Unstable Angina Pectoris. Unstable angina (the most commonly used term) is chest pain or discomfort that occurs at rest or with exertion and causes severe activity limitation. An increase in the number of attacks and in the intensity of the pressure indicates unstable angina. The pressure may last longer that 15 minutes or may be poorly relieved by rest or nitroglycerin. Unstable angina describes a variety of disorders , including new-onset angina, variant (Prinzmeatal’s) angina, and per-infarction angina. Patients with unstable angina will present with ST change on a 12-lead ECG but will not have changes in troponin or creatine kinase (CK) levels.