The initial assessment of patients presenting with chest pain involves considering the presentation, ECG, and troponin levels to determine the likelihood of acute coronary syndrome. A higher likelihood is present with factors like cardiorespiratory arrest, syncope, dyspnea, arrhythmias, age over 40, previous cardiovascular disease or risk factors. A lower likelihood is suggested by factors like age under 40, no prior disease or risk factors, and chest pain that is variable, short-lived or position-dependent. The assessment guides whether the diagnosis is likely to be cardiac ischemia, noncardiac chest pain, or another cause.