What is the diagnostic approach for a patient with suspected unstable angina?

Diagnostic Approach for Unstable Angina

Unstable angina is diagnosed clinically when a patient presents with one of three specific patterns: rest angina lasting up to 20 minutes, crescendo angina (rapidly worsening stable angina over ≤4 weeks), or new-onset severe angina causing marked limitation within 2 months of presentation. 1

Clinical Presentation Patterns

Unstable angina manifests in three distinct ways that differentiate it from stable angina:

• Rest angina: Characteristic anginal pain occurring at rest for prolonged periods up to 20 minutes 1
• Crescendo angina: Previously stable angina that progressively increases in severity, intensity, and occurs at lower thresholds over ≤4 weeks 1
• New-onset severe angina: Recent onset of severe symptoms causing marked limitation of ordinary activity within 2 months of initial presentation 1

Initial Clinical Assessment

Begin by characterizing the chest pain using specific descriptors: quality (squeezing, griplike, suffocating, heavy—rarely sharp or stabbing), substernal location, duration, radiation pattern, associated symptoms, and relationship to exertion or emotional stress. 1

• Typical angina meets three characteristics: substernal chest discomfort of characteristic quality and duration, provoked by exertion or emotional stress, and relieved by rest and/or nitroglycerin 1
• Atypical angina meets two of the above characteristics 1
• Women and elderly patients often present with atypical symptoms including sharp chest pain, nausea, vomiting, or midepigastric discomfort 1

Risk Stratification

Immediately classify patients into high-risk, intermediate-risk, or low-risk categories based on clinical features, as this determines the urgency of intervention and site of care. 1

High-Risk Features (requiring immediate emergency department or coronary care unit transfer):

• Rest pain lasting >20 minutes 1
• Pulmonary edema 1
• Angina with S3 gallop, rales, or new/worsening mitral regurgitation murmur 1
• Hypotension 1
• Dynamic ST-segment changes ≥1 mm 1
• Elevated cardiac troponin levels 1, 2
• Hemodynamic instability 3
• Major arrhythmias 3

Intermediate-Risk Features:

• Rest angina now resolved with moderate or high likelihood of CAD 1
• Rest angina (<20 minutes) relieved by rest or sublingual nitroglycerin 1
• Angina with dynamic T-wave changes 1
• New-onset Canadian Cardiovascular Society Class III or IV angina within 2 weeks 1

Low-Risk Features:

• No rest or nocturnal angina 1
• Normal or unchanged ECG 1
• Increased angina frequency, severity, or duration without rest pain 1

Laboratory and Diagnostic Testing

Obtain cardiac-specific troponin T or troponin I immediately in all patients with suspected unstable angina, as troponin-positive patients (class IIIB-Tpos) have up to 20% risk of death or MI at 30 days versus <2% in troponin-negative patients (class IIIB-Tneg). 1, 2

• Measure troponin or creatinine kinase MB (mass assay) when clinical suspicion of instability exists to exclude myocardial injury 1
• Obtain complete blood count (hemoglobin and total white cell count) for prognostic information 1
• Measure serum creatinine to evaluate renal function in all patients 1

Electrocardiographic Findings

Perform 12-lead ECG immediately upon presentation and initiate continuous ECG monitoring, as sudden ventricular fibrillation is the major preventable cause of early death. 3

• Dynamic ST-segment depression or elevation ≥1 mm indicates high risk 1
• T-wave inversions >2 mm in multiple precordial leads suggest high risk 1
• Normal or unchanged ECG does not exclude unstable angina but suggests lower risk 1

Assessment of Precipitating Factors

Systematically evaluate for secondary causes that increase myocardial oxygen demand or decrease oxygen supply, as these may precipitate unstable angina in the presence of underlying CAD. 1

Conditions Increasing Oxygen Demand:

• Hyperthermia with volume contraction 1
• Hyperthyroidism 1
• Cocaine abuse or sympathomimetic toxicity 1
• Severe uncontrolled hypertension 1
• Hypertrophic cardiomyopathy or aortic stenosis 1

Conditions Decreasing Oxygen Supply:

• Anemia 1
• Hypoxemia from pulmonary disease 1
• Polycythemia, leukemia, thrombocytosis, or hypergammaglobulinemia 1

Physical Examination Findings

Examine for signs of hemodynamic compromise, heart failure, valvular disease, or alternative diagnoses that may explain symptoms or alter management. 1

• Physical examination is usually normal or nonspecific in stable ischemic heart disease but may reveal heart failure, valvular disease, hypertrophic cardiomyopathy, or peripheral vascular disease 1
• Assess for pulmonary congestion (rales), S3 gallop, new mitral regurgitation murmur, or hypotension as markers of high risk 1

Common Pitfalls

• Do not rely on nitroglycerin response alone: Non-cardiac pain from esophageal spasm may also respond to nitroglycerin 1
• Do not dismiss atypical presentations: Women and elderly patients frequently present without classic substernal chest pressure 1
• Do not delay troponin measurement: Troponin status is the strongest predictor of 30-day outcomes and guides therapy with glycoprotein IIb/IIIa inhibitors and low-molecular-weight heparins 2
• Do not assume normal resting ECG excludes unstable angina: More than 50% of patients with chronic stable angina have normal resting ECG 1