Biomarkers of Myocardial Necrosis Cardiac troponins are the most sensitive and specific biomark- ers for NSTE-ACS. They rise within a few hours of symptom onset and typically remain elevated for several days (but may remain elevated for up to 2 weeks with a large infarction). A negative cardiac troponin obtained with more sensitive cardiac troponin assays on admission confers a >95% nega- tive predictive value for MI compared with high-sensitivity assays that confer a negative predictive value 99%.63 65 See Section 3.4 for a detailed review of biomarkers for the diag- nosis of MI. A chest roentgenogram is useful to identify potential pulmo- nary causes of chest pain and may show a widened mediasti- num in patients with aortic dissection. Computed tomography (CT) of the chest with intravenous contrast can help exclude pulmonary embolism and aortic dissection. Transthoracic echocardiography can identify a pericardial effusion and tamponade physiology and may also be useful to detect regional wall motion abnormalities. Transesophageal echocar- diography can identify a proximal aortic dissection. In low-risk patients with chest pain, coronary CT angiography can result in a more rapid, more cost-effective diagnosis than stress myocar- dial perfusion imaging.66 3.3. Prognosis Early Risk Stratification: Recommendations See Table 4 for a summary of recommendations from this section. Class I 1. In patients with chest pain or other symptoms sug- gestive of ACS, a 12-lead ECG should be performed and evaluated for ischemic changes within 10 min- utes of the patient s arrival at an emergency facility.21 (Level of Evidence: C) 2. If the initial ECG is not diagnostic but the patient remains symptomatic and there is a high clinical sus- picion for ACS, serial ECGs (eg, 15- to 30-minute in- tervals during the first hour) should be performed to detect ischemic changes. (Level of Evidence: C) 3. 