From the Guidelines
Stable and unstable angina can be differentiated based on their pattern, severity, and response to treatment, with unstable angina representing a medical emergency due to its association with progressive coronary artery narrowing and potential impending myocardial infarction, as noted in the 2017 ACC/AATS/AHA/ASE/ASNC/SCAI/SCCT/STS guidelines 1.
Key Differentiating Factors
- Pattern and Severity: Stable angina presents with predictable chest pain that occurs with exertion or stress, typically lasting 5-15 minutes, and reliably improves with rest or nitroglycerin. In contrast, unstable angina is characterized by new-onset chest pain, pain at rest, or a significant change in previously stable angina.
- Response to Treatment: Unstable angina may last longer than 20 minutes and responds less predictably to nitroglycerin.
- ECG Findings: Unstable angina is more likely to show ST-segment depression or T-wave inversions during episodes.
- Cardiac Biomarkers: Cardiac biomarkers like troponin remain normal in both stable and unstable angina, distinguishing them from myocardial infarction.
Underlying Pathophysiology
- Stable Angina: Results from fixed atherosclerotic narrowing causing temporary oxygen supply-demand mismatch.
- Unstable Angina: Involves active plaque rupture, thrombosis, and progressive coronary occlusion.
Clinical Classification
- Typical Angina: Meets three characteristics - substernal chest discomfort, provoked by exertion or emotional stress, relieved by rest and/or GTN.
- Atypical Angina: Meets two of the above characteristics.
- Non-cardiac Chest Pain: Meets one or none of the above characteristics. The differentiation between stable and unstable angina is crucial for determining the appropriate management strategy and preventing adverse outcomes, as emphasized by the European Society of Cardiology guidelines 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Differentiating Stable and Unstable Angina
To differentiate between stable and unstable angina, several factors must be considered, including the patient's clinical presentation, medical history, and diagnostic test results.
- Stable angina is characterized by a predictable pattern of chest pain, typically triggered by physical activity or emotional stress, and relieved by rest or nitroglycerin 2.
- Unstable angina, on the other hand, is marked by a change in the pattern of chest pain, such as an increase in frequency, severity, or duration, and may occur at rest or with minimal exertion 3.
Clinical Presentation
The clinical presentation of unstable angina can vary, but common features include:
- Recurrence of chest pain within 48 hours after admission, which carries a reduction in likelihood of survival of about 20% in patients with progressive or prolonged angina 3.
- ECG changes on admission, which have a negative prognostic implication, particularly in rest angina, as they predict recurrence of ischemia, myocardial infarction, or need for revascularization in 80% of patients 3.
- An abrupt course, or the rapidity with which symptoms develop, is the main determinant of prognosis in new-onset angina 3.
Diagnostic Tests
Diagnostic tests, such as coronary computed tomographic angiography, can help differentiate between stable and unstable angina by detecting nonobstructive atherosclerosis and improving risk assessment 2.
- Coronary computed tomographic angiography is a first-line diagnostic test in the evaluation of patients with stable angina due to its higher sensitivity and comparable specificity compared with imaging-based stress testing 2.
Treatment
The treatment of stable and unstable angina differs, with unstable angina requiring more aggressive management to prevent myocardial infarction and death.
- Beta-blockers and calcium antagonists are effective in treating effort-related angina, while combination therapy may be synergistic, but evidence to support this is controversial 4.
- Aspirin and possibly heparin should be considered as routine treatment for unstable angina, and dual antiplatelet therapy with aspirin plus either clopidogrel, prasugrel, or ticagrelor may be used depending on the clinical circumstances 5, 6.