What are the diagnostic criteria for unstable angina?

Diagnostic Criteria for Unstable Angina

Unstable angina is diagnosed by the presence of prolonged chest pain or ischemic symptoms that occur at rest or with minimal exertion, without elevation of cardiac troponins, and can present in three principal forms: rest angina, new-onset severe angina, or increasing angina pattern. 1

Three Principal Presentations of Unstable Angina

1. Rest angina: Angina occurring at rest and prolonged, usually greater than 20 minutes 2
2. New-onset angina: New-onset angina of at least Canadian Cardiovascular Society (CCS) class III severity 2
3. Increasing angina: Previously diagnosed angina that has become distinctly more frequent, longer in duration, or lower in threshold (i.e., increased by 1 or more CCS class to at least CCS class III severity) 2

Canadian Cardiovascular Society (CCS) Classification

The diagnosis of unstable angina is based on the duration and intensity of angina as graded according to the CCS classification:

• Class I: Ordinary physical activity does not cause angina; symptoms occur with strenuous, rapid, or prolonged exertion
• Class II: Slight limitation of ordinary activity; angina occurs when walking/climbing stairs rapidly, walking uphill, after meals, in cold/wind, under emotional stress, or only during few hours after awakening
• Class III: Marked limitations of ordinary physical activity; angina occurs when walking 1-2 blocks on level ground or climbing 1 flight of stairs under normal conditions
• Class IV: Inability to carry on any physical activity without discomfort—anginal symptoms may be present at rest 2

Key Diagnostic Features

• Clinical presentation: Prolonged pain (>20 minutes) that occurs at rest or with minimal exertion, acceleration of angina pattern in the last 48 hours, new-onset angina with significant activity limitation, or previously stable angina that worsens 1

• ECG findings: Transient ST-segment changes (≥0.5 mm), ST-segment depression (>1 mm) in two or more contiguous leads, T-wave inversion (>1 mm) in leads with predominant R waves, new or presumed new bundle branch block 1

• Biomarkers: Negative cardiac troponins (distinguishing it from NSTEMI) 1

Risk Stratification Features

High-risk features for adverse outcomes include:

• Accelerating tempo of ischemic symptoms in preceding 48 hours
• Prolonged ongoing rest pain (>20 minutes)
• Age >75 years
• Pulmonary edema likely due to ischemia
• New or worsening mitral regurgitation murmur
• Hypotension, bradycardia, or tachycardia
• Transient ST-segment changes >0.5 mm
• Bundle-branch block, new or presumed new
• Sustained ventricular tachycardia 2

Diagnostic Algorithm

1. Initial assessment:

   • Obtain detailed history of chest pain characteristics
   • Perform 12-lead ECG within 10 minutes of arrival for all patients with chest discomfort 2
   • If initial ECG is not diagnostic but patient remains symptomatic with high clinical suspicion for ACS, perform serial ECGs at 15-30 minute intervals 2

2. Biomarker measurement:

   • Measure cardiac biomarkers in all patients presenting with chest discomfort consistent with ACS
   • Cardiac-specific troponin is the preferred marker
   • For patients with negative biomarkers within 6 hours of symptom onset, remeasure in 8-12 hours after symptom onset 2

3. Diagnostic confirmation:

   • Confirm diagnosis based on clinical presentation (one of the three principal presentations)
   • Verify absence of troponin elevation (to differentiate from NSTEMI)
   • Document ECG changes if present (though ECG may be normal or unchanged) 1

Common Pitfalls to Avoid

• Not performing serial ECGs in patients with ongoing chest pain and normal initial ECG
• Dismissing unstable angina based solely on negative troponins
• Not adequately stratifying patient risk
• Failing to recognize that unstable angina can present with a normal or unchanged ECG 1

Remember that unstable angina is part of the acute coronary syndrome spectrum and has a high risk of progressing to myocardial infarction if not treated adequately. Prompt evaluation and appropriate treatment are essential to prevent this progression.