The physical exami- nation can indicate alternative diagnoses in patients with chest pain, several of which are life threatening. Aortic dissection is suggested by back pain, unequal palpated pulse volume, a difference of 15 mmHg between both arms in systolic blood pressure (BP), or a murmur of aortic regurgitation. Acute peri- carditis is suggested by a pericardial friction rub. Cardiac tam- ponade can be reflected by pulsus paradoxus. Pneumothorax is suspected when acute dyspnea, pleuritic chest pain, and dif- ferential breath sounds are present. A pleural friction rub may indicate pneumonitis or pleuritis. A 12-lead ECG should be performed and interpreted within 10 minutes of the patient s arrival at an emergency facility to assess for cardiac ischemia or injury.21 Changes on ECG in patients with NSTE-ACS include ST depression, tran- sient ST-elevation, or new T-wave inversion.21,58 Persistent ST-elevation or anterior ST depression indicative of true pos- terior MI should be treated according to the STEMI CPG.17 The ECG can be relatively normal or initially nondiagnostic; if this is the case, the ECG should be repeated (eg, at 15- to 30-minute intervals during the first hour), especially if symp- A normal ECG does not exclude ACS and occurs A normal ECG may also be associated with left circumflex or right coronary artery occlu- sions, which can be electrically silent (in which case posterior electrocardiographic leads [V7 ] may be helpful). Right- sided leads (V3 R to V4 R) are typically performed in the case of inferior STEMI to detect evidence of right ventricular infarc- tion. Left ventricular (LV) hypertrophy, bundle-branch blocks with repolarization abnormalities, and ventricular pacing may mask signs of ischemia/injury.62 3.2.4. Biomarkers of Myocardial Necrosis Cardiac troponins are the most sensitive and specific biomark- ers for NSTE-ACS. 