Unstable Angina Characteristics and Diagnosis

Unstable Angina Definition and Risk

The American College of Cardiology/American Heart Association defines unstable angina as "clear evidence of important reversible myocardial ischemia" and considers it more ominous when occurring without stimuli to increased oxygen consumption, representing a critical phase of coronary heart disease with variable prognosis 1, 2
The European Society of Cardiology notes that compared to NSTEMI patients, those with unstable angina have substantially lower risk of death but still require urgent evaluation 3

The American College of Cardiology/American Heart Association defines stable angina as "angina pectoris without a recent change in frequency or pattern" that is "relieved by rest and/or sublingual/transdermal medications" 4, 5
According to the Canadian Cardiovascular Society classification, stable angina occurs with varying levels of physical activity depending on severity, but follows a predictable pattern related to exertion 1, 2

Unstable angina characteristically occurs both at rest and with minimal exertion, distinguishing it fundamentally from stable angina 4, 5
The American College of Cardiology/American Heart Association specifically defines unstable angina/NSTEMI as including "symptoms at rest and prolonged, usually ≥20 min" as well as "new-onset symptoms of CCS grade III or grade IV severity" 4, 5
Unstable angina may present as: rest angina lasting up to 20 minutes, rapidly increasing crescendo angina, or new onset severe angina with marked limitation within 2 months 7

Patients with unstable angina may occasionally have "non-obstructive coronary atherosclerosis or no angiographic evidence of CAD, particularly in women" 3
Approximately 5% of patients with unstable angina may have completely normal ECG even during symptoms 8