Key Differences Between Stable and Unstable Angina
Based on guideline evidence, three of the four statements are TRUE: stable angina results primarily from exertion, unstable angina occurs at rest and with exertion, and unstable angina reflects a higher risk of myocardial infarction. The statement about degree of coronary blockage is FALSE—the distinction is based on clinical presentation and plaque stability, not degree of stenosis. 1, 2
Statement Analysis
Statement 1: Stable angina results primarily from exertion - TRUE
- Stable angina is characteristically aggravated by exertion or emotional stress and follows a predictable pattern related to physical activity. 1
- The American College of Cardiology/American Heart Association specifically defines stable angina as "angina pectoris without a recent change in frequency or pattern" that is "relieved by rest and/or sublingual/transdermal medications." 2
- According to the Canadian Cardiovascular Society classification, stable angina occurs with varying levels of physical activity depending on severity, but maintains a predictable exertional pattern. 2
Statement 2: Stable angina results from a higher degree of coronary arterial blockage than unstable angina - FALSE
- This statement is incorrect—the fundamental distinction between stable and unstable angina is NOT the degree of stenosis but rather plaque stability and clinical presentation. 3, 4
- Coronary angiographic pathology (morphology and number of vessels involved) is similar between stable and unstable angina subgroups. 4
- The underlying pathogenic substrate of unstable angina is the unstable coronary plaque with an overlying intracoronary thrombus, not necessarily a higher degree of blockage. 3
- Patients with unstable angina may occasionally have "non-obstructive coronary atherosclerosis or no angiographic evidence of CAD, particularly in women." 2
Statement 3: Unstable angina occurs at rest and with exertion - TRUE
- Unstable angina characteristically occurs both at rest and with minimal exertion, fundamentally distinguishing it from stable angina. 2, 5
- The American College of Cardiology/American Heart Association defines unstable angina as presenting in three principal ways: rest angina, severe new-onset angina, or increasing angina. 1
- Specifically, unstable angina includes "symptoms at rest and prolonged, usually ≥20 min" as well as "new-onset symptoms of CCS grade III or grade IV severity." 2
- The American College of Cardiology defines unstable angina as "dolor torácico típico u otros síntomas isquémicos que ocurren en reposo o con mínimo esfuerzo." 5
Statement 4: Unstable angina reflects a higher risk of myocardial infarction - TRUE
- Unstable angina represents a critical phase of coronary heart disease with high to moderate short-term risk for acute coronary events. 1, 2
- The American College of Cardiology/American Heart Association considers unstable angina "more ominous when occurring without stimuli to increased oxygen consumption, representing a critical phase of coronary heart disease with variable prognosis." 2
- The major risk of unstable angina is acute myocardial infarction, which may occur in approximately 25% of patients during the three months following onset of symptoms. 6
- Patients with unstable angina have "high to moderate short-term risk for an acute coronary event." 1
Clinical Pitfalls to Avoid
- Do not assume that absence of ECG changes excludes unstable angina—approximately 5% of patients with unstable angina may have completely normal ECG even during symptoms. 2
- Do not rely solely on angiographic severity—coronary artery morphology and number of vessels involved can be similar between stable and unstable presentations. 4
- Women may present atypically—they are more likely to have non-obstructive coronary atherosclerosis or no angiographic evidence of CAD despite unstable angina symptoms. 2