What is unstable angina in a patient with hypertension and intermittent chest discomfort?

What is Unstable Angina?

Unstable angina is myocardial ischemia at rest or with minimal exertion caused by acute coronary plaque instability (rupture, erosion, or thrombosis) that does NOT result in detectable myocardial necrosis—meaning cardiac troponin levels remain below the 99th percentile upper reference limit on at least 2 samples collected ≥6 hours apart. 1

Core Pathophysiology

The underlying mechanism is identical to myocardial infarction—rupture or erosion of an atherosclerotic plaque with superimposed thrombosis and distal embolization—but the degree of injury is insufficient to cause detectable myocardial cell death. 1 This distinguishes it from NSTEMI, where troponin elevation confirms myocardial necrosis has occurred. 1

Three Classic Clinical Presentations

Unstable angina manifests in three distinct patterns that differentiate it from stable angina: 1, 2

• Rest angina: Prolonged anginal pain (typically ≥20 minutes) occurring at rest without provocation 3, 1

• New-onset severe angina: Recent development (within 2 months) of angina with at least Canadian Cardiovascular Society Class III severity, meaning marked limitation of ordinary physical activity 3, 1

• Crescendo angina: Previously stable angina that becomes distinctly more frequent, longer in duration, or lower in threshold (increased by ≥1 CCS class to at least CCS III severity) 3, 1

Approximately 80% of patients present with prolonged rest pain, while only 20% present with new-onset or accelerated angina patterns. 3

Key Diagnostic Features in Your Patient with Hypertension

In a patient with hypertension and intermittent chest discomfort, consider these critical diagnostic elements:

Electrocardiographic findings (ideally obtained during symptoms and compared to pain-free tracings): 3, 1

• ST-segment depression ≥1 mm in two or more contiguous leads is highly suggestive 3
• T-wave inversions >1 mm in leads with predominant R waves (less specific) 3
• Deep symmetrical T-wave inversions in anterior chest leads suggest proximal left anterior descending artery stenosis 3
• Transient ST-segment elevation between 0.6-1 mm may occur 1
• Important caveat: Approximately 5% of patients have completely normal ECG even during symptoms 1

Hypertension-specific considerations: 2

• Severe uncontrolled hypertension increases myocardial oxygen demand and can precipitate unstable angina in the presence of underlying coronary disease 2
• Left ventricular hypertrophy from chronic hypertension increases oxygen demand and can complicate ECG interpretation 3

Atypical Presentations (Common Pitfalls)

Atypical presentations occur frequently in elderly patients (>75 years), younger patients (25-40 years), diabetics, and women: 3, 2

• Epigastric pain or recent-onset indigestion 3
• Sharp or stabbing chest pain (acute myocardial ischemia diagnosed in 22% of such patients) 3
• Chest pain with pleuritic features (ischemia in 13% of cases) 3
• Increasing dyspnea without chest pain 3

Mandatory Diagnostic Workup

Serial troponin measurements are non-negotiable: 1

• Obtain at least 2 samples ≥6 hours apart 1
• Troponin must remain below the 99th percentile upper reference limit on both samples 1
• A single negative troponin is insufficient to exclude NSTEMI 1
• High-sensitivity troponin assays have increased MI detection by 4% absolute (20% relative), meaning many patients previously labeled as unstable angina are now diagnosed with NSTEMI 1

Physical examination is usually normal but should specifically assess for: 3, 2

• Signs of hemodynamic instability or heart failure (pulmonary edema, S3 gallop, rales) 2
• New mitral regurgitation murmur 2
• Alternative diagnoses (pericarditis, valvular disease, pneumothorax) 3

Critical Distinction from NSTEMI

The only difference between unstable angina and NSTEMI is the presence or absence of detectable myocardial necrosis. 1 Both conditions share the same pathophysiology of acute coronary plaque activity, but NSTEMI has crossed the threshold into measurable cardiac injury. 1 Patients can progress from unstable angina to NSTEMI during their acute presentation, which is why serial troponin monitoring is mandatory. 1

Risk Implications

Compared to NSTEMI patients, those with unstable angina have substantially lower risk of death, derive less benefit from intensified antiplatelet therapy, and less benefit from early invasive strategy. 1 However, unstable angina remains a critical phase of coronary disease requiring urgent evaluation, as it represents acute coronary plaque instability with risk of progression to MI or death. 1

Variant Angina (Prinzmetal's Angina)

This is a specific form of unstable angina characterized by transient ST-segment elevation that spontaneously resolves or resolves with nitroglycerin without progression to MI. 3 It typically occurs spontaneously at rest (often in early morning hours) due to focal coronary spasm, and most patients have normal exercise tolerance. 3 The diagnosis requires documentation of ST-segment elevation during transient chest discomfort that resolves when symptoms abate. 3