2Strong Suspicion of AMI (n = 1,426)
3Vague Suspicion of AMI (n = 2,519)
4No Suspicion of AMI (n = 466)
Total (n = 4,690)
4 (2) 16 (6) 259 (237) 232 (216) 90 (81) 45 (40) 94 (90)
300 649 474 165 235 155 56
1,047 (37) 1,118 (91) 328 (64) 52 (15) 135 (32) 165 (27) 13 (5)
225 (1) 181 (4) 48 (1) 15 (1) 14 (0) 23 (0) 2 (0)
1,576 1,964 1,109 464 474 338 165
*Information is missing in 50 patients. tlnformation is missing in 72 patients. Numbers in parentheses are the patients who developed acute myocardial AMI = acute myocardial infarction; ECG = electrocardiogram.
infarction
(50) (167) (261) (136) (116) (73) (47)
(90) (268) (563) (368) (229) (140) (142)
during first 3 days in the hospital.
much higher in category 1, only 27% of all infarctions often in men (56%) than in women (42%) for all types were in this category. Becauseof the large number of of acute &hernia on the initial electrocardiogram (not patients in category 3, almost as many infarctions de- listed in the Table). Somepatients had > 1 type of elecveloped in this category (21% of total) as in category 1. trocardiographic abnormality. Eighty-nine of 258 patients with only ST depression (34%) and 53 of 186 Infarct development in relation to initial suspicion of with only T-wave inversion (28%) developedAMI. acute myocardial infarction and admission electrocarTen percent of all AMIs were diagnosedin patients diiram (Table II): A normal initial electrocardiogram in the emergency room was registered for 1,576 of the with a normal electrocardiogram on admission, 29% in patients (34%) admitted to the hospital. One percent of patients with a pathologic electrocardiogram but withthe patients in category 1, 21% in category 2, 42% in out acute ischemia, and 61% in patients whose electrocategory 3 and 49% in category 4 had normal electro- cardiogram showed acute ischemia. In patients with a normal admission electrocardiocardiograms. Abnormal electrocardiograms but withgram, 50% of the patients in category 1, 17% of those out signs of acute ischemia were found in 1,964 of admitted patients (42%), with almost similar percentages in category 2, 4% of those in category 3 and 0.4% of being found in categories 2, 3 and 4. Signs of acute the patients in category 4 developedAMI. Among pamyocardial &hernia on the electrocardiogram were tients with an abnormal electrocardiogram but with no present in 1,109 of all patients admitted (24%), with signs of acute ischemia, the percentageof patients who ST elevation in lo%, ST depression in lo%, T-wave developedAM1 ranged from 38% in category 1 to only inversion in 8% and Q waves in 4% (these figures add 2% in category 4. In patients with signs of acute ischup to >24, because some of the electrocardiograms emia on the initial electrocardiogram, the highest pershowed >l sign of acute ischemia). Ninety-three per- centagesof patients who developedAM1 were found in cent of patients in category 1, 33% in category 2, 13% category 1: 95% of those with new Q wavesand 93% of in category 3 and 11% in category 4 had acute isch- those with ST elevation. Also, in category 2, the percentagesof patients who developedinfarction were high emia on the electrocardiogram. For example, of 1,576 patients with a normal elec- 111patients wrth Q waves (82%) and ST elevation trocardiogram, 90 (6%) developed an AMI, a figure (82%), and were 49 and 47%, respectively, in patients that was higher in patients with (8%) than without with ST depressionand T-wave inversion. Twenty per(4%) a history of coronary artery disease.Among 1,964 cent of the patients in category 3 and 2% of those in patients with an abnormal electrocardiogram but with category 4 with electrocardiograms showing ischemia no signs of acute ischemia, 268 (14%) developeda con- developedan infarction. firmed AMI. In these patients, infarct developmentdid not differ between those with and without a history of DISCUSSION ischemic heart disease (14%). Among 1,109 patients Chest pain or other symptoms suggestiveof AM1 with signs of acute ischemia on the electrocardiogram, occur frequently. At our hospital, patients with these 563 (51%) developed a confkmed AMI. The propor- symptoms mad& up 19% of all those presenting to the tion was highest in patients with Q waves (86%), fol- medical emergencyroom.* The evaluation of these palowed by ST elevation (79%), ST depression (48%) tients is often difficult. The fact that only lessthan half and T-wave inversion (36%). An AM1 developedmore of the patients admitted to the coronary care units actuPREDICTION OF ACUTE MYOCARDIAL INFARCTION
173
ally develop AMP7 reflects the present strategy of most hospitals, i.e., to admit any patient with a suspicion of AM1 to the coronary care unit. Recently, the possibility of effective early intervention, especiallywith thrombolytic agents,has further emphasizedthe importance of the early diagnosis of AMI. In the emergencyroom the physician on duty traditionally uses history, clinical status and electrocardiogram to diagnose or exclude AMI. In this study, we looked at the accuracy of this early diagnosis, first when a combination of these variables was used, with the patients being prospectively categorized according to the initial degree of suspicion of AMI, and then when the electrocardiogram was used alone. In our study, 20% of the patients admitted actually developed AMI, and thus many patients without an infarct were hospitalized. This incidenceof infarction may seemlow; however, we did not study a coronary care unit population, but included in the analysis all patients admitted to a hospital bed. A similar infarction rate has previously been reported.g When we look at the results of our categorization of the patients, we find that categories 1 and 2 together make up 1,705 of the 4,690 patients (36%) admitted from the emergency room, and that 723 of the 921 AMIs (78%) developedin thesepatients. However, 192 of the AMIs (21%) developedin the 2,519 of all hospitalized patients (53%) belonging to category 3. Thus, 1 of 5 AMIs developedin patients with a vague suspicion of AM1 in the emergency room. These data strongly indicate that patients in category 3 should be admitted. However, only 8% of the patients in category 3 developed AMI, and it appearsjustifiable to observe these patients initially in a regular or intermediate ward for transfer to the coronary care unit when necessary. In previous studies on the possibility of diagnosing myocardial infarction in the emergency room, it has been shown that the physician’s estimate of the probability of infarction is a good predictor of infarction,5 and different meansto help the emergencyroom physicians have been developed.A predictive model basedon 4 clinical variables improved the accuracy of infarct diagnosis when compared with clinical judgment.‘O A computer-derived protocol combined with the physician’s clinical judgment improved the accuracy and positive predictive value of the admitting doctor’s decision that the patients should be admitted to an intensive care area.2A mathematic instrument basedon 9 variables increased diagnostic accuracy and reduced the admission rate to the coronary care unit.” However, thesedifferent diagnostic aids have not come into widespread clinical use. In our study, 1,109 of the admitted patients (24%) had an ischemic electrocardiogram. Of these patients, 174
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 68
563 (51%) developedAMI, totaling 61% of all AMIs. Most of the admitted patients - 1,964 (42%) - had an abnormal electrocardiogram without acute ischemic signs; 268 (14%) of these patients developedAMI, totaling 29% of all AMIs. Thus, 66% of the admitted patients had abnormal electrocardiograms.Of thesepatients, 27% developed AMI, totaling 90% of all 921 AMIs. In 2 studies on patients in coronary care units, 64 and 77%12J3had abnormal electrocardiograms,and AM1 developedin 57 and 41% of these patients, respectively. In 2 studies on patients admitted to the hospital (i.e., not just to the coronary care unit but to general wards as well) becauseof suspectedAMI, 63 and 83% had abnormal electrocardiograms, with rates of AM1 of 34 and 63%, respectively.3J4 We found ST elevation and new Q waves on the admission electr~ardiogram to. be the most predictive patterns for AMI, and ST depressionand T-wave inversion to be less predictive. These findings are in accordance with previous results.l 5 Of our admitted patients, 1,576 (34%) had a normal initial electrocardiogram. Only 90 (6%) of these patients developed AMI, but that still indicates that 10% of all AMIs developedin patients with a normal electrocardiogram in the emergency room. In other studies, between 12 and 37% of patients admitted for suspectedinfarction had normal initial electrocardioand AM1 occurred in 10 to 40% of grams,3~12~14~16~17 these patients3J2J4J7Thus, our study showed a lower rate of infarct development, and suggeststhat it is not necessaryto observepatients with normal electrocardiograms in the coronary care unit, unlessthey have typical symptomsof AMI, severeheart failure or any other reason for coronary care unit treatment. Table II showsthat the percentageof patients developing AM1 in relation to the initial electrocardiogram also varies with the clinical suspicionof AMI, expressed as categories 1 to 4. Thus, for patients with normal electrocardiograms, the percentages developing AM1 are high in categories 1 and 2, but, as expected,low in categories 3 and 4. Likewise, for patients with abnormal electrocardiogramswithout acute &hernia and for patients with acute ischemic electrocardiographic patterns, the rate of infarct developmentis lower the lower the clinical suspicion of AMI. Few patients were judged to belong to category 1, which probably reflects the difficulty of diagnosing AM1 without hospital observation. According to the defmition, all 279 patients in category 1 should have ST elevation. However, only 232 (83%) actually had ST elevation, and 4 patients (2%) even had a normal electrocardiogram, which is an example of the discrepancies between the reading of the doctor on duty and the official study reading of the electrocardiogram.
JULY 15, 1991
Other methods of early diagnosisof AM1 are cardiac enzyme determinations and thallium scintigraphy. Analysis of creatine kinase and creatine kinase-MB in the emergency room has not been shown to be a useful method,4J8J9but myoglobin analysis has been demonstrated to give early information on the diagnosis.20 Myocardial scintigraphy has been proposedas an additional method for evaluation of patients with suspected AMI in the emergency room.21*22 However, this method cannot be performed in every hospital and, like the enzyme analyses,takes considerabletime.
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