The diagnosis of acute myocardial infarction

[Biological markers of myocardial necrosis]

New biological markers of myocardial injury have improved the management of patients with acute coronary syndromes. Among these markers, the most relevant are the cardiac troponins (troponin I and troponin T) because of their cardiospecificity, and myoglobin because of its combination of diagnostic sensitivity and usefulness for an early diagnosis. The serial analysis and combined use of both markers fulfill all diagnostic and prognostic requirements, and are helpful in indicating therapeutic strategies for acute coronary syndromes. However, these markers also have limitations, and their concentrations should always be interpreted in the light of the patient's clinical status.

Serum markers in the emergency department diagnosis of acute myocardial infarction

No currently used cardiac-specific serum marker meets all the criteria for an "ideal" marker of AMI. No test is both highly sensitive and highly specific for acute infarction within 6 hours following the onset of chest pain, the timeframe of interest to most emergency physicians in making diagnostic and therapeutic decisions. Patients presenting to the ED with chest pain or other symptoms suggestive of acute cardiac ischemia therefore cannot make a diagnosis of AMI excluded on the basis of a single cardiac marker value obtained within a few hours after symptom onset. The total CK level is far too insensitive and nonspecific a test to be used to diagnose AMI. It retains its value, however, as a screening test, and serum of patients with abnormal total CK values should undergo a CK-MBmass assay. Elevation in CK-MB is a vital component of ultimate diagnosis of AMI, but levels of this marker are normal in one fourth to one half of patients with AMI at the time of ED presentation. The test is highly specific, however, and an abnormal value (particularly when it exceeds 5% of the total CK value) at any time in a patient with chest pain is highly suggestive of an AMI. There have been several improvements of CK-MB assay timing and subform quantification that appear highly useful for emergency physicians. Rapid serial CK-MB assessment greatly increases the diagnostic value of the assay in a timeframe suitable for ED purposes but unfortunately still misses about 10% of patients ultimately diagnosed with acute MI. Assays of CK-MB subforms have very high sensitivity, and, although unreliable within 4 hours of symptom onset, have excellent diagnostic value at 6 or more hours after chest pain begins. Automated test assays recently have become available and could prove applicable to ED settings. The cardiac troponins are highly useful as markers of acute coronary syndromes, rather than specifically of AMI, and abnormal values at any time following chest pain onset are highly predictive of an adverse cardiac event. The ED applicability of the troponins is severely limited, however, because values remain normal in most patients with acute cardiac events as long as 6 hours following symptom onset. Myoglobin appeared promising as a marker of early cardiac ischemia but appears to be only marginally more sensitive than CK-MB assays early after symptom onset and less sensitive than CK-MB at 8 hours or more after chest pain starts. Rapid serial myoglobin assessment, however, appears highly useful as an early marker of AMI. The marker has a very narrow diagnostic window. The clinician is left with several tests that are highly effective in correctly identifying patients with AMI (or at high risk for AMI), but none that can dependably exclude patients with acute coronary syndromes soon after chest pain onset. A prudent strategy when assessing ED patients with chest pain and nondiagnostic ECGs is to order CK-MB and troponin values on presentation in the hope of making an early diagnosis of AMI or unstable coronary syndrome. Although it is recognized that normal values obtained within 6 hours of symptom onset do not exclude an acute coronary syndrome, patients at low clinical risk and having normal cardiac marker tests could be provisionally admitted to low-acuity hospital settings or ED observation. After 6 to 8 hours of symptom duration has elapsed, the cardiac-specific markers are highly effective in diagnosing AMI, and such values obtained can be used more appropriately to make final disposition decisions. At no time should results of serum marker tests outweigh ECG findings or clinical assessment of the patient's risk and stability.

Bedside multimarker testing for risk stratification in chest pain units: The chest pain evaluation by creatine kinase-MB, myoglobin, and troponin I (CHECKMATE) study

BACKGROUND

Earlier, rapid evaluation in chest pain units may make patient care more efficient. A multimarker strategy (MMS) testing for several markers of myocardial necrosis with different time-to-positivity profiles also may offer clinical advantages.

METHODS AND RESULTS

We prospectively compared bedside quantitative multimarker testing versus local laboratory results (LL) in 1005 patients in 6 chest pain units. Myoglobin, creatine kinase-MB, and troponin I were measured at 0, 3, 6, 9 to 12, and 16 to 24 hours after admission. Two MMS were defined: MMS-1 (all 3 markers) and MMS-2 (creatine kinase-MB and troponin I only). The primary assessment was to relate marker status with 30-day death or infarction. More patients were positive by 24 hours with MMS than with LL (MMS-1, 23.9%; MMS-2, 18.8%; LL, 8.8%; P=0.001, all comparisons), and they became positive sooner with MMS-1 (2.5 hours, P=0.023 versus LL) versus MMS-2 (2.8 hours, P=0.026 versus LL) or LL (3.4 hours). The relation between baseline MMS status and 30-day death or infarction was stronger (MMS-1: positive, 18.8% event rate versus negative, 3.0%, P=0.001; MMS-2: 21.9% versus 3.2%, P=0.001) than that for LL (13.6% versus 5.5%, P=0.038). MMS-1 discriminated 30-day death better (positive, 2.0% versus negative, 0.0%, P=0.007) than MMS-2 (positive, 1.8% versus negative, 0.2%; P=0.055) or LL (positive, 0.0% versus negative, 0.5%; P=1.000).

CONCLUSIONS

Rapid multimarker analysis identifies positive patients earlier and provides better risk stratification for mortality than a local laboratory-based, single-marker approach.

Early diagnosis and exclusion of acute myocardial infarction by two hours' vector-ECG and determination of either myoglobin or CK-mb. BIOMACS-study. BIOchemical Markers in Acute Coronary Syndromes

This retrospective study assesses the early diagnostic potential of a combination of multilead continuous vectorcardiography (VCG) and biochemical markers (myoglobin, troponin-t and CK-mb mass) in patients with chest pain who present with suspected acute myocardial infarction (AMI), but without ST-elevation on resting 12-lead ECG on admission. Within a multicenter study 56 patients admitted for chest pain (< 12 h) and with a non-diagnostic 12-lead ECG on admission and a VCG recording were included. Venous blood samples were drawn on admission and the continuous VCG was monitored for 2 h. The results were related to the clinical diagnosis of AMI. Neither the biochemical markers nor VCG alone permitted the diagnosis or exclusion of AMI at admission. However, if either analysis of myoglobin on admission or 2 h of VCG recording were positive, they would have a sensitivity for detection of AMI of 100% and specificity of 69%. In a subset of patients with more than 4 h delay since start of chest pain, CK-mb could replace myoglobin and give a sensitivity of 100% and a specificity of 81%. Determination of myoglobin or CK-mb at admission and VCG monitoring for 2 h can reliably confirm or exclude AMI within 2 h. This combination seems useful for early stratifications of patients in chest pain or coronary care units.

Clinical utility of CKMB isoform determinations in patients who present to the emergency department with continuous or resolved chest pain

The object of this investigation was to demonstrate that the enhanced sensitivity of the diagnosis of acute myocardial infarction (AMI) using a more-inclusive criterion of CKMB Isoforms may detect earlier stages of AMI (designated Isoform Type 2) than the currently accepted marker for AMI by CKMB Isoform (designated Isoform Type 1) in a busy, urban Emergency Department (ED). Two features characterized the study of CKMB Isoforms in a prospective cohort of 223 ED patients: first, nontraumatic chest pain within 12 h before presentation, thought to be of ischemic etiology; and second, normal or nondiagnostic electrocardiogram (EKG). Patients were further divided into two groups characterized as either recent but resolved chest pain at ED visit, or ongoing or staccato chest pain. Sensitivity (S), specificity (SP), positive (PPV) and negative (NPV) predictive values, and 95% confidence intervals (CI) for AMI diagnosis were determined. Two criteria for AMI diagnosis by CKMB Isoforms were tested. The first and currently recommended criterion was identified as Isoform Type 1. An AMI diagnosis by Type 1 criterion requires both CKMB2> or =2.6 IU/L and CKMB2/CKMB1> or =1.7. The second criterion for AMI diagnosis was identified as Isoform Type 2, which is defined as either CKMB2> or =2.6 IU/L or CKMB2/CKMB1> or =1.7. Both Isoform types are predictive of AMI by the gold standard, and addition of EKG changes results in a small improvement. Type 1 demonstrates SP 0.94 (CI 0.90, 0.97) and NPV 0.90 (CI 0.86, 0.94), and Type 2 demonstrates S 0.90 (CI 0.80, 0.97) and NPV 0.97 (CI 0.93, 0.99) for AMI diagnosis. Type 2 criteria can confidently exclude the immediate risk of AMI in patients with resolved chest pain whereas in patients with continuous chest pain, Type 1 criteria may identify those at high risk for AMI.