Unstable angina is an acute coronary syndrome characterized by myocardial ischemia without necrosis. Unlike myocardial infarction (STEMI and NSTEMI), unstable angina does not show elevation of cardiac biomarkers but is defined by worsening symptoms compared to stable angina.
This condition is considered an intermediate stage between stable angina and acute myocardial infarction. It is a medical emergency due to the high risk of progression to true infarction.
Pathogenesis and pathophysiology
The pathogenesis of unstable angina is linked to a critical reduction in coronary blood flow, mainly caused by:
Partial rupture or erosion of an atherosclerotic plaque, leading to the formation of a non-occlusive thrombus.
Coronary vasospasm, which transiently reduces blood flow.
Coronary microembolization, due to the detachment of thrombotic material.
Imbalance between oxygen demand and supply, typical in patients with tachycardia, hypertension, or severe anemia.
The result is acute myocardial ischemia, which may remain transient or evolve into necrosis.
Clinical features
Patients with unstable angina report episodes of worsening chest pain, with characteristics that distinguish it from stable angina:
Pain at rest, occurring without physical exertion.
Increased frequency and duration of episodes, with more intense and prolonged symptoms than in the past.
Resistance to nitrate therapy, with poor response to sublingual nitroglycerin.
Typical radiation to the left arm, jaw, and back.
In elderly and diabetic patients, symptoms may be atypical, with predominant dyspnea, nausea and profuse sweating.
Diagnosis
The diagnosis of unstable angina is based on:
Electrocardiogram (ECG)
May show ST-segment depression or T-wave inversion, although it may be normal in many cases.
Cardiac biomarkers
High-sensitivity troponins are not elevated, helping to distinguish unstable angina from NSTEMI.
Functional tests and imaging
To assess residual ischemia, the following can be performed:
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Risk stratification
To guide therapeutic strategy, risk stratification systems such as the GRACE score are used to identify patients at greatest risk of progression to infarction.
The GRACE score (Global Registry of Acute Coronary Events) is a prognostic tool used to assess the risk of adverse events in patients with unstable angina and NSTEMI. It is based on various clinical and laboratory parameters and stratifies patients into three risk categories:
Low risk: mortality less than 3% at six months.
Intermediate risk: mortality between 3% and 8% at six months.
High risk: mortality greater than 8% at six months.
The parameters considered in the GRACE score calculation include:
Patient age.
Systolic blood pressure.
Heart rate.
Serum creatinine levels.
Killip classification for heart failure.
ECG changes (ST depression or bundle branch block).
Elevation of cardiac biomarkers.
Cardiac arrest at admission.
The final score guides therapeutic strategy, identifying patients who may benefit from an early invasive approach with coronary angiography and possible revascularization.
Treatment
The goal of treatment is to reduce ischemia and prevent progression to myocardial infarction.
1. Pharmacological therapy
Includes:
Antiplatelet agents: aspirin and P2Y12 inhibitors to reduce thrombotic risk.
Anticoagulants: low molecular weight heparin or fondaparinux.
Beta-blockers: reduce heart rate and oxygen consumption.
Nitrates: relieve symptoms by reducing cardiac workload.
2. Invasive strategy
In high-risk patients, early coronary angiography is indicated, followed by angioplasty with stent implantation or coronary artery bypass grafting, if necessary.
Complications
If not properly treated, unstable angina may evolve into:
Acute myocardial infarction, with documented myocardial necrosis.
Acute heart failure, in patients with prolonged ischemia.
Ventricular arrhythmias, due to the electrical instability of ischemic myocardium.
Prognosis
Prognosis depends on the promptness of intervention and the presence of advanced coronary artery disease. Patients treated early with medical therapy and/or revascularization have a reduced risk of progression to myocardial infarction. Secondary prevention, with control of cardiovascular risk factors, is essential to reduce recurrences.
References
Collet JP, et al. 2020 ESC Guidelines for NSTEMI and Unstable Angina. Eur Heart J. 2021;42(14):1289-1367.
Amsterdam EA, et al. 2014 AHA/ACC Guidelines for the Management of Unstable Angina. J Am Coll Cardiol. 2014;64(24):e139-e228.
Roffi M, et al. 2015 ESC Guidelines for Non-ST Elevation Acute Coronary Syndromes. Eur Heart J. 2016;37(3):267-315.
Beckman JA, et al. Unstable Angina and Therapies: New Perspectives and Approaches. Am Heart J. 2020;210:45-55.
Fuster V, et al. Management of patients with unstable angina: What’s new in 2021?. J Am Coll Cardiol. 2021;77(16):2021-2025.
Fox KA, et al. Acute coronary syndromes and their management in 2022. Circulation. 2022;146(1):12-23.
Patel T, et al. Management of unstable angina: The role of aggressive anti-ischemic therapy. J Am Coll Cardiol. 2019;73(4):315-324.
Cannon CP, et al. Acute coronary syndrome and mortality trends. JAMA Cardiol. 2022;7(7):789-797.
Yusuf S, et al. Comparison of management of unstable angina with early invasive strategy. Am Heart J. 2018;195:172-180.
Ferguson TB, et al. Coronary artery disease and unstable angina. J Am Heart Assoc. 2021;11(4):e1155-1161.
