Diagnosis of MI in the ED ========================= þ Most diagnoses of MI by "classic" protocols are made within 24 hours. [Lee TH, Rouan GW, Weisberg MC, et al. Sensitivity of routine clinical criteria for diagnosing myocardial infarction within 24 hours of hospitalization. Ann Intern Med 1987; 106:181-6.] Abstract: þ Shorter Protocols - Protocols with reasonable sensitivity have been developed to do this over a period of from 3 to 9 hours in the ED setting and are a definite improvement over reliance upon spot CK specimens (1,2,3,4). You may be able to 'compress' the time to dispo by using a marker such as myoglobin (4). Even in those who present with 'unstable angina' (who do not have infaction), risk stratification can be assigned based upon some more recent markers if those are available to you (5). (1) Hedges JR, Young GP, Henkel GF, Gibler WB, Green TR, Swanson JR Serial ECGs are less accurate than serial CK-MB results for emergency department diagnosis of myocardial infarction. Ann Emerg Med 1992 Dec;21(12):1445-50 ABSTRACT: HYPOTHESIS: Serial creatine kinase-MB (CK-MB) levels provide more accurate predictive information regarding myocardial infarction than serial ECGs in emergency department patients with chest discomfort and no ST-segment elevation on the initial ECG. DESIGN: Prospective, observational study. SETTING: University hospital and university-affiliated Veterans Affairs Medical Center EDs. PARTICIPANTS: Two hundred sixty-one patients 30 years or older with chest discomfort warranting an ECG and consenting to observation. Exclusions included hemodynamic or rhythm instability and ST-segment elevation of 0.1 mV or more in two or more electrically contiguous leads at presentation. MEASUREMENTS: ECGs were obtained at presentation and three to four hours after presentation. Significant serial ECG changes sought on comparison of initial and three- to four-hour ECGs were 0.05 mV or more ST elevation or depression, Q-wave development, or T-wave inversion changes in two or more electrically contiguous leads. CK-MB levels were obtained at presentation and hourly for three hours (positive level, 8 or more ng/mL). Myocardial infarction was determined by record review and was based on independent CK-MB measurements. RESULTS: Twenty-eight (11%) patients were diagnosed with a myocardial infarction. Thirty-eight (15%) patients had a serial ECG change. Eleven of the myocardial infarction patients (39%) had a serial ECG change compared with 27 (12%) of the non-myocardial infarction patients (P < .001). Sensitivities and specificities of a serial ECG change versus serial CK-MBs for myocardial infarction were 39% versus 68% (sensitivity) and 88% versus 95% (specificity), respectively. Serial CK-MBs were more accurate than a serial ECG change for predicting myocardial infarction (P < .03). CONCLUSION: Serial changes in ECGs during a three- to four-hour interval were associated with the diagnosis of myocardial infarction but were infrequent and less accurate than serial CK-MB levels obtained for the same interval. (2) Gibler WB, Young GP, Hedges JR, Lewis LM, Smith MS, Carleton SC, Aghababian RV, Jorden RO, Allison EJ Jr, Otten EJ, et al Acute myocardial infarction in chest pain patients with nondiagnostic ECGs: serial CK-MB sampling in the emergency department. The Emergency Medicine Cardiac Research Group. Ann Emerg Med 1992 May;21(5):504-12 ABSTRACT: STUDY OBJECTIVES: This study tested the hypothesis that serial creatine phosphokinase (CK)-MB sampling in the emergency department can identify acute myocardial infarction (AMI) in patients presenting to the ED with chest pain and nondiagnostic ECGs. DESIGN: Patients more than 30 years old who were evaluated initially in the ED and hospitalized for chest pain were studied. Serial CK-MB levels were analyzed prospectively using a rapid serum immunochemical assay for identification of AMI patients in the ED. Presenting ECGs showing new, greater than 1-mm ST elevation in two or more contiguous leads were considered diagnostic for AMI. All other ECGs were considered nondiagnostic ECGs. CK-MB levels were determined at ED presentation and hourly for three hours (total of four levels). Patients with at least one level of more than 7 ng/mL were considered to have a positive enzyme study. The in-hospital diagnosis of AMI was determined by the development of typical serial ECG changes or separate standard cardiac enzyme changes after admission. SETTING: Eight tertiary-care medical center hospitals. METHODS AND MAIN RESULTS: Of the 616 study patients, 108 (17.5%) were diagnosed in the hospital as AMI; 69 of these AMI patients (63.9%) had nondiagnostic ECGs in the ED. Of the patients with nondiagnostic ECGs, 55 (sensitivity, 79.7%) had a positive ED serial CK-MB enzyme study within three hours after presentation. Combining serial ED CK-MB assay results with diagnostic ECGs yielded an 88.4% sensitivity for AMI detection within three hours of ED presentation. The predictive value of a negative serial ED enzyme study for no AMI was 96.2% (specificity, 93.7%). CONCLUSION: Serial CK-MB determination in the ED can help identify AMI patients with initial nondiagnostic ECGs. Use of serial CK-MB analysis may facilitate optimal in-hospital disposition and help guide therapeutic interventions in patients with suspected AMI despite a nondiagnostic ECG. (3) Gibler WB, Lewis LM, Erb RE, Makens PK, Kaplan BC, Vaughn RH, Biagini AV, Blanton JD, Campbell WB Early detection of acute myocardial infarction in patients presenting with chest pain and nondiagnostic ECGs: serial CK-MB sampling in the emergency department [published erratum appears in Ann Emerg Med 1991 Apr;20(4):420] Ann Emerg Med 1990 Dec;19(12):1359-66 ABSTRACT: STUDY OBJECTIVES: Patients presenting to the emergency department with chest discomfort are a difficult problem for emergency physicians. Nearly 50% of patients with acute myocardial infarction (AMI) will initially have nondiagnostic ECGs on ED presentation. The purpose of this study was to determine if patients with AMI having nondiagnostic ECGs could be identified using new immunochemical assays for serial CK-MB sampling in the ED. DESIGN: Chest pain patients, more than 30 years old, with pain not caused by trauma or explained by radiographic findings, were eligible for the study. Serial serum samples were drawn on ED presentation (zero hours) and three hours after presentation, then analyzed for CK-MB using four immunochemical methods and electrophoresis. Standard World Health Organization criteria were used to establish the diagnosis of AMI, including new Q-wave formation or elevation of standard in-hospital serum cardiac enzyme markers. SETTING: A tertiary cardiac care community hospital. MEASUREMENTS AND MAIN RESULTS: The serum from 183 patients hospitalized for possible ischemic chest pain was collected and analyzed. Thirty-one of 183 patients (17%) were found to have AMI by standard in-hospital criteria. Sixteen of the 31 patients (52%) with AMI had nondiagnostic ECGs on presentation. Immunochemical determination of serial CK-MB levels provided a sensitive and specific method for detecting AMI in patients within three hours after ED presentation compared with standard electrophoresis. The four immunochemical methods demonstrated a range in sensitivity from 50% to 62.1% on ED presentation versus 92% to 96.7% three hours later. The immunochemical tests demonstrated specificities ranging from 83.0% to 96.4% at three hours, with three of the four tests having specificities of 92% or greater. Electrophoresis had a sensitivity of 34.5% on ED presentation, increasing to 76.9% at three hours, with a specificity of 98.6%. CONCLUSIONS: Immunochemical CK-MB methods allowed rapid, sensitive detection of AMI in the ED. Early detection of AMI offers many potential advantages to the emergency physician. Early detection of AMI, while the patient is in the ED, could direct disposition of this potentially unstable patient to an intensive care setting. Such information may prevent the ED discharge of patients with AMI having nondiagnostic ECGs. The diagnosis of AMI within a six-hour period after symptom onset may allow thrombolytic therapy to be given to patients with AMI not having diagnostic ECGs. This study served as a pilot trial for a multicenter study of the Emergency Medicine Cardiac Research Group, which is currently ongoing. (4) Montague C, Kircher T Myoglobin in the early evaluation of acute chest pain. Am J Clin Pathol 1995 Oct;104(4):472-6 ABSTRACT: Two thirds of patients hospitalized to rule out acute myocardial infarction (AMI) are eventually found to have a non-AMI diagnosis, whereas 2% to 8% of patients with AMI are inappropriately discharged from the emergency department. Myoglobin has been shown to increase within 2 to 3 hours of myocardial injury. This study evaluates the usefulness of myoglobin in acute chest pain. Serial blood samples were obtained from 89 suspected AMI patients evaluated in the emergency department. Testing included creatine kinase (CK), a creatine kinase isoenzyme (CK-MB), and myoglobin. Twenty five of 89 patients (28%) had a diagnosis of AMI. The sensitivity of myoglobin for the detection of AMI was 56% at the time of admission and 100% 2 hours after admission. Thirteen of 25 AMI patients (52%) had a positive myoglobin before increases in CK or CK-MB, including one patient discharged from the emergency department. More importantly, the negative predictive value for myoglobin at the time of admission was 83% and was 100% two hours after admission. This potential for 100% predictability in excluding AMI by the use of serial myoglobin determinations will be very helpful in the correct triage of patients presenting with acute chest pain. (5) Ravkilde J, Nissen H, Horder M, Thygesen K Independent prognostic value of serum creatine kinase isoenzyme MB mass, cardiac troponin T and myosin light chain levels in suspected acute myocardial infarction. Analysis of 28 months of follow-up in 196 patients. J Am Coll Cardiol 1995 Mar 1;25(3):574-81 ABSTRACT: OBJECTIVES. We sought to determine the incidence and independent prognostic value of increased serum levels of sensitive serologic markers in patients in whom a conventionally diagnosed acute myocardial infarction had been ruled out. BACKGROUND. Increased serum levels of creatine kinase (CK) isoenzyme MB mass and cardiac troponin T in patients with unstable angina pectoris are associated with a poor prognosis. METHODS. We analyzed data from 196 consecutive patients with suspected acute myocardial infarction, which was later ruled out in 124. Increased serum levels of CK-MB mass, troponin T and myosin light chains were compared with clinical findings, ST-T wave abnormalities and presence of arrhythmias. RESULTS. Of the patients in the noninfarction group, 28% had serum CK-MB mass > or = 6 micrograms/liter, 20% had troponin T > or = 0.20 micrograms/liter, and 26% had myosin light chains > or = 0.4 micrograms/liter (discrimination limits). The cardiac event rate (cardiac death, nonfatal acute myocardial infarction) within 28 months was significantly higher in patients in the noninfarction group with elevated marker levels (range 22% to 24%) than in patients with values below these discriminators (range 3% to 5%) but was not significantly different from that in patients with a definite diagnosis of acute myocardial infarction (29%). Further, significant predictors of cardiac events were previous myocardial infarction; myocardial infarction or angina pectoris, or both; previous congestive heart failure; ST-T wave abnormalities on admission; a transient ST-T wave shift on serial electrocardiograms (ECGs); recurrent chest pain; and occurrence of supraventricular or ventricular tachycardia, or both, during the 1st 48 h after admission. It was found that all three biochemical markers, in the main, convey independent prognostic information with respect to clinical findings and presence of arrhythmias but not ST-T wave abnormalities on admission or a transient ST-T wave shift on serial ECGs. CONCLUSIONS. Increased serum levels of CK-MB mass, troponin T and myosin light chains all detect a subgroup of 25% of patients without acute myocardial infarction who have as poor a prognosis as that of patients with a definite diagnosis of acute myocardial infarction. All three biochemical markers provide similar important independent prognostic information with regard to clinical findings and arrhythmias but add no additional prognostic information once ECG ST-T wave changes are considered.