Acute Coronary Syndromes without Persistent ST-Segment Elevation Diagnostics

ECG  

In patients with ongoing chest pain, ECG should be obtained immediately (within 10 minutes of the patient entering the hospital) and as soon as possible in patients with resolved symptoms at the time of the evaluation.  

ECG is key in the assessment of patients presenting with suspected ACS. An ECG taken during an episode of chest pain is particularly valuable. It must be noted that ECG should be repeated (15– to 30-minute intervals at the first hour) as necessary or if there is high suspicion for ACS. Importantly, serial ECGs can identify ST-segment elevation indicative of STEMI which warrants immediate reperfusion. Furthermore, serial ECGS can detect evolving ischemic changes in initial non-diagnostic ECGs.  

Comparison with a previous ECG, if available, is important, especially in patients with coexisting cardiac pathology (eg LV hypertrophy or a previous MI). Continuous multilead ST-segment monitoring is an acceptable alternative to serial 12-lead ECG recordings in patients with high clinical suspicion for ACS but with an initial ECG that is non-diagnostic.

Unstable Angina or NSTEMI  

In the ECG, UA or NSTEMI may show ST-segment depression (especially horizontal or downsloping) >0.1 mV in ≥2 contiguous leads. This finding is highly suggestive of ACS. There may be also inverted T-waves >0.1 mV in ≥2 contiguous leads with predominant R-waves, but this is less specific for ACS. Lastly, there may also be marked T-wave inversion >0.2 mV in the precordial lead or an R/S ratio of >1 or a transient ST-segment elevation.  

Other ECG Presentations  

Other ECG presentations include a persistent ST-segment elevation or new or presumed new left bundle-branch block (LBBB) has a high specificity for evolving STEMI. In which case, patient should then be immediately evaluated for reperfusion therapy.  

Please see Myocardial Infarction with ST-Segment Elevation disease management chart for further information.

It must be noted that a completely normal ECG does not exclude the possibility of ACS. Using additional leads is also considered, including posterior leads (V7-V9) and right-sided leads (V3R, V4R). If a normal ECG occurs during the episode of the chest pain, an alternative diagnosis should be suspected. 

Biochemical Indicators for Detecting Myocardial Necrosis  

Biochemical indicators serve as complementary tests in the diagnosis, risk stratification, and management of patients with suspected ACS. NSTE-ACS patients with very high- or high-risk features should receive immediate appropriate treatment based on clinical presentation and ECG findings, without waiting for cardiac biomarker results, which serve to support the diagnosis.

Cardiac Troponin T or I (Quantitative)  

A hs-cTn I assay is mandatory at presentation on patients with symptoms of possible or suspected ACS and have normal or non-diagnostic findings on ECG. It is preferred as it detects lower troponin concentrations and allows earlier diagnosis of ACS. It must be noted that it should be measured immediately on presentation (at least 1-3 hours after symptom onset) with results available within 60 minutes of blood sampling. MI is ruled in and the patient is admitted if there is a significant rise and/or fall of cTn with at least 1 value >99th percentile URL together with other clinical criteria. For values <99th percentile, algorithms for ruling out ACS include the HEART (history, ECG, age, risk factor, troponin) pathway, European Society of Cardiology (ESC) 1-hour pathway, and the ESC 2-hour pathway. The ESC 3-hour pathway is an alternative if ESC 1-hour or 2-hour pathway is not available. It must be noted that cut-off levels for the different hs-cTn are assay specific and that gender-specific cut-offs are also available.  

cTn T and I are the preferred markers for myocardial injury and necrosis because of their high sensitivity and specificity. They are detected in blood at least 6 hours after symptom onset using conventional assays (earlier with hs-cTn assays) and their levels may remain elevated for up to 14 days. Troponins accurately identify myocardial necrosis but should be used in conjunction with other criteria for MI which include ischemic symptoms and/or ECG and imaging findings. 






Myoglobin and/or Creatinine Kinase – Myocardial Band (CK-MB)  

CK-MB may be used as an alternative cardiac biomarker when cTn testing is unavailable. It should be measured in patients at the time of first assessment with recent (<6 hours) symptoms as an early marker of MI and in patients with recurrent ischemia after recent (<2 weeks) infarction to detect further infarction. In patients with suspected reinfarction based on clinical findings, a 20% rise in CK-MB or troponin between two samples obtained 3-6 hours apart supports the diagnosis.   

Other Biomarkers  

Other biomarkers include myosin-binding protein C and copeptin. These serve as alternatives to cTn and CK-MB.  

Other Diagnostic Tests as Indicated  

Other diagnostic tests that can be done include a complete blood count (CBC), electrolytes, creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate (eGFR), C-reactive protein (CRP), blood-glucose, B0type natriuretic protein (BNP), N-terminal pro-BNP, lipid profile, thyroid function, and coagulation studies. These tests can detect the presence of anemia, thyrotoxicosis, DM, and CAD. Furthermore, additional testing can identify the presence of infection. Several studies have shown that acute respiratory infection is associated with an increased risk for ACS within 1-2 weeks of the infection. The absence of an infection may be prognostic. Lastly, D-dimer determination should be considered instead of imaging studies to rule out pulmonary embolism. 

Other Diagnostic Tests as Indicated  

Chest X-ray can be done to identify pulmonary congestion or edema and thoracic causes of symptoms. While computed tomography (CT) can exclude pulmonary embolism and aortic dissection. Coronary CT angiography may be considered instead of invasive angiography in order to exclude CAD in patients with normal or inconclusive troponin or ECG results. Echocardiography may be used to assess LV function and to eliminate other CV causes of chest pain. It may be helpful in patients with a normal or uninterpretable ECG and ongoing chest pain suggestive of myocardial ischemia, to detect new or presumed new wall motion abnormalities. A transthoracic echocardiography (TTE) is recommended in patients with suspected ACS and with cardiogenic shock or suspected mechanical complications. Magnetic resonance imaging (MRI) may be used to determine myocardial viability and to exclude differential diagnoses (eg pulmonary embolism or aortic dissection). Rest myocardial scintigraphy may be helpful in patients with chest pain without ECG changes or evidence of ongoing MI.